JPS6343443B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for locally hardening alloy steel members.

Members made of alloy steel containing relatively large amounts of elements such as Cr, Mn, and Mo have higher hardenability than members made of carbon steel. Therefore, when quenching this type of component, using water with an extremely high cooling capacity as a coolant will cause quenching.
The use of water must be avoided at all costs.

Therefore, when quenching a member made of this type of alloy steel, for example, when quenching the entire cross section of the member or quenching the entire surface, the heated member is placed in an oil bath whose cooling capacity is lower than that of water. It is customary to perform quenching and cooling. However, when locally hardening a member made of alloy steel, especially when high efficiency productivity is required, if the coolant is oil, it will take time and effort for subsequent processing. To avoid this, a method has been adopted in which a gas having a much lower cooling capacity than oil, such as air, is injected into the heated local area to forcibly cool the heated local area.

A case in which a heated local area is forcibly cooled by gas injection will be explained with reference to FIGS. 1a to 1c.

In FIG. 1a, the local area of the member W indicated by the crossed or diagonal lines Q is the surface to be hardened. Therefore heating coil C
is formed to have a width approximately equal to the width of the local portion Q, and is disposed opposite to the local portion. A cooling ring G for gas injection is disposed adjacent to the left side of the heating coil C in the drawing, and is integrally formed with the heating coil C, for example. There are gas injection holes G _S on the inner periphery of the cooling ring G for gas injection.
A plurality of holes are provided, and the cooling gas g can be injected with a width approximately equal to the width of the local portion Q.
In this arrangement state, a high-frequency current is applied to the heating coil C from a power supply (not shown) to heat the local part Q to a predetermined hardening temperature, and then the power is turned off.Then, the integrated heating coil C and the cooling ring G for gas injection are assembled as members. W
After the cooling ring G for gas injection is displaced to the position shown in FIG.
The injection of gas g is started from G _S to forcibly cool down the local area Q whose temperature is rising.

Incidentally, in the conventional apparatus described above, air is normally used as the gas coolant. Of course, there are cooling gases that have a lower cooling capacity than water, but the reasons why air is used as a cooling medium are that it is easily available, highly economical, and does not require any post-treatment. However, even if the jet of air imparts a cooling capacity comparable to that of a stationary oil bath, this cooling rate is still lower than that of jet water, which has a cooling capacity more than 20 times that of stationary oil. It is much slower and requires longer cooling times. However, the use of water as a coolant must be avoided. From the standpoint of improving productivity, there was an urgent need to shorten the cooling time of forced cooling using air injection.

The present invention was made in order to solve the above-mentioned problems that exist when gas injection is used as a cooling medium when locally hardening a member made of alloy steel, and the cooling time can be increased without causing burnout. The present invention provides a method and apparatus that can be shortened to a large width.

In carrying out the present invention, the present inventor attempted to analyze the temperature transition during cooling in the heating layer of the heated local Q and its surrounding layer when the conventional method and apparatus described above are implemented. The analysis will be explained according to FIG. 1c. Figure 1c schematically shows the temperature distribution of the surrounding layer in the axial direction depending on the degree of cooling of the local heating layer, with the vertical axis representing temperature and the horizontal axis representing the axial left and right positions of the member from the center O of the heating section. This is shown by a curve. In the figure, the solid line shows the curve immediately after heating and before the start of cooling, the dashed line shows the state when the local area has been cooled to 50% of the heating temperature, and the dashed line shows the state after the local area has cooled down to 20% of the heating temperature. The temperature characteristics at the time of cooling to the temperature of % are displayed.

The temperature characteristic curve immediately after heating has its apex at the center O opposite the heating coil C, and slopes steeply as the position in the peripheral direction increases. The temperature characteristic curve at the time of cooling becomes a very gently sloped curve with the bottom part being higher temperature than that of the curve, and the temperature characteristic curve at the time when cooling has progressed to 20% of the temperature at the time of heating is the center O. It becomes a gently sloping curve with two high-temperature peaks on the left and right sides of the bottom, which becomes a valley. The inventor discovered that this curve and the high temperature at the hem and 2
The characteristic temperature characteristic curve shown by two high-temperature peaks is due to the slow cooling rate brought about by the low cooling ability of gas, and the heat in the heated local area during heating and the pent-up heat transmitted to the surrounding area are equalized. It is analyzed that this is a conflicting phenomenon between cooling and conductive heat, which tends to shift toward the heated local area that is being cooled in an attempt to reach an average equilibrium state. Of course, a similar phenomenon occurs even if other cooling media are used. However, in the case of gas injection cooling, in addition to the low cooling capacity, the slow cooling rate is further slowed down due to the heat conduction behavior that tends to shift toward the quenched local area due to thermal equilibrium. This necessitates long-term gas injection.

The present inventor made the following invention based on the above analysis.

The gist of the present invention is that when locally hardening an alloy steel member, a predetermined local part is heated to a predetermined hardening temperature, and then the heated local part is forcibly cooled by gas injection, and the vicinity of the local part is forcibly cooled. The main idea is to perform forced cooling by liquid injection to prevent latent heat in the vicinity of the local area from transferring to the local area through heat conduction.

The present invention will be explained with reference to FIGS. 2a to 2c. Second
In Figure a, C is a heating coil and G is a cooling ring for gas injection, which are the same as those in the conventional device. A liquid injection cooling ring L is disposed facing the material to be treated around the local part to be quenched from positions separated from each other by a predetermined same interval A, and is capable of injecting liquid from a plurality of holes L _S provided on the inner periphery thereof. ₁ and L ₂ . When the heating coil C, the cooling ring G for gas injection, and the two cooling rings L ₁ and L ₂ for liquid injection are fixed at predetermined positions on a frame (not shown) to form an integral structural member, the integral structure The member is configured to be movable relative to the member W to be processed in the axial direction thereof. If there is a cooling ring G for gas injection and two cooling rings L ₁ for liquid injection,
In the case where the heating coil C and the heating coil C are separated from _each other, a heating station and a cooling station are provided, and both stations and the workpiece W to be processed are configured to be movable relative to each other. may be of a split type, the material to be treated W may be placed there, and the integral structure member may be configured to pass through the opening when the split heating coil C is divided.

In the above configuration, a particularly important point in the present invention is the distance A between the cooling ring G for gas injection and the cooling ring L for liquid injection.
It is. The distance A is between the heating coil C and the local part Q of the member.
When the heated local Q
It must be set so as to avoid a range in which the temperature may rise to a temperature at which the material of the member can be hardened due to temperature rise due to heat conduction from the heating coil C and temperature rise due to induction heating due to leakage magnetic flux from the heating coil C. Therefore,
If both of the above forced cooling operations are to be started simultaneously immediately after heating, the interval A should be set large, and if forced cooling by liquid injection is to be started after a predetermined time has elapsed after the forced cooling by gas injection has started, the interval A should be set to a large value.
Set to small. However, in the latter case, the cooling time will naturally be longer than the former, so the size of the interval A will depend on the horizontal shape of the local part Q, the timing on the production line, and other factors. This will be determined in due consideration.

In addition to the above, an important point in the present invention is that the injection liquid l injected from the injection holes L _S of each of the liquid injection cooling rings L ₁ and L ₂ does not overlap the heated local part Q.
Or to prevent it from flowing in. This is to prevent the heated local area Q from being excessively rapidly cooled and causing burning. Therefore, each injection hole L _S is preferably arranged obliquely so that the liquid l injected through it is ejected in a direction opposite to the local area Q.

It is preferable to use water or a solution of a water-soluble coolant as the liquid 1, since no post-treatment is required and the part can be sent to the next step immediately after quenching.

When hardening the workpiece W from the local part Q using the apparatus having the above configuration, the arrangement shown in FIG. 2a is as shown in _FIG . The case where ₂ is an integral structural member will be explained as an example. Processed member W
After positioning the heating coil C at a position facing the local part Q to be quenched, and heating the local part Q to a predetermined quenching temperature by the heating coil C, the part to be treated W and the integral structure member are placed relative to each other. The gas injection cooling ring G is moved to face the local area Q which is being heated to raise its temperature. In this state, the liquid injection cooling rings L ₁ and L ₂ are each located at a position shown in FIG. 2b, facing the surface of the workpiece that is spaced apart from the heating local area Q by a predetermined distance A. Next, the gas g is injected from the gas injection cooling ring G to the opposing heated local area Q to forcibly cool the said local area Q, and at the same time, the liquid l is injected from the liquid injection cooling rings _L1 and _L2 to the opposing heated local area Q. It is injected onto nearby peripheral surfaces to forcibly cool the peripheral surfaces. The progress of cooling is shown in FIG. 2c. Similar to FIG. 1c, which shows the temperature transition during cooling in the heating layer of the heated local area Q and its surrounding layers when the heated local area is cooled by the conventional device, the vertical axis shows the temperature. The horizontal axis shows the left and right positions in the axial direction of the member from the center O of the heating part, and the solid line represents the temperature characteristics immediately after heating and before the start of cooling.
The temperature of the local Q and its surroundings at the time when the temperature has decreased to 20% are shown in curves and , respectively. The curve in Figure 2 c does not show the temperature characteristics that exceed the curve in the peripheral area as seen in the curve in Figure 1 c, and the curve also does not exhibit the temperature characteristics seen in the curve in Figure 1 c. The temperature characteristic with two peaks representing a high temperature region in the peripheral area is also not shown. Therefore, it is clear that the latent heat was effectively removed by the liquid 1 injected to the predetermined peripheral portion, and the phenomenon of uniform heat equilibrium in the local Q direction was prevented. Therefore, cooling depends on the cooling capacity of the gas used.
The process progresses only by absorbing the heating heat of the heated local area Q, and is completed in a short time.

By carrying out the method and apparatus according to the present invention, it is possible to significantly shorten the required cooling time for local hardening of alloy steel members without causing the burning phenomenon, compared to the conventional method. This greatly contributes to efficient operation of the quenching equipment and improvement of productivity, and the necessary equipment is extremely simple and inexpensive, and its practical effects are remarkable.

[Brief explanation of drawings]

Figures 1a and 1b are partial cross-sectional front views of the main parts of a device using the conventional method, respectively, and Figure 1c is a heating local area and its surroundings during cooling to explain the drawbacks of the conventional method and device. FIGS. 2a and 2b are a partial cross-sectional front view of a main part of an apparatus according to an embodiment of the method of the present invention, and FIGS.
FIG. c is a temperature characteristic curve diagram of a heated local area and its surrounding area during cooling progress according to the present invention. W...Part to be treated, Q...Part to be quenched, C...Heating coil, G...Cooling ring for gas injection, _L1 , _L2 ...Cooling ring for liquid injection, A...Cooling ring for gas injection and cooling ring for liquid injection A predetermined interval between.

Claims (1)

[Claims] 1. When locally hardening an alloy steel member, a predetermined local part is heated to a predetermined quenching temperature, and then the heated local part is forcibly cooled by gas injection. 1. A method for locally quenching an alloy steel member, comprising forcibly cooling the surrounding area by liquid injection to prevent latent heat near the local area from being transferred to the local area by heat conduction. 2. The alloy steel member according to claim 1, wherein the vicinity of the local area that is forcibly cooled by liquid injection is a portion that is below the quenchable temperature of the alloy steel member when the forced cooling starts. Local hardening method. 3. A method for locally quenching an alloy steel member according to claims 1 and 2, characterized in that forced cooling of a localized area where the temperature has risen and forced cooling of the vicinity of the localized area are started at the same time. 4. Local quenching of an alloy steel member according to claims 1 and 2, characterized in that the forced cooling of the vicinity of the local area is started after a predetermined period of time has elapsed from the start of the forced cooling of the local area where the temperature has increased. Method. 5. In an induction heating device equipped with a heating coil that can be placed opposite to the part to be quenched of the workpiece, a cooling ring for gas injection that can be placed opposite to the part to be quenched, and a cooling ring for gas injection that can be placed opposite to the part to be quenched; 1. An apparatus for local hardening of an alloy steel member, comprising cooling rings for liquid injection that can be disposed facing a workpiece around a hardened part from positions spaced apart from each other by a predetermined equal interval. 6. Claim No. 6, characterized in that the heating coil, the cooling ring for gas injection, and the cooling ring for liquid injection are formed into an integral structural member and are configured to be relatively movable in the axial direction of the material to be treated. The local hardening device for alloy steel members according to item 5. 7. Claim 5, characterized in that the cooling ring for gas injection and the cooling ring for liquid injection are an integral structural member and are configured to be relatively movable in the axial direction of the material to be treated. Local hardening equipment for alloy steel parts.