RU2338794C2 - Bar out of medium carbon chromium containing steel for cold die forging - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention refers to bar of 15-32 mm diameter used for fabrication of ball pins by method of cold die forging. To increase forging and cutability characteristics of parts a bar is fabricated out of steel containing wt %: C - 0.38-0.45, Mn - 0.60-0.90, Si - 0.05-0.40, Cr -0.90-1.20, S - 0.020-0.040, Mo - 0.005-0.30, 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 impurities at the ratio of (As+Sn+Pb+5×Zn)≤0.07, O₂/Ca=1÷4.5, Ca/S≥0.065, at that the bar is made continuous cast and hot-rolled, it has fine dispersed ferrite-pearlite structure and dimension of actual grain 5-9 points, the depth of carbon free layer not more, than 1.5% from diameter to the side, value of cold shrinkage not more, than 1/3 of height, non-metallic inclusions of sulphides with oxide coating, pointed oxides, stripped oxides, fragile silicates, plastic silicates, non-deformed silicates not more than 3.5 points in each kind of inclusions, on macrostructure it has central porosity, pointed non-uniformity, liquation square and sub-shrinking liquation not more, than 3 points in each kind, liquation strips not more, than 1 point. Mechanical properties are σ_t not more, than 730 Mpa, δ not less, than 14%, Ψ less, than 45%, hardenability on hardness of a sample at end hardening at the distance of 1.5 mm from the end 53-61 HRC, cutability for value of wear of back edge of cutter h₃ not more, than 0.20 mm at cutting path L-1320 m.

EFFECT: upgraded mechanical properties.

4 cl, 2 ex

Description

The invention relates to the field of metallurgy, in particular to the production of long products with a diameter of 15 to 32 mm from medium-carbon chromium-containing steel of increased stampability and machinability by cutting, used for manufacturing by cold forming of ball fingers.

Known long products from medium carbon steel of chrome-containing steel for cold forming, containing carbon, manganese, silicon, sulfur, chromium, vanadium, molybdenum, nickel, niobium, titanium, boron, aluminum, nitrogen, iron and impurities, hot-rolled, having specified non-metallic parameters inclusions on sulfides, oxides, silicates, nitrides, homogeneous spheroidized structure, actual grain size of 5-10 points, cold precipitation of at least 1/3 of the height, decarburized layer of not more than 1.5% of the diameter, temporary tensile strength not more than 640 MPa, elongation of at least 18%, relative contraction of at least 55%. (RU 2249626 C1, C21D 8/06, 04/10/2005).

Known long products from medium carbon chrome steel for cold forming, containing carbon, manganese, silicon, chromium, nickel, copper, molybdenum, sulfur, niobium, calcium, iron and impurities, hot-deformed, having a uniform spheroidized structure, the actual grain size of 5-10 points, the size of non-metallic inclusions: sulfides, oxides, silicates and nitrides does not exceed 3 points for each type, decarburized layer is not more than 1.5% of the diameter, cold sediment is not less than 1/3 of the height, temporary tensile strength not more than 620 MPa, elongation of at least 18%, relative contraction of at least 55%. (RU 2262539 C1, C21D 8/06, 20/10/2005).

The technical result of the invention is to provide favorable conditions for the stampability of complex thermally hardened parts and to increase the characteristics of grindability and machining while maintaining the increased characteristics of technological plasticity and a set of consumer properties during further heat treatment.

The technical result is achieved by the fact that round billets made of medium-carbon chromium-containing steel, hot rolled, having predetermined parameters of non-metallic inclusions, structure, mechanical properties, hardenability and machinability by cutting, are obtained from steel containing the following ratio of components in wt.%:

carbon 0.38-0.45 manganese 0.60-0.90 silicon 0.05-0.40 chromium 0.90-1.20 sulfur 0,020-0,040 molybdenum 0.005-0.30 calcium 0.001-0.010 nitrogen 0.005-0.015 oxygen 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 ratio:

(As + Sn + Pb + 5 × Zn) ≤0.07;

oxygen / calcium = 1 ÷ 4.5;

calcium / sulfur ≥0.065,

rolled metal has a finely dispersed ferrite-pearlite structure, the actual grain size is 5–9 points, the depth of the decarburized layer is not more than 1.5% of the diameter per side, non-metallic inclusions: sulfides with an oxide shell, point oxides, line oxides, brittle silicates, plastic silicates, non-deformable silicates with a size of not more than 3.5 for each type of inclusions, macrostructure: central porosity, point heterogeneity, segregation square of not more than 3 points for each type, shrinkable segregation - not more than 3 points, segregation strips no more than 1 point, mechanical properties: temporary tensile strength no more than 730 MPa, hardenability: hardness of the specimen at end hardening at a distance of 1.5 mm from the end of 53-61HRC, at a distance of 5.0 mm from the end of 50-61 HRC, at a distance of 9.0 mm from the end 41-60 HRC, 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, cold draft not less than 1/3 of the height.

As impurities, the steel additionally contains nickel up to 0.30%; phosphorus no more than 0.035%.

When the molybdenum content in the steel is 0.15-0.30%, the rolled product has mechanical properties: temporary tensile strength not more than 730 MPa, elongation not less than 14%, relative narrowing not less than 45%, hardenability: hardness of the sample at end hardening, at a distance 5.0 mm from the end 52-61 HRC, at a distance of 9.0 mm from the end 49-60 HRC.

When the molybdenum content in the steel is 0.005-0.10%, the rolled product has mechanical properties: temporary tensile strength of not more than 700 MPa, elongation of at least 16%, relative narrowing of at least 50%, hardenability: hardness of the specimen at end hardening, at a distance of 5, 0 mm from the end 50-60 HRC, at a distance of 9.0 mm from the end 41-58 HRC.

The given combinations of alloying elements (p. 1) make it possible to obtain a favorable structure with globular sandwich inclusions in the proposed hire, which provides, on the one hand, improved cutting characteristics, and on the other hand, a favorable combination of strength and ductility characteristics, as well as technological ductility during cold volume stamping.

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 (0.45%) is due to the need to ensure the required level of ductility of steel, and the lower - respectively 0.38% - to ensure the required level of strength and hardenability of this steel.

Manganese, molybdenum 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 steel austenite. The upper level of manganese is 0.90%, molybdenum is 0.30 and chromium is 1.20% is determined by the need to ensure the required level of ductility of steel, and the lower is 0.60%, 0.005% and 0.90%, respectively, by the need provide the required level of strength and hardenability of this steel.

Silicon refers to ferrite-forming elements. The lower limit for silicon - 0.40% is due to the technology of deoxidation of steel. A silicon content above 0.005% will adversely affect the ductility characteristics of steel.

Sulfur determines the level of ductility of steel. The upper limit (0.040%) is due to the need to obtain a given level of ductility and toughness of steel, and the lower limit (0.020%) 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 of -0.005% - due 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. Moreover, 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 general 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 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 is 1, respectively, the possibility of the formation of a two-layer sandwich-non-metallic inclusion.

The calcium / sulfur ratio of ≥0.065% determines the conditions for the formation of globular nonmetallic 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.

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

Smelting of the studied steels with the following chemical compositions in wt.%:

Example 1: carbon 0.44, manganese 0.76, silicon 0.32, chromium 1.12, sulfur 0.034, molybdenum 0.03, calcium 0.0029, nitrogen 0.005, oxygen 0.009, arsenic 0.008, tin 0.009, lead 0.009, zinc 0.002;

Example 2: carbon 0.43, manganese 0.79, silicon 0.30, chromium 1.10, sulfur 0.032, molybdenum 0.23, calcium 0.0030, nitrogen 0.008, oxygen 0.009, arsenic 0.010, tin 0.008, lead 0.010 Zinc 0.002 is carried out in 150-tonne arc steel-smelting furnaces (DSP-150, transformer power 80 mW) 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 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 products ⌀22 mm, length - 5900 mm, has:

Example 1: the structure is finely dispersed ferrite-pearlite, decarburized layer 0.16 mm, 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.

Tensile strength 690 MPa, elongation of 16.5%, relative narrowing of 58%. Hardenability characteristics: sample hardness at end hardening at a distance of 1.5 mm from the end - 56 HRC, at a distance of 5.0 mm from the end - 53 HRC, at a distance of 9.0 mm from the end - 50 HRC. 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 0.15 mm. The amount of cold precipitation is 1/3 of the height. As + Sn + Pb + 5 × Zn = 0.037, oxygen / calcium = 3.1; calcium / sulfur = 0.085;

Example 2: the structure is finely dispersed ferrite-pearlite, decarburized layer 0.21 mm, 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. Temporary tear resistance 710 MPa, elongation 13.5%, relative narrowing 52%.

Hardenability characteristics: sample hardness at end hardening at a distance of 1.5 mm from the end - 60 HRC, at a distance of 5.0 mm from the end - 59 HRC, at a distance of 9.0 mm from the end - 53 HRC. 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 0.11 mm. 1/3 height cold draft

As + Sn + Pb + 5 × Zn = 0.038, oxygen / calcium = 3.0; calcium / sulfur = 0.094.

Rolled steel has a high machinability and high cutting characteristics with a favorable ratio of strength, ductility and toughness of steel.

Claims (4)

1. High-quality round products from medium-carbon chromium-containing steel, hot-rolled, characterized in that it is obtained from steel containing the following ratio of components, wt.%: carbon 0.38-0.45 manganese 0.60-0.90 silicon 0.05-0.40 chromium 0.90-1.20 sulfur 0,020-0,040 molybdenum 0.005-0.30 calcium 0.001-0.010 nitrogen 0.005-0.015 oxygen 0.001-0.015 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; O ₂ / Ca = 1 ÷ 4.5; Ca / S≥0.065, moreover, it has a finely dispersed ferrite-pearlite structure, the actual grain size is 5–9 points, the depth of the decarburized layer is not more than 1.5% of the diameter per side, nonmetallic inclusions on sulfides with an oxide shell, point oxides, construction oxides, brittle silicates, silicates plastic, non-deformable silicates no more than 3.5 points for each type, macrostructure for central porosity, point heterogeneity, segregation square, shrink segregation no more than 3 points for each type, segregation strip not more than 1 point, temporary tensile strength not more than 730 MPa, hardenability by hardness of the sample at end hardening at a distance of 1.5 mm from the end face 53-61 HRC, at a distance of 5.0 mm from the end face 50-61 HRC, at a distance of 9, 0 mm from the end 41-60 HRC, machinability by the amount of wear of the rear edge of the cutter h ₃ not more than 0.20 mm when the cutting path L = 1320 m, cold draft not less than 1/3 of its height. 2. Long products according to claim 1, characterized in that the steel contains, as inevitable impurities, wt.%: Nickel not more than 0.30, phosphorus not more than 0.035. 3. Long products according to claim 1 or 2, characterized in that when the content of molybdenum in the steel is 0.15-0.30 wt.%, It has a temporary tensile strength of not more than 730 MPa, elongation of at least 14%, relative narrowing of less than 45%, hardenability by hardness of the sample at end hardening, at a distance of 5.0 mm from the end of 52-61 HRC, at a distance of 9.0 mm from the end of 49-60 HRC. 4. Long products according to claim 1 or 2, characterized in that when the content of molybdenum in the steel is 0.005-0.10 wt.%, It has a temporary tensile strength of not more than 700 MPa, a relative elongation of at least 16%, a relative narrowing of at least 50 %, hardenability by hardness of the sample at end hardening at a distance of 5.0 mm from the end of 50-60 HRC, at a distance of 9.0 mm from the end of 41-58 HRC.