RU2327747C1 - Medium carbon steel round profile characterised by increased cutting machinability - Google Patents

Abstract

FIELD: metallurgy; profile.

SUBSTANCE: profile is produced as steel bars, containing in mas.%: C (0.36-0.44), Mn (0.60-0.90), Si (0.15-0.30), Cr (0.80-1.10), S (0.040-0.75), Ca (0.001-0.010), N (0.005-0.015), O₂ (0.001-0.015), As (0.0001-0.03), Sn (0.0001-0.02), Pb (0.0001-0.01), Zn (0.0001-0.005), iron and unavoidable impurities - the rest, at a ratio: (As+Sn+Pb+5xZn)<0.07, O₂/Ca=(1-4.5); Ca/S>0.020. Profile has not less than 75% of oxy sulfides with a sulfide coat of a medium dimension not less than 3 points, the rest are oxides pointed, oxides lined, silicates fragile, silicates plastic, silicates warp-free with a dimension in total of not more than 2.0 points, it has laminar ferrite-pearlite structure, and the dimension of an actual grain of 5-9 points, it also has macrostructure as a central porosity, a liquating square has not more than 3 points in each type, subshrinkage liquation is not more, than 3 points, liquation strips -not more, than 1 point, and mechanical characteristics in annealed or thermo refined condition are: hardness 180-220 HB, ultimate tensile strength -not less, than 950 MPa, yield point - not less, than 800MPa, S- not less, than 12%, a_"н" - KCU⁺²⁰ not less, than 60 J/cm².

EFFECT: facilitating of rational conditions for cutting machining with simultaneous upgrading of strength, viscosity and plasticity.

2 cl, 1 ex

Description

The invention relates to the field of metallurgy, in particular to long products, turned, round, with a diameter of 30 to 70 mm, used for critical car parts.

Known long products, round of medium-carbon steel, made hot-rolled and having predetermined parameters of non-metallic inclusions, structure, actual grain size, mechanical properties, hardenability and technological ductility. (RU 2249629 C1, C21D 8/06, 04/10/2005).

Known long products of round carbon steel, made of hot rolled, having the specified parameters of the structure, macrostructure, non-metallic inclusions, mechanical properties, hardenability and elasticity. (Reference book, Modern materials in the automotive industry, Moscow, "Engineering", 1977, S.80-96).

Known long products of round carbon steel, containing carbon, manganese, silicon, chromium, nickel, copper, molybdenum, sulfur, niobium, calcium, iron and inevitable impurities, made of hot rolled and having the specified parameters of non-metallic inclusions, structure, size of actual grain, mechanical properties, hardenability and technological plasticity. (RU 2262539 C1, C21D 8/06, 20/10/2005).

The technical result of the invention is to provide rational processing conditions by cutting the rods while improving the characteristics of strength, viscosity and ductility.

To achieve a technical result, long products in mild steel bars, hot-rolled, having predetermined parameters of non-metallic inclusions, structure, mechanical properties, hardenability and machinability by cutting, characterized in that they are obtained from steel containing the following ratio of components in wt.%:

carbon 0.36-0.44 manganese 0.60-0.90 silicon 0.15-0.30 chromium 0.80-1.10 sulfur [S] 0,040-0,075 calcium [Ca] 0.001-0.010 nitrogen 0.005-0.015 oxygen [O ₂ ] 0.001-0.015 arsenic [As] 0.0001-0.03 tin [Sn] 0.0001-0.02 lead [Pb] 0.0001-0.01 zinc [Zn] 0.0001-0.005 iron and inevitable impurities rest,

when performing the following ratios:

the sum of (As + Sn + Pb + 5 × Zn) ≤0.07;

O ₂ / Ca = 1 ÷ 4.5;

Ca / S≥0.020,

the rolling stock has non-metallic inclusions containing not less than 75% oxysulfides with a sulfide shell with an average size of not less than 3 points, and point oxides, line oxides, brittle silicates, plastic silicates, non-deformable silicates in aggregate not more than 2.0 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, lamellar ferrite-pearlite structure, actual grain size - 5-9 points, mechanical properties: hardness 180-220 HB, tensile strength at least 950 MPa, yield strength - not less than 800 MPa, elongation not less than 12%, impact strength KCU ⁺²⁰ not less than 60 J / cm ² .

As impurities, steel additionally contains in wt.%: Nickel no more than 0.10, copper no more than 0.20, phosphorus no more than 0.020.

The given combinations of alloying elements (item 1) make it possible to obtain a favorable lamellar structure with globular sandwich inclusions in the proposed steel (hot-rolled section bar round), which provides, on the one hand, increased cutting characteristics even with wide cutters during transverse feeding of the cutting tool, with on the other hand, a favorable combination of strength and ductility characteristics.

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 (0.44%) is due to the need to ensure the required level of ductility of steel, and the lower - 0.36%, respectively - 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 — 0.90% and chromium — 1.10% is determined by the need to ensure the required level of ductility of steel, and the lower level of 0.60% and 0.80%, 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 0.30% will adversely affect the ductility characteristics of steel.

Sulfur determines the level of ductility of steel. The upper limit (0.075%) is due to the need to obtain a given level of ductility and toughness of steel, and the lower limit (0.040%) 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 - 0.015% is due to the need to obtain a given level of ductility and toughness of steel, and the lower limit - 0.005% - to 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 is due to issues 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. In this case, the upper level of oxygen content - 0.015% is 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 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 of oxygen / calcium = 1 ÷ 4.5 is responsible for the possibility of the formation of a sandwich-non-metallic inclusion. Moreover, the upper limit of the ratio of 4.5 is due to the need to ensure the required level of ductility of steel, and the lower one, 1, due to the possibility of the formation of a two-layer sandwich non-metallic inclusion.

The ratio of calcium / sulfur ≥0.020% determines the conditions for the formation of globular non-metallic inclusions (sulfides). If this ratio is fulfilled, the sulfides are globular, otherwise elongated sulfides are present in the steel, which increases the anisotropy of the properties of the steel and worsens the strength-toughness ratio, especially strongly in the transverse direction of the rolled product.

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

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; oxygen / calcium = 1 ÷ 4,5; calcium / sulfur≥0.020

An example embodiment of the invention, not excluding others in the scope of the claims.

Smelting of the test steel (chemical composition in wt.%: Carbon - 0.39%, manganese - 0.74%, silicon - 0.22%, chromium - 0.89%, sulfur - 0.056%, calcium - 0.0020% , nitrogen - 0.010%, oxygen - 0.005%, arsenic - 0.009%, tin - 0.005%, lead - 0.003%, zinc - 0.001%) was carried out in 150-ton steel-arc arc furnaces (DSP-150, transformer power 80 mVA) s the use of 60% metallized pellets and 40% metal scrap in the charge, which ensures that the mass fraction of nitrogen before release from the particleboard is not more than 0.003%, as well as a low content of colored impurities. Preliminary alloying of metal with manganese and silicon was carried out in a ladle when discharged from particleboard (releasing peroxidized metal into a ladle, metal deoxidation with aluminum, ferrosilicon — deoxidation, alloying with 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 billet is 900 ° C, which ensures a 15% reduction in energy consumption 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.

Long steel ⌀ 40 mm, length - 5900 mm, is obtained. The structure of lamellar perlite, no decarburization layer, the actual grain score is 7. Sulfide inclusions are globular, with an oxide shell, the volume fraction is 92%. The score for sulfide inclusions is 3.5. Point oxides - 0.5 points, line oxides - 0.5 points, brittle silicates - 0, plastic silicates - 0 points, non-deforming silicates - 0.5 points. Macrostructure: central porosity - 1 point, point heterogeneity - 1 point, segregation square - 0.5 points, shrink segregation - 0.5 points, segregation strips - 0.5 points.

Mechanical properties in the thermally improved state: the workpiece hardness is 197-205 HB, the tensile strength is 980 MPa, the yield strength is 890 MPa, the elongation is 14%, the impact strength KCU ⁺²⁰ 88 J / cm ² .

As + Sn + Pb + 5 × Zn = 0.022, oxygen / calcium = 2.5; calcium / sulfur = 0.0357.

Rolled steel has improved cutting characteristics and a favorable ratio of strength, ductility and toughness of steel.

Claims (2)

1. Long products in bars of medium carbon steel, hot rolled, having predetermined parameters of non-metallic inclusions, structure, mechanical properties, hardenability and machinability by cutting, characterized in that it is obtained from steel containing the following ratio of components, wt.%: carbon 0.36-0.44 manganese 0.60-0.90 silicon 0.15-0.30 chromium 0.80-1.10 sulfur (S) 0,040-0,075 calcium (Ca) 0.001-0.010 nitrogen 0.005-0.015 oxygen (O) 0.001-0.015 arsenic (As) 0.0001-0.03 tin (Sn) 0.0001-0.02 lead (Pb) 0.0001-0.01 zinc (Zn) 0.0001-0.005 iron and inevitable impurities  rest when performing the following ratios: (As + Sn + Pb + 5 Zn) ≤0.07; O ₂ / Ca = 1 ÷ 4.5; Ca / S≥0.020, it has non-metallic inclusions containing at least 75% oxysulfides with a sulfide shell with an average size of at least 3 points and point oxides, line oxides, brittle silicates, plastic silicates, undeformable silicates in aggregate no more than 2.0 points, macrostructure - central porosity , point heterogeneity, liquation square no more than 3 points for each species, shrink liquation no more than 3 points; segregation strips no more than 1 point, lamellar ferritoperlite structure with a real grain size of 5-9 points, mechanical properties: hardness 180-220 HB, tensile strength at least 950 MPa, yield strength at least 800 MPa, elongation at least 12%, impact strength KCU ⁺²⁰ not less than 60 J / cm ² . 2. Long products according to claim 1, characterized in that the steel further comprises, as impurities, wt.%: Nickel no more than 0.10, copper no more than 0.20, phosphorus no more than 0.020.