RU2336329C1 - Tube stock out of low carbon manganese containing steel - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention refers to metallurgy, particularly to production of tube stock with diameter from 75 to 180 mm. To facilitate upgraded level of consumer characteristics at optimal combination of hardness, plasticity and viscosity the stock is made out of steel, containing wt %: carbon 0.06-0.12, manganese 1.30-1.70; silicon 0.50-0.80, chromium 0.005-0.30, nickel 0.005-0.30; copper 0.005-0.30, sulphur 0.005-0.040, phoshorus 0.005-0.040, calcium 0.001-0.010, nitrogen 0.005-0.015, arsenic 0.0001-0.01, tin 0.0001-0.02, lead 0.0001-0.01, zinc 0.0001-0.005, iron and unavoidable impurities at maintaining of ratio: As+Sn+Pb+5×Zn≤0.055, calcium/sulphur ≥0.055, C+Mn/6+Cr/5+(Ni+Cu)/15≤0.45, continuous cast and hot rolled. As impurities steel contains wt %: niobium not more, than 0.02, vanadium not more, than 0.02. The stock has laminar ferrite-pearlite structure, the dimension of the actual grain is 6-9 points. Its macrostructure for central porosity, pointed non-uniformity, liquation square, sub-shrinking liquation - not more, than 3 points for each kind, liquation strips - not more, than 2 points. Non-metallic inclusions - sulphides, pointed oxides, stripped oxides, fragile silicates, plastic silicates, non-deformed silicates - not more, than 4.0 points for each kind of inclusions, ensile strength is not less, than 315 N/mm², yield point is not less, than 260 N/mm², specific elongation is not less, than 25%, impact resilience KCU+20°C not less, than 49 J/mm².

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

2 cl, 1 ex

Description

The invention relates to the field of metallurgy, in particular to the production of pipe billets with a diameter of 75 to 180 mm

Known steel for the manufacture of tube stocks containing carbon, manganese, silicon, chromium, aluminum, phosphorus, titanium, cerium, antimony, iron (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 (SU 1754790 A1, C22C 38/60, 15.08 .1992).

Known pipe billet of microalloy steel containing carbon, manganese, silicon, chromium, nickel, vanadium, niobium, titanium, aluminum, calcium, sulfur, phosphorus, nitrogen, copper, antimony, tin, arsenic, molybdenum, iron, hot rolled (RU 2252972 C1, C21D 9/08, 05/27/2005).

The most important requirement for an alloy steel pipe billet 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, improved weldability. The problem is solved in that in a pipe billet of low-carbon manganese-containing steel, hot rolled, the steel contains the following ratio of components, wt.%:

carbon 0.06-0.12 manganese 1.30-1.70 silicon 0.50-0.80 chromium 0.005-0.30 nickel 0.005-0.30 copper 0.005-0.30 sulfur 0.005-0.040 phosphorus 0.005-0.040 calcium 0.001-0.010 nitrogen 0.005-0.015 arsenic 0.0001-0.01 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) ≤0.055;

(calcium / sulfur) ≥0.055;

amount: [carbon + (manganese / 6) + (chromium / 5) + (nickel + copper) / 15] ≤0.45.

The continuously cast hot-rolled tubular billet has a lamellar 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 2 points, non-metallic inclusions: sulfides, point oxides, line oxides, brittle silicates, plastic silicates, undeformed silicates not more than 4.0 points for each type of inclusions, mechanical properties after normalization: tensile strength not less than 315 N / mm ² , yield strength not less than 260 N / mm ² , elongation not less than 25%, impact strength KCU + 20 ° C not less than 49 J / mm ² .

As impurities, the steel additionally contains niobium and vanadium in the following proportions, wt.%: Niobium not more than 0.02, vanadium not more than 0.02.

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

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 (0.12%) is due to the need to ensure the required level of ductility of steel, and the lower - respectively 0.06% - to ensure the required level of strength of this steel.

Manganese and chromium are used, on the one hand, as solid solution hardeners, and on the other hand, as elements that increase the stability of supercooled austenite of steel. The upper level of manganese (1.70%) and chromium (0.30%) is determined by the need to ensure the required level of ductility of steel, and the lower level of manganese (1.30%) and chromium (0.005%) is determined 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 (0.50%) is due to steel deoxidation technology. A silicon content above 0.80% will adversely affect the ductility of steel.

Nickel within the specified limits affects the characteristics of hardenability and toughness of steel. At the same time, the lower level of nickel content (0.005%) is due to the need to ensure a given level of steel viscosity, and the upper (0.30%) due to the need to obtain a martensitic structure during steel quenching (since nickel is an austenitizer).

Copper determines the characteristics of hot ductility of steel. Moreover, the lower level of its content - 0.005% is determined by the requirements to ensure a given level of ductility of steel. The upper level (0.30%) is due to the need to provide a given level of viscosity and strength of steel.

Sulfur determines the level of ductility of steel. The upper limit (0.040%) 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, as well as providing a given level of machinability by cutting this steel.

Phosphorus determines the level of ductility of steel and its tendency to reversible temper brittleness. The upper limit (0.040%) 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.

Calcium is an element that modifies non-metallic inclusions. The upper limit (0.010%), as in the case of sulfur, is due to the need to obtain a given level of ductility and toughness of steel, and the lower (0.001%) 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%) is 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 due to steel production technology, and the upper limit (0.01%, 0.02%, 0.01% and 0.005%, respectively) determines the increased the tendency of steel to reversible temper brittleness.

The ratio C + Mn / 6 + Cr / 5 + (Ni + Cu) / 15≤0.45 determines the weldability characteristics of the studied steel, while the ratio As + Sn + Pb + 5 × Zn≤0.055 determines the viscosity characteristics of steel.

The calcium / sulfur ratio of ≥0.055 determines the machinability parameters of steel by cutting.

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 - increasing the level of consumer properties while providing a favorable ratio of strength, ductility and viscosity, a minimum level of anisotropy of mechanical properties, a reduced tendency to reversible temper brittleness, satisfactory weldability and increased machinability by cutting, low content of non-metallic inclusions, homogeneous macro and microstructure rokata.

An example embodiment of the invention. Smelting of the test steel (chemical composition, wt.%: Carbon 0.10%, manganese 1.47%, silicon 0.69%, chromium 0.12%, nickel 0.07%, copper 0.09%, phosphorus 0.009% , sulfur 0.022%, calcium 0.006%, arsenic 0.009%, tin 0.005%, lead 0.003%, zinc 0.001%, nitrogen 0.010%) are produced in 150-ton steel-arc furnaces using 100% metallized pellets in the charge, which ensures mass production the proportion of nitrogen before release from the particleboard is not more than 0.003%, as well as a low content of colored 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 of the chemical composition is made. After evacuation, the metal is treated with silicocalcium and transferred to casting. Casting is carried out on four-strand radial-type ONRSs with an ingot of 300 × 360 mm in size with a drawing speed of 0.6 ÷ 0.7 m / min, with metal protection from oxidation by using coating 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 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 impact strength at room temperature are determined on samples of type I, GOST 9454-78. on a mechanical copra 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 tube billet with a diameter of 100 mm and a length of 1180 mm is 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, non-deforming silicates - 1 point. Mechanical properties after normalization at 920 ° С, 1 hour, air: temporary tensile strength 350 N / mm ² , yield strength 280 N / mm ² , elongation 28%, impact strength KCU + 20 ° C 62 J / mm ² .

As + Sn + Pb + 5 × Zn = 0.022

calcium / sulfur = 0.27

C + Mn / 6 + Cr / 5 + (Ni + Cu) / 15 = 0.38

The introduction of the production of tube billets 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 and increased machinability by cutting, low content of non-metallic inclusions, homogeneous macro and microstructure of rolled products.

Claims (2)

1. Continuous cast billet of low-carbon manganese-containing steel, hot-rolled, characterized in that the billet is made of steel containing the following ratio of components, wt.%: carbon 0.06-0.12 manganese 1.30-1.70 silicon 0.50-0.80 chromium 0.005-0.30 nickel 0.005-0.30 copper 0.005-0.30 sulfur 0.005-0.040 phosphorus 0.005-0.040 calcium 0.001-0.010 nitrogen 0.005-0.015 arsenic 0.0001-0.01 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) ≤0.055; Ca / S≥0.055; C + Mn / 6 + Cr / 5 + (Ni + Cu) / 15≤0.45, 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 2 points, non-metallic inclusions by sulfides, point oxides, line oxides, brittle silicates, plastic silicates, undeformed silicates not more than 4.0 points for each type, mechanical properties after normalization - temporary tensile strength not change e 315 N / mm ^2, yield stress of not less than 260 N / mm ^2, an elongation of not less than 25%, the toughness KCU + 20 ° C of at least 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, vanadium not more than 0.02.