SU1059009A1 - Method for casehardening steel products - Google Patents

Abstract

1, A method of thermochemical treatment of steel products by pretmstviteino after surface plastic defo1c5ation, including non-oxidative heating, aging in an oxidizing environment and a chemical effect, such as. in order to increase the operational durability of the product by fixing the fine-grained surface layer, the production is multistage, with the first stage ni ilOO-200 ° C, the second one by 100-200 seconds higher, the third stage by 100-300 0 above the second and fourth on the above first stage. 2, the method according to the claim: 1, about 1 t and a and y, and c and so that non-oxidative heating is carried out after the vacuum to a pressure of 10-10 mm Hg. 3. The method according to claim 1, which is based on the fact that the oxidizing medium is obtained by supplying oxygen. 4. The method according to claim 1, about tl and hay shchi and the fact that the oxidizing environment is obtained by feeding a mixture of oxygen and argon.

Description

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The invention relates to thermochemical machining of parts made from metals, alloys, stainless steel, and other steels, for example, TVEL shells, heat exchangers, steam generators, turbine parts and assemblies, etc.

A known method for inhibiting fatigue cracks in metals and alloys is based on braking growing fatigue cracks in metals and alloys by creating a local deformed zone in front of the crack front l.

There is also known a method of reducing the sensitivity of alloys to intergranular corrosion, based on desensitization of the alloy susceptible to intergranular corrosion after aging at a temperature of sensitization and providing for a hard blasting surface

alloy before aging alloy

IP -. /

at a sensitization temperature of i2j

There is also known a method of treating austenitic steel, which includes quenching, cold deformation and annealing at b50 ° C, in which cold deformation with a degree of reduction of 10–15% is carried out after annealing to increase corrosion resistance.

 However, the known methods of processing do not take into account the conditions of operation of the elements, operation at elevated temperatures, vibration loads, deformation stresses, as well as the effect of heat carriers, such as gas, liquid sodium, water, and steam, leading to the disappearance of the heating layer, an increase in defects at the grain boundaries, the emergence of cracks on the surface, cracking along the grain boundaries and the breakthrough of the coolant along the grain boundaries.

The closest to the proposed technical essence and the achieved result is a method of heat treatment of products, including non-oxidative heating to the annealing temperature, exposure and cooling, in which, in order to obtain a mechanically and electrically strong oxide film, during the heat treatment process, the oxidant J4J is injected.

However, the known method does not ensure the fixation of a fine-grained layer of hardening and, under the conditions of an experimental luatgidii, it disappears due to recrystallization, which will lead to an increase in defects at the grain boundaries and cracking at the grain boundaries.

The aim of the invention is to increase operational stability.

products by fixing fine grain. a large surface layer.

This goal is achieved by the fact that, according to the method of thermochemical treatment of steel products, mainly after surface plastic deformation, including non-oxidative heating, soaking in. oxidizing environment and cooling; holding a multistep stage, with the first stage at 100–200 ° C, the second one by 100–200 ° C higher than the first, and the third one by 100–300 ° C above the second and fourth by 100 ° C. above the first.

5 gri this is non-oxidative on. the heating is carried out after evacuation to a pressure of mm Hg.

An oxidizing medium is obtained by supplying oxygen or a mixture of an acidic type and argon.

An example. 1%) gadget t evacuates the surfaces of products in the cold to KG-I O mm Hg, and then evacuating when heated to

5 temperature of the first stage, for example for stainless steel up to 200s. Fall into the system portions of dry oxygen, purified from moisture, nitrogen and other impurities, then

Q is rinsed with portions of purified oxygen or a purified gas mixture; oxygen plus argon with exhaust through a water seal (oil, water, etc.). The temperature, the exposure time and the ratio of gases (oxygen + argon) are determined experimentally, taking into account the grade and thickness of the material being processed and maintained.

For carbon and low-alloy steel, the lower are recommended.

0 temperature limits, and for stainless steels, the upper ones, for example, for fuel elements of stainless steel fuel elements, the temperature at the first stage is 200 ° C, at the second stage - 400 ° C, at

5 third - 700 ° C and 300 ° C in the fourth; for products made of stainless steel contours, the temperature at the first stage, at the second - 400 ° C, at the third - 600 ° C, and at the fourth 0 300 ° C.

Depending on the thickness of the product wall, the depth of the fixed fine-grained structure of the hard-hardening layer is established experimentally.

e obtaining a dense, impermeable, environmentally passive oxide film over the grain boundaries and the entire surface of the products, jamming all cracks to the required depth of the products, for example, for TYL shells and packages - 0,010-0,050 mm,. for internal surfaces of contours - 0.3-1.0 mm, for rods TVEL0, 3-0.8 mm.

Thermochemical treatment method

5 ensures the fixation of the fine-grained 3 10590 structure of the hard-hardening layer over the entire depth, obtaining a dense, impermeable, passive to the environment, oxide film, wedging all of the vehicles to the required depth, along the grain boundaries and the entire surface, minimizing the energy surfaces to the minimum , relieving internal stresses in products caused by deformation and heat treatment, since the process is carried out at temperatures corresponding to tempering. The proposed method allows and thermochemical treatment of the internal surfaces of the contours and other components of nuclear power plants and other products, which increases the life, the technical and economic efficiency will be obtained by increasing the service life of products and the possibility of using low-alloyed steels.

Claims (4)

1. The method of thermochemical treatment of steel products mainly after surface plastic deformation, including oxidative-free heating and aging in an oxidizing medium and cooling, which are different from the fact that. in order to increase the operational stability of the grandfather by fixing the fine-grained surface layer, the shutter speed is multi-stage, with the first step at 100-200 ° C, the second 100-200 ° C higher than the first, the third 100-300 ° C above the second and fourth at 100 ^° C above the first stage. 2. The method according to π. 1, on the basis of the fact that the non-oxidative heating is carried out after-. cumulation to a pressure of 10 * - 1 (g mm Hg 3. The method according to π. 1, with the fact that the oxidizing medium is obtained by supplying oxygen. 4. The method according to π. 1, characterized in that the oxidizing medium is obtained by supplying a mixture of oxygen and argon.