NL2030335B1 - Low - temperature impact - resistant high - strenght as - cast nodular cast iron and production method thereof - Google Patents
Low - temperature impact - resistant high - strenght as - cast nodular cast iron and production method thereof Download PDFInfo
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- NL2030335B1 NL2030335B1 NL2030335A NL2030335A NL2030335B1 NL 2030335 B1 NL2030335 B1 NL 2030335B1 NL 2030335 A NL2030335 A NL 2030335A NL 2030335 A NL2030335 A NL 2030335A NL 2030335 B1 NL2030335 B1 NL 2030335B1
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- 229910001141 Ductile iron Inorganic materials 0.000 title claims abstract description 41
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 22
- 239000000126 substance Substances 0.000 claims abstract description 47
- 238000005266 casting Methods 0.000 claims abstract description 19
- 239000011573 trace mineral Substances 0.000 claims abstract description 18
- 235000013619 trace mineral Nutrition 0.000 claims abstract description 18
- 239000000463 material Substances 0.000 claims abstract description 16
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 155
- 229910052742 iron Inorganic materials 0.000 claims description 74
- 238000011081 inoculation Methods 0.000 claims description 49
- 239000002054 inoculum Substances 0.000 claims description 43
- 239000003795 chemical substances by application Substances 0.000 claims description 37
- 229910000831 Steel Inorganic materials 0.000 claims description 29
- 239000010959 steel Substances 0.000 claims description 29
- 238000000034 method Methods 0.000 claims description 24
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 20
- 239000004576 sand Substances 0.000 claims description 15
- 230000008569 process Effects 0.000 claims description 13
- 229910052710 silicon Inorganic materials 0.000 claims description 13
- 229910000805 Pig iron Inorganic materials 0.000 claims description 12
- 229910052751 metal Inorganic materials 0.000 claims description 12
- 239000002184 metal Substances 0.000 claims description 12
- 239000002994 raw material Substances 0.000 claims description 12
- 229910052749 magnesium Inorganic materials 0.000 claims description 11
- 229910052799 carbon Inorganic materials 0.000 claims description 10
- 206010037660 Pyrexia Diseases 0.000 claims description 7
- 238000010079 rubber tapping Methods 0.000 claims description 7
- 229910000600 Ba alloy Inorganic materials 0.000 claims description 6
- 229910001152 Bi alloy Inorganic materials 0.000 claims description 6
- 239000013078 crystal Substances 0.000 claims description 6
- 238000001816 cooling Methods 0.000 claims description 5
- 238000005422 blasting Methods 0.000 claims description 4
- 229910052748 manganese Inorganic materials 0.000 claims description 4
- 229910045601 alloy Inorganic materials 0.000 claims description 3
- 239000000956 alloy Substances 0.000 claims description 3
- 239000011819 refractory material Substances 0.000 claims description 3
- 229910052802 copper Inorganic materials 0.000 claims description 2
- 238000012545 processing Methods 0.000 claims description 2
- 230000015572 biosynthetic process Effects 0.000 claims 2
- 238000000465 moulding Methods 0.000 claims 2
- 229910052797 bismuth Inorganic materials 0.000 claims 1
- 238000005255 carburizing Methods 0.000 claims 1
- 239000000470 constituent Substances 0.000 claims 1
- 238000005087 graphitization Methods 0.000 claims 1
- 238000002844 melting Methods 0.000 claims 1
- 230000008018 melting Effects 0.000 claims 1
- 230000024121 nodulation Effects 0.000 claims 1
- 238000010438 heat treatment Methods 0.000 abstract description 5
- 230000002035 prolonged effect Effects 0.000 abstract description 4
- 239000010970 precious metal Substances 0.000 abstract description 3
- 239000011777 magnesium Substances 0.000 description 22
- 229910052761 rare earth metal Inorganic materials 0.000 description 22
- 150000002910 rare earth metals Chemical class 0.000 description 21
- 229910002804 graphite Inorganic materials 0.000 description 14
- 239000010439 graphite Substances 0.000 description 14
- 238000003723 Smelting Methods 0.000 description 11
- 239000010949 copper Substances 0.000 description 11
- 238000012360 testing method Methods 0.000 description 10
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 description 8
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 5
- 239000010703 silicon Substances 0.000 description 5
- 229910001209 Low-carbon steel Inorganic materials 0.000 description 4
- 238000006243 chemical reaction Methods 0.000 description 3
- 230000003247 decreasing effect Effects 0.000 description 3
- 238000001514 detection method Methods 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 239000011159 matrix material Substances 0.000 description 3
- 238000011160 research Methods 0.000 description 3
- 230000033764 rhythmic process Effects 0.000 description 3
- 239000002893 slag Substances 0.000 description 3
- 230000003595 spectral effect Effects 0.000 description 3
- 230000003009 desulfurizing effect Effects 0.000 description 2
- 230000005496 eutectics Effects 0.000 description 2
- 238000009863 impact test Methods 0.000 description 2
- 230000001590 oxidative effect Effects 0.000 description 2
- 238000007711 solidification Methods 0.000 description 2
- 230000008023 solidification Effects 0.000 description 2
- 238000010183 spectrum analysis Methods 0.000 description 2
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- 229910000519 Ferrosilicon Inorganic materials 0.000 description 1
- 229910000954 Medium-carbon steel Inorganic materials 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 229910052729 chemical element Inorganic materials 0.000 description 1
- 239000004927 clay Substances 0.000 description 1
- 238000004140 cleaning Methods 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 238000006477 desulfuration reaction Methods 0.000 description 1
- 230000023556 desulfurization Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000005562 fading Methods 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 238000002347 injection Methods 0.000 description 1
- 239000007924 injection Substances 0.000 description 1
- 230000002452 interceptive effect Effects 0.000 description 1
- 230000003137 locomotive effect Effects 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 238000005457 optimization Methods 0.000 description 1
- 229910001562 pearlite Inorganic materials 0.000 description 1
- 239000003208 petroleum Substances 0.000 description 1
- 238000005498 polishing Methods 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- 230000004044 response Effects 0.000 description 1
- 238000005070 sampling Methods 0.000 description 1
- 230000003746 surface roughness Effects 0.000 description 1
- 238000009864 tensile test Methods 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C37/00—Cast-iron alloys
- C22C37/04—Cast-iron alloys containing spheroidal graphite
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D1/00—Treatment of fused masses in the ladle or the supply runners before casting
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C1/00—Refining of pig-iron; Cast iron
- C21C1/10—Making spheroidal graphite cast-iron
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C33/00—Making ferrous alloys
- C22C33/08—Making cast-iron alloys
- C22C33/10—Making cast-iron alloys including procedures for adding magnesium
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C37/00—Cast-iron alloys
- C22C37/10—Cast-iron alloys containing aluminium or silicon
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Mechanical Engineering (AREA)
- Refinement Of Pig-Iron, Manufacture Of Cast Iron, And Steel Manufacture Other Than In Revolving Furnaces (AREA)
Abstract
The present invention discloses low - temperature impact - resistant high - strength as - cast nodular cast iron and a production method thereof, and relates to the field of new materials. The nodular cast iron comprises the chemical components in percent by weight: 3.5 - 3.9% of C, 1.8 - 2.1% of Si, less than or equal to 0.2% of Mn, less than or equal to 0.03% of P, 0.006 - 0.015% of S, 0.15 - 0.25% of Cu, 0.025 - 0.045% of Mg, 0.01 - 0.02% of RE and the balance trace elements, wherein CE is equal to C + 1/3(Si) and C + 1/3(Si) is equal to 4.3 - 4.6%, and an anti - nodulizing coefficient K of the trace elements is less than or equal to 1 +/- 0.1%. Precious metal such as Ni is added into a casting produced by the present invention to temper and heat treatment is not carried out, so that the cost is lower. As the nodular cast iron as cast condition has higher strength and toughness as well as excellent low - temperature impact performance, the nodular cast iron is suitable for low - temperature working environments with higher mechanical properties, and the service life is prolonged.
Description
TECHNICAL FIELD The present invention relates to the field of materials, in particular to low - temperature impact - resistant high - strength as - cast nodular cast iron and a production method thereof.
BACKGROUND Nodular cast iron which is an important metal structure material is applied increasingly widely in the fields of automobile, machine, ship and the like. Some mechanical components, for example, an automobile crankshaft, not only require higher strength, but also possess higher toughness. At present, high - strength and high - toughness nodular cast iron is obtained primarily by heat treatment which is high in cost, complex in process and low in rate of finished products. Therefore, it is of great practical significance in producing high - strength and high - toughness nodular cast iron as cast condition. There are still some machines and components and parts work in a high and cold environment for a long time, for example, a transmission, a wheel hub and a base of a wind power device, railway and metro accessories, locomotive and vehicle accessories, accessories of petroleum and petrochemical equipment. These nodular iron castings require better low - temperature performance simultaneously. At present, the market requirement on the low - temperature high - toughness nodular iron castings is higher and higher. In a standard GB1348 - 2009 in China, a low - temperature impact performance requirement is only stipulated for nodular cast iron materials with two low trade marks QT350 - 22L and QT400 - 18L. The toughness of the nodular cast iron is decreased while the trade mark is increased, the low - temperature toughness is lower, so that an application requirement cannot be met. Therefore, the low - temperature impact performance requirement is not stipulated by nodular cast iron standards at home and abroad on trade marks higher than QT450 - 10.
SUMMARY The objective of the present invention is to provide low - temperature impact - resistant high - strength as - cast nodular cast iron and a production method thereof to solve the problem raised in the background art that the toughness of the nodular cast iron is decreased while the trade mark is increased, the low - temperature toughness is lower, so that an application requirement cannot be met. In order to achieve the purpose, the present invention adopts a technical scheme as follows: Low - temperature impact - resistant high - strength as - cast nodular cast iron includes the chemical components in percent by weight: 3.5 - 3.9% of C, 1.8 - 2.1% of Si, less than or equal to 0.2% of Mn, less than or equal to 0.03% of P, 0.006 - 0.015% of S, 0.15 - 0.25% of Cu, 0.025 - 0.045% of Mg, 0.01 - 0.02% of RE and the balance trace elements, wherein CE is equal to C +
1/3(Si) and C + 1/3(Si) is equal to 4.3 - 4.6%, and an anti - nodulizing coefficient K of the trace elements is less than or equal to 1 +/- 0.1%.
A production method for nodular cast iron, including the following steps: S1, preparing a pure raw material: pure and rustless high - purity pig iron, comprising the chemical components in percent by weight: greater than or equal to 3.3% of C, 0.4 - 0.7% of Si, 0.05 - 0.10% of Mn, less than or equal to 0.03% of P, less than or equal to 0.02% of S, less than or equal to 0.025% of Ti and 11 trace elements, wherein Zw(Cr+V + Mo + Sn + Sb + Pb + Bi + Te + As + B + Al) is less than or equal to 0.07% and an anti - nodulizing coefficient K=4.4Ti + 1.6Al + 2.0As + 2.3Sn + 5.0Sb + 290Pb + 370Bi is less than or equal to 0.36; S2: carrying out shot blasting on same material recirculated iron: a high quality crystal carburant for high - temperature graphitizing treatment comprises the chemical components in percent by weight:
99.5 - 99.8% of C, 0.015 - 0.05% of S and 0.001 - 0.003% of N, wherein an absorptivity is greater than or equal to 95% and a granularity is 0.5 - 5 mm; S3, adjusting the components of smelted molten iron in an electric furnace before nodulizing in percent by weight as follows: 3.75 - 4.15% of C, 0.8 - 1.1% of Si, less than or equal to 0.2% of Mn, less than or equal to 0.03% of P, less than or equal to 0.025% of S, 0.15 - 0.25% of Cu, other trace elements and the balance Fe, wherein CE is equal to C + 1/3(Si) and C + 1/3(Si) is equal t0432-4.52%; S4, carrying out nodulizing treatment and primary inoculation on the molten iron: a nodulizing treatment temperature is 1510 +/- 10°C; a nodulizing agent is Mg6RE1, comprising the chemical components in percent by weight: 5.5 - 6.5% of Mg, 0.5 - less than 1.5% of RE (Ce/RE is greater than or equal to 46%), 1.5 - 3.0% of Ca, 35 - 45% of Si, less than or equal to 1.0% of Mn, less than or equal to 0.5% of Ti, less than or equal to 0.65% of MgO, less than or equal to 0.5% of Al and the balance Fe, wherein a granularity is 5 - 30 mm, and an adding amount is 1.1 - 1.4% of the treated molten iron by weight; and an inoculant is an Si - Ba alloy inoculant, comprising the chemical components in percent by weight: 65 - 70% of Si and 4 - 6% of Ba, a granularity thereof is 2 - 5 mm and an adding amount thereof is 0.3 - 0.5%; S5, carrying out secondary inoculation: ladle - to - ladle inoculation: adding a secondary inoculant into a bottom of a pouring ladle and then pouring the nodulised molten iron into the pouring ladle for secondary inoculation, wherein an inoculant is an Si - Ba alloy inoculant, components of which are identical to those in primary inoculation, and a granularity thereof is 1 - 2 mm and an adding amount thereof is 0.08 -
0.3%; S86, carrying out pouring and third - time inoculation:
pouring the molten iron subjected to nodulizing and secondary inoculation into a sand mould at a certain pouring temperature; and carrying out third - time inoculation, namely metal - stream instantaneous inoculation in the pouring process, wherein a metal - stream inoculant is an Si - Bi alloy, comprising the chemical components in percent by weight: 68 - 75% of Si, 0.8 - 1.2% of Bi, less than or equal to 2.0% of Ca, less than or equal to 1.2% of RE and less than or equal to 1.5% of Al, a granularity of which is 0.2 - 0.7 mm and an adding amount thereof is 0.08 - 0.15% of the poured molten iron by weight; and S7, sand shakeout: solidifying the poured molten iron in the sand mould, and carrying out mould - stream cooling to below 500 °C to shake out sand so as to form the nodular cast iron.
Further, high quality medium - low carbon scrap steel in the step 1 is pure and rustless, including the chemical components in percent by weight: less than or equal to 0.5% of C, less than or equal to 0.4% of Si, less than or equal to 0.3% of Mn, less than or equal to 0.03% of P, less than or equal to 0.02% of S, less than or equal to 0.1% of Cr, less than or equal to 0.3% of Cu and less than or equal to 0.3% of Ni.
Further, a smelting temperature of the electric furnace ranges from 1530°C to 1550°C. Further, the molten iron in the step 3 is left to stand for 5 - 10 minutes at a high temperature before iron is made, and drossing and slagging are carried out.
Further, the nodulizing treatment method in the step 4 is a tundish - cover nodulizing process: a dam type nodulised ladle, a height of a dam is 30 - 50 mm higher than a charging height, a ladle cover and a ladle top are compacted by a hermetical refractory material, a depth - diameter ratio is 1.5 - 2, the ladle is preheated to over 800°C before use, and the nodulizing agent, the inoculant and a small steel sheet are dried before use.
Further, it is necessary to enhance coverage during nodulised treatment in the step 4: the small steel sheet is used to cover the ladle tightly; the small steel sheet is rustless low - carbon steel, an adding amount thereof is 1.2 - 1.3% of the treated molten iron by weight, the nodulizing agent, the inoculant and the small steel sheet are charged sequentially and tamped layer by layer, and the charging height is lower than the top surface of the dam.
Further, a pitch time from tapping and nodulizing to ending of pouring of whole ladle molten iron is not longer than 10 minutes.
The present invention has the beneficial effects that precious metal such as Ni is added into a casting produced by the present invention to temper and heat treatment is not carried out, so that the cost is lower. As the nodular cast iron as cast condition has higher strength and toughness as well as excellent low - temperature impact performance, the nodular cast iron is suitable for low - temperature working environments with higher mechanical properties, and the service life is prolonged.
DETAILED DESCRIPTION Clear and intact description will be made on technical scheme in the embodiment of the present invention below in combination with drawings in the embodiment of the present invention. The described embodiments are merely a part of embodiments of the present invention and are not all the embodiments. A production method for nodular cast iron, including the following steps: S1, a pure raw material is prepared: pure and rustless high - purity pig iron, including the chemical components in percent by weight: greater than or equal to 3.3% of C, 0.4 - 0.7% of Si, 0.05 - 0.10% of Mn, less than or equal to 0.03% of P, less than or equal to 0.02% of S, less than or equal to 0.025% of Ti and 11 trace elements, wherein Zw(Cr + V + Mo + Sn + Sb + Pb + Bi + Te + As + B + Al) is less than or equal to 0.07% and an anti - nodulizing coefficient K=4.4Ti + 1.6Al + 2.0As + 2.3Sn + 5.0Sb + 290Pb + 370Bi is less than or equal to 0.36; S2: shot blasting is carried out on same material recirculated iron: a high quality crystal carburant for high - temperature graphitizing treatment comprises the chemical components in percent by weight:
99.5 - 99.8% of C, 0.015 - 0.05% of S and 0.001 - 0.003% of N, wherein an absorptivity is greater than or equal to 95% and a granularity is 0.5 - 5 mm; S3, the components of smelted molten iron in an electric furnace before nodulizing are adjusted in percent by weight as follows: 3.75 - 4.15% of C, 0.8 - 1.1% of Si, less than or equal to 0.2% of Mn, less than or equal to 0.03% of P, less than or equal to 0.025% of S, 0.15 - 0.25% of Cu, wherein CE is equal to C + 1/3(Si) and C + 1/3(Si) is equal to 4.32 - 4.52%; S4, nodulizing treatment and primary inoculation are carried out on the molten iron: a nodulizing treatment temperature is 1510 +/- 10°C; a nodulizing agent is Mg6RE1, including the chemical components in percent by weight: 5.5 - 6.5% of Mg, 0.5 - less than 1.5% of RE (Ce/RE is greater than or equal to 46%), 1.5 - 3.0% of Ca, 35 - 45% of Si, less than or equal to 1.0% of Mn, less than or equal to 0.5% of Ti, less than or equal to 0.65% of MgO, less than or equal to 0.5% of Al and the balance Fe, wherein a granularity is 5 - 30 mm, and an adding amount is 1.1 - 1.4% of the treated molten iron by weight; and an inoculant is an Si - Ba alloy inoculant, comprising the chemical components in percent by weight: 65 - 70% of Si and 4 - 6% of Ba, a granularity thereof is 2 - 5 mm and an adding amount thereof is 0.3 - 0.5%; S5, secondary inoculation is carried out: ladle - to - ladle inoculation: a secondary inoculant is added into a bottom of a pouring ladle and then the nodulised molten iron is poured into the pouring ladle for secondary inoculation, wherein an inoculant is an Si - Ba alloy inoculant, components of which are identical to those in primary inoculation, and a granularity thereof is 1 - 2 mm and an adding amount thereof is 0.08 -
0.3%;
S86, pouring and third - time inoculation are carried out: the molten iron subjected to nodulizing and secondary inoculation is poured into a sand mould at a certain pouring temperature; and third - time inoculation, namely metal - stream instantaneous inoculation is carried out in the 5 pouring process, wherein a metal - stream inoculant is an Si - Bi alloy, including the chemical components in percent by weight: 68 - 75% of Si, 0.8 - 1.2% of Bi, less than or equal to 2.0% of Ca, less than or equal to 1.2% of RE and less than or equal to 1.5% of Al, a granularity of which is 0.2 - 0.7 mm and an adding amount thereof is 0.08 - 0.15% of the poured molten iron by weight; and S7, sand shakeout: the poured molten iron is solidified in the sand mould, and mould - stream cooling is carried out to below 500 °C to shake out sand so as to form the nodular cast iron.
High quality medium - low carbon scrap steel in the step 1 is pure and rustless, including the chemical components in percent by weight: less than or equal to 0.5% of C, less than or equal to
0.4% of Si, less than or equal to 0.3% of P, less than or equal to 0.02% of S, less than or equal to 0.1% of Cr, less than or equal to 0.3% of Cu and less than or equal to 0.3% of Ni.
A smelting temperature of the electric furnace ranges from 1530°C to 1550°C.
The molten iron in the step 3 is left to stand for 5 - 10 minutes at a high temperature before iron is made, and drossing and slagging are carried out.
The nodulizing treatment method in the step 4 is a tundish - cover nodulizing process: a dam type nodulised ladle, a height of a dam is 30 - 50 mm higher than a charging height, a ladle cover and a ladle top are compacted by a hermetical refractory material, a depth - diameter ratio is 1.5 - 2, the ladle is preheated to over 800°C before use, and the nodulizing agent, the inoculant and a small steel sheet are dried before use.
It is necessary to enhance coverage during nodulised treatment in the step 4: the small steel sheet is used to cover the ladle tightly; the small steel sheet is rustless low - carbon steel, an adding amount thereof is 1.2 - 1.3% of the treated molten iron by weight, the nodulizing agent, the inoculant and the small steel sheet are charged sequentially and tamped layer by layer, and the charging height is lower than the top surface of the dam.
A pitch time from tapping and nodulizing to ending of pouring of whole ladle molten iron is not longer than 10 minutes.
Ni is not added and heat treatment is not needed in manufacturing the material, the as cast condition tensile strength Rm is greater than or equal to 450 MPa and the ductility A is greater than or equal to 18%. The mean value of the impact energy of the separately casted sample with Charpy (V - shaped notch) among the three samples at a low temperature of 20°C below zero is not smaller than 12J, and an individual value is not smaller than 9J; the mean value of the impact energy of the separately casted sample with Charpy (V - shaped notch) among the three samples at a low temperature of 40°C below zero is not smaller than 9J, and an individual value is not smaller than 8J. Normal temperature performance and low - temperature performance are both superior to those of a trade mark QT400 - 18L. According to the low - temperature impact - resistant high - strength as - cast nodular cast iron produced by the method, by taking high purity pig iron and pure medium - and low - carbon scrap steel as a raw material and modifying the raw material with a high quality nodulizing agent and an inoculant, a casting is high in nodulizing rate, fine and close in tissue, good in mechanical property and good in low - temperature resistance by means of component optimization, process improvement, rhythm production and the like. According to GB/T1348 - 2009, the trade mark of the material is defined as QT450 - 18L. The material is suitable for nodular iron castings for wind power devices, engineering machines, railways and the like working in a low temperature environment with higher requirement on mechanical property. Mechanical characteristics of QT450 - 18L and related materials are shown in table 1, the impact energy of a separately casted sample with a V - shaped notch is shown in table 2, and metallographic characteristics of QT450 - 18L are shown in table 3. Table 1 Mechanical characteristics of QT450 - 18L and related materials Tensile strength Elongation Yield strength Brinell Rm at break A Trade mark Rp0.2(MPa) hardness (MPa) (%)
HB Table 2 Impact energy of a separately casted sample of QT450 - 18L and related material with a V - shaped notch he Minimum impact energy/J Room temperature | Low temperature ( - | Low temperature ( - (23£5)°C 20£2)°C 40£2)°C Trade Mean value Mean value Mean value mark Individual Individu Individu of three of three of three value al value al value QT400 - 12 QT450 - 12
Table 3 Metallurgical requirements of QT450 - 18L Size of nodule graphite eutectic Greater than or Grade 8-8 | Less than Less than or m= Ee 20% The production process and method optimize casting components, improve as - cast structures and improve the normal temperature mechanical property and the low temperature impact performance.
|. The nodulizing rate and the number of graphite are increased.
(1) High purity pig iron is used, so that the purity of the raw material is improved; the contents of S and other anti - nodulizing elements are controlled strictly, so that the adding amount of the nodulizing agent and the Mgresiauat content in the casting are reduced while it is nodulised well, and the chilling tendency is reduced.
(2) Coverage the nodulizing agent is improved. Charging is performed according to a sequence of the nodulizing agent, the inoculant and the small steel sheet, each layer is flattened and tamped by using a flat hammer, and the upper coverage layer is improved into the small steel sheet from scrap iron, so that the smelting point of the coverage layer is improved and the nodulizing response time is prolonged, and therefore, the nodulizing reaction is performed under a condition with a certain iron hydraulic pressure head. Thus, the loss of iron scale of Mg is reduced and the absorptivity of Mg reaches over 70%. Finally, MQresiduar is kept between 0.025% to 0.045%, thereby the nodulizing action of Mg is exerted fully.
(3) The content of RE is reduced. Rare earth (RE) plays a role of counteracting adverse effect of the anti - nodulizing elements on graphite nodulizing, and meanwhile, the rare earth elements (primarily Ce) easily promote the graphite to be bulked and agglomerated. A too large RE content affects the rounding degree of the graphite nodules, so that the RE content shall be lowered properly to further improve the number of the spherical graphite. As the content of the anti - nodulizing trace elements in the high purity pig iron is controlled strictly, a low RE nodulizing agent is selected. In order to make the bulk graphite not exceed 20%, the RE content in the nodulizing agent is between 0.5% and 1.5%.
(4) In order to improve the absorptivity of magnesium, when the RE content in the nodulizing agent is 1% under an electric furnace production condition, it is determined that the magnesium content is about 6%.
(5) In order to improve the content of effective magnesium in the nodulizing agent to improve the nodulizing effect, it is stipulated that the content of MgO in the nodulizing agent does not exceed 1/10 of the magnesium content thereof.
According to the above factors, it is finally determined that the nodulizing agent Mg6RE1 is composed of the following components by weight: 5.5 - 6.5% of Mg, 0.5 - less than 1.5% of RE,
1.5 - 3.0% of Ca, 35 - 45% of Si, less than or equal to 1.0% of Mn, less than or equal to 0.5% of Ti, less than or equal to 0.65% of MgO and less than or equal to 0.5% of Al.
(6) Drossing is performed in time after nodulizing treatment, so that a “resulphurization” phenomenon is reduced.
(7) The time from nodulizing treatment to pouring does not exceed 8 minutes.
By means of fine proportioning and strict processing operation, the nodulizing rate is increased to over grade 2, and the bulk graphite is lower than 20%.
II. The purity of molten iron is improved.
(1) Inclusions are reduced from the source by using the clean raw material, and a strict control standard is formulated for chemical components and physical states of furnace charges.
(2) The molten iron is subjected to “self - deoxidizing” reaction at the time by high - temperature standing treatment, so that the molten iron is oxidized and the oxidizing slag inclusion tendency is reduced greatly, and it becomes high - temperature lowly oxidized high quality molten iron.
(3) As the absorptivity of Mg is improved, the effective Mg content in the nodulizing agent is improved and the content of the anti - nodulizing elements in the high purity pig iron is reduced, the adding amount of the nodulizing agent is reduced and the slagging amount is reduced.
{4) By using the patent of our factory to cover the ladle, the nodulizing treatment is performed in a relatively closed ladle and contact with external air is reduced, so that oxidizing slag inclusion is reduced.
(5) Drossing and deslagging of the original molten iron are performed before nodulizing, and full drossing is performed in timely after nodulizing.
Ill. The inoculating effect is enhanced. Inoculation fade is prevented effectively through nodulizing ladle bottom Si - Ba inoculation, ladle - to - ladle inoculation and metal - stream Si - Bi thrice inoculation. The Si - Ba alloy long - acting inoculant prolongs the fading time. An Si - Bi alloy inoculant is used in metal - stream inoculation, so that the number of graphite nodules is increased greatly, and the solidification quality is improved. The comprehensive performance of ductile iron is improved correspondingly, and shrinkage cavity, shrinkage porosity and chilling tendency are reduced.
IV. Components are optimized, including reasonable chemical components and matrix tissues. According to influence of chemical elements to casting tissues and performance, the reasonable chemical components of the casting is determined by researches for many times, and a narrow scope control production scheme determined according to a wall thickness and a pouring temperature of the casting, the matrix tissues of QT450 - 18L in the table 3, mechanical properties in the table 1 and the low - temperature performance in the table 2 are guaranteed. The chemical component scheme is described in a technical scheme below in detail.
V. Raw materials are improved. The raw materials are optimized by fully considering influence of trace interfering nodulizing elements, and the value K of the anti - nodulizing elements is controlled strictly to be smaller than 1 +/- 0.1; the nodulizing agent and the inoculant are improved, the alloy Si - Bi compound inoculant is selected for metal - stream inoculation and is cooperated with a material plant to research the nodulizing agent MgBRE1, and the components are optimized and adjusted; the furnace charge is purified, and is clean and rustless; measures of regulating C by using a high - temperature graphitized crystal carburant are and the like employed.
VI. Rhythm production is performed. Standardized management must be carried out on the above - mentioned production method, the shakeout temperature is consistent by rhythm production, it is ensured that the time from nodulizing to pouring does not exceed 8 minutes, and in order for actual control of production, the pitch time from tapping and nodulizing to whole ladle molten iron pouring does not exceed 10 minutes.
By carrying out the above - mentioned measures, the comprehensive indexes of the casting are improved greatly. The nodulizing rate is greater than or equal to 90%, and bulk graphite does not exceed 20%.
Precious metal such as Ni is added into a casting produced by the present invention to temper and heat treatment is not carried out, so that the cost is lower. As the nodular cast iron as cast condition has higher strength and toughness as well as excellent low - temperature impact performance, the nodular cast iron is suitable for low - temperature working environments with higher mechanical properties, and the service life is prolonged.
The technical scheme adopted by the present invention is as follows: Requirement on chemical components (mass fraction) of the material A carbon equivalent CE=C + 1/3(Si) is 4.3 - 4.6%, where C accounts for 3.5 - 3.9%, Si accounts for 1.8 - 2.1%, Mn is less than or equal to 0.2%, Cu accounts for 0.15 - 0.25%, S accounts for 0.006 - 0.015%, P is less than or equal to 0.03%, Mg accounts for 0.025 - 0.045% and RE accounts for 0.01 - 0.02%.
The anti - nodulizing coefficient of trace elements is less than 1 + /0.1.
Requirements on raw materials Pig iron for smelting is high - purity pig iron, including the chemical components in percent by weight: greater than or equal to 3.3% of C, 0.4 - 0.7% of Si, 0.05 - 0.10% of Mn, less than or equal to 0.03% of P, less than or equal to 0.02% of S, less than or equal to 0.025% of Ti and 11 trace elements, where Zw(Cr+V + Mo + Sn + Sb + Pb + Bi + Te + As + B + Al) is less than or equal to 0.07% and an anti - nodulizing coefficient K=4.4Ti + 1.6Al + 2.0As + 2.3Sn + 5.0Sb + 290Pb + 370Bi is less than or equal to 0.36.
Scrap steel for smelting is medium - and low - carbon steel which includes the chemical components in parts by mass: less than or equal to 0.5% of C, less than or equal to 0.4% of Si,
less than or equal to 0.3% of Mn, less than or equal to 0.03% of P, less than or equal to 0.02% of S, less than or equal to 0.05% of Cr, less than or equal to 0.3% of Cu and less than or equal to
0.1% of Ni. Foundry returns for smelting are same materials. Pig iron, scrap steel and foundry returns are purified, for example, polishing cleaning and derusting. A smelting carburant is a high - temperature graphitized high quality crystal carburant, including the chemical components in percent by mass: 99.5 - 99.8% of C, 0.015 - 0.05% of S and 0.001 - 0.003% of N, wherein an absorptivity is greater than or equal to 95% and a granularity is0.5-5mm. Electric furnace smelting The smelting temperature ranges from 1530°C to 1550°C. The components of the original molten iron are adjusted in percent by weight as follows: 3.75 -4.15% of C, 0.8 - 1.1% of Si, less than or equal to 0.2% of Mn, less than or equal to 0.03% of P, less than or equal to 0.025% of S, 0.15 - 0.25% of Cu, other trace elements and the balance Fe, where CE is equal to C + 1/3(Si) and C + 1/3(Si) is equal to 4.32 - 4.52% (the C loss decreased is 0.25%, and Si is increased by nodulizing and inoculating to 1%, adjusted according to conditions), and the sum of mass fraction of the other trace elements is less than or equal to
0.1%. The molten iron is left to stand for 5 - 10 minutes at a high temperature, and drossing and slagging are carried out. Nodulizing inoculation is carried out. Nodulizing treatment is carried out on the molten iron with the components, the bottom of the ladle is nodulizing for primary inoculation. The nodulizing treatment method is tundish - cover nodulizing process. The dam type nodulised ladle is used, and the dam is 30 - 50 mm higher than a charging surface. The ladle cover covers the top of the ladle body tightly, and a depth - diameter ratio of the ladle body is 1.5 - 2. Residual iron is cleaned before the nodulised ladle is used, is dried and is preheated to be orange - yellow (higher than or equal to 800°C). The nodulizing agent, the inoculant and the small steel sheet are dried before use, and layer - by - layer charging, flattening and tamping are carried out on the nodulizing agent, the inoculant and the small steel sheet in sequence on the opposite side of a molten iron injection side separated by the dam. Selection and adding amount of the nodulizing agent: the nodulizing agent is Mg6RE1, including the chemical components in percent by weight: 5.5 - 6.5% of Mg, 0.5 - less than 1.5% of RE (Ce/RE is greater than or equal to 46%), 1.5 - 3.0% of Ca, 35 - 45% of Si, less than or equal to 1.0% of Mn, less than or equal to 0.5% of Ti, less than or equal to 0.65% of MgO, less than or equal to 0.5% of Al and the balance Fe, where a granularity thereof is 5 - 30 mm. The adding amount accounts for 1.1 - 1.4% of the weight of the treated molten iron. Selection and adding mount of the primary inoculant: the Si - Ba inoculant is used, including the chemical components in percent by mass: 65 - 70% of Si and 4 - 6% of Ba, the granularity is
1.5 - 3 mm, and the adding amount is 0.3 - 0.5%. Small steel sheet coverage: the small steel sheet is rustless low - carbon steel, and an adding amount thereof is 1.2 - 1.3% of the treated molten iron by weight. The nodulizing treatment temperature is 1510 +/- 10°C. Drossing: drossing thorough is performed after nodulizing, and drossing is performed for at least three times. Pouring Drossing is performed again after ladle - to - ladle operation. Secondary inoculation: ladle - to - ladle inoculation performed at the bottom of the pouring ladle, an Si - Ba inoculant is used, including the chemical components in percent by weight: 65 - 70% of Si and 4 - 6% of Ba, a granularity thereof is 1 - 2 mm and an adding amount thereof is 0.1 - 0.3%. A reasonable pouring temperature (1350 - 1450°C) is determined for the molten iron subjected to nodulizing and secondary inoculation according to a key wall thickness of the casting. Thrice inoculation: third - time inoculation is performed in the pouring process, i.e., metal - stream instant inoculation. The inoculant is the Si - Bi alloy inoculant, including the chemical components in percent by weight: 68 - 75% of Si, 0.8 - 1.2% of Bi, less than or equal to 2.0% of Ca, less than or equal to 1.2% of RE and less than or equal to 1.5% of Al, a granularity of which is 0.2 - 0.7 mm and an adding amount thereof is 0.1 - 0.15% of the poured molten iron by weight. A spectral test block is poured to each nodulised ladle in the later pouring period. A 25 mm thick standard test block is poured to each nodulised ladle in the later pouring period. A pitch time from tapping and nodulizing to ending of pouring of whole ladle molten iron is not longer than 10 minutes. Shakeout Mould - stream cooling is carried out to below 500 °C to shake out sand. Production practice of as cast QT450 - 18L A certain bracket is made of QT450 - 18L, is 18 kg heavy and the key wall thickness is 30 mm. It is determined that the final chemical components w(%) are as follows in the table 4.
Table 4 Compo- Stee than or | 0.006 - 0.025 - | than or equal 0.015 0.045 equal High quality raw materials are selected.
High - purity pig iron is clean and rustless, including the chemical components w(%) as follows in the following tables.
Table 5 EEE | 3 |T lee elements Scrap iron is clean and rustless, including the chemical components w(%) as follows in the table: Table 6 (os [Ww Tse TN Recirculated iron is selected, including the chemical components w(%) as follows in the table: Table 7 ers TET] & GW [RE _ Shot blasting is performed on the foundry returns for 15 minutes.
The crystal carburant, the absorptivity is greater than or equal to 95%, the granularity is 0.5 - 5 mm, including the chemical components w (%) as follows in the table: Table 8
Electric furnace smelting The smelting temperature ranges from 1530°C to 1550°C.
The chemical components w(%) in the original molten iron in the electric furnace is adjusted as indicated in table ©: Table 9 Compo- RN ee C | Si CE S caval | 4 0.025 The contents of P, S and Mn in the above components are primarily controlled by raw materials. When the content of S exceeds the standard, desulfurization is needed. The contents of C and Si are adjusted by adding the carburant, the scrap steel or a ferrosilicon alloy into the electric furnace according to the analysed values of C and Si before the original molten iron is adjusted. Cu is adjusted by adding cathode copper in the electric furnace according to the analysed value of Cu before the original molten iron is adjusted. The CE value in each scheme is controlled by a target value +/- 0.05% in the table.
It is necessary to seize a condition in adjustment that the components of the original molten iron are determined according to final chemical components, increment of nodulised inoculated elements and process burning loss of elements; the C loss drop is counted as 0.25% and the Si loss drop is counted as 5% of silicon, and the burning loss amount of each element is adjusted according to an actual condition; the carbon increment of nodulised inoculation is equal to Sineduiized + Siinoculated 1 + SÎnocuated It + Siinocutated u and is approximately equal to 1%.
The adjusted molten iron is left to stand for 8 minutes at a high temperature and drossing and slagging are carried out.
Nodulizing inoculation is carried out.
Nodulizing treatment is carried out on the molten iron with the components, the bottom of the ladle is primarily inoculated, where the weight of the primarily treated molten iron is 700 Kg.
Nodulizing treatment - tundish - cover nodulizing process: a dam type nodulised ladle is repaired qualified according to a technical requirement before use.
The nodulised ladle is preheated to be higher than or equal to 800°C before use.
The nodulizing agent, the inoculant and the small steel sheet are dried before use, and layer - by - layer charging, flattening and tamping are carried out on the nodulizing agent, the inoculant and the small steel sheet in sequence, where the height shall be 30 - 50 mm lower than the dam; Selection and adding amount of the nodulizing agent: the nodulizing agent is MgS6RE1, including the chemical components w(%) in the following table 10.
Table 10 CW | Re [somes | Fw [moe | Granularity: 5 — 30 mm. The adding amount is calculated as follows: According to our research trials and production practice, the w (M@resiqual) can be controlled within 0.025 - 0.045 when the nodular cast iron is produced by using the Mg6RE1 nodulizing agent and the high purity pig iron. When the Mgresiua in the nodular cast iron is greater than
0.04%, the solidification scope is widened rapidly and the shrinking tendency is enlarged, so that the Mresiua Shall be low to the greatest extent under the premise of guaranteeing good nodulizing. A calculating formula of the adding amount of the nodulizing agent is as follows: A=0.76(Soriginal motten iron = Snodulized) + {(MGresiduat + MQattenuation)/ NM content where A is the adding amount of the nodulizing agent, Soriginat motten iron iS the content of S in the original molten iron before being nodulised, Snoduized is the content of S in the nodulised molten iron, Mgresdua: is the content of Mg in the casting, MQatenuation is an attenuation amount of Mg from nodulizing to pouring, n is the absorptivity of magnesium and the Mgenen: is the content of Mg in the nodulizing agent. It is obtained from a test that a desulfurizing amount (Soriginat motten iron = Snoduiized) iS less than
0.01%, the desulfurizing magnesium amount is 0.76 (Soriginal moten iron = Snodutized) is less than
0.0076%; the attenuation rate of magnesium per minute is 0.001 - 0.003%, a mean value 0.002% being taken. The time from nodulizing reaction to ending of pouring is shorter than or equal to 8 minutes. An in - mold attenuation amount within 1 minute is increased according to wall thickness of the casting, and Mgatenustion is equal to 0.002%*(8 + 1)=0.018%; the absorptivity n of magnesium is greater than or equal to 70% and is counted as 70% the MQcontent is counted as 6%, and Mgresiduat is counted as 0.025%. A is less than (0.0076% + 0.025% + 0.018%)/(70%*6%), i.e., when 4 is less than 1.2%, the requirement on graphite nodulizing shall be met. In combination with production experience, it is determined that the adding amount of the nodulizing agent is 1.3%, which fully meets the requirement on graphite nodulizing. The nodulised silicon increment is as follows: Snoquized is equal to 1.3%*43%*95%=0.53%. Selection and adding amount of the primary inoculant: The Si - Ba inoculant, the granularity thereof being 1.5 - 3 mm, including the chemical components w(%) in the following table 11. Table 11 (me
The adding amount is 0.5%, and then the silicon increment for primary inoculation is as follows: Siinscutatea | is equal to 0.5%*69%*95%=0.328%.
Small steel sheet coverage: the small steel sheet shall be clean and rustless, otherwise derusting treatment is carried out. The chemical components w(%) are in the following table 12.
Table 12 (© Ta] Es ww [WN The adding amount is 1.2% - 1.3%; the nodulizing treatment temperature is 1510 +/- 10°C; the tapping weight is 700 +/- 10 Kg.
Drossing: drossing is performed for many times after nodulizing, and a layer of slag gathering agent is scattered to the surface of the molten iron after drossing every time continuously and rapidly. Drossing is performed for at least three times, not exceeding 2 minutes.
Pouring Secondary inoculation: secondary inoculation is performed when the nodulised ladle is poured into the pouring ladle, the Si - Ba inoculant is used, the granularity thereof being 1-2 mm, including the chemical components w(%) in the following table 13.
Table 13 si | Ba The adding amount is 0.15%, and then the silicon increment for secondary inoculation is as follows: Siinocutatea 11 is equal to 0.15%*69%*95%=0.098%.
It is determined that the pouring temperature is 1360 - 1400°C according to the wall thickness of the casting, and the molten iron is poured into a clay green sand cast at a stipulated pouring speed by using an automatic pouring machine.
In the pouring process, metal - stream instantaneous inoculation (thrice inoculation) is performed; the Si - Bi alloy inoculant is used, including the chemical components w(%) in the following table 14.
Table 14 sa [wm [eA Granularity: 0.2 - 0.7 mm; the adding amount is 0.12%, and then the silicon increment for thrice inoculation is as follows: Siinocutated m is equal to 0.12%*72%*95%=0.082%.
A spectral test block is poured to each nodulised ladle in the later pouring period.
A 25 mm thick standard test block is poured to each nodulised ladle in the later pouring period. The whole ladle molten iron pouring time, the time from tapping and nodulizing to ending of pouring of whole ladle molten iron is not longer than 10 minutes. Shakeout: cooling is carried out after pouring to below 500°C to shake out sand. Detection Chemical components Spectral analysis is performed on the spectral test block. Table 15 Spectral analysis result (trace element not included) Chemical components w(%) Sche- | Sample Cu 1 1# 0.12 | 0.026 0.01 0.030 0.012 0.17 CE=4.40 2 2# 0.16 | 0.022 0.009 0.032 0.013 0.20 CE=4.49 3 3# 0.19 | 0.020 0.012 0.031 0.015 0.23 CE=4.58 Metallographic structure Table 16 Metallographic detection result taken from a Y type test block Sampl Size of == / Bulk graphite | Phosphid | Cementi Sche e Nodulizin graphite number e eutectic te Matrix tissue me Numb | g rate (%) nodule (%) (%) (%) er (um) Greater Less than or Pearlite is than or equal to 20% less than or Requirements Grade 6-8 None None equal to equal to 90% 25%.
Mechanical properties
Table 17 Mechanical property detection result taken from a Y type test block Brinell number Rm (MPa) Rp0.2(MPa) break A(%) HB equal to 450 equal to 280 equal to 18 Low - temperature impact energy Table 18 Impact energy test result of Charpy (V - shaped notch) taken from a Y type separately casted test block Sche | ple me num Low temperature( - 2012) °C Low temperature( - 4012) °C EE eene [rm [|| Sw] Teta | Saw | Tete Mean Mean Mean Mean Indivi
OEFEN ETEE three value three value three value three value samples samples samples samples : Conclusion: the performance indexes of the nodular cast iron produced by the method in the embodiment meet the requirement of QT450 - 18L.
The invention is also further exemplified by the figures, wherein Figure 1 shows a Charpy (V-shaped notch) impact test block in a side view and a cross section of the samples . The refence numbers are explained in table 19 below. Figure 2 is a schematic diagram of relative positions of the sample and a support and an anvil block of a bob impact tester. Figure 3 shows the sizes of a tensile sample. Figure 4 shows a tensile test sample and impact test sample sampling method.
Table 19 Name Symbol and number deviation deviation Length L 55 mm + 0.60 mm 55 mm + 0.60 mm Height H 10 mm + 0.075 mm 10 mm £0.11 mm Width w Standard 10 mm +£0.11 mm 10 mm £0.11 mm sample Notchangle [ 1 | 48 [ x22 | OL | Bottom height 2 8 mm + 0.075 mm 8 mm + 0.09 mm of notch 5mm + 0.09 mm notch Distance 4 27.5 mm + 0.42 mm 27.5 mm + 0.42 mm between end portions of symmetrical surfaces of notch Angle between 2° 2° symmetrical surface of notch and longitudinal axis of sample Included angle 5 2° 2° between longitudinal surfaces of sample Except for end portions, the surface roughness of the sample shall be superior to Ra 5 um Disclosed above is merely the several specific embodiment of the present invention but is not intended to limit the scope of protection of the present invention.
Equivalent changes or modifications made by those skilled in the art within the technical scope of the disclosure according to the technical scheme and concepts thereof of the present invention shall be within the scope of protection of the present invention.
Claims (8)
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