RU2337150C1 - Tube stock out of boron containing steel - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: tube stock with diameter from 80 to 180 mm is produced out of steel containing elements, wt %: carbon 0.19-0.24, manganese 0.40-0.60, silicon 0.17-0.30, chromium 0.40-0.60, nitrogen 0.003-0.010, vanadium 0.020-0.040, aluminium 0.020-0.040, titanium 0.020-0.040, boron 0.001-0.003, iron and unavoidable impurities - the rest at maintaining conditions: 500-(Ti/24-N/7)+2.2≥0; 30≥C/0.01+B/0.001≥13, at that stock is hot rolled and has ferrite-pearlite structure, dimension of actual grain is 5-8 points, its macrostructure for central porosity, pointed non-uniformity, liquation square, sub-shrinking liquation - not more than 2 points in each kind, liquation strips - not more than 1 point, 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. As impurities steel contains wt %: niobium not more than 0.020, molybdenum not more than 0.02, copper not more than 0.10, nickel not more than 0.10, sulphur not more than 0.012, phosphorus not more than 0.15. Stock possesses tensile strength of 480-650 H/mm², yield strength not less than 360 H/mm², specific elongation not less than 16%, contraction ratio not less than 50%, hardenability in water with critical diameter of Dcr=35mm, hardness at end tempering 40 HRC.

EFFECT: 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 80 to 180 mm from boron-containing steel, intended for the production of seamless pipes for various purposes.

Known tube stock made of boron-containing steel containing (wt.%): Carbon 0.05-0.10, silicon no more than 0.6, manganese 1.7-2.50, phosphorus no more than 0.015, sulfur no more than 0.003, nickel 0.1-1.0, molybdenum 0.15-0.60, niobium 0.01-0.10, titanium 0.005-0.030, aluminum no more than 0.06, boron up to 0.0020, copper up to 1.2, chrome up to 0.8, vanadium up to 0.10, nitrogen 0.001-0.006, iron and unavoidable impurities, the rest, hot-rolled, tube billet has a high level of steel purity by non-metallic inclusions and a certain microstructure (RU 2136776 C1, 10.09.1999, C21C 38 / fourteen).

The closest analogue is the known tube stock made of boron-containing steel, hot rolled, having predetermined parameters of the structure, nonmetallic inclusions, actual grain size, a certain microstructure, hardenability (RU 2210604 C2, B21B 21/00, 03/27/2004).

The most important requirement for a boron-containing steel billet is, on the one hand, ensuring a given structure, improving metallurgical quality parameters: uniformity of micro- and macrostructure with a low content of non-metallic inclusions, and on the other hand, providing a high range of consumer properties.

The technical result of the invention is to provide a high level of consumer properties while providing a favorable ratio of strength, ductility, viscosity and hardenability, a minimum level of anisotropy of mechanical properties, low content of non-metallic inclusions, homogeneous macro- and microstructure of rolled products.

To achieve a technical result in a pipe billet made of boron-containing steel, continuously cast, hot rolled, having predetermined parameters of non-metallic inclusions, structure, mechanical properties, hardenability, real grain size, steel contains the following ratio of components in wt.%:

carbon 0.19-0.24 manganese 0.40-0.60 silicon 0.17-0.30 chromium 0.40-0.60 nitrogen 0.003-0.010 vanadium 0,020-0,040 aluminum 0,020-0,040 titanium 0,020-0,040 boron 0.001-0.003 iron and inevitable impurities rest

under the following conditions:

The preform has a ferrite-pearlite structure, the actual grain size is 5-8 points, according to the macrostructure, central porosity, point heterogeneity, segregation square, shrink segregation no more than 2 points for each species, segregation strips no more than 1 point, for non-metallic inclusions: sulfides , point oxides, line oxides, brittle silicates, plastic silicates, non-deformable silicates, not more than 4.5 points for each type of inclusions. As inevitable impurities, steel additionally contains niobium no more than 0.020%, molybdenum no more than 0.02%, copper no more than 0.10%, nickel no more than 0.10%, sulfur no more than 0.012%, phosphorus no more than 0.015%.

The mechanical properties of the workpiece after normalization - temporary tensile strength - 480-650 N / mm ² , yield strength of at least 360 N / mm ² , elongation of not less than 16%, relative narrowing of not less than 50%. Hardenability in water (critical diameter) Dcr = 35 mm, hardness at 6 mm at end hardening 40 HRC.

The given combinations of alloying elements make it possible to obtain a ferrite-pearlite 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 this steel in order to ensure a given level of its strength and hardenability. The upper limit of the carbon content (0.24%) is due to the need to ensure the required level of ductility of steel, and the lower - respectively 0.19% - to ensure the required level of strength and hardenability 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. In this case, the upper level of manganese — 0.60% and chromium — 0.60% is determined by the need to ensure the required level of ductility of steel, and the lower — 0.40% and 0.40%, respectively, by the need to provide the required level of strength and hardenability and heat resistance of this become.

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 0.30% adversely affects the ductility of 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 0.04 due to the need to ensure the required level of ductility of steel, and the lower - respectively 0.020% - to ensure the required level of strength of this steel.

Boron contributes to a sharp increase in the hardenability of steel. Moreover, the upper limit of the boron content is determined by considerations of ductility of steel, and the lower - the need to ensure the required level of hardenability.

Aluminum and titanium are used as deoxidizers and protect boron from binding to nitrides, which contributes to a sharp increase in the hardenability of steel. Thus, the lower level of the content of these elements (0.02 and 0.02%, respectively for aluminum and titanium) is determined by the requirement to ensure hardenability of steel, and the upper level (0.04% and 0.04%) is determined by the requirement to ensure a given level of ductility of steel.

Nitrogen is an element involved in the formation of carbonitrides, while the lower level of its content (0.003%) is determined by the requirement to ensure a given level of strength, and the upper level (0.010%) is determined by the requirement to ensure a given level of ductility and hardenability.

в противном случае не обеспечивается защита бора от связывания его в нитриды и резко снижаются характеристики прокаливаемости стали.To ensure complete binding of nitrogen to nitrides such as TiN and AlN as a result of the reactions [Ti] + [N] = TiN, the following ratio of elements is required:

otherwise, boron is not protected from binding to nitrides and the hardenability characteristics of steel are sharply reduced.

определяет условия сохранения в стали более 50% "эффективного" бора, что обеспечивает заданные характеристики прокаливаемости стали.Ratio

determines the conditions for preserving in steel more than 50% of the “effective” boron, which ensures the specified characteristics of hardenability of steel.

An example of obtaining a tube billet.

и

производят в 150-ти тонных дуговых сталеплавильных печах (ДСП) с использованием в шихте 100% металлизованных окатышей, что обеспечивает получение массовой доли азота перед выпуском из ДСП не более 0,003%, а также низкое содержание цветных примесей. Предварительное легирование металла по марганцу и кремнию производят в ковше при выпуске из ДСП. После выпуска производят продувку металла аргоном через донный продувочный блок, во время которой сталь раскисляется алюминием. После этого металл поступает на агрегат комплексной обработки стали (АКОС), на котором имеется возможность нагрева металла до необходимой температуры, продувки его аргоном через донный продувочный блок, дозированной присадки необходимых ферросплавов и обработки стали порошковой проволокой с различными наполнителями. На АКОСе производят наведение рафинировочного шлака присадкой извести и плавикового шпата, раскисление шлака гранулированным алюминием, легирование металла алюминием до содержания 0,050%, доводку металла по содержанию марганца, нагрев до температуры, обеспечивающей дальнейшую обработку. После обработки на АКОС металл подвергают вакуумной обработке на порционном вакууматоре. Во время вакуумирования производят окончательную корректировку по химическому составу. После вакуумирования металл обрабатывают силикокальцием и передают на разливку. Разливку производят на четырехручьевых УНРС радиального типа в слиток размерами 300×360 мм со скоростью вытягивания 0,6÷0,7 м/мин, с защитой металла от окисления путем использования покровных шлаковых смесей в промежуточном ковше и кристаллизаторе, защитных труб, погружных стаканов и подачей аргона. Это также обеспечивает получение низкого содержания азота и кислорода и чистоту металла по неметаллическим включениям. После разливки и пореза на мерную длину полученные непрерывнолитые заготовки охлаждались в печах контролируемого охлаждения. Горячую прокатку проката начинают при температуре 1180-1150°С и заканчивают при температуре 840-950°С.Smelting of the studied steel with a chemical composition in wt.%: Carbon 0.21, manganese 0.55, silicon 0.27, chromium 0.42, vanadium 0.032, titanium 0.02, aluminum 0.034, boron 0.0026, nitrogen 0.007 with fulfillment of conditions

and

they are 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 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), on which 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. Casting is carried out on radial four-strand UNRS in an ingot with dimensions of 300 × 360 mm 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 were cooled in controlled cooling furnaces. Hot rolling of rolled products begins 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 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 - average values of the compared values; S ₁ ² and S ₂ ² - variance of the average; t _cr ^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.

The hardenability characteristics (critical diameter D ₅₀ ) were determined by the end hardening method of cylindrical samples with a diameter of 25.0 mm and a length of 100 mm with shoulders according to GOST 5657. Before manufacturing the sample, the workpieces were heat treated in chamber furnaces according to the following regime: normalization, 950 ° C, 1 hour air. Two samples were tested for melting. Quenching of the samples is carried out by a stream of water in a special installation. In connection with the need to prevent oxidation and decarburization of the end face of the sample directly in contact with the water jet during quenching, the samples are heated in chamber furnaces (without a protective atmosphere) in special glasses. The end face of the sample is placed on a special graphite plate. The sample is heated in a chamber furnace to a temperature of 950 ° C. The duration of heating the sample to the quenching temperature is 30–50 min. Deviation from the set quenching temperature does not exceed ± 5 ° С. Sample exposure at quenching temperature after heating is 30 min. The time from the moment the sample is removed from the furnace to the start of cooling does not exceed 5 s. The sample was under a stream of water until completely cooled (about 15–20 min). The temperature of the cooling water was 20 ± 5 ° C.

To measure hardness along the entire length of the hardened sample, two diametrically opposite sites are ground to a depth of 0.5 ± 0.1 mm. Pads C are ground with plenty of water cooling. The surface roughness of the sites was not coarser than the 7th grade of cleanliness according to GOST 2789. Burns are not allowed, causing structural changes in the metal. To construct the steel hardenability curve, hardness measurement is started at a distance of 1.5 mm from the hardened end in the axial direction. The first 16 measurements from the end of the sample are made with an interval of 1.5 mm, and then through 3 mm. If it is necessary to re-measure the hardness at the site on which measurements were taken, the site is resurfaced. The depth of metal removal during re-grinding is 0.1 ÷ 0.2 mm. Hardness is determined according to Rockwell (HRC) in accordance with the requirements of GOST 9013. For each pair of points located at the same distance from the end of the sample at two opposite sites, the arithmetic mean value of the hardness is calculated.

Hot rolling yields a заготов150 mm pipe billet, 11800 mm long, ferrite-pearlitic structure, real grain score of 7. Macrostructure: 1 point central porosity, 1 point point heterogeneity, 1 point segregation square, 1 point segregation segregation, segregation strips 0.5 points Non-metallic inclusions: sulfides 1.0 point, point oxides 0.5 points, line oxides 1 point, brittle silicates 0.5 points, plastic silicates 0.5 points, non-deforming silicates 1.5 points.

The mechanical properties of the workpiece after normalization are the temporary tensile strength of 520 N / mm ² , yield strength 392 N / mm ² , elongation of 19%, relative narrowing of 58%. Hardenability in water critical diameter Dcr = 39 mm, hardness at 6 mm at end hardening 41 HRC.

The introduction of a boron-containing steel billet made it possible to provide an increased level of consumer properties of rolled products while ensuring 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 boron-containing steel, hot-rolled with predetermined parameters of non-metallic inclusions, structure, mechanical properties, hardenability and actual grain size, characterized in that it contains the following ratio of components, wt.%: carbon 0.19-0.24 manganese 0.40-0.60 silicon 0.17-0.30 chromium 0.40-0.60 nitrogen 0.003-0.010 vanadium 0,020-0,040 aluminum 0,020-0,040 titanium 0,020-0,040 boron 0.001-0.003 iron and inevitable impurities rest, when performing the following ratios:

at the same time, it has a ferrite-pearlite structure, the actual grain size is 5-8 points, the macrostructure according to central porosity, point heterogeneity, segregation square, shrink segregation is not more than 2 points for each species, segregation strips are not more than 1 point, 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 tensile strength 480-650 N / mm ² , yield strength not less than 360 N / mm ² , relative total elongation of at least 16%, relative narrowing of at least 50%, hardenability in water with a critical diameter Dcr = 35 mm, hardness at end hardening of 40 HRC. 2. The pipe billet according to claim 1, characterized in that the steel contains inevitable impurities, wt.%: Niobium not more than 0.020, molybdenum not more than 0.02, copper not more than 0.10, nickel not more than 0.10, sulfur is not more than 0.012, phosphorus is not more than 0.015.