JPH0192315A - Method for hardening and tempering steel - Google Patents

Abstract

PURPOSE:To stabilize the hardness of each stock obtd. by heat treatment by heating the stock, detecting the Ms point of the heated stock with an eddy- current detector during forced cooling with a forced cooling agent and suspending the feed of the cooling agent after the lapse of a prescribed time on the basis of the detected Ms point. CONSTITUTION:Stock to be hardened is heated by high frequency heating or other method and subjected to forced cooling with a forced cooling agent. In the cooling stage, the Ms point of the stock is detected with an eddy-current detector. The feed of the cooling agent is suspended after the lapse of a prescribed time T on the basis of the detected Ms point. The time T is experimentally set according to the designated hardness of the stock. Thus, the tempering temp. of each stock is made constant and the hardness of each stock obtd. by heat treatment can be stabilized.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for quenching and tempering steel mechanical parts by heating at 1@.

BACKGROUND OF THE INVENTION As shown in FIG. 4, a material to be hardened is induction hardened and then induction tempered.

Problems to be Solved by the Invention According to this method, heating is performed twice, resulting in a large amount of energy loss, and the number of heat treatment steps is also increased.

In this regard, it may be possible to perform tempering by interrupting the supply of forced coolant during forced cooling after high-frequency heating, but this method is effective because the cooling rate of the material is fast and there are slight variations in heating temperature.
Point at which coolant supply is interrupted as shown in Figure 5) S
l, 82. sa changes.

Therefore, there was a problem in that the tempering temperatures A, C, and C varied from material to material, and the material hardness in the heat-treated portion became unstable from material to material.

Another means of solving the problem is to heat the material to be hardened, then detect the Ms point during forced cooling, and interrupt the supply of forced coolant after a required period of time has elapsed based on the detected internal point.

Action When the magnetic properties of the steel suddenly change from non-magnetic to ferromagnetic at point M8, the phase of the eddy current detector that uses eddy currents also changes significantly at the force point, so it is difficult to accurately detect the force point during forced cooling. can be detected.

Example The present invention will be explained below with reference to drawings of embodiments.

FIG. 3 shows a state in which a portion of a steel crankshaft, which is the material 3 to be hardened, is being heat-treated with a heating film 5. In the figure, reference numerals 1 and 2 support a material 3 at the center so that it can be rotated.

5 is a heating coil. 6 is a control device that controls high frequency heating, coolant supply, etc.

Reference numeral 7 denotes an eddy current detector, which is equipped with a probe-type sensor 8 that can move forward and backward.

The method for heat treatment of the material 3 will be explained. First, the material 3 is placed between the two centers 1 and 2 and rotated, and then the material is subjected to high solid wave heating to a predetermined temperature as shown in FIG.

Then, the heated material is forcibly cooled by a coolant such as cooling water or cooling oil, and during this time, the sensor 8 of the eddy current detector 7 is brought close to the desired hardening region 4, so that the steel changes from austenite to martensite. That is, the Ms point is detected.

Note that if the heating coil becomes an obstacle and the sensor 8 cannot be brought close to the desired hardening site, the material 3 may be moved in the axial direction. Furthermore, the hardening of the material is not limited to induction hardening, but may also be flame hardening, submerged hardening, or the like.

Based on the detected Ms point, as shown in FIG. 2, the forced coolant supply is interrupted after a predetermined time T has elapsed.

This time T is appropriately set through experiments in order to correspond to the specified hardness of the material. Further, control of these series of operations is performed by a control device 6.

Effects As described above, according to the present invention, when the magnetic properties of steel suddenly change from non-magnetic to ferromagnetic at the moving point, the phase of the eddy current detection signal that uses eddy current also changes significantly at the moving point. Therefore, the excitation point can be detected accurately during forced cooling. However, by using the Ms point detected by eddy current detection as a reference, it is possible to eliminate variations in tempering temperature for each material, stabilize the heat treatment hardness for each material, and reduce energy consumption because heating can be done only once. The number of heat treatment steps is also reduced.

[Brief explanation of the drawing]

1 to 3 show examples of the present invention, and FIG. 1 is a temperature-time diagram. Figure 2 is a continuous cooling transformation curve diagram. FIG. 3 is a plan view of the material in a heat-treated state. FIG. 4 is a conventional temperature-time diagram. FIG. 5 is a conventional continuous cooling transformation curve diagram. (Explanation of symbols) 3...Material. T...time
while.

Claims (1)

[Claims] Steel quenching characterized by heating the material 3 to be quenched, then detecting an eddy current at the Ns point during forced cooling, and interrupting the supply of forced coolant after a predetermined time T has elapsed based on the detected Ns point. Tempering method.