RU2330893C2 - Pipe shell made of low-alloy steel - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention concerns the metallurgy field. Particularly it concerns manufacturing of pipe shell of diameter from 80 to 180 mm, intended for producing seamless pipe for various purposes. For supporting of heightened level of consumer behavior pipe shell is made from steel which consists in mass % of: C - (0.1-0.20), Mn - (1.0-1.35), Si - (0.15-0.40), V - (0.025-0.080), N - 0.005-0.009, As - (0.0001-0.03), Sn -(0.0001-0.02), Pb - (0.0001-0.01), Zn - (0.0001-0.005), iron and inevitable admixtures, in ratio: As+Sn+Pb+5×Zn≤0.07; [C+(Mn/6+V/5)] ≤0.42. Blank is made as hot-rolled, normalised, has ferrite-pearlite structure, effective grain size is 5-10 points, macrostructure is: center porosity, spot inhomogeneity, liquating square, undershrinked sweat is not more than 2.0 points, liquating strip is not more than 1 point, nonmetallic: spot sulphides, spot oxide, stitch oxide, fragile silicate, plastic silicate, unstrained silicate - not more than 3.0 points for every kind. Admixtures: P is not more than 0.025%; S is not more than 0.010%; Cr is not more than 0.20%, Cu is not more than 0.15%; Mo is not more than 0.07%, tensile strength is 400-585 N/mm², yield strength is not less than 220 N/mm², percentage elongation is not less than 30%, impact strength is KCV (+20°C) is not less than 39.2 J/cm².

EFFECT: pipe shell possesses favourable ratio of strength, plasticity and viscosity, mechanical anisotropy floor, low content of nonmetallic, homogeneous macro and microstructure of section iron, heightened hardening characteristics.

4 cl, 2 ex

Description

The invention relates to the field of metallurgy, in particular to the production of a turned tubular billet with a diameter of 80 to 180 mm from medium carbon medium alloy steel, intended for the production of seamless pipes for various purposes.

Known pipe billet of alloy steel containing carbon, manganese, silicon, chromium, nitrogen, aluminum, sulfur, phosphorus, zinc, lead, tin, bismuth, antimony, having specified mechanical properties and a given structure (SU 1754790 A1, C22C 38 / 60, 08/15/1992).

Known tube billet made of alloy steel containing carbon, silicon, manganese, chromium, sulfur, phosphorus, copper, nickel, aluminum, antimony, tin, arsenic and iron, the rest having specified mechanical properties and a given structure. (RU 2252972 C1, C21D 9/08, 05/27/2005).

The most important requirement for a pipe billet made of medium-carbon medium alloyed steel is, on the one hand, to ensure uniformity of micro and macrostructure, low content of non-metallic inclusions, and, on the other hand, to provide an increased complex of consumer properties and a given morphology of non-metallic inclusions.

The objective of the invention is to provide a high level of consumer properties while providing a favorable ratio of strength, ductility and viscosity, a minimum level of anisotropy of mechanical properties, low content of non-metallic inclusions, homogeneous macro- and microstructure of rolled products, increased hardenability characteristics. The problem is solved in that the tubular billet of low alloy steel, having the specified parameters, structure, mechanical properties, hardenability, is made of steel containing the following ratio of components, wt.%:

carbon [C] 0.10-0.20 Manganese [Mn] 1.0-1.35 silicon [Si] 0.15-0.40 vanadium [V] 0.025-0.080 nitrogen [N] 0.005-0.009 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 the relations are satisfied: (As + Sn + Pb + 5 × Zn) ≤0.07; [C + (Mn / 6) + (V / 5)] ≤0.42, hot-rolled, normalized, has a ferrite-pearlite structure, actual grain size is 5-10 points, macrostructure is central porosity, point heterogeneity, segregation square, shrink segregation - not more than 2.0 points, segregation strips - not more than 1 point, non-metallic inclusions: point sulphides, point oxides, line oxides, brittle silicates, plastic silicates, undeformed silicates - not more than 3.0 points, average for each type of inclusions , mechanical properties in a normalized state Phenomena: temporary tensile strength 400-585 N / mm ² , yield strength - not less than 220 N / mm ² , relative elongation not less than 30%, impact strength KCV (+ 20 ° С) not less than 39.2 J / cm ² .

As impurities, steel additionally contains, wt.%: Phosphorus not more than 0.025, sulfur not more than 0.010, chromium not more than 0.20, copper not more than 0.15, molybdenum not more than 0.07.

When the content in steel C is (0.10-0.15)%, the workpiece has mechanical properties in a normalized state: temporary tensile strength 400-560 N / mm ² , yield strength not less than 220 N / mm ² , elongation not less than 32 %, impact strength KCV (+ 20 ° С) not less than 44.2 J / cm ²

At a content of C - (0.15-0.20)%, the workpiece has mechanical properties in a normalized state: temporary tensile strength 415-585 N / mm ² , yield strength - not less than 241 N / mm ² , elongation - not less than 30 %, impact strength KCV (+ 20 ° С) not less than 39.2 J / cm ² .

The given combinations of alloying elements (item 1) make it possible to obtain a finely dispersed ferrite-pearlite structure, optimal content and morphology of nonmetallic inclusions, a homogeneous macrostructure, and a favorable combination of strength and ductility characteristics in the finished product.

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 (0.20%) is due to the need to ensure the required level of ductility of steel, and the lower, respectively 0.10%, to ensure the required level of strength and hardenability of this steel.

Manganese is used, on the one hand, as a solid solution hardener, and on the other hand, as an element that increases the stability of supercooled austenite of steel. The upper level of 1.35% manganese is determined by the need to ensure the required level of ductility of steel, and the lower by 1.0%, respectively, by the need to provide the required level of strength and hardenability of this steel.

Silicon refers to ferrite-forming elements. The lower silicon limit of 0.15% is due to steel deoxidation technology. A silicon content above 0.40% will adversely affect the ductility characteristics of steel.

Nitrogen promotes the formation of nitrides in steel. The upper limit of nitrogen content of 0.009% is due to the need to obtain a given level of ductility and toughness of steel, and the lower limit of 0.005% is due to issues of manufacturability.

Vanadium is introduced into the composition of this steel in order to provide a finely dispersed, uniform grain structure. Moreover, it controls the processes in the lower part of the austenitic region (determines the tendency to growth of austenite grain, stabilizes the structure during thermomechanical processing, increases the temperature of recrystallization and, as a result, affects the nature of the γ-α transformation. The upper limit of vanadium content is 0.080%, due to the need ensuring the required level of ductility of steel, and the lower - respectively 0.025% - providing the required level of strength of this 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 due to the technology of steel production, and the upper limit (0.03%, 0.02%, 0.01% and 0.005%, respectively) determines an increased tendency steel to reversible temper brittleness.

The ratio (As + Sn + Pb + 5 × Zn) ≤0.07 determines the reduced tendency of steel to manifest reversible temper brittleness. The ratio [C + (Mn / 6) + (V / 5)] ≤0.42 determines the parameters of the viscosity and hardenability of steel.

The analysis of patent and scientific and technical information did not reveal solutions having a similar set of features that would achieve a similar effect - providing an increased level of consumer properties, while ensuring a favorable ratio of strength, ductility and viscosity, a minimum level of anisotropy of mechanical properties, low content of non-metallic inclusions, homogeneous macro and microstructure rolled. Therefore, the claimed combination of features corresponds to the novelty and inventive step.

Examples of carrying out the invention, not excluding others in the scope of the claims. Smelting of the investigated steel; chemical composition, wt.%:

Example 1: carbon - 0.12%, manganese - 1.19%, silicon - 0.29%, vanadium - 0.044%, nitrogen - 0.007%, arsenic - 0.011, tin - 0.011, lead - 0.009, zinc - 0.002%;

Example 2: carbon - 0.18 manganese - 1.22%, silicon - 0.27%, vanadium - 0.034%, nitrogen - 0.007%, arsenic - 0.010, tin - 0.011, lead - 0.010, zinc - 0.002%) is produced in 150-ton arc steel-smelting furnaces (DSP) using 100% metallized pellets in the charge, which ensures that the mass fraction of nitrogen before discharge from the DSP is no more than 0.003%, as well as 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 imposed with an additive of lime and fluorspar, slag is deoxidized with granulated aluminum, the metal is alloyed with aluminum to a content of 0.050%, the metal is refined according to the manganese content, and it is heated 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. After evacuation, the metal is treated with silicocalcium and transferred to casting. 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 of at least 20% in the last passes. Heat treatment of rolled products included normalization from 910-930 ° C.

As a result of hot rolling we get a pipe billet with a diameter of 110 mm, a length of 4800 mm.

From steel according to example 1: lamellar ferrite-pearlite structure, the actual grain score is 9. Macrostructure: central porosity - 1 point, point heterogeneity - 1 point, segregation square - 1 point, shrink segregation - 1 point, segregation strips - 1 point. Non-metallic inclusions: point sulfides - 2 points, point oxides - 2 points, line oxides - 2 points, brittle silicates - 2 points, plastic silicates - 0.5 points, undeformed silicates - 1.5 points. Mechanical properties in a normalized state: temporary tensile strength 487 N / mm ² , yield strength 291 N / mm ² , elongation 33%, Impact strength KCV (+ 20 ° C) 51.5 J / cm ²

(As + Sn + Pb + 5 × Zn) = 0.041; [C + (Mn / 6) + (V / 5)] = 0.327

From steel according to example 2: lamellar ferrite-pearlite structure, the actual grain score is 8. Macrostructure: central porosity - 2 points, point heterogeneity - 2 points, segregation square - 1 point, shrink segregation - 1 point, segregation strips - 1 point. Non-metallic inclusions: point sulfides - 2.0 points, point oxides - 1.0 points, line oxides - 0.5 points, brittle silicates - 1.0 points, plastic silicates - 1.0 points, undeformed silicates - 1.0 points . Mechanical properties in a normalized state: temporary tensile strength 521 N / mm ² , yield strength 324 N / mm ² , elongation 30%, Impact strength KCV (+ 20 ° С) 41.4 J / cm ²

(As + Sn + Pb + 5 × Zn) = 0.041; [C + (Mn / 6) + (V / 5)] = 0.417

A low-alloy steel billet provides an increased level of consumer properties of rolled products, a favorable ratio of strength, ductility and toughness, a minimum level of anisotropy of mechanical properties, a low content of non-metallic inclusions, and a homogeneous macro- and microstructure.

Claims (4)

1. The pipe billet of low alloy steel having predetermined parameters of the structure, mechanical properties, characterized in that it is made of steel containing the following ratio of components, wt.%: carbon [C] 0.10-0.20 Manganese [Mn] 1.0-1.35 silicon [Si] 0.15-0.40 vanadium [V] 0.025-0.080 nitrogen [N] 0.005-0.009 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 fulfilling the relations: (As + Sn + Pb + 5 Zn) ≤0.07; [C + (Mn / 6) + (V / 5)] ≤0.42, hot-rolled, normalized, while it has a ferritic perlite structure, the actual grain size is 5-10 points, macrostructure: central porosity, point heterogeneity, segregation square, shrink segregation not more than 2.0 points, segregation strips not more than 1 point, non-metallic inclusions: sulfides point, point oxides, oxides stitch, brittle silicates, silicates plastic, undeformed silicates with an average score of not more than 3.0 for each type, tensile strength 400-585 N / mm ^2, yield stress not less than 220 N / mm ^2, an elongation of not less than 30%, impact strength KCV (+ 20 ° C) not less than 39.2 J / cm ^2. 2. The pipe billet according to claim 1, characterized in that the steel contains inevitable impurities, wt.%: Phosphorus not more than 0.025, sulfur not more than 0.010, chromium not more than 0.20, copper not more than 0.15, molybdenum not more than 0.07. 3. The pipe billet according to any one of claims 1 and 2, characterized in that when the carbon content in the steel is (0.10-0.15) wt.%, The billet has a temporary tensile strength of 400-560 N / mm ² , the yield strength is not less than 220 N / mm ² , elongation not less than 32%, impact strength KCV (+ 20 ° С) not less than 44.2 J / cm ² . 4. The pipe billet according to any one of claims 1 and 2, characterized in that when the carbon content is (0.15-0.20) wt.%, The billet has a temporary tensile strength of 415-585 N / mm ² , yield strength of at least 241 N / mm ² , elongation not less than 30%, impact strength KCV (+ 20 ° С) not less than 44.2 J / cm ² .