RU2339705C2 - Section iron made of low-carbon chrome-bearing steel for cold extrusion - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention concerns metallurgy field. Particularly it concerns production pf section iron of diameter 20-50 mm for manufacturing piston pins by method of cold extrusion. For providing of rational conditions for piston pins upset forging at simultaneous increasing of processing plasticity and low level of strain hardening section iron is received from steel, containing wt %: C 0.12-0.18, Mn 0.40-0.60, Si 0.15-0.25, Cr 0.70-1.15, N 0.005-0.010, S 0.005-0.035, O₂ 0.001-0.010, As 0.0001-0.03, Sn 0.0001-0.02, Pb 0.0001-0.01, Zn 0.0001-0.005, iron and admixtures at ratios: As+Sn+Pb+5×Zn<0.07; 0.19<(C+Mn/6)<0.27, at that rolled iron has lamellar ferrite - pearlite structure, size of effective grain is 5-9 points, cold yielding not less then 1/3 of its height, nonmetallic by dotted sulfides, dotted oxides, stitch oxides, frail silicates, plastic silicates, silicates by non-straining with point not more then 3.0 for each kind, macrostructure by center porosity, spot inhomogeneity, liquation square, sweat is not more than 3 points for every kind, liquating strip is not more than 1 point, hardness is not more then 207 HB, σ_B not more than 500 MPa, δ not less than 18%, ψ not less than 55%.

EFFECT: providing of rational upset forging conditions of piston pins at simultaneous increasing of processing plasticity and low level of strain hardening.

4 cl, 1 ex

Description

The invention relates to the field of metallurgy, in particular the production of long products with a diameter of 20-50 mm, round, both with a special surface finish and hot rolled, made from low-carbon chromium-containing steel of high hardenability, used for manufacturing by cold extrusion of piston fingers.

Known long products from low carbon steel containing carbon, manganese, silicon, chromium, vanadium, niobium, sulfur, aluminum, calcium, nitrogen, iron and impurities, having predetermined parameters of non-metallic inclusions for sulfides, oxides, silicates, nitrides, a uniform spheroidized structure, the actual grain size is 5-10 points, the cold draft is not less than 1/3 of the height, the decarburized layer is not more than 1.5% of the diameter, the tensile strength is not more than 520 MPa, the elongation is not less than 22%, the relative narrowing is not less than 65% ( RU 2262 538 C1, C21D 8/06, 10.20.2005).

Known long products from low-carbon chromium-containing steel, including carbon, manganese, silicon, sulfur, chromium, nickel, niobium, titanium, boron, aluminum, nitrogen, iron and impurities, having predetermined parameters of non-metallic inclusions for sulfides, oxides, silicates, nitrides, uniform spheroidized structure, actual grain size 5–10 points, cold precipitation not less than 1/3 of the height, decarburized layer not more than 1.5% of the diameter, tensile strength not more than 520 MPa, elongation not less than 20%, relative narrowing e not less than 65% (RU 2249624 C1, C21D 8/06, 04/10/2005).

The technical result of the invention is the provision of rational conditions for the displacement of the piston fingers while providing enhanced characteristics of technological plasticity and a low level of strain hardening.

To achieve a technical result, long products from low-carbon chromium-containing steel, having predetermined parameters of non-metallic inclusions, structure, mechanical properties, and hardenability of technological plasticity, are made of steel containing the following ratio of components, wt.%:

carbon 0.12-0.18 manganese 0.40-0.60 silicon 0.15-0.25 chromium 0.70-1.15 nitrogen 0.005-0.010 sulfur 0.005-0.035 oxygen 0.001-0.010 arsenic 0.0001-0.03 tin 0.0001-0.02 lead 0.0001-0.01 zinc 0.0001-0.005 iron and inevitable impurities  rest,

when performing the following ratios:

(As + Sn + Pb + 5 × Zn) ≤0.07;

0.19≤ (C + Mn / 6) ≤0.27,

rolled products have a lamellar ferrite-pearlite structure, the actual grain size is 5–9 points, the cold precipitation is not less than 1/3 of the height, non-metallic inclusions — the average score for point sulfides, point oxides, building oxides, brittle silicates, plastic silicates, non-deformable silicates - not more than 3.0 for each type of inclusions, macrostructure - central porosity, point heterogeneity, segregation square - not more than 3 points for each type, shrinkable segregation - not more than 3 points; segregation strips - not more than 1 point, hardness not more than 207NV, tensile strength not more than 500 MPa, elongation not less than 18%, relative narrowing not less than 55%.

Steel additionally contains impurities, wt.%: Nickel - not more than 0.20, copper - not more than 0.20, sulfur - not more than 0.015, phosphorus - not more than 0.025.

When the content in steel, wt.%: Carbon is 0.12-0.18, chromium is 0.70-1.0, sulfur is 0.005-0.015, rolled products with special surface finishes have a hardness of not more than 207NV, tensile strength is not more than 500 MPa, elongation of at least 18%, relative contraction of at least 55%.

When the content in steel, wt.%: Carbon 0.15-0.18, chromium 0.85-1.15, sulfur - 0.015-0.035, hot rolled products have a hardness of 137-197 HB, temporary tensile strength - not more than 480 MPa, relative elongation - not less than 20%, relative narrowing - not less than 60%.

The given combinations of alloying elements (p. 1) make it possible to obtain a favorable structure at the box office, which ensures obtaining the specified strength and ductility parameters.

Carbon is introduced into the composition of this steel in order to ensure a given level of its strength and hardenability. The upper limit of the carbon content (0.18%) is due to the need to ensure the required level of ductility of steel, and the lower - respectively 0.12% - to ensure the required level of strength and hardenability of this steel.

Manganese and chromium are used, on the one hand, as solid solution hardeners, and on the other hand, as elements that significantly increase the stability of supercooled austenite of steel. At the same time, the upper level of manganese — 0.60% and chromium — 1.15% is determined by the need to ensure the required level of ductility of steel, and the lower — 0.40% and 0.70%, respectively, by the need to provide the required level of strength and hardenability of this steel.

Silicon refers to ferrite-forming elements. The lower limit on silicon - 0.15% is due to the technology of deoxidation of steel. A silicon content above 0.25% will adversely affect the ductility characteristics of steel.

Sulfur determines the level of ductility of steel. The upper limit (0.035%) is due to the need to obtain a given level of ductility and toughness of steel, and the lower limit (0.005%) is due to issues of manufacturability, as well as providing a given level of machinability by cutting this steel.

Nitrogen promotes the formation of nitrides in steel. The upper limit of nitrogen content - 0.010% - is due to the need to obtain a given level of ductility and toughness of steel, and the lower limit - 0.005% - to questions of manufacturability.

Oxygen, forming an oxide film on sulfides, helps to increase the machinability of steel by cutting while maintaining a high complex of consumer properties of steel. The upper level of oxygen content - 0.010% due to the need to ensure the required level of ductility of steel, and the lower - 0.001%, respectively, the need to provide the required level of strength and machinability by cutting steel.

Arsenic, tin, lead and zinc are colored impurities that determine the overall level of ductility of steel and its tendency to manifest reversible temper brittleness during subsequent heat treatment of finished products from the pipe billet under consideration. The lower limit for arsenic, tin, lead and zinc (0.0001% for each element, respectively) is due to steel production technology, and the upper limit (0.03, 0.02, 0.01 and 0.005%, respectively) determines the increased tendency of steel to reversible temper embrittlement.

Ratios:

The ratio As + Sn + Pb + 5 × Zn≤0.05 determines the reduced tendency of steel to manifest reversible temper brittleness.

The ratio of 0.19≤C + Mn / 6≤0.27 determines the characteristics of the viscosity and ductility of steel.

Comparative analysis with the prototype allows us to conclude that the claimed composition is different from the known introduction of new components - and the ratio:

As + Sn + Pb + 5 × Zn≤0.07; 0.19≤C + Mn / 6≤0.27.

Examples of the invention, not excluding others in the scope of the claims

Smelting of the investigated steels with a chemical composition, wt.%:

Example 1: carbon 0.14, manganese 0.55, silicon 0.16, chromium 0.81, sulfur 0.007, nitrogen 0.009, oxygen 0.008, arsenic 0.009, tin 0.005, lead 0.003, zinc 0.001;

Example 2: carbon 0.17, manganese 0.56, silicon 0.17, chromium 0.99, sulfur 0.031, nitrogen 0.009%, oxygen 0.008, arsenic 0.011, tin 0.008, lead 0.009, zinc 0.002 was carried out in 150-ton arc steelmaking furnaces (DSP-150, transformer capacity 80 mVA) using 60% metallized pellets and 40% metal scrap in the charge, which ensures that the mass fraction of nitrogen before being released from the chipboard is not more than 0.003%, as well as a low content of color impurities. Preliminary alloying of metal with manganese and silicon was carried out in a ladle when discharged from particleboard (Release of peroxidized metal into a ladle. Metal deoxidation — when released by aluminum, ferrosilicon — deoxidation, alloying — FeMn (SiMn), FeCr). After release, the metal was purged with argon through the bottom purge unit for 5-7 minutes. Then evacuation on a portion vacuum, while doping (fine) - carbon, manganese and silicon. After evacuation - processing on a ladle furnace. 15-30 minutes before the end of the treatment, an oxidizing agent is introduced, in this case, oxidized pellets. Then again introduced aluminum (wire). For 10-15 minutes treatment with flux-cored wires with silicocalcium and pure sulfur. Steel casting was carried out on a high-quality radial type continuous casting machine in NLZ 300 × 360 mm with a draw speed of 0.6-0.7 m / min. During casting, the jet was protected from secondary oxidation as follows: steel ladle-blast furnace - immersion pipe with argon supply; promkovsh - slag-forming mixture; bucket mold - immersion cup (corundum-graphite); in the mold - slag-forming mixture. After casting and cutting to a measured length, continuously cast billets were cooled in controlled cooling furnaces. Next, the ingots were rolled in a mill 700 into a billet (170 mm square). The entire initial billet was subjected to dressing, descaling, and surface control. The billets were heated before rolling in two walking-hearth furnace furnaces. The heating temperature of the workpiece is 900 ° C, which provides a reduction in energy consumption by 15% and significantly reduces the decarburization of rolled products. Dross from the surface of the workpiece was removed with high-pressure water at a descaling unit. Rolling was carried out in continuous lines - small-grade and medium-grade. High rigidity of the stands, automatic adjustment of the speed of the stands, and a loop control system in the finishing group of the small-sorted line made it possible to obtain high-precision rolled products. Finishing of the rolled products was carried out off-stream. Finishing included the operations of dressing, control of surface defects and ultrasonic control of internal defects, selective abrasive cleaning, continuous abrasive grinding, turning of round bars. The accuracy of rolling after turning corresponds to the h11 quality. At the BUNT-PRUTOK installation, from coils of hot-rolled steel, turned rods of up to 6 meters in length are obtained with a cutting accuracy of ± 5 mm.

Example 1. As a result of hot rolling and subsequent surface finishing, we obtain long products ⌀22.5 mm, length 5900 mm, the curvature of the rods is not more than 0.7 mm / m.

The structure of lamellar perlite, the decarburized layer is absent, the actual grain score is 7. Sulfide inclusions globular with an oxide shell. Macrostructure: central porosity - 1 point, point heterogeneity - 1 point, segregation square - 0.5 points, shrink segregation - 0.5 points, segregation strips - 0.5 points. Non-metallic inclusions: point sulfides - 2 points, point oxides - 1 point, line oxides - 2 points, brittle silicates - 1 point, plastic silicates - 1 point, non-deforming silicates - 1 point.

The hardness of the workpiece is 197NV, the temporary tensile strength is 460 MPa, the elongation is 20%, the relative narrowing is 62%. The amount of cold draft 1/3 of the height

As + Sn + Pb + 5 × Zn = 0.022, C + Mn / 6 = 0.23.

Example 2. As a result of hot rolling we get hot-rolled long products прокат22 mm, length 5900 mm. The structure of lamellar perlite, the actual grain score is 8. Sulfide inclusions globular with an oxide shell. Macrostructure: central porosity - 1.0 point, point heterogeneity - 1.0 point, segregation square - 1.0 point, shrink segregation - 0.5 point, segregation strips - 0.5 point. Non-metallic inclusions: point sulfides - 2.5 points, point oxides - 2.0 points, line oxides - 2.0 points, brittle silicates - 1.5 points, plastic silicates - 1 point, non-deforming silicates - 1 point.

The hardness of the workpiece is 191NV, the tensile strength of 689 MPa, an elongation of 7%, a relative narrowing of 41%

As + Sn + Pb + 5 × Zn = 0.038, oxygen / calcium = 4.09; calcium / sulfur = 0.080.

The introduction of long products from medium carbon steel with increased machinability provides a favorable ratio of strength, ductility and toughness of steel.

Claims (4)

1. High-quality rolled products from low-carbon chromium-containing steel, having predetermined parameters of non-metallic inclusions, structure, mechanical properties, hardenability, technological ductility, characterized in that it is made of steel containing the following ratio of components, wt.%: carbon 0.12-0.18 manganese 0.40-0.60 silicon 0.15-0.25 chromium 0.70-1.15 nitrogen 0.005-0.010 sulfur 0.005-0.035 oxygen 0.001-0.010 arsenic 0.0001-0.03 tin 0.0001-0.02 lead 0.0001-0.01 zinc 0.0001-0.005 iron and inevitable impurities - rest, when performing the following ratios: (As + Sn + Pb + 5 Zn) ≤0.07; 0.19≤ (C + Mn / 6) ≤0.27, Moreover, it has a lamellar ferrite-pearlite structure, the actual grain size is 5–9 points, the cold precipitation is at least 1/3 of its height, non-metallic inclusions for point sulfides, point oxides, building oxides, brittle silicates, plastic silicates, non-deformable silicates an average score of not more than 3.0 for each species, the macrostructure for central porosity, point heterogeneity, segregation square, shrink segregation of not more than 3 points for each species, segregation strips of not more than 1 point, hard st not more than 207 HB, tensile strength less than 500 MPa, elongation at least 18%, contraction ratio is not less than 55%. 2. Rolled steel according to claim 1, characterized in that the steel contains inevitable impurities, wt.%: Nickel not more than 0.20, copper not more than 0.20, sulfur not more than 0.015, phosphorus not more than 0.025. 3. Long products according to claim 1 or 2, characterized in that when the content in steel, wt.%: Carbon 0.12-0.18, chromium 0.70-1.0, sulfur 0.005-0.015 rolled with a special finish the surface has a hardness of not more than 207 HB, a tensile strength of not more than 500 MPa, an elongation of at least 18%, a relative contraction of at least 55%. 4. Long products according to claim 1 or 2, characterized in that when the content in steel, wt.%: Carbon 0.15-0.18, chromium 0.85-1.15, sulfur 0.015-0.035 hot rolled has a hardness 137-197 HB, temporary tensile strength not more than 480 MPa, elongation of at least 20%, relative narrowing of at least 60%.