RU2355785C2 - Section iron made of boron steel of increased hardenability - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy field. Particularly it relates to section iron for manufacturing of tooth gears, shafts, other critical parts, operating in conditions of load impacts. For cutability improvement with simultaneous increasing of plasticity and viscosity rolled metal is received from the steel, containing, wt %: C 0.16-0.23, Mn 0.60-0.90, Si 0.17-0.37, Cr 0.70-1.10, S 0.005-0.035, Ni 0.80-1.00, Al 0.02-0.05, Ti 0.01-0.06, N 0.005-0.010, B 0.001-0.005, Ca 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 unavoidable admixtures - the rest, at ratios: (As+Sn+Pb+5×Zi)≤0.07; (Ti/48)+(Al/27)-(N/14)≥(0.6×10^-3). Admixtures, wt %: Cu no more than 0.30, Mo no more than 0.03, P no more than 0.035. Tempered and annealed rolled stock allows lamellar ferrite - pearlite structure, size of effective grain 5-9 points, nonmetallics by punctated sulfides, punctated oxides, stitch oxides, fragile silicates, plastic silicates, rigid silicates with average grades no more than 3.5 per each kind, macrostructure by center porosity, punctated nonuniformity, segregation square, undershrinked gathering no more than 3 point per each kind, segregation streamers no more than 1 point, σ_B no more than 1200 MPa, σ_t no more than 1110 MPa, 5 no more than 12%, ψ no more than 62%, a_H KCU(+20) no more than 1470 kJ/m². Cutability - magnitude of wear by flank of cutting tool (h₃) with equal cutting path (L) - with L=1320 m, h₃ no more than 0.30 mm.

EFFECT: cutability improvement with simultaneous increasing of flexibility and viscosity of rolled stock.

4 cl, 2 ex

Description

The invention relates to the field of metallurgy, in particular to the production of long products, round, used for the manufacture of gears, shafts, other critical parts operating under shock loads.

Known long products from boron-containing steel are hot-rolled, hardened and tempered, having specified parameters of macro- and microstructure and mechanical properties (DE 3434744 A1, 04/03/1986, C21D 8/06).

Known long products from high-hardenability boron-containing steel containing carbon, manganese, silicon, chromium, boron, niobium, aluminum, titanium, nitrogen, iron and inevitable impurities, the hire has the specified parameters of macro- and microstructure and mechanical properties (RU 2238335 C1, C21D 8/06, 10.20.2004).

Known long products, round of high-hardenability boron-containing steel, containing carbon, manganese, silicon, sulfur, chromium, vanadium, molybdenum, nickel, niobium, titanium, boron, aluminum, nitrogen, iron and inevitable impurities, hot-rolled and heat-treated, the steel has the specified pollution parameters became non-metallic inclusions on sulfides, oxides, silicates and nitrides, a homogeneous spheroidized perlite structure, real grain size 5-10 points and specified mechanical properties (RU 2249626 C1, C21D 8/06, 04/10/2005).

The objective of the invention is to obtain long products with a diameter of up to 80 mm, having improved machinability by cutting, while increasing the characteristics of hardenability and ensuring through hardenability

The problem is solved in that the long products, round, in bars, made of boron steel, hot rolled, having predetermined parameters of non-metallic inclusions, structure, actual grain size, mechanical properties, hardenability, according to the invention are obtained from steel containing the following ratio of components, wt. %:

carbon 0.16-0.23 manganese 0.60-0.90 silicon 0.17-0.37 chromium 0.70-1.10 sulfur 0.005-0.035 nickel 0.80-1.00 aluminum 0.02-0.05 titanium 0.01-0.06 nitrogen 0.005-0.010 boron 0.001-0.005 calcium 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 the following relationships are true, the amount:

As + Sn + Pb + 5 × Zn≤0.07;

Rolled products have non-metallic inclusions for point sulphides, point oxides, line oxides, brittle silicates, plastic silicates, non-deformable silicates with an average score of not more than 3.5 for each type of inclusions, lamellar ferritoperlite structure, actual grain size 5 to 9 points, macrostructure - central porosity, point heterogeneity, liquation square not more than 3 points for each species, shrink liquation - not more than 3 points; segregation strips - not more than 1 point, mechanical properties after hardening and low tempering: temporary tensile strength not less than 1200 MPa, yield strength not less than 1110 MPa, elongation not less than 12%, relative narrowing not less than 62%, impact strength KCU (+ 20) not less than 1470 kJ / m ² . Machinability by cutting - the amount of wear along the rear edge of the cutter (h ₃ ) with an equal cutting path (L) - at L = 1320 m, h ₃ - not more than 0.30 mm.

As impurities, steel additionally contains in wt%: copper not more than 0.30, molybdenum not more than 0.03, phosphorus not more than 0.035.

When the content of carbon in the steel is 0.16-0.20% and sulfur 0.005-0.020%, rolled metal has mechanical properties after hardening and low tempering: temporary tensile strength not less than 1200 MPa, yield strength not less than 1110 MPa, elongation not less than 14% , a relative narrowing of at least 64%, impact strength KCU (+20) of at least 1800 kJ / m ² , machinability - the amount of wear along the rear edge of the cutter (h ₃ ) with an equal cutting path (L) - at L = 1320 m, h ₃ - not more than 0.30 mm.

When the content of carbon in the steel is 0.18-0.23% and sulfur 0.020-0.035%, the rolled metal has mechanical properties after hardening and low tempering: temporary tensile strength at least 1250 MPa, yield strength at least 1180 MPa, elongation at least 12% , relative narrowing of at least 62%, impact strength KCU (+20) of at least 1470 kJ / m ² , machinability - the amount of wear along the rear edge of the cutter (h ₃ ) with an equal cutting path (L) - at L = 1320 m, h ₃ - not more than 0.20 mm.

The above combinations of alloying elements (p. 1) make it possible to obtain a favorable lamellar structure with globular sandwich inclusions at the box office, which provides, on the one hand, improved cutting characteristics even with wide cutters during transverse feeding of the cutting tool, and, on the other hand, a favorable combination of strength characteristics, ductility, viscosity and hardenability.

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 (0.23%) is due to the need to ensure the required level of ductility of steel, and the lower - respectively 0.16% - 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. In this case, the upper level of manganese — 0.90% and chromium — 1.10% is determined by the need to ensure the required level of ductility of steel, and the lower - 0.60% 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 for silicon - 0.17% due to the technology of deoxidation of steel. A silicon content above 0.37% 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%) due to issues of manufacturability, as well as providing a given level of machinability by cutting this steel.

Boron contributes to a sharp increase in the hardenability of steel. The upper limit of boron content - 0.005% is determined by considerations of ductility of steel, and the lower - 0.001%, the need to ensure the required level of hardenability.

Nickel in the specified range (0.80-1.00%) affects the characteristics of hardenability and toughness of steel.

Aluminum and titanium are used as deoxidizers of steel, elements that provide the formation of a finely dispersed homogeneous grain structure, and also effectively protect boron from binding to nitrides. The upper limit of the content of admixture of 0.050% and titanium of 0.06% is due to the need to obtain a given level of ductility and toughness of steel, and the lower limit of 0.020% and 0.01%, respectively, due to technological issues of production, as well as ensuring a uniform grain structure of 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 is -0.005% by issues of manufacturability.

Calcium is an element that modifies non-metallic inclusions. The upper limit (0.010%), as in the case of sulfur, is due to the need to obtain a given level of ductility and toughness of steel, and the lower (0.001%) limit due to issues of manufacturability.

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 determined by the technology of steel production, and the upper limit (0.03%, 0.02%, 0.01% and 0.005%, respectively) determines the increased the tendency of steel to reversible temper brittleness.

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

определяет эффективность защиты бора от связывания в нитриды и, как следствие, обеспечивает требуемый уровень прокаливаемости стали.Ratio

determines the effectiveness of boron protection from binding to nitrides and, as a result, provides the required level of hardenability of steel.

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

Smelting of the studied steels, each of which has a chemical composition in wt.%:

Example 1: carbon 0.19, manganese 0.75, silicon 0.25, chromium 0.91, nickel 0.99, sulfur 0.011, aluminum 0.037, titanium 0.022, calcium 0.0025, boron 0.0023, nitrogen 0.010, arsenic 0.009, tin 0.005, lead 0.003, zinc 0.001.

Example 2: carbon 0.22, manganese 0.70, silicon 0.31, chromium 1.02, nickel 0.95, sulfur 0.032, aluminum 0.031, titanium 0.025, calcium 0.0025, boron 0.0029, nitrogen 0.007, arsenic 0.011, tin 0.008, lead 0.009, zinc 0.002; was carried out in 150-ton arc steel-smelting furnaces (DSP-150, transformer power 80 mVA) using 60% metallized pellets and 40% metal scrap in the charge, which ensures the mass fraction of nitrogen before being released from the chipboard is not more than 0.003%, and low content of color impurities. The preliminary alloying of the metal with manganese and silicon is carried out in a ladle when released from particleboard. Peroxidized metal is released into the bucket. Deoxidation during release is carried out by aluminum, ferrosilicon and alloying - FeMn (SiMn), FeCr. After release, the metal is purged with argon through the bottom purge unit for 5-7 minutes. Then, evacuation is carried out on a batch vacuum, while doping (fine) - carbon, manganese and silicon. After evacuation, the treatment is carried out 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 enter aluminum (wire). For 10-15 minutes, they are treated 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 300x360 mm with a draw speed of 0.6-0.7 m / min. When casting, the jet is protected from secondary oxidation as follows: steel ladle-blast furnace - immersion pipe with argon feed; 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. The entire initial billet was subjected to dressing, descaling, and surface control. To test the billets of the test steel, they were heat treated in the following mode: normalization 930 ° C, air, quenching 880 ° C, oil, tempering 200 ° C, air. Long products ⌀ 85 mm, length 5900 mm, with a curvature of not more than 0.7 mm / m has:

In Example 1: the structure of lamellar perlite, there is no decarburized layer, the actual grain score is 7. 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. Tensile strength 1250 MPa, yield strength 1180 MPa, elongation 15%, relative narrowing 66%, impact strength KCU (+20) 1910 kJ / m ² . Machinability by cutting is the amount of wear along the rear edge of the cutter (h ₃ ) with an equal cutting path (L) - at L = 1320 m, h ₃ = 0.27 mm. As + Sn + Pb + 5 × Zn = 0.022,

According to example 2: the structure of lamellar perlite, decarburized layer is absent, 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 points, segregation strips - 0.5 points. 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. Tensile strength 1290 MPa, yield strength 1210 MPa, elongation 13%, relative narrowing 64%, impact strength KCU (+20) 1510 kJ / m ² . Machinability by cutting - the amount of wear along the rear edge of the cutter (h ₃ ) with an equal cutting path (L) - at L = 1320 m, h ₃ = 0.19 mm. As + Sn + Pb + 5 × Zn = 0.038,

Long products provide improved machinability by cutting and a favorable ratio of ductility and toughness of steel.

Claims (4)

1. High-quality round bars of boron-containing steel in bars, hot-rolled, having predetermined parameters of non-metallic inclusions, structure, actual grain size, mechanical properties, hardenability, characterized in that it is obtained from steel containing the following ratio of components, wt.%:
carbon 0.16-0.23 manganese 0.60-0.90 silicon 0.17-0.37 chromium 0.70-1.10 sulfur 0.005-0.035 nickel 0.80-1.00 aluminum 0.02-0.05 titanium 0.01-0.06 nitrogen 0.005-0.010 boron 0.001-0.005 calcium 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 fulfilling the relations:
(As + Sn + Pb + 5 · Zn) ≤0.07,

Moreover, it has a lamellar ferritic-pearlite structure, the actual grain size is 5–9 points, non-metallic inclusions for point sulphides, point oxides, line oxides, brittle silicates, plastic silicates, non-deformable silicates with an average score of no more than 3.5 for each species, macrostructure by central porosity, point heterogeneity, segregation square, shrink segregation not more than 3 points for each species, segregation strips not more than 1 point, temporary tensile strength not less than 1200 MPa, before l stress of not less than 1110 MPa, elongation at least 12%, contraction ratio is not less than 62%, the toughness KCU (+20) is not less than 1470 kJ / m ^2, machinability largest wear rear face cutter ₃ h not greater than 0, 30 mm with a cutting path of L = 1320 m. 2. Rolled steel according to claim 1, characterized in that the steel contains inevitable impurities, wt.%: Copper not more than 0.30, molybdenum not more than 0.03, phosphorus not more than 0.035. 3. Long products according to claim 1 or 2, characterized in that when the content in steel, wt.%: Carbon 0.16-0.20 and sulfur 0.005-0.020, it has a temporary tensile strength of at least 1200 MPa, yield strength not less than 1110 MPa, elongation of not less than 14%, relative narrowing of not less than 64%, impact strength
KCU (+20) not less than 1800 kJ / m ² , machinability by the amount of wear along the rear edge of the cutter h ₃ not more than 0.30 mm with a cutting path L = 1320 m. 4. Long products according to claim 1 or 2, characterized in that when the content in steel, wt.%: Carbon 0.18-0.23 and sulfur 0.020-0.035, it has a temporary tensile strength of at least 1250 MPa, yield strength not less than 1180 MPa, elongation of not less than 12%, relative narrowing of not less than 62%, impact strength
KCU (+20) not less than 1470 kJ / m ² , machinability according to the amount of wear along the rear edge of the cutter h ₃ not more than 0.20 mm with a cutting path L = 1320 m.