RU2025539C1 - Method of chemical heat treatment of articles of tool steel - Google Patents

Abstract

FIELD: mechanical engineering. SUBSTANCE: chemical heat treatment of articles of tool steel comprises heating up to process temperature in endothermic-base atmosphere with ammonia addition, holding at this temperature in atmosphere containing nitrogen, and article cooling. Heating up to process temperature is performed in two stages. First, the article is heated up to 480 - 500 C temperature in endothermic gas, and then it is heated up to 560 - 580 C in gas mixture of 50 per cent of nitrogen, and 50 per cent of endothermic gas. Holding at this temperature and this mixture content is carried out during 0.5 - 1.0 h. Then holding is performed at the same temperature and in gas mixture of 25 per cent of ammonia and 75 per cent of nitrogen. Then the article is cooled down to 480 - 500 C in mixture of 10 per cent of ammonia, and 90 per cent of nitrogen. The article is hold at this temperature and in nitrogen atmosphere for 1.5 to 2.0 h. EFFECT: tool steel of improved properties. 1 dwg

Description

 The invention relates to mechanical engineering and can be used in various industries in the chemical-thermal processing of products from tool steels, mainly in the processing of finally manufactured cutting and stamping tools.

 A known method of two-stage gas nitriding of steel products, including processing in dissociated ammonia at two stages of heating.

 However, the known method is a relatively lengthy and inefficient process, and also does not provide high quality processing.

 There is also a method of nitrocarburizing parts from heat-resistant steels in an endothermic atmosphere with the addition of natural gas and ammonia.

 This method does not provide increased wear resistance of the surface layer of products from tool steels and is a lengthy process.

 The technological result obtained by using the invention is to improve the operational characteristics of products from tool steels by increasing the wear resistance of the surface layer, as well as reducing the processing time.

Obtaining a technical result is ensured by the fact that in the method of chemical-thermal processing of products from tool steels, including heating to a processing temperature in an endothermic atmosphere with the addition of ammonia, holding at this temperature in an atmosphere containing nitrogen, and cooling the products, it is new that heating to a processing temperature is carried out in two steps, first to a temperature of 480-500 ^{° C} in a medium endogas, then to a temperature of 560-580 ^{° C} in a medium consisting of 50% ammonia and 50% endogas and kept at this evap ur and in this composition of the medium is performed for 0.5-1.0 hours, then at the same temperature and in a gas mixture consisting of 25% ammonia and 75% nitrogen, the shutter speed is 0.5-1.0 hours, after which is cooled products to a temperature of 480-500 ^about In a gas mixture consisting of 10% ammonia and 90% nitrogen, and maintained at this temperature in a nitrogen atmosphere of 1.5-2.0 hours

 The drawing in General view shows the process of gas chemical-thermal treatment.

 The process is as follows.

Thoroughly fat-free products are placed in the fixture and put in the oven. Then, after purging with nitrogen, endogas is supplied to the furnace in the amount of 1 furnace volume for 1 h at a furnace pressure of 60-80 mm water column. Turn on heating furnace and heated to a temperature of 480-500 ^C. endogas is fed with a dew point of (-3) - (- 5) ^{° C} by passing it through a desiccant (silica gel, or the like.).

When the temperature reached 480-500 ^{° C} is fed into the furnace atmosphere gas consisting of 50% ammonia and 50% endogas and produce temperatures of 560-580 ° ^C at temperature ^of 560-580 C and a gas composition environment - 50 % ammonia + 50% endogas is carried out depending on the cross-section of the workpiece for 0.5-1.0 hours, after which at the same temperature and in a gas mixture consisting of 25% ammonia and 75% nitrogen, extract 0.5- 1.0 hours. Then the product is cooled to a temperature of 480-500 ^about With in a gas mixture consisting of 10% ammonia and 90% nitrogen. At a temperature of 480-500 ^C. ammonia flow is stopped and produce an extract 1.5-2.0 hours under a nitrogen atmosphere, after which the parts cool with the furnace to a temperature of 150 ^{° C,} and then the furnace was opened and the take out finished articles.

 All types of process gases are fed into the furnace through a dehumidifier. The amount of gases supplied to the furnace in any composition amounts to 1 furnace volume per hour. The color of the products after the end of the process has a grayish-bluish tint, which corresponds to the presentation.

Due to the use of endogas during heating (97% N ₂ , 2.9% H ₂ , 0.04% CO, CO _{2 the} rest), which provides protective and reduction functions, at the beginning of the process, the steel is intensively saturated predominantly with carbon to the depth necessary for forming carbide zone. At the second stage of heating, when the temperature reaches 480-500 ^о С, ammonia (50% NH ₃ + 50% endogas) is introduced into the furnace atmosphere, as a result of which the surface of the products is saturated with nitrogen. At the first stage of exposure, endogas is present together with ammonia, and already at the second stage of exposure, the composition of the gas medium is changed (25% NH ₃ + 75% N ₂ ). This treatment contributes to the creation on the surface of the products carbonitride layer with a thickness of 10-15 microns. Further cooling the product in an atmosphere containing 90% N ₂ and 10% NH ₃ and then holding at a temperature of 480-500 ^{° C} for 1.5-2.0 hours under a nitrogen atmosphere, lead to diffusion and disintegration of carbon nitride crust, reducing brittleness but not reducing the hardness of the surface layer. An exposure in nitrogen of less than 1.5 hours does not completely eliminate surface brittleness, and more than 2.0 hours leads to a decrease in hardness.

 The inventive method of chemical-thermal treatment, based on a gradual decrease in the processing percentage of ammonia (50%, 25%, 10%, 0%) and an increase in the percentage of nitrogen (75%, 90%, 100%), allows you to evenly distribute with a thin surface layer, all formations doped with nitrogen and carbon stabilize the heterophase layer and thereby improve the operational characteristics of the products. So, during the chemical-thermal treatment of the tool from high-speed steels according to the claimed method, cases of peeling and chipping are excluded, the surface becomes less adhesion to the metal being treated, and cases of metal enveloping are excluded.

PRI me R. Chemical-thermal treatment of products (taps M8) is carried out from steel P6M5. Pre-fat-free taps are installed in a special device and placed in the oven. Then, after purging with nitrogen, endogas is supplied to the furnace in the amount of 1 furnace volume for 1 h at a furnace pressure of 70 mm water. Art. Turn on heating furnace and heated to a temperature of 490 ± 10 ° ^C endogas is fed with a dew point of -3 ^{° C} by passing it through silica gel previously. When the temperature reached 490 ± 10 ^{° C} is fed into the furnace atmosphere gas consisting of 50% ammonia and 50% endogas and produce further heating to a temperature of 570 ± 10 ° ^C. At the temperature in the furnace 570 ± 10 ^{° C} and the composition of the gas environment - 50% NH ₃ + 50% of endogas is held for 40 minutes, after which, at the same temperature and in a gas mixture consisting of 25% NH ₃ + 75 N ₂ , they hold for 40 minutes. Then the furnace with the products is cooled to a temperature of 490 ± 10 ^about With the supply of a gas mixture of 10% NH ₃ + 90% N ₂ . When the temperature reached 490 ± 10 ^{° C} flow was stopped and ammonia produce exposure 1 hour 40 minutes under a nitrogen atmosphere, after which the oven is switched off and the articles cool with the furnace to a temperature of 150 ^{° C,} and then the furnace was opened and the take out finished articles.

For comparison, chemical-thermal treatment of M8 taps was carried out according to the known method of two-stage gas nitriding:
I stage - temperature 560 ^о С, time 15 hours;
II stage - temperature 500 ^о С, time 12 hours

 Tests of M8 taps carried out during the processing of parts made of 5XHM steel show that after processing by the proposed method, their resistance increased by 1.5-1.8 times in comparison with the known method. Moreover, the processing time of the proposed method is significantly reduced.

 Thus, the technical and economic effect when using the proposed method is obtained by increasing the wear resistance and reducing the total processing time of the products.

Claims (1)

METHOD FOR CHEMICAL AND THERMAL TREATMENT OF PRODUCTS FROM INSTRUMENTAL STEELS, including heating to a treatment temperature in an endothermic atmosphere with the addition of ammonia, holding at this temperature in an atmosphere containing nitrogen, and cooling products, characterized in that heating to a processing temperature is carried out in two stages, first to a temperature of 480 - 500 ^o C in an endogas medium, then to a temperature of 560 - 580 ^o C in an environment containing 50% ammonia and 50% endogas, and exposure at this temperature and this composition of the medium is performed for 0.5 - 1.0 h, then at this e exposure is carried out a temperature of 0.5 - 1.0 hours in a gas mixture consisting of 25% ammonia and 75% of nitrogen, after which the product is cooled to 480 - 500 ^o C in a gas mixture consisting of 10% ammonia and 90% of nitrogen, and maintained at this temperature in a nitrogen atmosphere of 1.5 - 2.0 hours

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