RU2337152C1 - Tube stock out of medium carbon low alloyed steel - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: tube stock with diameter from 80 to 180 mm produced out of steel containing wt %: carbon 0.41-0.48, manganese 0.90-1.15, silicon 0.17-0.37, nitrogen 0.005-0.015, arsenic 0.0001-0.03, tin 0.0001-0.02, lead 0.0001-0.01, zinc 0.0001-0.005, iron and unavoidable impurities - the rest at following ratio: As+Sn+Pb+5×Zn≤0.07; C+Mn/6≤0.65. Impurities are: chromium not more, than 0.30%, nickel not more, than 0.30%, molybdenum not more, than 0.10%, vanadium not more, than 0.02%, titanium not more than 0.02%, sulphur not more than 0.030%, calcium not more than 0.01%, niobium not more than 0.02%, phosphorus not more than 0.035%, copper not more than 0.30%. Tube stock is continuous cast, hot rolled, normalized, it has ferrite-pearlite structure, dimension of actual grain is 6-9 points, its macrostructure for central porosity, pointed non-uniformity, liquation square, sub-shrinking liquation, liquation strips - not more than 3 points in each kind, non-metallic inclusions - sulphides, pointed oxides, stripped oxides, fragile silicates, plastic silicates, non-deformed silicates - not more, than 4.5 points for each kind of inclusions.Stock possesses tensile strength of 638 H/mm², yield strength not less than 373 H/mm², contraction ratio not less than 40%, impact resilience KCU+20°C not less than 39 J/cm².

EFFECT: upgraded level of consumer characteristics.

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Description

The invention relates to the field of metallurgy, in particular to the production of tube billets with a diameter of 80 to 180 mm from medium-carbon low alloy steel.

Known pipe billet of low alloy steel containing carbon, manganese, silicon, chromium, nickel, vanadium, niobium, titanium, aluminum, calcium, sulfur, phosphorus, nitrogen, copper, antimony, tin, arsenic, iron - the rest, made from hot rolled sheet (RU 2180691 C1, 20.03.2002, C21D 9/08).

Known mild steel low-alloy steel for the manufacture of tube stocks containing carbon, silicon, manganese, niobium, molybdenum, sulfur, phosphorus, chromium, copper, nickel, aluminum, titanium and iron - the rest subjected to hot rolling (RU 2252972 C1, C21D 9/08 May 27, 2005).

The most important requirement for a pipe billet made of medium-carbon low alloy 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 range of consumer properties.

The objective of the invention is to provide an increased level of consumer properties with favorable ratios of strength, ductility and viscosity, a minimum level of anisotropy of mechanical properties, low content of non-metallic inclusions, homogeneous micro- and macrostructure of rolled products.

To solve this problem, the pipe billet of medium-carbon low alloy steel contains the following ratio of components, wt.%:

carbon 0.41-0.48 manganese 0.90-1.15 silicon 0.17-0.37 nitrogen 0.005-0.015 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:

amount: (arsenic + tin + lead + 5 × zinc) ≤0.07;

amount: (carbon + manganese / 6) ≤0.65.

The workpiece is made of continuously cast, hot-rolled, has a ferrite-pearlite structure, the actual grain size is 6–9 points, macrostructure: central porosity, point heterogeneity, segregation square, shrink segregation no more than 3 points for each type, segregation strips no more than 3 points, non-metallic inclusions: sulfides, point oxides, line oxides, brittle silicates, plastic silicates, undeformed silicates not more than 4.5 points for each type of inclusions, mechanical properties after normalization: the apparent tensile strength is not less than 638 N / mm ² , the yield strength is not less than 373 N / mm ² , the relative narrowing is not less than 40%, the impact strength KCU + 20 ° C is not less than 39 J / mm ² .

As impurities, the steel additionally contains chromium, nickel, molybdenum, vanadium, titanium, sulfur, calcium, niobium, phosphorus and copper in the following proportions, wt.%:

chromium no more than 0.30% nickel no more than 0.30% molybdenum no more than 0.10% vanadium no more than 0,02% titanium no more than 0,02% sulfur no more than 0,030% calcium no more than 0,01% niobium no more than 0,02% phosphorus no more than 0,035% copper no more than 0.30%.

The given combinations of alloying elements make it possible to obtain a ferrite-pearlite finely dispersed structure in the finished product with a favorable combination of strength and ductility characteristics, weldability, and reduced tendency to reversible temper brittleness.

Carbon is introduced into the composition of this steel to ensure a given level of its strength and hardenability. The upper limit of the carbon content (0.48%) is due to the need to obtain the required level of ductility of steel, and the lower - 0.41%, respectively - of 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. Moreover, the upper level of manganese content - 1.15% is determined by the need to ensure the required level of ductility of steel, and the lower - 0.90% - by the need to obtain the required level of strength and hardenability of this 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.

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% - due to issues of manufacturability.

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 C + Mn / 6≤0.66 determines the strength and toughness characteristics of the studied steel, while the ratio As + Sn + Pb + 5 × Zn≤0.07 determines the reduced tendency of the steel to manifest reversible temper brittleness.

An example embodiment of the invention. Smelting of the test steel (chemical composition in wt.%: Carbon - 0.45%, manganese - 1.06%, silicon - 0.25%, arsenic - 0.009%, tin - 0.005%, lead - 0.003%, zinc - 0.001 %, nitrogen (0.010%)) is produced in 150-ton steel-arc furnaces using 100% metallized pellets in the charge, which ensures that the mass fraction of nitrogen before discharge from the particleboard is not 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 a ladle upon discharge from particleboard. After release, the metal is purged with argon through the bottom purge unit, during which the steel is deoxidized with 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 adjusted according to the manganese content, and it is heated to a temperature that ensures further processing. After processing on AKOS, the metal is subjected to vacuum treatment on a batch vacuum. During evacuation, a final adjustment is made in chemical composition. After evacuation, the metal is treated with silicocalcium and transferred to casting. The casting is carried out on a four-strand radial-type ONRS with an ingot of 300 × 360 mm in size with a drawing speed of 0.6-0.7 m / min with protection of the metal from oxidation by using cover slag mixtures in the intermediate ladle and mold, protective tubes, immersion glasses and feeding argon. 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 are cooled in controlled cooling furnaces. Hot rolling of long products starts at a temperature of 1180-1150 ° C and ends at a temperature of 840-950 ° C.

The mechanical characteristics at room temperature are determined on type I samples, GOST 1497-84, on an INSTRON-1185 testing machine with strain-strain registration. The loading speed of the sample is 5 mm / min. The strength characteristics σ _b and σ _0.2 and ductility - δ are determined. The characteristics of the impact strength at room temperature are determined on samples of type I, GOST 9454-78, on a mechanical head MK-30. The viscous component in the fractures of shock samples is determined visually.

The average values of the characteristics calculated according to the test results of at least three samples per point. The significance of the differences in the average values of the analyzed values is evaluated using the student criterion, calculated as follows:

where M ₁ and M ₂ are the average values of the compared values; S ₁ ² and S ₂ ² - variance of the average; t _KR ^0.05 (α) is the critical value of the Student criterion at a significance level of 0.95 and the number of degrees of freedom is α.

The macrostructure is controlled in accordance with TU 14-1-5212-93 and GOST 10243-75.

As a result of hot rolling, a заготов120 mm pipe billet is obtained, length - 11,800 mm, plate perlite structure, real grain score - 9. 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: sulfides - 1 point, point oxides - 0 points, strox oxides - 1 point, brittle silicates - 1 point, plastic silicates - 1 point, non-deforming silicates - 1 point. Mechanical properties after normalization at 870 ° С, 1 hour, air: temporary tensile strength 651 N / mm ² , yield strength 395 N / mm ² , relative narrowing 58%, impact strength KCU + 20 ° C 55 J / mm ² .

As + Sn + Pb + 5 × Zn = 0.022, C + Mn / 6 = 0.627.

The introduction of the production of pipe billets from medium-carbon low alloy steel provides an increase in the level of consumer properties while ensuring a favorable ratio of strength, ductility and toughness, a minimum level of anisotropy of mechanical properties, a reduced tendency to reversible temper brittleness, satisfactory weldability, low content of non-metallic inclusions, homogeneous macro- and microstructure of rolled products .

Claims (2)

1. The pipe billet of medium-carbon low alloy steel, characterized in that it is obtained from steel containing the following ratio of components, wt.%: carbon 0.41-0.48 manganese 0.90-1.15 silicon 0.17-0.37 nitrogen 0.005-0.015 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, subject to the following ratios: (arsenic + tin + lead + 5 · zinc) ≤0.07; (carbon + manganese / 6≤0.65, Moreover, it is made of continuously cast, hot-rolled, normalized, has a ferrite-pearlite structure, the actual grain size is 6–9 points, the macrostructure is central porosity, point heterogeneity, segregation square, shrink segregation no more than 3 points for each type, segregation strips no more than 3 points, non-metallic inclusions for sulfides, point oxides, line oxides, brittle silicates, plastic silicates, undeformed silicates no more than 4.5 points for each type, temporary resistance e rupture of at least 638 N / mm ^2, yield stress of not less than 373 N / mm ^2, contraction ratio of not less than 40%, the toughness KCU + 20 ° C of at least 39 J / mm ^2. 2. The pipe billet according to claim 1, characterized in that as inevitable impurities, the steel contains components in the following proportions, wt.%: chromium no more than 0.30 nickel no more than 0.30 molybdenum no more than 0.10 vanadium no more than 0,02 titanium no more than 0,02 sulfur no more than 0,030 calcium no more than 0,01 niobium no more than 0,02 phosphorus no more than 0,035 copper no more than 0.30.