JPS61231115A - Heat treatment of machine parts - Google Patents

Abstract

PURPOSE:To partially increase the hardness of a member and to provide high strength and toughness to the other part by CONSTITUTION:In the 1st stage, a track link 1 is heated to the A1 transformation temp. or above, and the whole link is.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for heat treating mechanical parts used under severe conditions, such as track links of crawlers used in construction machinery.

BACKGROUND OF THE INVENTION Required qualities for the track link α shown in FIG.

In general, heat treatments for obtaining mechanical parts with high hardness (high strength) and high toughness include (1) a method of quenching + tempering, and a method of (2B bainitization (austempering treatment)).

Problems to be Solved by the Invention The conventional heat treatment method described above requires several heat treatment steps, which causes many problems in terms of efficiency, and is cumbersome to operate when it is desired to increase the hardness of a portion of the product, such as in a track link. there were.

Means and Effects for Solving the Problems The present invention was conceived in view of the above-mentioned problems, and involves water quenching the entire austenite region at a temperature higher than the transformation temperature so that the temperature of the portion where toughness is required is the bainite transformation temperature. When the steel is cooled to a certain temperature, only the portion requiring the above-mentioned toughness is pulled out of the water and left to cool, and then the entire structure is cooled with water again.

Embodiment An embodiment of the present invention will be described in the case of a track link.

First, in the first step, the track link 1 heated to a quenching temperature (more than λ1 transformation state) is subjected to water quenching in its entirety using still water or an underwater spoon [see Figure 1].Then, in the second step, the track link 1 is Water quenching is continued on only the tread part 2 which is pulled up halfway and requires high hardness, and the base part 3 is released into the air [as shown in Fig. 1].Then, in the third step, the track link 1 is formed. Put it back into the water and water-cool the whole thing [Figure 1 (Q)].

The holding time of water quenching in the first step is 40
The time is set to the time required for cooling to the bainite transformation temperature of 0 to 500°C. The second step is a stage in which the base portion 3 is austempered, and the holding time varies depending on the amount of bainite required, but is 1 to IO minutes for 80M material.

FIG. 2 shows the temperature changes in the tread portion 2 and base portion 3 of the track link 1 during each of the above steps. In the figure, the curved line indicates the cooling curve of the tread portion 20, and the white line B indicates the cooling curve of the base portion 3. In the figure, M indicates the martensite region, F indicates the ferrite region, P indicates the pearlite region, and B indicates the bainite region.

Figure i3 shows an actual track link made of 80M 435H, which was heat-treated in accordance with the method of the present invention, with the entire body water-cooled for 10 seconds, only the substrate portion left to cool for 40 seconds, and then the entire portion water-cooled. In the figure, d is the cooling curve of the 15 part from the tread surface, '1m'* is the cooling curve of the part from the base surface, and 4 is the cooling curve of the part from the base surface. It is. In each of these curves, −8. (L, 82, 14 are actually measured values.

FIG. 4 shows the hardness distribution of the tread portion, and FIG. 5 shows the hardness and impact value of the base portion (near the window).

It was also confirmed that the tensile strength of the tread portion was 170-180.

Effects of the Invention According to the present invention, high hardness (high strength) can be achieved in some parts by a simple heat treatment process, and high strength and high toughness can also be imparted to other parts.

Therefore, it is possible to improve the efficiency and simplify the heat treatment work for mechanical parts used under severe conditions, such as track links.

[Brief explanation of drawings]

Figure 1 (2), (Bl, (C1 is an explanatory diagram showing the heat treatment process, Figure 2 is a cooling curve diagram, Figure 3 is a diagram showing the measured values and calculated values of the cooling curve, Figure 4 is a diagram showing the track A hardness distribution diagram of the tread portion of the link, FIG. 5 is a diagram showing the hardness and impact value of the base portion, and FIG. 6 is a front view of the track link.

Claims (1)

[Claims] A_1 Water quenching is performed on the entire part starting from the austenite region above the transformation temperature, and when the temperature of the part where toughness is required reaches the bainite transformation temperature, only the part where toughness is required is pulled out of the water and allowed to cool. A method for heat treatment of mechanical parts, characterized in that the entire body is then cooled with water again.