RU2336328C1 - Tube stock out of micro alloyed steel - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention refers to metallurgy, particularly to production of tube stock with diameter from 80 to 180 mm. To facilitate upgraded level of consumer characteristics at a minimal level of anisotropy of mechanical properties the tube stock is fabricated continuous cast, hot rolled, out of steel, containing, wt %: carbon 0.14-0.20, manganese 1.00-1.40, silicon 0.03-0.10, titanium 0.002-0.03, aluminium 0.02-0.05, vanadium 0.002-0.02, sulphur 0.005-0.012, phosphorus 0.005-0.013, 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 the ratio: As+Sn+Pb+5xZn<0.07, C+Mn/6+V/5≤0.40. As impurities steel contains wt %: niobium not more, than 0.02, chromium not more, than 0.30, nickel not more, than 0.30, copper not more, than 0.30. The stock has ferrite-pearlite structure with the dimension of the actual grain of 6-9 points. It also has macrostructure for central porosity, pointed non-uniformity, liquation square and subshrinking liquation not more, than 3 points for each kind, and liquation strips - not more, than 1 points. Non-metallic inclusions for sulphides, pointed oxides, stripped oxides, fragile silicates, plastic silicates and non-deformed silicates are not more, than 5.0 points for each kind. Tensile strength is not less, than 480 N/mm², yield point is not less, than 335 N/mm², specific elongation is not less, than 23%, impact viscosity KCU+20°C is not less, than 49 J/mm².

EFFECT: production of tube stock with upgraded level of consumer characteristics.

1 cl, 1 ex

Description

The invention relates to the field of metallurgy, in particular to the production of pipe billets with a diameter of from 80 to 180 mm

Known steel for the manufacture of tube billets containing carbon, manganese, silicon, chromium, aluminum, phosphorus, titanium, cerium, antimony, iron and the rest (SU 899705, C22C 38/60, 01/23/1982).

Known steel for the manufacture of tube stocks containing carbon, manganese, silicon, molybdenum, vanadium, chromium, aluminum, nitrogen, sulfur, phosphorus, zinc, lead, tin, bismuth, antimony, iron and the rest (SU 1754790 A1, C22C 38/60, 08/15/1992).

Known pipe billet made of microalloyed steel containing carbon, manganese, silicon, chromium, nickel, vanadium, niobium, titanium, aluminum, calcium, sulfur, phosphorus, nitrogen, copper, antimony, tin, arsenic, molybdenum, the rest, hot rolled (RU 2252972 C1, C21D 9/08, 05.27.2005).

The most important requirement for a pipe billet made of microalloy 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 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, a homogeneous macro- and microstructure of rolled products, as well as a reduced tendency to temper brittleness.

The problem is solved in that the tubular billet of microalloy steel, hot rolled, is made of continuously cast steel containing the following ratio of components, wt.%:

carbon 0.14-0.20 manganese 1.00-1.40 silicon 0.03-0.10 titanium 0.002-0.03 aluminum 0.02-0.05 vanadium 0.002-0.02 sulfur 0.005-0.012 phosphorus 0.005-0.013 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) + (vanadium / 5)] ≤ 0.40,

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 species, segregation strips no more than 1 point, non-metallic inclusions: sulfides, point oxides, construction oxides, brittle silicates, plastic silicates, undeformed silicates no more than 5 points for each type of inclusions, mechanical properties after normalization: temporary tensile strength not less than 480 N / mm ² , a viscosity of at least 335 N / mm ² , elongation of at least 23%, impact strength KCU + 20 ° C of at least 49 J / mm ² .

As impurities, the steel additionally contains niobium, nickel, chromium, copper in the following proportions, wt.%:

niobium - not more than 0.02

nickel - no more than 0.30

chrome - no more than 0.30

copper - not 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, ductility and weldability characteristics.

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 0.14% - to ensure the required level of strength and hardenability of this steel.

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 the vanadium content is 0.02%, due to the need to ensure the required level of ductility of steel, and the lower - respectively 0.002% - to ensure the required level of strength 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 - 1.40% is determined by the need to ensure the required level of ductility of steel, and the lower, manganese - 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 limit on silicon is 0.03% due to the steel deoxidation technology. A silicon content above 0.10% adversely affects the ductility of steel.

Sulfur determines the level of ductility of steel. The upper limit (0.012%) 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.

Phosphorus determines the level of ductility of steel and its tendency to reversible temper brittleness. The upper limit (0.013%) 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.

Titanium and aluminum are strong carbonitride former and steel deoxidizers. The upper limit of titanium content - 0.03% and aluminum - 0.05% is due to the need to obtain a given level of ductility and toughness of steel, and the lower limit (0.002% and 0.02%, respectively) - due to issues of manufacturability.

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 + V / 5≤0.40 determines the weldability characteristics of the studied steel, while the ratio As + Sn + Pb + 5 × Zn≤0.07 determines the reduced tendency of steel to manifest reversible temper brittleness.

An example embodiment of the invention.

Steel smelting (chemical composition, wt.%: Carbon - 0.16%, manganese - 1.23%, silicon - 0.09%, vanadium - 0.01%, titanium - 0.012%,%, aluminum - 0.04 %, sulfur - 0.010%, phosphorus - 0.009%, arsenic - 0.009%, tin - 0.005%, lead - 0.003%, zinc - 0.001%, nitrogen - 0.010%) is produced in 150-ton arc steel furnaces using in the charge 100% metallized pellets, which ensures that the mass fraction of nitrogen before release 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 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 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 1050-1100 ° C and ends at a temperature of 840-950 ° C.

The mechanical characteristics at room temperature are determined on samples of type I, GOST 1497-84. on the test machine "INSTRON-1185" with strain gauge registration of deformation. The loading speed of the sample is 5 mm / min. The characteristics of strength and σ _b and σ _0.2 ductility - δ are determined. The characteristics of 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 - 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 billet of ную120 mm and a length of 11800 mm are obtained. The structure is ferrite-pearlite, the real grain score is 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 point, strox oxides - 1 point, brittle silicates - 1 point, plastic silicates - 1 point, undeformed silicates - 1 point. Mechanical properties after normalization at 900 ° С, 1 hour, air: temporary tensile strength 510 N / mm ² , yield strength 367 N / mm ² , elongation 25%, impact strength KCU + 20 ° C 59 J / mm ² .

As + Sn + Pb + 5 × Zn = 0.022; C + Mn / 6 + V / 5 = 0.367.

The introduction of the production of tube billets from 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, a low content of non-metallic inclusions, and a homogeneous macro- and microstructure of rolled products.

Claims (2)

1. Continuous cast billet of microalloyed steel, hot rolled, having non-metallic inclusions, the specified values of the macrostructure and mechanical properties, characterized in that it is made of steel containing the following ratio of components, wt.%: carbon 0.14-0.20 manganese 1.00-1.40 silicon 0.03-0.10 titanium 0.002-0.03 aluminum 0.02-0.05 vanadium 0.002-0.02 sulfur 0.005-0.012 phosphorus 0.005-0.013 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 ratios: (As + Sn + Pb + 5 × Zn) ≤0.07; (C + Mn / 6 + V / 5) ≤0.40, at the same time, it has a ferrite-pearlite structure, the actual grain size is 6–9 points, the macrostructure by central porosity, point heterogeneity, segregation square, shrink segregation is not more than 3 points for each species, segregation strips are not more than 1 point, non-metallic inclusions by sulfides, point oxides, line oxides, brittle silicates, plastic silicates, undeformed silicates no more than 5 points for each type of inclusions, tensile strength at least 480 N / mm ² , yield strength not less e 335 N / mm ² , elongation not less than 23%, impact strength KCU + 20 ° C not less than 49 J / mm ² . 2. The pipe billet according to claim 1, characterized in that the steel contains inevitable impurities, wt.%: Niobium not more than 0.02, nickel not more than 0.30, chromium not more than 0.30, copper not more than 0, thirty.