RU1788045C - Method of quenching high-speed steel - Google Patents

Abstract

SUMMARY OF THE INVENTION: the method includes cyclic multiple heating and cooling, wherein at all stages the cooling is carried out in a liquid medium until the end of bubble boiling at a rate of 0.25 a GG - Tk) / K-, V Ј a (T Tk) / K. where a is the thermal diffusivity of steel; T is the temperature in the center of the part; K is the coefficient of the form of Kondratiev; V is the cooling rate of the center of the part, and in the first and last stages, the products are cooled, maintaining the temperature of the wall fluidized bed at a level of 120 f 350 ° C; in the intermediate stage, the product is cooled to a temperature of AC3 + (20, .. 40 ° C) maintaining the temperature of the wall fluidized bed at a level of 100-120 ° C. Moreover, for products of a simple form, cooling is carried out from a standard temperature, and for products of a complex form, from a temperature of 40-60 ° C; below standard. with C

Description

The invention relates to the heat treatment of metals and can be used in the hardening of tools made of high speed steels.

A known method for hardening parts made of high alloy steel grades, allowing intensive cooling in the martensitic interval without fear of hardening cracks. The essence of the method is that the intensive cooling process is carried out until the maximum compressive stresses on the surface of the hardened parts are reached, corresponding to the optimum depth of the hardened layer, after which isothermal exposure is carried out at the temperature of the onset of martensitic transformation until complete decomposition

supercooled austenite in the central layers.

The disadvantage of this method is that the core is not thermally hardened enough. A common disadvantage of the considered methods is that with a single hardening, sufficiently high mechanical properties of the metal cannot be achieved, which reduces the tool life and performance.

The closest to the proposed technical essence and the achieved result is a method of heat treatment of high speed steel, including cyclic 3-5 times heating and cooling, the last heating to the upper temperature of thermal cycling combined with quenching heating according to the standard mode, characterized in that

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Joint venture

the goal is to increase strength, hardness and redness, heating in the first cycle is carried out to temperature, quenching, cooling to AI - (210 ... 215 ° С), and processing in subsequent cycles is carried out in the range AC1 - (2 ... 215 ° C) Ac3 + (35 ... 40 ° C) (2).

The disadvantage of the prototype is that multi-cycle heating and cooling is carried out by repeatedly passing only through the critical points AC1 and AC3. In this case, the possibilities of multiple passage through the region of martensitic transformations are not used, contributing to an increase in the mechanical properties of the metal due to grain refinement and the creation of a high density of dislocations in the material.

Repeated quenching with the formation of martensite is not used for the simple reason that hardening cracks are observed under conditions of intensive cooling.

To eliminate cracking under conditions of intensive cooling and increase the durability of the tool, a method for hardening high-speed steels is proposed, which includes cyclic multiple heating and cooling, characterized in that for products of simple configuration at all stages of cooling, they are carried out in a liquid medium to the end of bubble boiling at a rate

0.253 (1-10 a (T-Tk) KV K

moreover, at the first and last stages, the products are cooled, maintaining the temperature of the wall fluidized bed at the level of 120 ... 350 ° С, at the intermediate stage, the product is cooled from the temperature АСз + + (20 ... 40 ° С), maintaining the temperature of the wall fluidized bed at a level of 100 ... 120 ° C, moreover, for products of simple form, cooling is carried out from the standard heating temperature for hardening, and for products of complex shape from a temperature of 40-60 ° C below the standard.

The proposed method of heat treatment of steel products makes it possible to increase tool life and eliminate the possibility of hardening cracks under intensive cooling.

The essence of the proposed method is described below on the example of multiple hardening of high speed steels.

At the first stage of cooling, P6M5 steel is heated to a temperature of 1200 ° C - 1220 ° C, as a result of which carbides dissolve, and the temperature of the onset of martensitic transformation (Mn) is in the range of 150-200 ° C.

Cooling a heated part or tool from the indicated temperature, for example, in a concentrated CaCl2 solution (p 1300 - 1360 kg / m, having a boiling point of the wall layer of 120 ° or higher, you can partially delay the transformation of austenite to martensite in the bubble boiling section. During boiling, very intense cooling is achieved, vacancy hardening of austenite and partial conversion of austenite to martensite (50%) are observed. Therefore, the possibility of hardening cracks is eliminated. m heating to Ac3 + temperature (35 - 40 ° С), i.e. 900 - 920 ° С, carbides are crushed and precipitated, and the material is austenized at the same time.When cooled from a temperature of 900 - 920 ° С, due to the lower amount of carbide dissolution, Mn therefore increases

upon repeated cooling in aqueous solutions of optimum concentration having a temperature of 100–150 ° C in the wall layer, a high cooling rate of the material is achieved at a supercritical rate, since the bulk of the conversion of austenite to martensite in this case ceases when the maximum compressive stresses on the surface are reached hardened parts, which are determined by calculation. Therefore, hardening cracks are also excluded at this stage.

The final quenching heating is carried out from the austenitization temperature, which is 20-60 ° C lower than usually accepted. Cooling is carried out in a concentrated solution of CaCl2 (p 1300 - -1360 kg / m until the bubble boiling terminates, and then cooling in air and three times tempering are carried out according to standard technology.

The novelty of the developed technology consists in the fact that, with multi-cycle heating and cooling, the temperature of the onset of martensitic transformations (Mn) is shifted to a region of higher temperatures in order to ensure a supercritical cooling rate in the martensitic range in the region of bubble boiling and at each stage of cooling control of the boiling temperature of the wall layer, the value of which depends on

amounts of dissolved carbides in austenite.

The proposed method for hardening high-speed steels has a number of advantages:

the method eliminates alkaline environments used for hot baths and oil, which are environmentally harmful substances;

in comparison with the prototype, the tool life is increased by 1.5-2 times;

labor productivity is increased due to the intensification of tool cooling in aqueous solutions by 80%;

there is no need for preliminary heat treatment of the material (improvement).

Claims (1)

The claims A method for hardening high-speed steel, comprising cyclic heating and cooling, characterized in that, in order to increase the resistance and eliminate crack formation, cooling at all stages is carried out in a liquid medium until the end of bubble boiling at a rate 0.25a (T - T, s) / K V a / T - TK) / K, where a is the thermal diffusivity of steel; T is the temperature in the center of the part; K-coefficient form Kondratiev; V is the cooling rate of the center of the part; Tk is the boiling temperature of the wall layer, and at the first and last stages, the products are cooled, maintaining the temperature of the wall boiling layer at the level of 120 t-350 ° C, at the intermediate stage the product is cooled from ACE + temperature (20 - 40 ° C), maintaining the temperature of the wall fluidized bed at a level of 100 - 120 ° C, moreover, for products of simple form, cooling is carried out from the standard heating temperature for hardening, and for a product of complex shape - from a temperature of 40 g 60 ° C below the standard.