RU2286395C2 - Method of production of the rolled section steel in the form of bars made out of the medium-carbon chromium-containing steel - Google Patents

Abstract

FIELD: metallurgy industry; method of production of the circular rolled section steel in the form of circular bars made out of the medium-carbon chromium-containing steel.

SUBSTANCE: the invention is pertaining to the field of metallurgy, in particular, to production of the circular rolled section steel made out of the medium-carbon steel of the heightened cutability and used for manufacture of the ball studs, the tie-rod ends and the ball supports of the motor car suspension produced by the method of the cold die forging. The technical result of the invention is the increased characteristics of the cutability at the simultaneous raise of the characteristics of the hardenability at provision of a throughout hardenability of the rolled section steel bars of up to 25 mm diameter, and also at conservation of the high level of the technological pliability of the steel. For realization of the technical problem the invention presents the method of production of the circular rolled section steel from the medium alloy steel includes the smelting of the steel in the electric furnace, the metal tapping from the furnace, the deep metal deoxidation by aluminum and the doping, the metal dressing in compliance with the chemical composition for all the components, except for aluminum and sulfur, reoxidation of the metal and the slag by the oxidized pellets, addition of aluminum, the treatment with calcium, the microalloying by sulfur with production of the steel at the following ratio of the components (in mass %): carbon - 0.35-0.420, manganese - 0.50-0.80, silicon - 0.17-0.37, chromium - 0.8-1.1, sulfur - 0.020-0.040, vanadium - 0.005-0.020, calcium - 0.001-0.010, oxygen - 0.001-0.015, nickel - up to 0.25, copper - no more than 0.25, molybdenum - no more than 0.10, arsenic - no more than 0.08, nitrogen - no more than 0.015, iron and the inevitable impurities - the rest, at fulfillment of the ratios: oxygen/calcium = 1-4.5 and calcium/sulfur ≥ 0.065, the continuous casting of the steel with protection of the spray by argon, the hot rolling of the continuous casting blank with usage of the mode of the thermomechanical working, winding the bars into the bars coils, the bars coils uncoiling, the bars cutting into pieces of 6 m length with accuracy of the cutting of ±5 mm, finishing the rolled metal by the roll dressing, inspection of the surface defects and the ultrasonic control of the internal flaws, the sample abrasive dressing, the solid abrasive polishing and the turning.

EFFECT: the invention ensures the increased characteristics of the cutability at the simultaneous raise of the characteristics of the hardenability at provision of a throughout hardenability of the rolled section steel bars of up to 25 mm diameter and also at conservation of the high level of the technological pliability of the steel.

1 ex

Description

The invention relates to the field of metallurgy, in particular to the production of long products of round machining of medium-carbon chromium-containing steel of high machinability, used for the manufacture of ball fingers, tie rods and ball bearings of a vehicle suspension obtained by cold forming.

Known long products of round steel made of (wt.%): Carbon 0.36-0.44%, manganese 0.50-0.80%, silicon 0.25-0.45%, chromium 0.85-1 , 50%, titanium 0.02-0.04%, aluminum 0.005-0.015%, boron 0.003-0.005%, calcium 0.001-0.004%, copper 0.2-0.6%, nickel 0.2-0.5 , barium 0.01-0.04%, iron - the rest, while the ratio Cu / Mn + Ni = 0.15-0.75 (RF Patent RU 2023048 C1, C 22 C 38/54 from 06.22.1992, , published November 15, 1994). The disadvantage of this steel is the relatively high nitrogen content and the absence of elements in the composition that protect boron from binding to nitrides, which in some cases will not allow the authors claimed effect to increase the hardenability characteristics.

Known long products of round steel made of (wt.%): Carbon 0.35-0.45%, manganese 0.50-0.80%, silicon 0.17-0.37%, chromium 0.8-1 , 10%, vanadium 0.04-0.09%, aluminum 0.005-0.015%, calcium 0.001-0.004%, nitrogen 0.005-0.009%, copper, 0.25-0.40%, magnesium 0.0005-0, 0009%, iron and inevitable impurities - the rest. Moreover, the sulfur content is 0.01-0.02 wt.%; the phosphorus content is 0.015-0.020 wt.% (USSR Author Certificate SU 1216241 A, C 22 C 38/24, published on 03/07/1986). The disadvantage of this steel is an unregulated sulfur content, which will lead to a significant deterioration in cutting characteristics, a decrease in the resistance of the cutting tool, an increase in tool loads at a lower level of sulfur content in the proposed interval, i.e. less than 0.012%. The disadvantages include the high phosphorus content in steel, which will contribute (given the presence of manganese and chromium in the steel and the absence of molybdenum) to the intensive development of reversible temper brittle processes during heat treatment.

A known method for the production of long products, including smelting of boron-containing steel, metal production, casting, hot rolling, cooling (Patent DE 343744 A1, 04/03/1986, C 21 D 8/06, claims).

The closest analogue is the known method for the production of long products, including steelmaking in an electric furnace, metal production, after-furnace treatment, continuous casting, hot rolling of a continuously cast billet, cooling (RU 2156313 C1, C 21 D 8/02, 09/20/2000 )

The technical result of the invention is to increase the characteristics of machinability by cutting while increasing the formability and hardenability while providing through hardenability of long products with a diameter of up to 25 mm, as well as maintaining a high level of technical ductility of steel. To achieve a technical result, a method for producing round sections from medium alloyed steel includes steel smelting in an electric furnace, metal extraction from a furnace, deep metal deoxidation with aluminum and alloying, metal refinement by chemical composition for all elements except aluminum and sulfur, oxidized metal and slag oxidized pellets, the addition of aluminum, calcium treatment, microalloying with sulfur, to obtain steel in the following ratio of components, wt.%:

carbon 0.35-0.420 manganese 0.50-0.80 silicon 0.17-0.37 chromium 0.8-1.1 sulfur 0,020-0,040 vanadium 0.005-0.020 calcium 0.001-0.010 oxygen 0.001-0.015 nickel            up to 0.25 copper no more than 0.25 molybdenum no more than 0.10 arsenic no more than 0.08 nitrogen no more than 0.015 iron and inevitable impurities rest,

when fulfilling the ratios: oxygen / calcium = 1-4.5 and calcium / sulfur ≥0.065, continuous casting of steel with argon protection, hot rolling of a continuously cast billet using thermomechanical processing, winding rods into riots, unwinding rods, cutting rods with length up to 6 m with a cutting accuracy of ± 5 mm, rolled finish by dressing, inspection of surface defects and ultrasonic inspection of internal defects, selective abrasive cleaning, continuous abrasive grinding and turning.

The given combinations of alloying elements make it possible to obtain a favorable lamellar structure with globular sandwich inclusions in the proposed steel (a bar of hot-rolled sections of round diameter up to 25 mm), which provides, on the one hand, improved cutting characteristics even with wide cutters during transverse feeding of the cutting tool, on the other hand, a favorable combination of strength and ductility 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 (0.42%) is due to the need to ensure the required level of ductility of steel, and the lower - respectively 0.35% - to ensure the required level of strength and hardenability of this steel.

A carbonitride-forming element, vanadium, is introduced into the composition of this steel in order to provide a finely dispersed, uniform grain structure, which will increase both its strength level and provide a given level of ductility. In this case, vanadium controls the processes in the lower part of the austenitic region and in the intercritical temperature range (determines the tendency to growth of austenite grain, stabilizes the structure during thermomechanical processing, increases the recrystallization temperature, and, as a result, affects the nature of the γ-α transformation). Vanadium also contributes to the hardening of steel during thermal improvement. The upper limit of vanadium content - 0.02% - is due to the need to ensure the required level of ductility of steel, and the lower - respectively 0.005% - 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 significantly increase the stability of supercooled austenite of steel. In this case, the upper level of manganese — 0.80% and chromium — 1.10% is determined by the need to ensure the required level of ductility of steel, and the lower — 0.50% of manganese and 0.80% of chromium, 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 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.

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 (0.020%) is due to technological issues of production, as well as providing a given level of machinability by cutting this steel.

Calcium is an element modifying 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%) limit due to issues of manufacturability.

Oxygen, forming an oxide film on sulfides, helps to increase the machinability of steel by cutting while maintaining a high complex of consumer properties of steel. The upper level of oxygen content - 0.015% due to the need to ensure the required level of ductility of steel, and the lower - 0.001%, respectively, the need to provide the required level of strength and machinability by cutting steel.

Ratios:

The ratio of oxygen / calcium = 1 ÷ 4.5 is responsible for the possibility of the formation of a sandwich-non-metallic inclusion. Moreover, the upper limit of the ratio — the oxygen content level of 4.5 — is due to the need to ensure the required level of ductility of steel, and the lower one — 1, respectively, to the formation of a two-layer non-metallic sandwich inclusion.

The calcium / sulfur ratio ≥0.065% determines the conditions of globular non-metallic inclusions (sulfides). If this ratio is fulfilled, the sulfides are globular, otherwise elongated sulfides are present in the steel, which increases the anisotropy of the properties of the steel and worsens the strength-toughness ratio, especially strongly in the transverse direction of the rolled product.

Comparative analysis with the prototype allows us to conclude that the claimed composition is different from the known claimed combination of features and meets the criterion of "significant differences".

The following is an example implementation of the invention.

Smelting of the test steel (chemical composition in wt.%: Carbon - 0.40%, manganese - 0.65%, silicon - 0.32%, chromium - 0.92%, vanadium - 0.01%, sulfur - 0.036%, calcium - 0.0024%, oxygen - 0.007% ) was carried out in 150-ton arc steel-smelting furnaces (DSP-150, transformer capacity 80 mVA) using 60% metallized pellets and 40% metal scrap in the charge, which ensures that the mass fraction of nitrogen before being released from the chipboard is not more than 0.003%, and low content of color impurities. Preliminary alloying of metal with manganese and silicon was carried out in a ladle when discharged from particleboard (Release of peroxidized metal into a ladle. Metal deoxidation — when released by aluminum, ferrosilicon — deoxidation, alloying — FeMn (SiMn), FeCr). After release, the metal was purged with argon through the bottom purge unit for 5-7 minutes. Then evacuation on a portion vacuum, while doping (fine) - carbon, manganese and silicon. After evacuation - processing on a ladle furnace. 15-30 minutes before the end of the treatment, an oxidizing agent is introduced, in this case, oxidized pellets. Then again introduced aluminum (wire). For 10-15 minutes - treatment with flux-cored wires with silicocalcium and pure sulfur. Steel casting was carried out on a high-quality radial type continuous casting machine in NLZ 300 × 360 mm with a draw speed of 0.6-0.7 m / min. During casting, the jet was protected from secondary oxidation as follows:

- steel-ladle-industrial ladle - immersion pipe with argon feed;

- tundish - slag-forming mixture;

- tundish-crystallizer - immersion cup (corundum-graphite);

- in the mold - slag-forming mixture.

After casting and cutting to a measured length, continuously cast billets were cooled in controlled cooling furnaces. Next, the ingots were rolled in a mill 700 into a billet (170 mm square). The entire initial billet was subjected to dressing, descaling, and surface control. The billets were heated before rolling in two walking-hearth furnace furnaces. The heating temperature of the billet is 900 ° C, which ensures a 15% reduction in energy costs and significantly reduces the decarburization of rolled products. Dross from the surface of the workpiece was removed with high-pressure water at a descaling unit. Rolling was carried out in continuous lines - small-grade and medium-grade. High rigidity of the stands, automatic adjustment of the speeds of the stands, and a loop control system in the finishing group of the small-grade line made it possible to obtain high-precision rolled products. Finishing of the rolling was carried out off-stream. Finishing included the operations of dressing, control of surface defects and ultrasonic control of internal defects, selective abrasive cleaning, continuous abrasive grinding, turning of round bars. The accuracy of rolling after turning corresponds to the h11 quality. At the BUNT-PRUTOK installation, from coils of hot-rolled steel, turned rods of up to 6 meters in length are obtained with a cutting accuracy of ± 5 mm.

As a result of hot rolling, we get long products with a diameter of 21 mm with a granular perlite structure (99%), a decarburized layer with a depth of 0.09 mm, a real grain score of 8, cold wire gauge with a diameter of 21 mm by 67%, with a temporary tensile strength of 580 MPa, elongation of 21%, narrowing of 63%.

Ratio

oxygen / calcium = 2.92, calcium content - 0.0024%, oxygen - 0.007%, calcium / sulfur = 0.067, calcium content - 0.0024%, sulfur - 0.036%.

Implementation of the proposed method for the production of long products from medium carbon steel with increased machinability provides two-layer sandwich-non-metallic inclusions, which guarantee, on the one hand, improved cutting characteristics and, on the other hand, a favorable correlation of ductility and toughness of steel.

Claims (1)

A method for the production of long sections in mild steel bars, including steel smelting in electric furnaces, metal discharge from a furnace, deep deoxidation of metal with aluminum and alloying, metal refinement by chemical composition for all elements except aluminum and sulfur, reoxidation of metal and slag with oxidized pellets , the addition of aluminum, calcium treatment, microalloying sulfur to obtain steel in the following ratio, wt.%: Carbon 0.35-0.420 Manganese 0.50-0.80 Silicon 0.17-0.37 Chromium 0.8-1.1 Sulfur 0,020-0,040 Vanadium 0.005-0.020 Calcium 0.001-0.010 Oxygen 0.001-0.015 Nickel Up to 0.25 Copper No more than 0.25 Molybdenum No more than 0.10 Arsenic No more than 0,08 Nitrogen No more than 0.015 Iron and inevitable impurities Rest when oxygen / calcium ratios = 1-4.5 and calcium / sulfur ratios ≥0.065, continuous casting of steel with argon protection, hot rolling of a continuously cast billet using thermomechanical processing, winding rods into riots, unwinding rods, cutting rods in length up to 6 m with a cutting accuracy of ± 5 mm, rolled finish by dressing, inspection of surface defects and ultrasonic inspection of internal defects, selective abrasive cleaning, continuous abrasive grinding and turning.