SU1617011A1 - Method of thermal treating of billets - Google Patents

Abstract

The invention relates to metallurgy, specifically to methods for the heat treatment of structural steel blanks after hot deformation. The purpose of the invention is to improve the machinability and increase the surface finish. The method includes austenitization, hot deformation, repeated austenitization, cooling to the temperature of the beginning of the formation of perlite at a speed of 70-100 ° C / min, then to 400 ° C at a speed of 5-15 ° C / min, final cooling and tempering at a temperature of 120 -150 ° C below the temperature of the minimum stability of austenite. The method allows to increase the machinability during turning and drilling and significantly improve the surface quality. 1 hp f-ly, 2 tab.

Description

 The invention relates to metallurgy, in particular to methods for heat treatment of structural steel blanks after hot plastic deformation to improve machinability.

The purpose of the invention is to improve the machinability and the purity of the treated surface.

Billets for details like gears from steel 18HGN2MFB are heated in a 2-chamber slit gas furnace to 1100 - and then stamped

EXAMPLE 1. Upon completion of the hot plastic deformation of the blanks (temperature of the punching end yJU 950 ° C), they are cooled in a cooling chamber at different air flow rates. First, increase by 9/35, 70, 85, 100 and 125 C / min to the temperature at which pearlite begins to form, then slowly

up to 4 So «r ™ ° And 5 ° С / min up to 400 С and further on in air. After

This is tempering at temperatures of 450, 500, 515, 530 and for 2 hours.

PRI mme R 2. Once completed, the hot plastic deformation of the workpiece is cooled in air in a container to room temperature. Then, the blanks are reheated in a CHO-type chamber furnace to the austenitization temperature (930 - 950 ° C) and subjected to cooling and tempering according to the mode shown in Example 1.

The feasibility of the proposed limits of change of technological parameters is explained as follows.

When cooled from austenitic temperature at rates lower than the CCR / min, no suppression of diffusion processes is provided, which leads to the redistribution of carbon and the formation of low and high carbon zones and the formation of a structural strip.

An increase in cooling rates of more than 100 C / min leads to the release of structural free ferrite from the area of separation and the formation of bainite or martensite structures with very high hardness.

Conducting an accelerated cooling to a temperature higher than the temperature of the onset of the formation of pearlite does not suppress the diffusion redistribution of elements and leads to the formation of banding and deterioration of chip formation and purity of the processed surface.

Conducting accelerated cooling to a temperature below the onset of the formation of perlite leads to falling into the area of bainite transformation and, consequently, an increase in hardness and deterioration of workability.

Increasing the speed of a cool stone over 13 ° C / min in the area of pearlite formation leads to the formation of a larger amount of bainitic component and to an increase in hardness, and consequently, to a deterioration in workability by cutting.

A decrease in the cooling rate below 5 ° C / min is impractical because of the increase in the duration of the heat treatment, and at very low cooling rates, conditions similar to isothermal aging are created, which leads to the formation of structural banding.

Increasing the tempering temperature to a temperature higher than the proposed limits leads to a significant increase in the toughness of the steel, the formation of stripiness and the deterioration of the workability and cleanliness of the treated surface.

Reducing the tempering temperature to a temperature below the proposed limits does not provide sufficient softening of the steel.

For comparison, heat treatment according to the proposed and known methods is carried out, the modes and parameters of which are given in Table 1.

The microstructure is determined on an MMP-2P microscope on microsections after etching in 4% alcoholic solution of nitric acid. 1 microhardness test on the device PMT-3 with a load of 50 g. Banding is estimated in accordance with GOST 5640-68.

The machinability is estimated by the tool wear value on the turning and drilling operations. The workpieces are ground on a 1M63 turning lathe with a stepless control of the cutting speed 5 with the installation of the following cutting modes: cutting depth 1.5 mm; feed 0.3 mm / rev; cutting speed YuOm / min. The material of carbide plates - T5K10. The drilling was carried out on a Q 2H135 vertical drilling machine with cooling by sulfofresol; drill material - Р6М5; drill diameter 25 mm; feed 0.35 mm / rev; cutting speed 15 m / min. 5 The machinability assessment is carried out according to the machining time until the cutting edge reaches 1.2 mm and the drill wear 0.3 mm.

The surface finish is assessed after finishing turning with a T15K6 cutter on a 1M63 screw-cutting machine. Cutting modes: feed 0.15 mm / rev; cutting depth 0.5 mm; cutting speed 0.5 mm; cutting speed 150 m / min. Cutter cutting parameters: J. -. 10 pC 60; q, 45 °; g 1 mm ..

The data of metallographic analysis, estimates of machinability and surface finish are given in Table 2.

As can be seen from the data of table 2, experiments 2-4, corresponding to the optimal parameters of the mode, in examples 1 and 2 provide a satisfactory machinability. Thus, the time to a specified tool wear — 1.2 mm when turning and 0.3 mm when drilling — is 50 47 - 52 minutes and 44 - 48 minutes, respectively. This is 2 - 3 times more than. When processed according to a known regime. Roughness processed

the surface after heat treatment according to 55 to the proposed method is 30% less than that known.

The data of metallographic analysis confirm the results of the evaluation.

0

40

45

five

machinability: the hardness of the workpieces is lower after heat treatment according to the proposed method, the microhardness also decreases, and the difference in the values of microhardness, which has a significant effect on the machinability, is 4 times less than when processed according to a known regime. The phenomenon of structural banding after processing by the proposed method is not observed, while by a known method it corresponds to 3-6 points.

The proposed method of heat treatment of blanks in comparison with the known has the following technical advantages:

improvement of machinability by 2 times in turning operations and 3 3 times in drilling;

an increase in the purity of the treated surface by 30%;

providing the opportunity to work on high-performance automatic lines due to the formation of compact segmented chips during machining of workpieces by cutting; .

reduction of deformations in the following heat treatment operations due to the high homogeneity of the structure and the removal of internal stresses during tempering

70116

Claims (2)

1. The method of heat treatment of workpieces, including heating to austenitization temperature, hot plastic deformation, accelerated and delayed cooling to and final cooling in air) 0 to room temperature, characterized in that, in order to improve machinability and improve the cleanliness of the treated surface, after hot plastic deformation, reheating to the austenitization temperature is carried out, accelerated cooling is carried out at a rate of 70 - 10 ° C / min in the temperature range of 0 structurally free ferrite before the formation of pearlite, then slow cooling at a rate of 5 - IS C / MHH is carried out, and after cooling in air, tempering 5 is carried out at a temperature 120 below the temperature of the minimum stability of austenite. 2. The method according to Claim 1, which means that the cooling is carried out after a hot plastic deformation without re-heating to the austenitization temperature 6lit2