SU1749252A1 - Method of heat treatment of steel products - Google Patents

Abstract

Usage: metallurgical engineering, induction heating of the rolls. SUMMARY OF THE INVENTION: Multiple cyclic heating is carried out up to a temperature of Asz + (180-190 ° C) at a speed of 16-30 ° C / s to the Curie point, then at a speed of 8-15 ° C / s, holding for 5–10 s, cooling at a rate of 14–17 ° C / s to the Curie point, and then to a temperature of troobainite transformation at a rate of 10–12 ° C / s. During the last cooling from the austenization temperature, the wire t isothermal aging at a trostanobenite transformation temperature of 1500-2000 ° C. 1 silt, 1 tab.

Description

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The invention relates to the heat treatment of steel products and can be used, for example, in the manufacture and restoration of mill rolls.

A known method of heat treatment of hot rolling mill rolls involves heating the roll for quenching by industrial frequency currents with five preheatings on a TFC-700 installation (650 ... 670 ° С, 780 ... 800 ° С, 920 ... 940 ° C, 1080 ... 1100 ° C, 1X0 ... 1200 ° C) at a speed of 10 .., 12 ° C / s, quenching of continuous-sequential action using a ring inductor and a water sprayer, cooled to a temperature of 130 170 ° С and double tempering for secondary hardness at

540 ... 10 ° С.

The disadvantage of this method is that as a result of this heat treatment it is impossible to grind the grain, and perhaps even some of its coarsening, that

reduces the resistance of the material to cracking and increases the likelihood of chippings and fatigue cracks. The closest to the invention is a method of heat treatment of low-carbon martensitic stainless steels, which includes repeated heating of the product at a speed of 10, 30 ° C / min to a temperature of Asz + H220. .240) ° С and holding for 0.5-0.7 min / mm.

The disadvantage of this method is that it does not allow to increase the contact resistance and wear resistance of steel products, as heating to the temperature of Asz + (200 .. 230) ° C and aging at this temperature from 50 to 800 min causes grain growth, which reduces the contact resistance and wear resistance of steel products.

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 ABOUT

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The aim of the invention is to increase the operational durability (durability) of steel products by increasing the contact resistance and wear resistance.

This goal is achieved due to the fact that according to the method of heat treatment of steel products, which includes thermal cycling with heating to austenitization temperature, exposures and cooling and final cooling, heating is carried out to Asz + 180 ... 190 ° C, and to the Curie point at a speed of 16–30 ° C / s, and then at a speed of 8–15 ° C, exposures are carried out for 5–10 s, and cooling is carried out to the temperatures of hydrostatic transformation, and to the Curie point at a rate of 14– 17 ° C / s, then at a speed of 10-12 ° C / s, and after the thermo-cyclic treatments at the temperature of trostanobenite transformation are isothermal aging for 1500-2000s.

Known and proposed methods are methods of heat treatment, include multiple heating to a temperature above Asz 1 exposure at a given temperature.

Thermocyclic treatment in such conditions allows to increase the level of strength, toughness, hardness and grind grain, which allows to increase the operational durability (durability) of steel products by reducing wear and chipping of the working layer.

To determine the optimal modes of heat treatment, samples of 9HF steel with a diameter of 16 ... 27 m and a length of 60 mm are used. Chemical composition of steel,%; carbon 0.85; silicon 0.39; manganese 0.43; 1,4 chromium; Nickel 0.13; vanadium 0.17, copper 0.14; sulfur 0.007; phosphorus 0.02. Critical points of steel 9HF: Aci "740 ° C; Asz 760; Mel 185-215 ° C.

The backing rolls of the continuous hot-strip machine 2000 are characterized by the following properties: hardness 286 HB, OB 907 MPa, from - 506 MPa, KCU 11.8 J / cm2. For testing, the samples are annealed at 800 ° C for 2 hours and then cooled with a furnace. At the same time provide a hardness of 15 ... 25 HRCa.

Thermal cycling of the samples is carried out at the installation of currents of increased frequency {8000 Hz) IGZ-108. In the TCO process, the sample temperature is continuously recorded using a chromel-alumel thermocouple and potentiometer KSP-4. The evaluation criteria are the following properties: limit

strength, toughness, grain number, hardness, number of cycles before pitting occurrence, contact fatigue testing is carried out on an MCF with Ok 650 MPa.

The test results are given in

table. i

Example. HF 9 steel supporting roll

continuous broadband mill 200b

set in roll grinding machine, where he was given the profiling. The initial hardness of the support roll barrel is measured using the TBP-4 hardness tester. In this case, the hardness is 40 HSD. Then the swath is set

In the thermocyclic treatment plant, the roller is closed with a thermocasing and heated by gas burners to 520 ° C. The roller then rotates at a speed of 30 m / h.

After holding for 3 hours at 320 ° C, an annular inductor with a diameter of 1620 mm was introduced, connected to a power source with a frequency of 50 Hz and a voltage of 1000 V and a power of 1800 kW. Inductor width 140

mm

The inductor is turned on and heated to 940 ° C at speeds in the first stage up to the Curie point 20 ° C, in the second stage from the Curie point to the austenization temperature, respectively. The inductor moves along the roll barrel at a speed of 20 mm / s, which ensures a holding time at 940 ° C for 7 seconds.

Behind the inductor, the sprayer moves along with it, which respectively provides cooling in the first and second stages at speeds of 15 and 10 ° C / s, respectively.

After the first pass, the inductor returns to its original position and the process is repeated, and the cycles 6, 9 are repeated many times. At the end of the last cycle, the roller, when rotated in a thermocasing, is kept at 520 ° C for

1800 s, and its further cooling is performed in a thermostat. After cooling, the roll is polished and its hardness is checked, the hardness of the roll corresponds to 55 ... 60 HSD.

Using the proposed method of heat treatment of steel products allows increasing the service life of mill rolls by 1.5 ... 2 times.

Claims (1)

Invention Formula The method of heat treatment of steel products, mainly rolls, including thermocyclic treatment with heating to austenization temperature, exposures and cooling and final cooling, characterized in that, in order to increase operational durability and wear resistance, heating is carried out to AES + 180 ... 190 ° C, and to the Curie point, at a speed of 16-30 ° C / s, and then at a speed of 8-15 ° C / s, exposures were carried out for 5-10 seconds, and cooling was carried out. t is the austenitization temperature; t - temperature costs during trostanobaim transformation; tt-time aderti at a temperature of eusteniaation} ре - ре y and Exposure at a temperature of one-way transformation; (O is the heating rate to the point K ri; "is the heating rate from the Curie point to the austeniation temperature; t 0 is the cooling rate from the austimization temperature to the ori point; a, is the cooling rate from the Kern point; NCSE, hardness, "Erna; 5L - ultimate strength; KSO - impact capacity, I. number of cycles to penetrate contact fatigue water to temperatures of one-way transformation, and up to the Curie point, at a speed of 14-17 ° C / s. then, at a rate of 10–12 ° C / s, and after thermocyclic treatment at a temperature of trostanobenite transformation, isothermal aging is carried out for 1500–2000 ° C.