RU2296017C1 - Method for making rolled bars from springy alloy steel - Google Patents

Abstract

FIELD: rolled stock production, possibly hot rolling of round bars and rods of alloy springy steel.

SUBSTANCE: method comprises steps of heating blank till austenization temperature; further multi-pass hot rolling at reducing in grooved rolls at normalized temperature of rolling process termination; spontaneous cooling in air. Rolling is realized during two stages; at first with total elongation no less than 2. Then rolled piece is cooled. After cooling rolled piece is heated again till temperature 1150 - 1300°C and subjected to secondary rolling with total elongation degree no less than 16 at final temperature of rolling 950 - 1100°C. Before cooling rolled piece in air it is cooled in addition by means of water at cooling rate 30 - 60°C/s till temperature 790 - 910°C. Invention provides possibility for homogenizing chemical composition and microstructure of steel, for increasing its plasticity and other mechanical properties.

EFFECT: improved quality of steel, less loss of yield.

2 cl, 1 tbl

Description

The invention relates to rolling production and can be used for hot high-speed rolling of round profiles and wire rod from alloy spring steel.

Long products of circular cross section with a diameter of 8.0-28.0 mm from alloy spring steel used for the manufacture of elastic elements of railway fasteners after simulating heat treatment (heating to 870-885 ° C, quenching in water, tempering at 470-500 ° C) must have the following set of mechanical properties (table 1):

Table 1
Mechanical properties of spring steel round steel Product standard σ _in , N / mm ² Ψ,% δ ₁₀ % HB TS 105-433-04 not less than 800 not less than 40 not less than 10 no more than 250 Note: HB hardness is measured in a hot-rolled state.

There is a method of high-quality rolling of round sections, including heating the steel billet to austenitizing temperature, multi-pass rolling in rolls with gauges of roughing and finishing groups of stands to a final diameter with a regulated temperature of the rolling end, cooling with water and forming a riot, according to which the middle section of the roll of regulated length is subjected interstitial forced cooling [1].

The disadvantage of this method is that the profile of the circular cross section of alloy spring steel acquires low and unstable mechanical properties along the length due to uneven cooling of the roll, which reduces the quality and yield of rolled products.

There is also a known method for the production of long products from alloy steels, including heating the workpieces to an austenitizing temperature, rolling in rolls with calibers. Then the preform is heated, and the surface layer of the front end of the regulated length is overheated by 30-100 ° C relative to the rest of the metal and rolled again in a continuous group of stands, after which the rolling is cooled [2].

The disadvantage of this method is that when using cast billets, long products from alloy spring steel have low quality and yield.

The closest in technical essence and the achieved results to the proposed invention is a method for the production of long products from alloy steel, comprising heating the workpiece to an austenitizing temperature of 950-1000 ° C, subsequent multi-pass hot rolling with compression in vertical and horizontal rolls with calibrated end temperature gauges rolling 700-720 ° C and air cooling [3] - prototype.

The disadvantages of this method are that long products obtained from cast billets, after simulating heat treatment, have low mechanical properties and surface defects, which reduces the quality and yield of rolled products.

The technical problem solved by the invention is to improve the quality and yield.

To solve the technical problem in the known method for producing rolled steel from alloy spring steel, which includes heating the workpiece to austenitizing temperature, subsequent multi-pass hot rolling with compression in rolls with calibers with a regulated rolling end temperature and air cooling, according to the proposal, hot rolling is carried out in two stages , initially with a total hood of at least 2, after which the roll is cooled, heated to a temperature of 1150-1300 ° C and subjected to repeated rolling with a total stretch of at least 16 and the rolling end temperature 950-1100 ° C. In addition, before spontaneous cooling in air, the rolled products are additionally cooled with water at a rate of 30-60 ° C / s to a temperature of 790-910 ° C.

The essence of the proposed invention is as follows. Cast billets of alloy spring steel have an uneven chemical composition (segregation of elements) in the volume of dendrites and along their boundaries, as well as carbide inhomogeneity, which leads to uneven structure and mechanical properties of long products. Hot rolling at the first stage with a total exhaust of at least 2, subsequent cooling and reheating contribute to the grinding of dendrites, the intensification of diffusion processes in alloy spring steel. Due to this, before repeated hot rolling, segregation of alloying elements, carbide and structural heterogeneity are completely eliminated.

Rolling at the second stage in the temperature range from 1150-1300 ° C to 950-1100 ° C with a total exhaust of at least 16 provides both the necessary degree of study and grinding of the microstructure of alloyed spring steel necessary to obtain the desired mechanical properties, and high technological ductility of the metal , contributing to the accurate execution of the profile in calibers and the elimination of the formation of surface defects.

The cooling of hot-rolled sections with water at a speed of 30-60 ° C to a temperature of 790-910 ° C contributes to the formation of a finer-grained and stable microstructure along the section and length of the strip, and subsequent cooling in air from a temperature of 790-910 ° C normalizes the steel, reduces it residual phase and thermal stresses. This additionally improves the quality and yield of varietal profiles.

It was experimentally established that during the hot rolling of a billet at the first stage with a total drawing of less than 2, the required degree of grinding of dendrites and an increase in the diffusion activity of carbon and alloying elements are not achieved, which is necessary for homogenization of the microstructure and chemical composition of alloyed spring steel during its cooling and heating before the second stage of rolling.

At a temperature of heating the roll to a temperature below 1150 ° C, the homogenization of the structure upon heating is not ensured, the technological ductility of steel in the last passes in the rolls with gauges decreases, and the quality of the rolled products deteriorates. An increase in this temperature above 1300 ° C leads to weakening of the grain boundaries, their oxidation, and the formation of cracks on the surface, which reduces the quality and yield of rolled products.

When the total hood is less than 16 or the temperature of the end of rolling above 1100 ° C, a coarse-grained, uneven microstructure of alloyed spring steel is formed, as a result of which the strength and plastic properties in the heat-treated state are reduced. Lowering the temperature of the end of rolling less than 950 ° C increases the strength of the steel in the hot-rolled state, its hardness exceeds 250 HB, which is unacceptable in the manufacture of elastic elements.

With a decrease in the rate of water cooling below 30 ° C / s or an increase in the temperature of the end of this cooling to more than 910 ° C, there is an increase in the microstructure grains, especially on profiles with a larger section, an increase in the quality of varietal profiles is not achieved. An increase in the cooling rate above 60 ° C, as well as a decrease in the temperature of its end less than 790 ° C, led to steel hardening, an increase in hardness in the hot-rolled state of more than 250 HB, which is unacceptable in the manufacture of elastic elements.

Method implementation examples

For the production of round rolled products with a diameter of 18 mm, continuously cast square billets with a cross section of S ₁ = 150 × 150 mm were used from alloyed spring steel of grade 40C2 of the following chemical composition, wt.%:

FROM Mn Si P S Cr Ni Cu Fe 0.42 0.80 1.8 0.015 0,020 0.12 0.20 0.25 rest.

The billets are heated in a methodical gas furnace to an austenitizing temperature T _n1 = 1250 ° C and after holding for 2 hours to equalize the temperature over the cross section, they are successively pushed onto the furnace rolling table of a high-grade mill 350.

The heated billet is set in rolls with calibers and the first stage of its hot rolling in the roughing group of stands is carried out in 5 passes in horizontal and vertical rolls with a rhomb-square gauge system in semi-finished products of square section S ₂ = 100 × 100 mm. The total hood λ _Σ1 is equal to:

The resulting semi-finished products are cooled, then loaded into a gas-fired heating furnace, where they are _reheated to a temperature T _n2 = 1220 ° C and subjected to the second stage of hot rolling in vertical and horizontal rolls with calibers of section rolling mill 250. Rolling is carried out in 17 passes in a circular cross-sectional profile with an area of S ₃ (diameter d = 18 mm) at a temperature of the end of rolling T _kp = 1025 ° C. The total hood λ _Σ2 at the second stage of rolling is:

A rolled profile of circular cross-section emerging from the rolls of the last stand is passed through a tubular refrigerator, to which cooling water is supplied. In a tubular refrigerator, the rolled products are cooled at a speed of V _o = 45 ° C / s from a temperature T _kn = 1025 ° C to a temperature T _o = 850 ° C. After that, the rental is cooled in air at a spontaneous rate.

Samples were taken from the rolled profile for measuring the hardness in the hot-rolled state and for simulating heat treatment. After quenching in water from a temperature of 880 ° C and tempering at a temperature of 480 ° C, tensile mechanical properties of the samples are tested. According to the results of the control of mechanical properties, accuracy of the profile and surface quality, metal is sorted.

Implementation options for the production of rolled metal and indicators of their effectiveness are given in table.2.

From table 2 it follows that when implementing the proposed method (options No. 2-No. 4) is achieved by improving the quality of rolled alloy steel spring, which helps to increase the yield. In cases of transcendental values of the declared parameters (options No. 1 and No. 5), as well as the prototype method (option No. 6), there is a decrease in the quality and yield of long products.

The technical and economic advantages of the proposed method are that after hot rolling in the first stage with a hood of at least 2.0, cooling and heating to a temperature of 1150-1300 ° C, grinding of the cast dendritic steel structure is achieved and diffusion processes are intensified. As a result, steel acquires a homogeneous chemical composition and microstructure. Repeated hot rolling of the roll with a total hood of at least 16 and a temperature of the end of rolling of 950-1100 ° C provides high technological ductility of steel, the profile of the strip and the absence of defects on the surface, the formation of mechanically worked out fine-grained austenitic microstructure. The cooling of such steel by water to a temperature of 790-910 ° C at a speed of 30-60 ° C prevents the uncontrolled growth of microstructure grains and an increase in its variability, which increases the mechanical properties of long products and increases the yield. Using the proposed method on a wire mill 250 will increase the profitability of the production of long products from alloy spring steel by 15-20%.

Information sources

1. Patent of Russia No. 2148443, IPC В 21 В 1/16, 2000

2. Auth. testimonial. USSR No. 1692691, IPC B 21 V 1/00, 1991

3. Benyakovsky M.A. and other rolling technology. Directory. Book 1. M .: Metallurgy, 1990, p. 396-404 - prototype.

table 2
Modes of production of rolled round steel alloy steel and their effectiveness No. p / p λ _Σ1 T _n2 , ° C λ _Σ2 T _CP , ° C V _o , ° C / c T _o , ° C σ _in , N / mm ² Ψ,% δ ₁₀ % HB Yield,% one. 1.9 1140 15.0 940 29th 780 1100 22-40 6-8 270-310 - 2. 2.0 1150 16,0 950 thirty 790 950 41 10 250 99.6 3. 2.25 1220 39.3 1025 45 850 900 46 16 220 99.8 four. 9.5 1300 44.1 1100 60 910 800 44 fifteen 200 99.7 5. 10,4 1310 45,2 1110 61 920 760-800 35-40 9-12 180-210 35.9 6. (prototype) - 1000 40,4 720 not regl. not regl. 800-1200 15-40 6-10 250-320 33,2

Claims (2)

1. A method for the production of long products from alloy spring steel, including heating the billet to austenitizing temperature, subsequent multi-pass hot rolling with compression in rolls with calibers with a regulated temperature of the rolling end, and air cooling, characterized in that hot rolling is carried out in two stages, initially with a total hood of at least 2, after which the roll is cooled, heated to a temperature of 1150-1300 ° C and subjected to repeated rolling with a total hood of at least 16 and the end temperature of atki 950-1100 ° C. 2. The method according to claim 1, characterized in that before cooling in air, the rolled products are additionally cooled with water at a speed of 30-60 ° C / s to a temperature of 790-910 ° C.