RU2330891C2 - Section iron, round made of low-carbon high-plastic steel for cold forging - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention concerns the metallurgy field. Particularly it concerns manufacturing of section iron of diameter from 12 to 36 mm. Technica result is obtained by getting section iron from steel which consists in mass % of: C - 0.04-0.11, Mn - 0.25-0.60, Si - 0.01-0.055, Al - 0.03-0.05, S - 0.005-0.015, P - 0.005-0.020, N - 0.005-0.015, O₂ - 0.00-0.015, As - 0.0001-0.03, Sn - 0.0001-0.02, Pb - 0.0001-0.01, Zn - 0.0001-0.005, iron and inevitable admixtures are the rest, in ratio: As+Sn+Pb+5×Zn≤0.07. Section iron has following macrostructure - center porosity, spot inhomogeneity, liquating square - not more than 3 points for every kind, undershrinked sweat - not more than 3 points; liquating strip - not more than 1 point, nonmetallic by sulphides, oxides, silicates and nitrides of dimension not more than 3 points for every kind of inclusions, homogeneous length spheroidised structure, which consists of not less than 60% granular pearlite, effective grain size is - 5-10 points, value of cold yielding is not less than 1/3 of height and mechanical properties: σ_"в" - not more than 460 MPa, δ - not less than 28%, ψ - not less than 65%, solidity is not more than 160 HB.

EFFECT: obtaining of heightened specifications technological plasticity and viscosity of section iron for supplying of efficient conditions for cold forging of figurine fasteners.

3 cl, 2 ex

Description

The invention relates to the field of metallurgy, in particular the production of long products in coils, hot-rolled, round, with a diameter of 12 to 36 mm, from low-carbon high-ductility steel for cold forming.

Known long products of round steel from low-carbon steel containing carbon, manganese, silicon, sulfur, vanadium, niobium, calcium, iron and impurities, steel has a maximum steel pollution rating of non-metallic inclusions for sulfides, oxides, silicates and nitrides of no more than 3 for each type, homogeneous spheroidized structure, consisting of at least 80% granular perlite, the size of the actual grain is 5-10 points. The amount of cold draft is not less than 1/3 of the height. (RU 2249628 C1, C21D 8/06, 04/10/2005).

The closest analogue is round billets made of low-carbon steel containing carbon, manganese, silicon, chromium, vanadium, niobium, sulfur, aluminum, calcium, nitrogen, iron and impurities; rolled products have a maximum grade of steel contamination by non-metallic inclusions for sulfides, oxides, silicates and nitrides no more than 3 points for each species, a homogeneous spheroidized structure consisting of at least 80% granular perlite, the actual grain size is 5-10 points, the cold precipitation is at least 1/3 of the height (RU 2262538 C1, C21D 6 / 06.20.10. 2005).

The most important requirements for low-carbon steel bars for cold forming for fasteners of particularly complex shapes are, 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 to provide improved characteristics of technological plasticity and viscosity.

The technical result is achieved by the fact that round billets made of low-carbon steel in coils, hot-rolled, having predetermined parameters of steel contamination with non-metallic inclusions, structure, mechanical properties and technological ductility, are obtained from steel containing the following ratio of components in wt.%:

carbon 0.04-0.11 manganese 0.25-0.60 silicon 0.01-0.055 aluminum 0.03-0.05 sulfur 0.005-0.015 phosphorus 0.005-0.020 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 - the rest,

when the relation is fulfilled: the sum (As + Sn + Pb + 5 × Zn) ≤0.07,

the maximum contamination score of steel with non-metallic inclusions for sulfides, oxides, silicates and nitrides does not exceed 3 points for each type of inclusions, the rolled product has a uniform spheroidized structure in length, consisting of at least 60% granular perlite, the actual grain size is 5-10 points, size cold precipitation of at least 1/3 of the height, macrostructure - central porosity, point heterogeneity, segregation square - not more than 3 points for each species, shrink liquation - not more than 3 points, segregation strips - not olee 1 point, mechanical properties: tensile strength - not more than 460 MPa, elongation - at least 28%, relative narrowing - no less than 65%, the hardness - no more than 160 HB.

As impurities, steel additionally contains in wt%: nickel not more than 0.10, copper not more than 0.10, chromium not more than 0.10.

When the carbon content in the steel is 0.04-0.07%, manganese 0.25-0.40%, the rolled metal has mechanical properties: temporary tensile strength not more than 420 MPa, elongation not less than 30%, relative narrowing not less than 70%, hardness no more than 110 HB.

When the carbon content in the steel is 0.04-0.11%, manganese 0.30-0.60%, the rolled product has mechanical properties: temporary tensile strength not more than 460 MPa, elongation not less than 28%, relative narrowing not less than 65%, hardness no more than 160 HB.

The given combinations of alloying elements (item 1) make it possible to obtain a uniform finely dispersed ferrite-pearlite structure with a favorable combination of strength and ductility characteristics in the finished product (bolt, nut, stud with a diameter of up to 16 mm).

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 (0.11%) is due to the need to ensure the required level of ductility of steel, and the lower (respectively 0.04%) - to ensure the required level of strength and hardenability of this steel.

Manganese is used, on the one hand, as a hardener of a solid solution, and on the other hand, as an element that significantly increases the stability of supercooled austenite. Moreover, the upper level of manganese content - 0.55% is determined by the need to ensure the required level of ductility of steel, and the lower - 0.25% by the need to provide the required level of strength of steel.

Silicon refers to ferrite-forming elements. The lower limit on silicon is 0.01% due to the steel deoxidation technology. A silicon content above 0.055% will adversely affect the ductility characteristics of steel.

Aluminum is used as a deoxidizing agent. So the lower level of aluminum content - 0.03% is determined by the requirement to ensure the viscosity of steel, and the upper level - 0.05% by the requirement to ensure a given level of ductility of steel.

Nitrogen, 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 is due to the need to obtain a given level of ductility and toughness of steel, and the lower limit is due to issues of manufacturability.

Phosphorus determines the level of ductility of steel and its tendency to reversible temper brittleness. The upper limit (0.020%) 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.

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 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 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.

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

Smelting of the studied steels with different chemical composition in wt.%:

Example 1: carbon — 0.05, manganese — 0.32, silicon — 0.015, aluminum — 0.041, sulfur — 0.008, nitrogen — 0.008, phosphorus — 0.011, oxygen — 0.006, arsenic — 0.010, tin — 0.008, lead — 0.009 zinc - 0.002;

Example 2: carbon - 0.09%, manganese - 0.52%, silicon - 0.045%, aluminum - 0.044%, sulfur - 0.007%, nitrogen - 0.006%, phosphorus - 0.012%, oxygen - 0.006, arsenic - 0.012% , tin - 0.007%, lead - 0.006%, zinc - 0.001%

It is produced 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 ladle upon discharge from the 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 made. The casting is carried out on radial four-strand UNRS in 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%.

Get long products ⌀16 mm, in riots weighing 2300 kg, which has:

Example 1: the structure of spheroidized perlite, the proportion of spheroidized perlite is 87%, the actual grain score is 8. Macrostructure: central porosity - 1.0 point, point heterogeneity - 1.0 point, segregation square - 1 point, shrinkage segregation - 1.5 point, liquidation strips - 0.5 points. 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-deforming silicates - 1.0 point . Temporary tear resistance - 360 MPa, elongation - 34%, relative narrowing - 73%, Hardness - 98 HB.

As + Sn + Pb + 5 × Zn = 0.037

Example 2: the structure of spheroidized perlite, the proportion of spheroidized perlite is 91%, the real grain score is 7. Macrostructure: central porosity - 1.0 point, point heterogeneity - 1.0 point, segregation square - 1.5 points, shrinkage 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-deforming silicates - 1.5 points. Temporary tensile strength - 410 MPa, elongation - 30%, relative narrowing - 68%, Hardness - 110 HB.

As + Sn + Pb + 5 × Zn = 0.030

The introduction of rolled products in coils, hot-rolled, round, made of low-carbon 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, a low content of non-metallic inclusions, homogeneous macro- and microstructure of rolled products.

Claims (4)

1. Round billets, smelted from mild steel, hot rolled, having predetermined parameters of non-metallic inclusions, structure, mechanical properties and technological ductility, characterized in that the steel contains the following ratio of components, wt.%: carbon 0.04-0.11 manganese 0.25-0.60 silicon 0.01-0.055 aluminum 0.03-0.05 sulfur 0.005-0.015 phosphorus 0.005-0.020 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 the relation is satisfied: (As + Sn + Pb + 5 · Zn) ≤0.07, in this case, the hire has non-metallic inclusions for sulfides, oxides, silicates and nitrides with a size not exceeding 3 points for each type of inclusions, a homogeneous spheroidized structure in length, consisting of at least 60% granular perlite, the size of the actual grain is 5-10 points, the macrostructure is central porosity, point heterogeneity, segregation square - not more than 3 points for each type, shrink segregation - not more than 3 points, segregation strips - not more than 1 point, mechanical properties - temporary fracture resistance y is not more than 460 MPa, elongation at least 28%, contraction ratio is not less than 65%, the hardness is not more than 160 HB, the magnitude of cold precipitation do not less than 1/3 of the height. 2. Rolled steel according to claim 1, characterized in that the steel contains inevitable impurities, wt.%: Nickel not more than 0.10, copper not more than 0.10, chromium not more than 0.10. 3. Long products according to any one of claims 1 or 2, characterized in that when the content in steel (wt.%) Of carbon is 0.04-0.07, manganese 0.25-0.40, it has mechanical properties - temporary resistance a gap of not more than 420 MPa, an elongation of at least 30%, a relative narrowing of at least 70%, a hardness of not more than 110 HB. 4. Long products according to any one of claims 1 or 2, characterized in that when the carbon content in the steel (wt.%) Is 0.04-0.11, manganese 0.30-0.60, it has mechanical properties - temporary resistance a gap of not more than 460 MPa, elongation of not less than 28%, relative narrowing of not less than 65%, hardness not more than 160 HB.