JPS62192523A - High frequency tempering method for carburized parts - Google Patents

Abstract

PURPOSE:To uniformly lower the hardness of a member having an ununiform heating temp. distribution by high frequency tempering by successively tempering the part heated to a lower temp. and the part heated to a higher temp. CONSTITUTION:A member of a complex shape having a ununiform heating temp. distribution, e.g., a carburized member 2 having a rounded part R and a thread part S is subjected to high frequency tempering. At this time, the member 2 is set in a heating coil 1 and the rounded part R heated to a lower temp. is first tempered by supplying a high frequency current to the coil 1 from a high frequency generator 4. The thread part S heated to a higher temp. is then tempered.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a technique for improving a heating method for induction tempering of carburized parts, particularly complex-shaped parts.

(Prior Art) Conventionally, when a threaded part of a carburized part is continuously subjected to a high tensile stress load in an assembled state, material failure, so-called delayed failure, occurs from that part. In order to prevent this, the threaded portions of carburized parts are often subjected to induction tempering. Conventionally, in order to obtain the required tempering hardness, induction tempering was carried out by holding the treatment temperature at a temperature of 600° C. to 720° C. (below the Am transformation point) for as long as possible.

This induction tempering temperature is not suitable for heat treatment because the transformation from the martensitic structure in the quenched state to the nulupite structure in the tempered state does not occur completely at temperatures lower than 600°C.
Further, at a temperature higher than 720° C. (A, above the transformation point), the steel becomes a re-hardened structure (martensitic structure) in the cooled state, and the hardness after tempering rapidly increases, making it unsuitable for heat treatment.

From this, the appropriate temperature range for induction tempering is 600℃.
It is limited to temperatures above and below the transformation point.

(Problem to be solved by the invention) Therefore, for the above reasons, the induction tempering temperature is 60°C.
There is a limit to lowering the hardness of carburized parts after tempering, as the temperature is limited to 0° or above and below the transformation point, so there is a limit to reducing the hardness of carburized parts after tempering, and as a result, the heating temperature distribution is not uniform. In this case, sufficient tempering hardness required for functionally beautiful products cannot be obtained. Especially carburized parts
In the case of 0M material, it is difficult to obtain a material with good hardenability, that is, a material with a high Diminy value.

The present invention has been made in view of the above-mentioned problems, and is designed to make the temperature distribution of the heat-treated surface substantially uniform in induction tempering to prevent delayed fracture of functional parts of carburized parts with complex shapes. By changing the heat cycle, the tempering quality is improved.

(Means for solving the problem) The purpose of this is to first heat the parts with low heating temperature (parts that are difficult to heat) to 600°C during induction tempering of carburized parts whose heating temperature distribution is not uniform throughout due to their complex shapes.
This is achieved by an induction tempering method for carburized parts, in which tempering is performed at a temperature below the lagoon transformation point, and then the high heating temperature portion is tempered at 600°C or above and below the transformation point.

(Function) In induction tempering using conventional methods, tempering was performed by holding the material for a long time at 720°C (Am transformation point) or lower in order to reduce the hardness after tempering. Due to the shape and arrangement of the coil, it is difficult to sufficiently reduce the hardness of functional parts necessary for quality. For example, if the heating temperature is set to sufficiently lower the hardness of the threaded portion S in FIG.
℃ or below, the tempering hardness of the rounded portion R becomes insufficient. On the other hand, if the heating temperature is increased to sufficiently reduce the hardness of the rounded portion R, the threaded portion S will reach a temperature of 720° C. or higher and will be re-hardened, increasing the tempering hardness of the threaded portion S.

In the present invention, by changing the conventional tempering method, first of all, among the heat-treated parts necessary for quality, the part where tempering hardness is least likely to decrease, that is, the part where the heating temperature distribution is low, is
Induction tempering treatment is performed at a temperature of .degree. C. or higher and 720.degree. C. or lower.

In this heat treatment, other portions of the member to be tempered, that is, portions with a high heating temperature distribution, reach a temperature of 720° C. or higher, that is, a nine-transformation point or higher, resulting in a re-hardened structure and increased hardness.

Therefore, this time, the part where the hardness has increased due to the re-quenching structure is subjected to induction tempering at a temperature of 600° to 720°0. Then, among the heat-treated parts of the part to be tempered that are necessary for quality, the part where tempering hardness is least likely to decrease has been sufficiently reduced in hardness by the first tempering, and is also re-tempered by the first tempering. In the part where the hardness has increased due to the formation of a microstructure, a sufficient reduction in hardness will be obtained in the second tempering.

In this way, the present invention performs induction tempering in two stages at heating temperatures suitable for the parts where tempering hardness is least likely to decrease and the other parts, thereby ensuring that the functional parts necessary for quality are sufficiently maintained as a whole. It becomes possible to reduce the hardness.

(Example) The present invention will be described in detail below based on the accompanying drawings.

FIG. 2 is a schematic diagram showing the main parts of an apparatus used to carry out the high-frequency heating method of the present invention. In this figure, 1 is a stern-type heating coil made of electric steel, and inside this heating coil 1 is a carburized part to be treated, here a threaded part S.
Case-hardened steel (material: 80M) with The heating coil 1 is connected to a high-frequency oscillation device 4, and by passing a high-frequency current from the high-frequency oscillation device t4 to the heating coil 1, the treated region 3 of the carburized component 2 in the heating coil 1 is heated.

FIG. 1 shows a comparison of temperature cycles and heat patterns according to the method of the present invention and the conventional method in induction tempering of the head side rounded portion R and threaded portion S of the treated portion 3. In the figure, the imaginary line and the actual line a are temperature characteristic graphs at the rounded part and the threaded part S, respectively.

As is clear from this figure, in the conventional method, the threaded part S of the part to be treated 3 is heated in a temperature range of 600°C or more and below the transformation point, whereas in the method of the present invention, first the carburized part 2 to be treated is heated.
The head side rounded portion R is heated in a temperature range of 600° C. or more and below the transformation point. Therefore, in the method of the present invention, 1. The temperature of the threaded portion S of the part to be treated 3 becomes equal to or higher than the transformation point. Therefore, after being cooled, the threaded portion S of the treated portion 3 is heated once again to a temperature range of 600° C. or higher and lower than the transformation point.

The hardness of the carburized layer of the thus obtained carburized part 2 after induction tempering according to the present invention was examined and compared with that obtained by the conventional method.

Hardness d(:1) As shown in FIG. 5, the fixed portions are the rounded part and the first, second, fifth, fourth, and fifth thread valleys S1°82.
85, 84, 85, and the points are 0.2 points below the surface. Figure 6 is a hardness distribution graph after tempering by the conventional method, Figure 4 is a hardness distribution graph after the first tempering by the method of the present invention, and Figure 5 is the hardness distribution graph after the second tempering by the method of the present invention. This is a distribution graph.

As is clear from the figure, in the method of the present invention, the hardness of the rounded part R decreases in the first tempering, but on the other hand,
The hardness of No. 5 is increased by re-quenching. However, by subjecting the thread root portions S1 to S5 to tempering again after the second tempering, an overall decrease in hardness was obtained.

According to the method of the present invention, it was possible to temper the threaded portion S of the complicated carburized part 2 as uniformly as possible5. The hardness after tempering was not uniform, and the hardness after tempering varied greatly depending on the part to be treated. However, in the uninvented method, the hard part of the Jl1m part was tempered in the first heating, and the hardness after tempering was tempered in the second heating. This is because the hardened parts were tempered.

Further, according to the present invention, there is a great effect in preventing delayed fracture of the carburized component 2. This is due to the fact that a good reduction in hardness can be obtained throughout the carburized part after tempering, and the amount of hydrogen in the carburized part decreases when the heating temperature is raised in the first tempering. It improves the performance.

(Effects of the Invention) As described in the paper, when the method of the present invention is carried out, even if the carburized part has a complicated shape and the temperature distribution is not uniform as a whole, the tempering process can be performed in stages starting from the part where the temperature distribution is low. Therefore, the decrease in hardness after tempering is made as uniform as possible over the entire carburized part, and the round tempering hardness required for product quality can be satisfied better than before.

In addition, delayed fracture resistance improves as the amount of hydrogen in carburized parts decreases.

[Brief explanation of drawings]

Fig. 1 is a temperature cycle/heat pattern diagram showing the induction tempering method of the present invention in comparison with a conventional method, Fig. 2 is a schematic configuration diagram showing the induction tempering apparatus of the invention, and Fig. 3 is a diagram of carburized parts. 4 and 5 are graphs showing the hardness distribution according to the method of the present invention after the first heating and the second heating/heating wave, respectively. It is a graph showing hardness distribution depending on the method. 1... Heating coil, 2... Carburized parts to be treated, 4
...High frequency oscillator, S...Threaded part, R...Head side rounded part. Patent applicant Toyota Motor Corporation agent Patent attorney Yumi Sae (and 1 other person)...τ
M・、H″ too

Claims (1)

[Claims] A carburized part characterized in that, in induction tempering of a complex-shaped part in which the heating temperature distribution is uneven as a whole, the part where the heating temperature is low is first tempered, and then the part where the heating temperature is high is tempered. Induction tempering method.