JP2000309821A - Quenching method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a quenching method by which a stable quality product having sufficiently small martensite strain and hardly developing uneven hardness can be secured. SOLUTION: An agitator 3 is not rotated after charging a head bolt into quenching oil 10 until the temp. difference among the portions of the head bolt in the quenching oil 10 reduced by rotating the agitator 3 at a fixed speed becomes smaller than that without rotating the agitator 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a quenching method. This quenching method is suitable for use, for example, when quenching steel bolts.

[0002]

2. Description of the Related Art As a conventional quenching method, a quenching apparatus having a rotator capable of storing quenching oil in an oil tank and stirring the quenching oil is used, and the rotator is heated to a high temperature while rotating at a constant speed. A work made of steel is put into quenching oil of the quenching apparatus to quench the work (for example, Japanese Utility Model Laid-Open No. 5-96051).
Here, the work may be a single product or a plurality of products.

When the work is quenched in this way, martensitization proceeds from the surface of the work, and the hardness of the work can be increased. At this time, in this quenching method, the temperature of the quenching oil in the oil tank is made uniform by rotating the rotating body at a constant speed, thereby quenching each part of the work with quenching oil of the same temperature. I have. Here, each part of the work means each part of the work. In this way, for each part of the work, martensitic transformation strain is suppressed, and variation in hardness is prevented, so that a product of stable quality is secured.

[0004]

However, in the above-described conventional method, the martensitic transformation strain is still large for each part of the work. In other words, such a method has not yet been able to secure a product of stable quality. The present invention has been made in view of the above-mentioned conventional circumstances, and provides a quenching method capable of securing a stable quality product with sufficiently small martensitic transformation strain and little variation in hardness. It is an issue to be solved.

[0005]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and have found that the problems can be solved by adjusting the rotation speed of the rotating body. Reached. That is, the quenching method of the present invention uses a quenching device having a rotating body capable of storing quenching oil in an oil tank and stirring the quenching oil, and using a quenching oil of the quenching device to heat a steel workpiece heated to high temperature. In the quenching method of quenching the work by throwing it into the inside, the rotation speed of the rotating body is adjusted so that martensitization proceeds uniformly from the surface of the work.

That is, according to the test results of the inventors,
If the rotating body is simply rotated at a constant speed as in the past, low-temperature quenching oil directly contacts the part of the work close to the rotating body. The time at which the site transformation starts is shortened, which causes a difference in the time at which the martensitic transformation is started between the respective parts of the work. For this reason, each part of the workpiece does not become martensite equally from the surface, and martensitic transformation strain occurs.

On the other hand, in the quenching method of the present invention, the rotation speed of the rotating body is adjusted so that martensitization proceeds uniformly from the surface of the work. In such a case, each part of the work is uniformly transformed into martensite from the surface, and the martensitic transformation strain can be effectively suppressed. In the quenching method of the present invention, the temperature difference between the parts of the work in the quenching oil by rotating the rotating body at a constant speed is higher than the temperature difference between the parts of the work in the quenching oil by not rotating the rotating body. Until it becomes smaller, it can be embodied by not rotating the rotating body after the work is put into the quenching oil. That is, according to the test of the present inventors, after the work is put into the quenching oil, the rotation of the rotating body at a constant speed is more effective than the case of not rotating the rotating body. The temperature difference between the parts becomes smaller. For this reason, if the time until the temperature difference between the parts of the work in the quenching oil is reversed is controlled by time, after the work is put into the quenching oil, the rotating body is not rotated until the time elapses. If the rotating body is rotated at a constant speed after the elapse of the time, the temperature difference between the parts of the work in the quenching oil becomes smaller as compared with the case where the rotating body is not rotated. Thus, if the temperature difference between the parts of the work in the quenching oil is small, the difference in the time at which the martensitic transformation is started between the parts of the work is small, and each part of the work is easily martensite equally from the surface, Martensitic transformation strain can be suppressed.

Therefore, according to the quenching method of the present invention, it is possible to secure a product of stable quality with sufficiently small martensitic transformation strain and little variation in hardness.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, Tests 1 and 2 for confirming the operation of the present invention and Examples and Comparative Examples embodying the present invention will be described with reference to the drawings.

[0010]

[Test 1] In test 1, the quenching apparatus 1 shown in FIG. 1 is used. A quenching oil 10 is stored in the oil tank 2 of the quenching device 1 up to a height h from the bottom surface.
A pair of agitators 3 are provided as rotating bodies capable of stirring 0. Further, a tray fixing base 4 is provided in the oil tank 2. The tray fixing base 4 supports the tray 5 shown in FIG. As shown in FIG. 3, each of the trays 5 can hold a five-stage basket 6 with the uppermost stage being the first stage and the lowermost stage being the fifth stage.
00 head bolts W are arranged. These head bolts W are made of C25% boron steel.
It has the outer shape shown in (A) and (B).

Then, each head bolt W is hardened under the temperature conditions shown in FIG. That is, first, the head bolt W is heated at 900 ° C. for 70 minutes. Then, the quenching device 1
And the head bolt W is hardened with quenching oil 10
Quench for a minute. At this time, after the head bolt W is put into the quenching oil 10, the agitator 3 is stopped, and the agitator 3 is set at 250 rpm. p. m. It is evaluated as if it was rotated with. First stage in each case, 3
The head bolt W at the end of the basket 6 at the fifth and fifth stages
For, the relationship between elapsed time (seconds) and temperature (° C) was determined. FIG. 5 shows the result when the agitator 3 was stopped.
FIG. 6 shows the results when the agitator 3 was rotated. Further, from FIGS. 5 and 6, a graph of the relationship between the elapsed time (second) and the temperature (° C.) was obtained for the head bolt W of the fifth stage basket 6. FIG. 7 shows the results. In each figure, Ms is the temperature (415 ° C.) at which martensitic transformation starts.

FIGS. 5 and 7 show that when the agitator 3 is stopped, the martensitic transformation starts at substantially the same time for the head bolts W of the baskets 6 at all stages. On the other hand, from FIG. 6 and FIG.
250 g of agitator 3 p. m. It can be seen that the martensitic transformation starts earlier in the head bolt W of the fifth stage basket 6 than in the other stages of the basket 6 in the case of the rotation in the above.

[0013]

[Test 2] In test 2, the head bolt W
After the charging, the agitator 3 is stopped and the agitator 3 is set at 250 r. p. m. The variation in temperature and time due to the portion of the head bolt W of a single product was examined with respect to the case where the rotation was performed in the above. Here, the temperature measurement portions of the head bolt W are four locations in the circumferential direction of the head bolt W of the fifth stage basket 6, as shown in FIG. Other conditions are the same as in Test 1.

With respect to the plurality of head bolts W, the temperature of each part is measured, the time at which martensitic transformation is started is measured for each part, and the temperature (° C.) of each part is measured.
And the maximum time difference (second). FIG. 9 shows the results. From FIG. 9, when the agitator 3 is stopped while the head bolt W is at a high temperature, the agitator 3
50r. p. m. It can be seen that the time difference between the temperatures at which the martensitic transformation starts is smaller than in the case where the rotation was performed at. Conversely, when the head bolt W becomes 386 ° C. or less, the agitator 3 is set to 250 r. p. m. It can be seen that the time difference between the temperatures at which the martensitic transformation starts is smaller when the agitator 3 is stopped than when the agitator 3 is stopped. The time when the head bolt W reached 386 ° C. was 35 seconds after the head bolt W was put into the quenching oil 10. More precisely, since the time for charging the head bolt W into the quenching oil 10 is 20 seconds, it is 15 seconds after the charging is completed.

[0015]

The following examples were carried out while confirming the effects of the tests 1 and 2. Other conditions are the same as those in Tests 1 and 2. In the embodiment, as shown in FIG.
Before the head bolt W is thrown into the agitator 3 at 250 r. p. m. , The head bolt W is put into the quenching oil 10, the agitator 3 is stopped for 15 seconds after the completion, and the agitator 3 is again rotated at 250 rpm after 15 seconds. p. m. Rotate with.

[0016]

Comparative Example In the comparative example, the agitator 3 was set at 250 rpm. p.
m. Except that it was constantly rotated.

[0017]

[Evaluation] The head bolt W according to the embodiment and the head bolt W according to the comparative example in the basket 6 from the first stage to the fifth stage
With respect to and, the axial runout was measured as a strain index. Here, the larger the number of the distortion index, the larger the distortion amount.
FIG. 11 shows the result of the head bolt W according to the example, and FIG. 12 shows the result of the head bolt W according to the comparative example.

FIG. 11 shows that the head bolt W according to the embodiment is
Shows that the distortion indices are small and almost equal in all stages. On the other hand, from FIG. 12, it can be seen that in the head bolt W according to the comparative example, the strain index of the fifth stage is larger than that of the other stages, and the variation is large. For this reason, it can be seen that in the example, the axial runout of the head bolt W in the basket 6 at the lowermost fifth stage can be significantly reduced as compared with the comparative example. According to the embodiment, since the temperature difference between the respective head bolts W in the quenching oil 10 is small, the difference in the time at which the martensitic transformation is started between the respective head bolts W is small. It can also be seen that martensite is equally easily formed and the martensitic transformation strain is suppressed.

The surface hardness (Hv) and the internal hardness (Hv) of the head bolt W in the first, third, and fifth stages of the basket 6 were measured in Examples and Comparative Examples. FIG. 13 shows the measurement results of the surface hardness, and FIG. 14 shows the measurement results of the internal hardness. FIGS. 13 and 14 show that there is almost no difference in the surface hardness and the internal hardness between the example and the comparative example.

Therefore, according to the example, it can be seen that a head bolt W of stable quality with sufficiently small martensitic transformation strain and little variation in hardness can be manufactured.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a quenching apparatus used in Examples, Comparative Examples, and Tests 1 and 2.

FIG. 2 is a front view of a tray used in Examples, Comparative Examples, and Tests 1 and 2.

FIG. 3 is a plan view of a basket used in Examples, Comparative Examples, and Tests 1 and 2.

FIG. 4 is a graph showing temperature conditions in Examples, Comparative Examples, and Tests 1 and 2.

FIG. 5 is a graph showing a relationship between elapsed time and temperature when an agitator is stopped in Test 1.

FIG. 6 is a graph showing the relationship between elapsed time and temperature when an agitator was rotated in Test 1.

FIG. 7 is a graph showing the relationship between elapsed time and temperature when the agitator is stopped and when the agitator is rotated in Test 1.

FIG. 8 is a side view (A) and a schematic cross-sectional view (B) showing the external shape of a head bolt used in Examples, Comparative Examples, and Tests 1 and 2.
It is.

FIG. 9 is a graph showing the relationship between the temperature and the maximum time difference when the agitator is stopped and when the agitator is rotated in Test 2.

FIG. 10 is a graph showing a relationship between agitator time and rotation speed in the example.

FIG. 11 is a graph showing a relationship between a basket and a strain index according to the example.

FIG. 12 is a graph showing a relationship between a basket and a strain index according to a comparative example.

FIG. 13 is a graph showing a relationship between a basket and surface hardness according to an example and a comparative example.

FIG. 14 is a graph showing a relationship between a basket and internal hardness according to an example and a comparative example.

[Explanation of symbols]

 2 ... oil tank 10 ... quenching oil 3 ... agitator (rotary body) 1 ... quenching device W ... head bolt (work)

Claims (2)

[Claims] 1. A quenching apparatus having a rotating body capable of storing quenching oil in an oil tank and stirring the quenching oil,
In a quenching method in which a steel work heated to a high temperature is put into the quenching oil of the quenching apparatus to quench the work, the rotation of the rotating body is performed so that martensitization proceeds equally from the surface of the work. A quenching method characterized by adjusting the speed. 2. The temperature difference between the parts of the work in the quenching oil by rotating the rotating body at a constant speed, rather than the temperature difference between the parts of the work in the quenching oil due to not rotating the rotating body. 2. The quenching method according to claim 1, wherein the rotating body is not rotated after the work is put into the quenching oil until the quenching oil becomes smaller.