SU753912A1 - Method of calibrated steel production for cold upsetting - Google Patents

Description

The invention relates to ferrous metallurgy and mechanical engineering, in particular, to the production of calibrated steel for cold heading. In modern engineering, calibrated steel is widely used for cold heading. One of the main requirements for it is the presence of the structure of granular perlite and the ability to begin to perceive sediment with a high degree of deformation. The development of new capacities in the Mgiino structure requires obtaining calibrated steel for cold heading with a cross section of up to 38-40 mm. A known method for the production of calibrated large-grade steel, which is associated with repeated operations of continuous annealing, it includes hot rolling, accelerated cooling, dark spheroidizing annealing, surface preparation, calibration with a degree of deformation of 10–20%, light recrystallization annealing. All this greatly complicates the production of calibrated steel ll. There is also known a method of manufacturing calibrated steel, which includes hot rolling, cooling, reheating above Ac, deformation and subsequent annealing at subcritical temperature 2. A disadvantage of the known method is that the deformation has become higher than Ac with a degree up to 25% in certain sections of rolled products. with a critical degree, thereby causing the formation of large grains, during recrystallization, which leads to a drop in properties. The closest to the proposed technical essence and the achieved positive effect is a method of manufacturing calibrated steel for cold heading, including hot rolling, cooling at a speed greater than critical to a temperature of 7.60-500 ° C and then in air, etching, surface preparation, drawing with a degree of deformation of 21–40%, annealing at 550–700 ° C for 2–5 h, followed by cooling with a furnace to 500 ° C and then in air. However, the known treatment method does not allow to obtain calibrated steel for cold heading with a cross section above 20-22 mm.

This is due to the fact that for a cross section of 20–22 mm, accelerated cooling is not effective, since the core of the rolled core is not accelerated accelerated, which does not allow to obtain fine perlite (sorbitol) throughout the cross section and further structure of granular perlite.

To solve the problem of obtaining a calibrated cold steel dL section above 20-22 mm by increasing the heat sink is almost impossible, since in the case of a large section with accelerated cooling, the surface is cooled rapidly, while the inner layers remain hot, because in existing installations cooling is impossible to realize - the coefficient of thermal diffusivity of the metal. Microalloying also does not solve this problem, since it can give an increase in the depth of the accelerated cooled layer by no more than 2–4 mm, and at present, calibrated steel is required for mechanical engineering for cold heading with a cross section of 38–40 mm.

The purpose of the invention is to obtain a granular perlite structure in large profiles x.

The goal is achieved by drawing the wire with a degree of deformation of 45-52% after pre-heating the steel to 580-650 ° C, and the annealing is carried out in steps, while at the first stage it is carried out at 740-76 ° C with a holding time of 10 -30 min., And the shutter speed at the second stage is 5-7 h.

The proposed method for the production of calibrated steel for cold heading is carried out as follows.

Hot rolling, cooling from the temperature of the rolling end to air or in a cooling unit, followed by etching, surface preparation for drawing - calibration (including applying high temperature lubricant), heating to 580-650 ° С (heating is possible induction, electrocontact, etc.) , dragging at this temperature with a degree of deformation of 45-52% in one pass. Calibrated steel is annealed at 740-760 for 10-30 minutes, cooled with a furnace to 680 ° C-690 C, maintained at this temperature for 5-7 hours and then in air.

The sufficiently high ductility of steel at a temperature of 580–650 ° C makes it possible to calibrate it with a high degree of deformation. When heated below 5, the plastic properties became insufficient and, at given degrees of reduction, the resistance of plastic deformation is so great that a breakage is possible. Heating above 650 ° C is undesirable, since in this case distortions are reduced during deformation

structures that facilitate the subsequent spheroidization of cementite. Heating up to 580-650®С is chosen as the most technological for structural carbon steels, while a greater degree of deformation is provided and the stability of the structure is significantly reduced, which further contributes to the accelerated process of spheroidization.

Drawing with a degree of deformation of 45-52% in one pass at a temperature of 580-650 ° C increases the rate of spheronization of perlite. This is due to the fact that the deformation at these temperatures significantly changes the initial arrangement and shape of the ferrite and cementite plates. Cementite plates are bent; many defects appear in them in the form of microcracks and dislocation clusters. The lattice of ferrite is distorted, this increases the solubility of cementite in it and increases the mobility of carbon atoms. In general, plastic deformation at temperatures of 580-650-s significantly reduces the stability of the structure of perlite and facilitates the flow of diffusion processes that increase the stability of the system. One such process is the spheroidization of cementite plates. Calibration with a degree of deformation of less than 45% does not allow deforming perlite sufficiently to obtain the effect of spheroidization acceleration, and calibration with deformation above 52% cannot be performed in one pass due to metal breakage.

Although deformation by 52% and accelerates spheroidization-cementite, however, it proceeds faster after short-term heating of calibrated steel in the interval of critical temperatures. At these temperatures, austenite occurs in the steel in which the cementite dissolves. Cements of cementite dissolve most rapidly in areas whose structure is disturbed during deformation. As a result, after a short period of time, the structure of calibrated steel consists of excess ferrite, austenite, and small (point) inclusions in it of underexposed cementite. If the steel with such a structure is cooled below the eutectoid temperature and held at this temperature, then atectoidal decomposition of austenite into cementite and ferrite will occur, the eutectoid cementite will accumulate on the inclusions that are not dissolved during heating of the cementite. As a result, the structure of the granular (spheroidized) pearlite is formed. This process proceeds much faster if the steel was deformed at subcritical temperatures with a sufficient degree of reduction before heating to the critical temperature region.

A significant acceleration of the spheroidization of cementite steel, calibrated at 580-650 ° C, is achieved after stepwise annealing, with it being conducted in the first stage in the interval of critical temperatures at 740-7 b.

The duration of annealing at these temperatures is shorter, the higher the temperature is 10-30 minutes. At temperatures below 740 ° C, even a 30-minute exposure does not provide sufficient dissolution of cementite and its spheroidizing at 680-690 ° C is not completed in seven hours. At an annealing temperature above 7 ° C, the complete dissolution of cementite in austenite occurs within 10 minutes and the effect of the complex of the preceding operations on spheroidization at subcritical temperatures practically disappears.

After heating in the first stage at 740 7 BOOC, spheroidizing annealing at 680-690 ° G (second stage) is completed in 5-7 hours, depending on

on the chemical composition of the steel, the heating temperature and the time of the alloy in the first stage of annealing.

For example, in the factory after hot rolling, the tackle from the temperature of the end of rolling was cooled in air, followed by etching, preparing the surface for drawing. Then, a high-temperature lubricant was applied to the tackle of steel 35 with a cross section of 34 mm (preparation V-1 Akvodag). Heating was carried out in a furnace of electrical resistance to temperature, drawing at this temperature was carried out in a laboratory setup with a degree of deformation of 48%. Then, annealing was performed at a temperature of 750 ° C for 20 minutes, cooling with a furnace to 680 ° C, isothermal aging at this temperature for seven hours, and then cooling in air.

0 Granular perlite in steel was 95-100%. In the same way, the steel was processed 35 different sections with different degrees of deformation. The data obtained are given in table5.

44 45

32 ,.

48 & 2 34, 36

53 (open)

44

45

48

32

760 30

75 - 80

760 30 80 - 85

690

750 20

95

740 10 100

40 - 50

770

10 40

770 10

770 10

thirty

52

650

44

580

45

580

32

48

620

52

Claims (3)

.6-.0 The use of the proposed method of manufacturing calibrated steel for cold heading will allow to get steel of large sections with the structure of granular perlite, which, with further processing at hardware factories, will make it possible to produce products of higher quality using cold heading with lower costs. The invention The method of manufacturing calibrated steel for cold heading mainly from carbon structural steels, including hot rolling, cooling in air, etching surface preparation, roll drawing in one pass and annealing at 680-690 ° С with subsequent cooling. 690 7 35 690 60 7 690 7 70 690 7 80 690 100 in air, characterized in that, in order to obtain the structure of granular perlite in large profiles, drawing is carried out with a degree of deformation of 45-52% at 580-650 ° C, and the annealing is performed stepwise at first at 740-760 s with an exposure time of 10- 30 min, and then at 680-690 ° С with an exposure of 5--7 h. Sources of information taken into account during the examination 1. N. Sheftel. Production of calibrated steel bars. Metallurgists, 1970, p. 42-60. 2. US patent number 3285789, cl. 148-12, 1963. 3. USSR author's certificate number 588245, cl. C 21 O 1/78, 1976 (prototype.