RU2164348C2 - Method establishing heat stability of steel - Google Patents

Abstract

FIELD: chemical and heat treatment of steel. SUBSTANCE: method establishing heat stability of steel includes manufacture of samples, chemical and heat treatment of samples together with parts to obtain specified hardness with use of standard technology to form surface diffusion layer, determination of starting hardness of samples in three zones: on surface of diffusive layer, at depth of layer specified by technology and in core of sample without diffusive layer, additional heating at 500 C and repeat determination of hardness in three zones. After this loss of hardness in each zone is found as percentage of starting hardness, relative heat stability of diffusive layer in specified zone is calculated as difference of losses of hardness of core and diffusive layer referenced to losses of hardness of core and diffusive layer expressed in percentage. EFFECT: prediction of heat stability of working parts of tools made of economically alloyed steels with surface alloying and hardening which provides for increased durability of tools. 1 dwg, 2 tbl

Description

The invention relates to the field of mechanical engineering and can be used in the manufacture of tools with chemical heat treatment (CTO) and final tempering at a temperature not exceeding 500 ^o C.

Known methods for determining the heat resistance (redness) of steel by repeated heating with a shutter speed of 1 h at a temperature that ensures the preservation of a given level of hardness, for example 50 or 45 HRC (Geller Yu.A. "Tool steel". - M.: Metallurgizdat, 1961, p. 56), or with a holding time of 4 hours and a level of "residual" hardness of 59 HRC _e (GOST 19265-73. Rods and strips of high-speed steels).

 As the closest analogue, a method for determining the heat resistance of steel is presented, including the production of samples, heat treatment to a given hardness using the established technology, additional heating for 4 hours to temperatures at which irreversible softening is expected to develop, determination of hardness and assessment of heat resistance of steel (Geller Yu.A Tool steel. - M.: Metallurgy, 1983, S. 66, ab. 2-4, Fig. 35).

However, all these methods are not widely used, because it is not known what level of hardness to set for non-quick cutting and non-stamping steels. GOST 19265-73 does not ensure the effectiveness of the method due to a small fluctuation in the heat resistance temperature equal to 620-630 ^o C for all steels. These methods are unacceptable for products with XTO, when the hardness has a variable value along the depth of the diffusion layer.

 The technical result of the implementation of the proposed method lies in the ability to predict the relative heat resistance of the diffusion layer of products made from different steels with different levels of hardness. Also, the claimed method allows you to reasonably assign XTO methods and determine the level of technological hardness, based on operation under conditions of increasing metal temperature, provides control of heat resistance, especially of tool working parts, cutting edges after sharpening, grinding, when a part of the diffusion layer having a variable chemical composition in depth, removed. All this allows you to increase the efficiency of the use of XTO, especially the new method - complex alloying, and to increase the tool life.

 The objective of the invention is to expand the technological capabilities of the method and make it acceptable for products with a diffusion layer made of any steel.

The problem is achieved in that the method for determining the heat resistance of steel includes the production of samples, chemical-thermal treatment of samples together with parts to a given hardness and using the established technology, determination of hardness in three zones: on the surface of the diffusion layer, at the technological depth, in the core without a layer the XTO, additional heating at 500 ^o C, is again determined in three zones of firmness, loss of hardness are in each zone as a percentage of the original, calculated relative heatproof diffusion layer in a predetermined zone of the core loss as the difference in hardness and the diffusion layer, referred to the hardness of the core loss, expressed as a percentage. It is believed that the heat resistance of the core products, i.e. all steels, like hardness after tempering at different temperatures, is known from reference books.

The difference between the claimed method and the closest analogue is that, as a heat treatment, the samples together with the parts are subjected to chemical-heat treatment to create a surface diffusion layer, after heat treatment, the initial hardness of the samples is determined in three zones: on the surface of the diffusion layer, at the depth of the layer specified by the technology and the core sample without the diffusion layer, then additional heating is carried out at 500 ^o C, is again determined in three zones of firmness, loss of hardness are in each district n otsentah to source, calculated relative heat resistance of the diffusion layer in the predetermined zone of the core loss as the difference in hardness and the diffusion layer, referred to the hardness of the core loss, expressed as a percentage.

To implement the method perform the following operations:
1. Samples are made by subjecting them to chemical-thermal treatment together with parts or using a similar technology.

 2. The initial hardness is determined in three zones: on the surface of the diffusion layer, at the technological depth (as in the manufacture of parts, for example, sharpening, grinding), in the core without the XTO layer.

3. Carry out heating at 500 ^o C for 4 hours. If heating is not protected against oxidation, then after heating they protect the place for measuring hardness, removing metal no more than 0.05 mm.

 4. Re-determine the hardness of the three zones in the same places where they were determined before the test by heating.

 5. Calculate the loss of hardness in each zone as a result of heating as a percentage of the original, considering the drop in hardness with increasing annealing temperature monotonic.

 6. Calculate the relative heat resistance (%) of the surface of the diffusion layer or at the technological depth as the difference in the loss of hardness of the core and the diffusion layer to the loss of hardness of the core in this zone.

The invention is illustrated by the scheme (see drawing) - graphs of the loss of hardness by the diffusion layer and the core as a result of testing heat resistance by heating at 500 ^o C.

 The method was tested practically during testing the manufacturing technology of tools from structural steels 40X and 38X2MUA with a surface diffusion layer created by nitrocarburizing (RF patent N 2082820, C 23 G 8/32) with subsequent quenching and tempering - tables 1 and 2.

где ОТ д/с - относительная теплостойкость диффузионного слоя, %;
ΔТВс, ΔТВ д/с - потеря твердости сердцевины и диффузионного слоя в результате испытания нагревом на 500^oC, %.Relative heat resistance calculated by the formula

where RT d / s is the relative heat resistance of the diffusion layer,%;
ΔTVS, ΔTV d / s - loss of hardness of the core and diffusion layer as a result of testing by heating at 500 ^o C,%.

 In the first case (table 1), the relative heat resistance of the diffusion layer on the surface and at any depth is estimated to be higher than 100%, since the intensity of the decrease in the hardness of the layer is less than that of the core.

 In the second case (table 2), on the contrary, the hardness of the diffusion layer decreases faster than the core, the relative heat resistance is less than 100%.

 The claimed method allows you to reasonably assign methods of XTO, the level of technological hardness, based on operation in conditions of increasing temperature of the metal. The shortage of high-speed steels, especially tungsten-containing steels, necessitates the development of technologies for the use of low-alloy, low-alloy steels for the manufacture of tools with their subsequent surface alloying and heat treatment. In this case, it is necessary to control the heat resistance, especially the working parts of the tool, cutting edges after sharpening, grinding, when a part of the diffusion layer having a variable chemical composition in depth is removed. All this allows you to increase the efficiency of the use of XTO, especially the new method - complex alloying, and to increase the tool life. Implementation of the proposed method is possible on standard equipment.

Claims (1)

A method for determining the heat resistance of steel, including the manufacture of samples, heat treatment to a given hardness using the established technology, additional heating, determination of hardness and assessment of heat resistance of steel, characterized in that, as heat treatment, the samples together with the parts are subjected to chemical-thermal treatment to create a surface diffusion layer, after heat treatment, the initial hardness of the samples is determined in three zones: on the surface of the diffusion layer, at the depth of the layer specified by the technol Gia, and the core sample without the diffusion layer is carried out the additional heating at 500 ^o C, again determine the hardness in three zones, are loss of hardness in each zone as a percentage of the original, calculated relative heat resistance of the diffusion layer in the job area as the difference in loss core hardness and diffusive layer, referred to the loss of core hardness, expressed as a percentage.

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