RU2333969C1 - Tubing stock made from chrome-molybdenium-containing steel - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention concerns metallurgy field. Particularly it concerns manufacturing of tubing stock of diameter from 100 till 180 mm, intended for weldless drawn pipe manufacturing for heat-and-power engineering. For realisation of technical result stock is made from steel containing further components ratio mass %: carbon 0.07-0.15, manganese 0.40-0.70, silicon 0.7-0.37, chrome 0.80-1.10, molybdenum 0.40-0.55, copper 0.005-0.25, nickel 0.005-0.30, nitrogen 0.005-0.015, iron and unavoidable admixtures - the rest. In the capacity of unavoidable admixtures steel contains, mass %: niobium not more than 0.02, vanadium not more than 0.02, sulphur not more than 0.025, phosphorus not more than 0.035. Stock is made as continuously cast, hot-rolled, at that stock is of lamellar ferrite-pearlitic structure, dimension of valid grain 5-8 points. Macrostructure: center porosity, spot heterogeneity, segregation square, subshrink segregation is not more than 2 points for each kind, segregation streaks are not more than 1 point. Nonmetallic inclusions - sulphides, spot oxides, stitch oxides, fragile silicates, flexible silicates, non-strained silicates are not more than 4.0 points for each kind of inclusions. Mechanical properties after normalisation - tensile strength is not less than 400-600 N/mm², yield strength is not less than 290 N/mm², percentage elongation is not less than 22%, contraction ratio is not less 45%.

EFFECT: receiving of steel tubing stock with high mechanical properties.

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 100 to 180 mm from chromium-molybdenum-containing steel, intended for the production of seamless pipes for heat power engineering.

The closest analogue to the invention is the known tubular billet of chromium-molybdenum-containing steel, hot rolled, having predetermined parameters for non-metallic inclusions, structure, mechanical properties (JP 2-25969 A, C21D 8/10, 06.06.1990).

The most important requirement for a pipe billet made of chromium-molybdenum-containing steel is, on the one hand, to ensure a certain structure, to improve metallurgical quality parameters: uniformity of micro- and macrostructures with a low content of non-metallic inclusions, and, on the other hand, to provide an increased range of consumer properties.

The technical result of the invention is to provide an increased 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.

The technical result is achieved in that in a pipe billet of chromium-molybdenum-containing steel, continuously cast, hot-rolled, having predetermined parameters of metallurgical quality, structure, mechanical properties, the steel contains the following ratio of components, wt.%:

carbon 0.07-0.15 manganese 0.40-0.70 silicon 0.17-0.37 chromium 0.80-1.10 molybdenum 0.40-0.55 copper 0.005-0.25 nickel 0.005-0.30 nitrogen 0.005-0.015 iron and inevitable impurities rest

the tube billet has a ferritoperlite structure, the actual grain size is 5-8 points, according to the macrostructure: central porosity, point heterogeneity, segregation square, shrink segregation not more than 2 points for each species, segregation strips not more than 1 point, for non-metallic inclusions: sulfides, point oxides, line oxides, brittle silicates, plastic silicates, non-deforming silicates, not more than 4.0 points for each type of inclusions. As unavoidable impurities, steel additionally contains components, wt.%: Niobium not more than 0.02, vanadium not more than 0.02, sulfur not more than 0.025, phosphorus not more than 0.035. Mechanical properties after normalization: temporary tensile strength 400-600 N / mm ² , yield strength not less than 290 N / mm ² , elongation not less than 22%, relative narrowing not less than 45%.

The given combinations of alloying elements make it possible to obtain a ferritoperlite finely dispersed structure, a low content of non-metallic inclusions, a homogeneous macrostructure, and a favorable combination of strength and ductility characteristics in the finished product.

Carbon is introduced into the composition of steel in order to ensure a given level of its strength and hardenability. The upper limit of the carbon content of 0.15% is due to the need to ensure the required level of ductility of steel, and the lower - respectively 0.07% - to ensure the required level of strength and hardenability of this steel.

Manganese, chromium and molybdenum 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. Moreover, the upper level, wt.%: Manganese - 0.70, chromium - 1.10 and molybdenum - 0.55 is determined by the need to ensure the required level of ductility of steel, and the lower - 0.40, 0.80 and 0.40, respectively , the need to provide the required level of strength, and hardenability, and heat resistance 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% adversely affects the ductility 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% by issues of manufacturability.

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 level is 0.30 - the need to obtain a martensitic structure during hardening of steel (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 - 0.25% due to the need to provide a given level of hardenability of steel.

An example of manufacturing a pipe billet.

Smelting of the investigated steel with a chemical composition, wt.%: Carbon - 0.12, manganese - 0.55, silicon - 0.22, chromium - 0.99, molybdenum - 0.31, copper - 0.09 , 15, nitrogen - 0.007 is produced in 150-ton steel arc furnaces using 100% metallized pellets in the charge, which ensures that the mass fraction of nitrogen before being released 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 1080-1100 ° C and ends at a temperature of 840-950 ° C. To determine the mechanical properties of the workpiece, it is subjected to normalization.

The mechanical characteristics at room temperature are determined on type I specimens, GOST 1497-84 on an INSTRON-1185 test 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 and φ are determined.

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 мм110 mm pipe billet is obtained, 11800 mm long, ferritic perlite structure, real grain score is 7. Macrostructure: central porosity - 2 points, point heterogeneity - 0.5 points, segregation square - 1 point, shrinkage segregation - 1 point, segregation strips - 0.5 points. Non-metallic inclusions: sulfides - 1.5 points, point oxides - 0.5 points, strox oxides - 1 point, brittle silicates - 0.5 points, plastic silicates - 0.5 points, non-deforming silicates - 1.5 points. Mechanical properties after normalization of 920 ° C, 1 hour: temporary tensile strength - 495 N / mm ² , yield strength - 330 N / mm, elongation of 26%, relative narrowing of 55%.

The introduction of the production of tube billets from chromium-molybdenum-containing steel provides an increased level of consumer properties of rolled products with 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 of rolled products.

Claims (2)

1. Continuous cast billet of chrome-molybdenum-containing steel, hot-rolled with specified parameters of non-metallic inclusions, mechanical properties, macrostructure and actual grain size, characterized in that it is made of steel containing components in the following ratio, wt.%: carbon 0.07-0.15 manganese 0.40-0.70 silicon 0.17-0.37 chromium 0.80-1.10 molybdenum 0.40-0.55 copper 0.005-0.25 nickel 0.005-0.30 nitrogen 0.005-0.015 iron and inevitable impurities rest, the preform has a ferritoperlitic structure, the actual grain size is 5-8 points, the macrostructure of the species: central porosity, point heterogeneity, segregation square, shrink segregation no more than 2 points for each type segregation strips no more than 1 point, non-metallic inclusions of the species: sulfides, oxides point, line oxides, brittle silicates, plastic silicates, undeformed silicates not more than 4.0 points for each type of inclusions and mechanical properties after normalization: temporary resistance times yvu 400-600 N / mm ^2, yield stress of not less than 290 N / mm ^2, an elongation of at least 22%, relative narrowing of at least 45%. 2. The pipe billet according to claim 1, characterized in that the steel contains the following components as inevitable impurities, wt.%: Niobium not more than 0.02, vanadium not more than 0.02, sulfur not more than 0.025, phosphorus not more than 0.035.