SU1014925A1 - Method for heat treating precision steel parts - Google Patents

Abstract

1. METHOD OF THERMAL TREATMENT OF STEEL. GETTING ALEI OF HIGH ACCURACY, mainly plane-parallel end gauges, including preliminary thermal treatment, followed by overlapping ZYL2 lLiif-l S- -. and, in order to increase the depth of the hardened layer, to obtain noBiai hardness and dimensional stability of the workpieces, preliminary heat treatment is carried out on sorbitol and troostite. 2. Method according to Claim 1, which is based on the fact that preliminary heat treatment for troostite is carried out by quenching and tempering at 300-500 s or by isothermal quenching with an exposure at 300-500 ° C .3. The method, according to claim 1, distinguishing with. the fact that the preliminary heat treatment on sorbitol is carried out by quenching and tempering at 500-650 ° C and isothermal quenching with an exposure at 500-650 ° C

Description

The invention relates to heat treatment and can be used in the tool; and machine tool industry.

In order to strengthen the working surfaces of some types of high-precision measuring tools, including plane-parallel end gauges, standard (.volume) heat treatment is used, which does not provide one of the most important properties - dimensional stability of the tool during long-term operation and storage. The technological cycle of heat treatment of the measuring instrument consists of normalization, quenching, cold treatment and long-term tempering at 130 ° C for 12. The structure obtained after heat treatment consists of martensite, carbides and residual austenite. One of the main reasons leading to a change in tool size is the transformation of residual austenite into martensite over a long period of time. To eliminate this drawback and increase the dimensional stability of the tiles, tool processing plants use cold treatment and long-term aging.

However, this treatment does not lead to the complete transformation of austenite. As a result, the method of stabilizing the structure is not sufficiently effective for high precision instruments. After cold treatment, changes in tool dimensions are less significant, but still the magnitude of these changes is greater than that provided by GOST. For example, for plane-parallel measures of length at a nominal value of a length of measure 10 mm, the limiting deviation from the nominal is + 0.05 µm Class 00, GOST 9038-73), and after cold treatment this value is sometimes (+ 0.06) - ( + 0.07 micron. In order to significantly increase the dimensional stability of high-precision parts, it is advisable to use surface hardening, not volumetric but hardening. This eliminates the operation of processing and long aging.

The known method of laser hardening of tool steels, including irradiation of tool steels with a stable structure of perlite, using a pulsed laser system KVANT-16 12.

However, the existing method of laser hardening is not suitable for impacting the working surfaces of measuring instruments, especially plane-parallel end gauges.

since the depth of the laser-hardened steel layer having the original perlite structure is 100-130 microns. The working surfaces of all high-precision parts must have a high surface cleanliness (10-14 cells), which is provided by grinding and fine-tuning: Thus, taking into account the allowance for mechanical processing, the depth of the laser-hardened layer

0 must be at least 250-300 microns.

The purpose of the invention is to obtain sufficient depth, high hardness and wear resistance of the hardened layer of working surfaces of high-precision parts, as well as stability of their dimensions.

The goal is achieved by using steels with an initial sorbitol or troostite structure with hardness HNS 28-47 and subsequent laser hardening of working surfaces.

In laser hardening of parts having an initial sorbitol structure

5 or troostit. The depth of the hardened layer is greater than that of the parts with the original pearlite structure, which is explained by the different thermal conductivities of the structures under consideration. Heatproj. the water content depends on the size of the internal interphase surface, and the separation of ferrite from cementite with a roll.

It is known that the thermal conductivity of ferrite is 0.184 cal / cm "grad.c,

5 a cementite 0,017 cal / smrads,

those. less than ferrite on the order. Consequently, the thermal conductivity of a layer with fine sorbite and troostite structures, where the size of the internal interphase surface is large and the greatest amount of crystallite cementite occurs on the heat flow path, will be less than the thermal conductivity of the layer with

The perlite structure, consisting of a mixture of ferrite and larger, but less commonly located in the structure of cementite crystallites. The thermal conductivity of sorbitol is 10 a troostite 20% by

 perlite thermal conductivity

 (/ vO, 105 "al / cm" grad s).

Thus, when irradiating a sample with an initial sorbitol or trussity structure, the laser beam energy heats up to quenching temperatures a thicker surface layer of steel than in the case of the initial pearlite structure, since the heat flux is less

scatters deep into the metal.

Upon irradiation of annealed steel with a pearlitic structure, the radiation energy is dissipated as a result of increased thermal conductivity deep into

tool, and to quenching temperatures, the surface layer of lower thickness is heated.

The structure of martensite obtained after laser hardening also depends on the initial structure.

Melkongolchaty (unstructured) Martensite is formed after laser quenching of samples with a preliminary structure of coarseness. Larger needles of martensite result from the hardening of steel with a sorbitol structure.

The largest and more pronounced needles of Mertensite are formed in the initial structure of perlite, which reduces the quality of the surface layer after grinding and fine-tuning.

The structures of sorbitol and troostite are obtained by quenching and tempering at 30 ° -5.5 O C to obtain a troostite structure or quenching and tempering at 500-650 ° C to obtain the structure

sorbitol; by isothermal quenching with a holding at 300-500 s to obtain a troostite structure or isothermal quenching with a holding at SOO-eSO C to obtain a structure

sorbitol.

Modes of subsequent laser hardening are chosen in such a way as to obtain the surface of the samples without melting.

The results are shown in Table. 1. T and l and c and 1

45-47 28-30 18-20

Experimental work on the hardening of the samples was carried out on a laser technological installation of continuous action with radiation power in the order of 1 kW.

In order to better absorb the radiation energy, the surface of the tiles is black (soot, black paint, oxygrain perlite)

Annealing and carbides. Lamellar sormonization with eeoc bits

Granular sorbitol

Quenching and tempering at

Grainy troos 415

vacation TIT423

-

(2-2, 2) -10

-

(3,5-4) - 10 С4-4,5) 10

dated), the samples are pre-heat treated to obtain various structures; perlite, sorbitol, troostite.

The depth of the hardened layer with different initial structures are given in Table. 2

table 2

207-212

0.08 + 0.039 0.15 + 0.042

0.28 + 0.086 0.30 + 0.038 0.45 + 0.082

0.50 + 0.052 0.53 + 0.064 0.75 + 0.024

428 272-2770,24 + 0,056 0,26 + 0,086 The microhardness and depth of the ordered zone are measured on a thin section made perpendicular to the laser track. The results of the performed studies show that during laser irradiation the depth of the hardened layer substantially depends on the initial structure of the irradiated sample. A reinforced layer of the greatest depth (L 0.75 mm) and hardness HRRC 6566} is formed in tiles with an initial trostitis structure. The layer with the smallest thickness (LO, 10 mm and hardness (HHC 62-63) and even its absence on some samples is observed with the initial structure of perlite. The following experiments were carried out to study the stability of sample sizes during storage. Steel SHKh15SH samples). Part of the samples are subjected to heat treatment according to a known technological process. The structure after heat treatment - martensite .НН-62-64). Another part of the samples is subjected to heat treatment to obtain structures of sorbitol. (Us 28-30) and troostite (HRC 45-47) and then these samples are subjected to laser hardening according to the proposed conditions and tempering at 150 ° C for 3 hours without cold treatment and without. long aging. After 12 months storage dimensions of the samples. The change in the sizes of the samples with the original maosensite structure is 1.57 µm, while no samples with the original structure of troostite and sorbitol were found. The economic effect of the application of the proposed method is achieved by increasing the hardness on the working surfaces to 65-66 instead of H8C 63-64 after bulk quenching, which increases the wear resistance. It makes it possible to replace scarce hard-alloy tiles (made from VK8M alloy) with sizes up to 10 mm with cheaper and technological steel ones. The dimensional stability of parts is increased; whether (lack of martensitic structure; in the whole volume of the metal; the number of operations is reduced compared with the known technological process of manufacturing high-precision parts and tools, many of which are expensive (for example, cold working and etc.). The heat treatment time decreases (2-5 times depending on the size).

Claims (3)

1. METHOD FOR THERMAL TREATMENT OF STEEL PARTS OF HIGH ACCURACY, mainly plane-parallel end measures of length, including preliminary heat treatment and subsequent surface hardening by laser irradiation of working surfaces, so that with the aim of increasing the depth of the hardened layer, obtaining increased hardness and dimensional stability of the machined parts, preliminary heat treatment is performed on sorbitol and troost. 2. The method according to claim 1, with the fact that the preliminary heat treatment for troostite is carried out by hardening and tempering at 300-500 ° C or by isothermal hardening with holding at 300- 500 ° C. - ' 3. The method according to π. 1, from the list the fact that the preliminary heat treatment for sorbitol is carried out by quenching and tempering at 500-650 ° C isothermal quenching-holding at 500-650 ° C.