SU711130A1 - Method of tool thermal treatment - Google Patents

Description

I

The invention relates to the heat treatment of tooling, mainly dies for hot hydrodynamic extrusion.

A known method of heat treatment of the working part of the finished tool from high-speed and die steels by carbonitration in the molten salt mixture consisting of sodium cyanide, potassium cyanate, sodium carbonate, and potassium carbonate with an exposure at austenite stability temperature (about 570 ° C) for 90 min 1.

However, with the di (|) fusion method, the nitrogen and carbon saturation layer is small and makes up for the cutting tool a thickness of the order of 10-90 microns, and the core remains unstrengthened. Therefore, there is a decrease in the resistance of the thermal depreciation of the surface layer, as a result of which a network of hot cracks is formed, which subsequently serve as foci for the formation of linear cracks in the metal. At the same time, the saturated layer ceases to be the protective shell against the metal softening and the softening layer gradually decreases, the so-called metal fluidity under the influence of large loads under high temperature conditions. If we consider that the frequency of extrusion of parts is on average 20-30 seconds, then the saturated worker heats up quickly due to the transfer of heat generated as a result of excessive friction and from direct contact with the red-hot billet.

A method of deep cold treatment is also known, which includes quenching followed by shock immersion of an instrument in a liquid medium (for example, liquid nitrogen), with a temperature of the order of (-150 ° C) - (- 269 ° C), holding it for 5-30 minutes , air cooling to the full on the surface and tempering in a non-oxidizing environment at 200-250 ° С for 1-1.5 h 2}.

The disadvantage of this method with respect to the matrix of high-speed and die steels is that the redness of the latter is not ensured, since the matrix for hot hydrodynamic extrusion all the time working in direct contact with the red-hot metal to 1100-150 ° C, and this is the reason decomposition of the martensite solid solution of high-speed and stamping steels; coagulation of the dispersed phases of the reinforcers precipitated during the previous tempering, as a result, the surface layers of the metal soften.

The purpose of the invention is to increase the red-resistance of the working surface of the dies for hot hydrodynamic extrusion of high-speed and die steels and increase their durability.

The goal is achieved by the fact that, after quenching, before treatment with cold, the matrix is subjected to tempering at an isothermal temperature in alkali and cooled in oil to a temperature of incomplete transformation of residual austenite, and after cold treatment, a two-time tempering is performed at a decomposition temperature of residual austenite preceding mechanical treatment, after carbonitration is carried out at a tempering temperature followed by deep cold and alkali tempering at an isothermal temperature. excerpts.

Example. Matrices made of steel P18 or 4H4BMFS steel (die) are quenched from 1270 ° C, subjected to isothermal aging for 2 minutes in alkali (mixture of 70 ° / about equal parts of barium chloride and sodium chloride and 30% chloride calcium) at a temperature of about 450 ° C, and then further cooled in oil to 200 ° C - 300 ° C, after which it is immediately transferred to a bath with liquid nitrogen (-196 ° C) and held for 60 minutes. In this way, the core of the dies is hardened due to the significant compressive forces resulting from unequal removal of the points of the outer surface from the center. After cold treatment, the dies are heated in air and two-fold tempering is performed successively at a decomposition temperature of residual austenite (560 ° C) for 60 minutes each and cooled in air, after which the dies are ready for machining. The final dimensions of the matrices are machined. The finished matrix is subjected to carbonitration, i.e., immersed in a bath with potassium cyano-acid melt (sodium cyano-acid can) with a temperature of stability of martensite equal to the tempering temperature in this case, i.e. 560 ° C for 60 minutes. Due to the diffusion of nitrogen and carbon atoms, the surface layer is saturated with carbides and nitrides of tungsten and chromium, thereby increasing the wear resistance of the outer surfaces along with the preservation of the hardened core. The matrices are then transferred to liquid nitrogen.

and held for 60 minutes to consolidate previously obtained properties. After a time sufficient for complete thawing, the dies are subjected to tempering at 450 ° C for 60 minutes in a silk panel, cooled in air and washed in

hot 5-10% aqueous solution of soda ash. The test matrices worked for two shifts without interruptions, while the grid of hot melts and the hard cores are absent, the decarbonization of the working matrix layer is not observed due to an increase in heat resistance and high heat resistance of the saturated working layer, which was not achieved during deep cold treatment, as well as carbonitration.

Claims (2)

Invention Formula . The method of heat treatment of the tool, mainly matrices, including hardening, subsequent cold treatment during impact immersion in a liquid medium, tempering in a non-oxidizing medium, and mechanical processing, characterized in that they are subjected to isothermal to increase the operational durability of the dies alkali hardened, cooled in oil to 200--300 ° C, 3 after cold working, double tempering, mechanical treatment, carbonitration followed by cold treatment and holiday are carried out. 2. A method according to claim 1, characterized in that the double tempering of the dies made of steels R18 and 4X4BMFS is carried out at 560 ° C and the final in. alkali at 450 ° C. Sources of information taken during the examination. USSR Author's Certificate No. 221586, cl. C 23 C 9/00, 1965. 2. USSR author's certificate No. 485161, cl. C 21 D 9/22, 1972.