RU2338793C2 - Bar out of medium alloyed steel for cold die forging - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention refers to production of bar of 12-36 mm diameter for cold die forging of parts. To facilitate rational conditions of cold die forging simultaneously upgrading process plasticity and viscosity bar is produced out of steel containing wt %: C 0.37-0.43, Mn 0.70-1.00, Si 0.17-0.37, Ni 0.40-0.70, Cr 0.40-0.60, Mo 0.15-0.25, S 0.005-0.035, P 0.005-0.035, 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 maintaining the ratio: (As+Sn+Pb+5×Zn)≤0.07; 0.60≤(C+Mn/6)+(Cr+Mo)/5≤0.76, at that a bar has uniform spheroidising structure, containing of not less, than 60% of grain pearlite, dimension of actual grain 5-10 points, non-metallic inclusions for suplhides, oxides, and nitrides not more, than 3 points in each kind, macrostructure for central porosity, pointed non-uniformity, liquation square, sub-shrinking liquation not more, than 3 points in each kind, liquation strips not more, than 1 point, σ_t not more, than 660 Mpa, δ not less, than 15%, Ψ less, than 55%, hardenability on hardness of a sample at end hardening at the distance of 1.5 mm from the end 43-58 HRC, at the distance 5.0 mm from the end 40-55 HRC at the distance 9.0 from the end 38-54 HRC, cutability for value of wear of back edge of cutter h₃ not more, than 0.40 mm at cutting path L-1320 m, cold shrinkage not less, than 1/3 of bar height.

EFFECT: facilitating rational conditions of cold die forging of parts at simultaneous upgrading of process plasticity and viscosity.

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 12 to 36 mm for cold volume stamping of heat-improving, high-strength fasteners.

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, 10.20.2005).

The most important requirement for long products, round, from alloy steel for cold forming of high-strength fasteners, is, on the one hand, high technological ductility and low coefficient of strain hardening in the delivery state and, on the other hand, the ability to provide a given level of consumer properties after disembarkation.

The technical result of the invention is the provision of rational conditions for cold forming of high-strength fasteners while providing increased characteristics of technological plasticity and viscosity and reduced tendency to various types of brittle fracture.

In order to achieve a technical result, hot-rolled sections of medium alloyed steel, hot-rolled, having predetermined parameters of non-metallic inclusions, structure, mechanical properties and technological ductility, are obtained from steel containing the following ratio of components in wt.%:

carbon 0.37-0.43 manganese 0.70-1.00 silicon 0.17-0.37 nickel 0.40-0.70 chromium 0.40-0.60 molybdenum 0.15-0.25 sulfur 0.005-0.035 phosphorus 0.005-0.035 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 performing the following ratios:

(As + Sn + Pb + 5 × Zn) ≤0.07;

0.60≤ (C + Mn / 6) + (Cr + Mo) / 5≤0.76,

the rolled product has a uniform spheroidized structure, consisting of at least 60% granular perlite, the actual grain size is 5-10 points, the maximum degree of steel contamination with non-metallic inclusions for sulfides, oxides, silicates and nitrides does not exceed 3 points for each type of inclusions, the macrostructure is central porosity , point heterogeneity, liquation square no more than 3 points for each species, shrink liquation no more than 3 points; segregation strips of not more than 1 point, temporary tensile strength of not more than 660 MPa, elongation of not less than 15%, relative narrowing of not less than 55%, hardenability: hardness of the sample at end hardening at a distance of 1.5 mm from the end of 43-58 HRC, at a distance of 5.0 mm from the end 40-55 HRC, at a distance of 9.0 mm from the end 38-54 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 0.40 mm, cold draft not less than 1/3 of the height.

As an impurity, steel additionally contains copper not more than 0.10%.

When the content of sulfur in the steel is 0.005-0.020%, phosphorus 0.005-0.020%, the steel has a temporary tensile strength of not more than 640 MPa, and an elongation of at least 16%.

When the content of sulfur in the steel is 0.020-0.035%, phosphorus 0.005-0.020%, the machinability 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 not more than 0.25 mm .

The given combinations of alloying elements (item 1) make it possible to obtain a homogeneous finely dispersed ferrite-pearlite structure with a favorable combination of strength and ductility characteristics in the finished product (bolt, nut, stud).

Carbon is introduced into the composition of this steel in order to ensure a given level of its strength and toughness. The upper limit of the carbon content (0.43%) is due to the need to ensure the required level of ductility of steel, and the lower - respectively 0.37% - 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 austenite. Moreover, the upper level of manganese is 1.00%, molybdenum is 0.25% and chromium is 0.60% is determined by the need to ensure the required level of ductility of steel, and the lower is 0.70%, 0.15% and 0.40% accordingly, the need to provide the required level of strength of 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.

Nickel in the specified range (0.40-0.70%) affects the characteristics of hardenability and toughness of steel.

Nitrogen is an element involved in the formation of carbonitrides, while the lower level of its content (0.005%) is determined by the requirement to ensure a given level of strength, and the upper level (0.015%) is determined by the requirement to ensure a given level of ductility and hardenability.

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.

Phosphorus determines the level of ductility of steel and its tendency to reversible temper brittleness. 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.

Oxygen, forming oxides, contributes to the formation of the level of viscosity of steel. Moreover, the upper level of oxygen content - 0.015% 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 toughness.

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.

The ratio 0.60≥C + Mn / 6 + (Cr + Mo) / 5≤0.76 determines the hardenability characteristics of steel.

Examples of carrying out the invention, not excluding others in the scope of the claims. Smelting of the studied steels with chemical compositions in wt.%:

Example 1: carbon 0.39, manganese 0.92, silicon 0.22, nickel 0.52, chromium 0.51, molybdenum 0.21, sulfur 0.009, phosphorus 0.015, nitrogen 0.008, oxygen 0.007, arsenic 0.011, tin 0.009 lead 0.012; zinc 0.002;

Example 2: carbon 0.37, manganese 0.95, silicon 0.26, nickel 0.55, chromium 0.58, molybdenum 0.19, sulfur 0.032, phosphorus 0.025, nitrogen 0.010, oxygen 0.008, arsenic 0.009, tin 0.011 , lead 0,010, zinc 0,002 - is carried out in 150-tonne arc steel-smelting furnaces using 100% metallized pellets in the charge, which ensures a low content of color impurities. The preliminary alloying of the metal with manganese and silicon is carried out in the bucket when released from particleboard. After the release, the metal was purged with argon through the bottom purge unit during which the steel was deoxidized by aluminum. After that, the metal enters the integrated steel processing unit (AKOS), where it is possible to heat the metal to the required temperature, purge it with argon through the bottom blowing unit, dosed the necessary ferroalloys and treat the steel with flux-cored wire with various fillers. At AKOS, refining slag is induced with an additive of lime and fluorspar, heating to a temperature that ensures further processing. After processing at AKOS, the metal is subjected to vacuum treatment at a batch vacuum. During evacuation, a final adjustment of the chemical composition is carried out. Casting is carried out on a four-strand radial-type ONRS with an ingot 300 × 360 mm in size with a drawing speed of 0.6 ÷ 0.7 m / min, with metal protection from oxidation by using cover slag mixtures in the intermediate ladle and mold, protective tubes, immersion glasses and argon feed. It also provides a low nitrogen and oxygen content and metal purity from non-metallic inclusions. After casting and cutting to a measured length, the continuously cast billets obtained were cooled in controlled cooling furnaces. Hot rolling of long products starts at a temperature of 900-950 ° C and ends at a temperature of 740-850 ° C, with a deformation in the last passes of at least 20%.

Long products ⌀16 mm, in riots weighing 2300 kg, has:

Example 1. The structure of finely divided perlite, real grain score 8. Macrostructure: central porosity 1.0 point, point heterogeneity 1.0 point, segregation square 1 point, shrink segregation 1.5 point, segregation strips 0.5 point. Non-metallic inclusions: point sulfides 0.5 points, point oxides 0.5 points, line oxides 0.5 points, brittle silicates 1.0 points, plastic silicates 0.5 points, non-deformable silicates 1.0 points.

Temporary tensile strength 630 MPa, elongation of 17%, relative narrowing of 58%. Hardenability characteristics: hardness of the sample during end hardening at a distance of 1.5 mm from the end face of 48 HRC, at a distance of 5.0 mm from the end face of 46 HRC, at a distance of 9.0 mm from the end face of 40 HRC. Machinability by cutting - the amount of wear along the rear edge of the cutter (h ₃ ) with an equal cutting path (L) - with L = 1320 m h ₃ not more than 0.31 mm. The amount of cold draft 1/3 of the height

As + Sn + Pb + 5 × Zn = 0.042; C + Mn / 6 + (Cr + Mo) / 5 = 0.69

Example 2. The structure of fine perlite, the actual grain score 7. Macrostructure: central porosity 1.0 point, point heterogeneity 1.0 point, segregation square 1.5 point, shrink segregation 1.0 point, segregation strips 1.0 point. Non-metallic inclusions: point sulfides 1.5 points, point oxides 0.5 points, line oxides 0.5 points, brittle silicates 1.5 points, plastic silicates 0.5 points, non-deformable silicates 1.5 points.

Temporary tensile strength 650 MPa, elongation 15.5%, relative narrowing 56%. Hardenability characteristics: specimen hardness at end hardening at a distance of 1.5 mm from end face 49 HRC, at a distance of 5.0 mm from end face 47 HRC, at a distance of 9.0 mm from end face 41 HRC. Machinability by cutting - the amount of wear along the rear edge of the cutter (h ₃ ) with an equal cutting path (L) - with L = 1320 m h ₃ not more than 0.18 mm. The amount of cold draft 1/3 of the height

As + Sn + Pb + 5 × Zn = 0.040; (C + Mn / 6) + (Cr + Mo) / 5 = 0.68

The introduction of long products in coils, hot-rolled, round, made of medium alloyed steel, provides an increase in the level of consumer properties of rolled products while ensuring a favorable ratio of strength, ductility and toughness, a minimum level of anisotropy of mechanical properties, low content of non-metallic inclusions, homogeneous macro- and microstructure of rolled products.

Claims (4)

1. Sections of medium alloyed steel, hot rolled, having predetermined parameters of non-metallic inclusions, structure, mechanical properties and technological ductility, characterized in that it is obtained from steel containing the following ratio of components, wt.%: carbon 0.37-0.43 manganese 0.70-1.00 silicon 0.17-0.37 nickel 0.40-0.70 chromium 0.40-0.60 molybdenum 0.15-0.25 sulfur 0.005-0.035 phosphorus 0.005-0.035 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; 0.60≤ (C + Mn / 6) + (Cr + Mo) / 5≤0.76, Moreover, it has a homogeneous spheroidized structure, consisting of at least 60% granular perlite, real grain size of 5-10 points, non-metallic inclusions for sulfides, oxides, silicates and nitrides no more than 3 points for each type, macrostructure by central porosity, point heterogeneity , segregation squad, shrink segregation of not more than 3 points for each species, segregation strips of not more than 1 point, temporary tensile strength of not more than 660 MPa, elongation of at least 15%, relative narrowing of less than 55%, hardenability by hardness of the sample at end hardening equal to 1.5 mm from the end, 43-58 HRC, 5.0 mm from the end 40-55 HRC, 9.0 mm from the end 38- 54 HRC, machinability according to the amount of wear of the rear edge of the cutter h ₃ not more than 0.40 mm with a cutting path L = 1320 m, cold draft not less than 1/3 of the rolled height. 2. Long products according to claim 1, characterized in that the steel contains inevitable impurities, wt.%: Copper, not more than 0.10. 3. Long products according to claim 1 or 2, characterized in that when the content in steel, wt.%: Sulfur 0.005-0.020, phosphorus 0.005-0.020, it has a temporary tensile strength of not more than 640 MPa, elongation of at least 16%. 4. Long products according to claim 1 or 2, characterized in that when the content in steel, wt.%: Sulfur 0,020-0,035, phosphorus 0,005-0,020 machinability by cutting the amount of wear along the rear edge of the cutter h ₃ not more than 0.25 mm when cutting path L = 1320 m.