JPH01215927A - Heat treatment of revolving wheel with small strain - Google Patents

Abstract

PURPOSE:To unnecessitate a straightening process after heat treatment and to improve productivity when a revolving wheel having a toothed part on the inner circumferential side and a race groove part on the outer circumferential side is heat-treated by hardening and tempering the outer race groove part before the heat treatment of the inner toothed part. CONSTITUTION:When a revolving wheel having a toothed part on the inner circumferential side and a race groove part on the outer circumferential side is heat-treated, the outer race groove part is first subjected to surface hardening and intermediate tempering. The mechanical properties of the outer material are enhanced and allowed to act as restraint during the heat treatment of the inner toothed part. The inner toothed part is then hardened and tempered.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a low distortion heat treatment method for swing wheels that are frequently used in construction machinery, equipment, and the like.

(Prior Art) A relatively large number of turning wheels have a shape in which a crest is formed on the inner circumferential side and a race groove is formed on the outer circumferential side. Therefore, the race grooves are given high wear resistance, and the teeth are made to remove residual strain caused by deep machining such as cutting, and to give wear resistance and toughness. It is well known to individually perform heat treatment including quenching and tempering, and usually, high frequency induction heating is used as the quenching heating means, and electric furnace heating is used as the tempering heating means. Further, it is well known to those skilled in the art that the finished hardness due to heat treatment does not depend on the temperature and time during tempering.

In heat treatment of the slewing ring, the highest priority is given to high wear resistance of the race groove, in other words, hardness.

Based on the viewpoint of q, the conventional heat treatment method for a slewing ring that has a crest on the inner periphery and a race groove on the outer periphery is a quenching process for the ridge on the inner periphery, as shown in Table 1 as [Heat treatment process]. ■
, the intermediate tempering step Q was preceded, and then the quenching step (2) of the race groove on the outer circumferential side and the tempering step (2) were performed. This is because the teeth are deep and intricately machined, and in order to sufficiently remove the residual strain generated during machining down to the tooth bottom, it is necessary to heat the teeth for quenching and tempering with a large amount of input energy. There is. On the other hand, the degree of machining of the race groove is small, so there is no need to take into account the removal of residual strain, and the input energy for quenching and heating the race groove surface layer is small, and it is difficult to ensure high hardness. This was considered to be because the tempering temperature also needed to be slightly lower than in the previous process.

A specific example of heat treatment according to the conventional method is shown below.

For example, if a turning ring is made of the following two dimensions and has a race groove on the outer periphery, and the target quenched layer described below is to be formed on each of the teeth and the race groove,
Heat treatment was performed according to the conditions described in [Heat treatment conditions].

In this case, the teeth are hardened in an unrestrained state, and the race grooves are hardened in a restrained state. The reason for this is as shown in Table 2, which shows the results of roundness measurement tests conducted in accordance with JIS regulations at each stage of heat treatment in the specific example. The roundness is relatively high (because there is no need for restraint hardening).

☆Swivel ring W: Material: S 48 C equivalent dimensions; Outer diameter 1018mm Inner diameter 872mm Height 62mm Mountain module 10 Groove depth R12,73rn rn ☆Target quenched hardened layer race groove; Surface hardness---4 (Rc 55-60(
1-1s 7 4~8 1) Effective depth (HRC43 or more) -------3,1~4.3mm Tooth part; Surface hardness---4 (Rc 52~6
0 (Hs'69 to 81) Effective depth 2 Q m rn or less from the top of the tooth ----- HRc 50 or less 1 to 3 mm from the bottom ------- HRc 45 or more, that is, [ in Table 1] As shown in [Heat treatment conditions], a large amount of input energy is required during quenching.

And the tempering temperature is 220°C. After pre-processing the teeth, only a small amount of energy is required and the tempering temperature is 180°C.
Process the race groove section C. The slewing ring that underwent the heat treatment process had extremely large quenching distortions even if the race grooves were subjected to restraint quenching, so the distortions were corrected in the subsequent straightening process (2) and the product was made into a heat-treated product.

(Problems existing in the prior art) The above-mentioned conventional method requires the straightening step (2). The work of correction is
A hydraulic jack, etc. equipped with a rod that moves linearly is placed inside the ring of the swivel ring, and the diametrical direction of the distorted short diameter is enlarged to obtain a perfect circle approximation, but a certain diametrical direction is corrected. If you do this, distortion may occur in other angular directions, so
The work involved repeating roundness measurements many times,
This process is extremely time consuming and complicated, and greatly impedes productivity.

15= Also, since the above-mentioned straightening is mechanical straightening, the straightening effect gradually disappears over time, and some people return to the distorted state after heat treatment, making long-term quality assurance unstable. I had a point.

Furthermore, the mechanical straightening described above reduces the compressive residual stress in the treated area, which is expected as a heat treatment effect, and therefore causes negative effects such as a decrease in fatigue strength and wear resistance. Avoidance was desired as a palliative measure.

(Object of the Invention) The present invention has been made in order to solve the above-mentioned problems in the conventional method when heat treating a turning ring having a peak on the inner circumference side. In addition to making it possible to reliably impart mechanical properties, there is no need for a straightening process after heat treatment, and therefore the imparted mechanical properties can be guaranteed for a long period of time, and furthermore, fatigue strength and wear resistance can be improved. The purpose of the present invention is to provide a heat treatment method.

(Process leading up to the invention) In the process leading to the present invention, the present inventor reexamined the conventional methods.

The preceding tooth processing includes hardening and intermediate tempering performed in an unrestrained state, but the turning ring at the end of this tempering is
As shown in Table 2, the roundness is high.

However, the roundness of the turning wheel that has undergone the trailing race groove treatment is significantly reduced.

The inventor focused on this point, and realized that the race groove part, which is an untreated part, of the slewing ring at the end of the intermediate tempering is not completely dissipated, and the residual stress during cutting is not completely eliminated and remains inside. Because the distortion remains accumulated and latent, the roundness is high.
It was also assumed that these internal stresses manifested all at once when the race groove part was processed, causing the above-mentioned chamfer to peel off, resulting in a significant decrease in roundness at the end of the heat treatment.

The accuracy of this conjecture was confirmed by the results of numerous experiments conducted subsequently, and this became the basis for the first invention of the present application.

(Summary of the first invention) The summary of the first invention is as follows: (1) In the case of heat-treating a turning ring in which a mountain portion is formed on the inner circumference side and a race groove portion is formed on the outer circumference side, (2)
A low strain heat treatment method for a turning ring, characterized in that the race groove portion is surface hardened and subjected to intermediate tempering, and (3) the mountain portion is then hardened and tempered.

In other words, in the method of the present invention, the preceding treatment section is opposite to that of the conventional method, and is expressed as shown in Table 3 as [heat treatment step]. In this case, there is no limit to the type of heating means for any type of quenching heating, but high-frequency heating means is preferred from the viewpoint of control, as in the conventional method, and as in the conventional method, the race groove requires less input energy as described above. Therefore, moving quenching is used, and single-shot quenching, which uniformly heats the entire mountain area at once, is preferable.

Heating during hardening of the surface, race grooves and teeth,
The cooling conditions are the same as those according to the conventional method, but in order not to reduce the hardness of the preceding treatment section, the tempering conditions for the subsequent treatment section are set to the same temperature or slightly higher than the temperature during intermediate tempering, and Consideration must be given to keeping the time approximately the same as that for intermediate tempering.

When the method of the present invention is applied, for example, to a turning wheel having the dimensions and shape listed as the specific example of the conventional method listed above, the conditions shown in Table 3 as [Heat treatment conditions] will be followed.

(Function of the first invention) The present invention is based on the inference obtained from the reexamination of the conventional method mentioned above, and reverses and strengthens 110, which is estimated to be a factor that significantly reduces the finished roundness in the conventional method. This is the technical idea of the present invention.

That is, the present invention involves hardening the race groove on the outer circumferential side.

By performing tempering treatment in advance, the mechanical properties of the material on the outer periphery are strengthened, and the strengthened material acts as a strong restraining force when processing the teeth on the inner periphery, thereby reducing residual stress and quenching strain on the inner periphery. It has the effect of ensuring high finished roundness by allowing full development in the centripetal direction on the side, while restricting development in the radial direction on the outer peripheral side.

(Experiment Example: 1) =9- The present inventor conducted a roundness measurement experiment in order to prove that the method of the present invention is effective in ensuring high finished roundness.

Strange experimental method: The above-mentioned rotating material was used as a specimen, heat treated according to the method of the present invention and the conventional method, and the circularity of both specimens was measured as the raw material changed sequentially as the treatment progressed.
A comparative investigation was made of the changes in roundness between the two.

☆Heat treatment conditions 2 The inventive implementation specimens are shown in Table 3 [
The conventional method specimens were treated according to the description in [Heating Conditions] in Table 1.

The target hardened layer is the same as in the conventional example described above.

☆Roundness measurement test results: Figure 1 G, a) shows the measurement values for the finished standard dimension (perfect circle) at each circumferential position of the specimen to which the conventional method was applied, and (b) to the specimen to which the present invention method was applied. This is a line graph showing the difference between
Line B is the result of ■ IO- after intermediate tempering, line C is after ■ tempering, and 1=S is the quenching start position during race groove movement quenching, and 2 to 8 are 45° clockwise. Indicates the position in each direction.

In addition, FIG. 2 is a schematic diagram showing the directionality of strain produced based on the above measurement values, in which (a) is the conventional method and (b) is the case where the present invention method is applied, respectively. In the figure, line A drawn as a solid line with respect to a perfect circle shown as a broken line shows the shape of the raw material, line B shows the shape of the material after intermediate tempering, and line C shows the shape of the material after tempering. Note that S in the figure is the race groove portion movement hardening start position.

Furthermore, FIG. 3 is a line graph showing the change in roundness obtained through this test, where line A is for the specimen to which the conventional method was applied, and line opening is for the specimen to which the method of the present invention was applied. In addition, ■ on the horizontal axis represents the raw material, and ■ to ■ represent the material after the corresponding process has passed.

The following considerations can be obtained from the above FIGS. 1 and 21.

The specimen to which the conventional method was applied (1) After intermediate tempering, slight concavities were observed in the S position reference directions of 135° and 315°, and convexities in the 45° and 225° directions, but the roundness was relatively high. However, after tempering, a significant decrease in roundness occurred in non-specific directions.

On the other hand, in the specimen to which the present invention method has been applied, (1) After intermediate tempering, unevenness occurs in almost the opposite direction to that in the specimen to which the conventional method has been applied, and the amount thereof is greater than that in the specimen to which the conventional method has been applied. However, the irregularities tend to be slightly corrected after tempering, and irregularities in non-specific directions are not clearly observed.

Furthermore, considering FIG. 3, the product to which the conventional method is applied, shown by line A, has a finished roundness of 0.86 mm or more, whereas the finished roundness of the product to which the present invention is applied is 0.6 mm. The amount of distortion was reduced by approximately 30% compared to the product to which the conventional method was applied, demonstrating the effectiveness of the method of the present invention.

3. The roundness indicated by the experimental results of the present invention indicates that (1) the straightening step is not required unless the required roundness is particularly strict.

Based on the above experimental results, the present inventor conducted intensive research in pursuit of a finish with even lower distortion, and as a result, completed the second invention.

(Summary of the Second Invention) The gist of the second invention of the present application is as follows: (a) The process is the same as the first invention of the present application, but (b) when the race groove is hardened, a plurality of The present invention provides a low-distortion heat treatment method for a swing wheel, characterized in that the bridge members are brought into contact with each other from equiangularly spaced directions, and the swing wheel is placed in a restrained state.

In other words, the present invention is based on the assumption that the roundness of the finished product can be further improved by further suppressing the amount of distortion during the process of processing the race grooves. As shown, a plurality of bridge members K are placed in contact with and arranged at equal angular positions on the race groove U side of the slewing ring W, and then hardening is performed. In the case of 5, the amount of restraint on the swinging wheel W on the bridge member is 0. In other words, there is no gap,
There is no need to apply pressure. Furthermore, it goes without saying that the bridge member is set at a height that avoids the race groove U so as not to interfere with hardening.

(Effect of the second invention) The roundness of the turning wheel W that descends after the race groove U treatment is sufficiently ensured, and the high roundness restraining force is achieved due to the reinforcement of mechanical properties imparted by the preceding race groove U treatment. This works effectively during the subsequent tooth G treatment, and has the effect of further improving the roundness of the finished product compared to the case of the first invention.

(Experimental Example = 2) An experimental example demonstrating that the second invention achieves a finish with a roundness higher than that of the first invention will be disclosed below. For convenience of comparison, a swing ring having the same size and shape as in Experimental Example 1 was used as a specimen, and was treated in the same manner as in Experimental Example 1 according to the [heat treatment conditions] in Table 3.

Odd roundness measurement test: For multiple specimens, roundness measurements were performed on raw materials that vary sequentially over the course of the processing process.

Table 4 shows the roundness of all specimens after each step. - As an example, for convenience of comparison, the difference between the measured value after each process with respect to the finished standard value for sample 1 is shown as a graph in Fig. 1 (C), and a schematic diagram showing the direction of strain is shown. , is shown in FIG. 2(c) for convenience of comparison.

Further, the change in roundness after each step is shown as line C in FIG. 3 for ease of comparison.

From Table 4 and each figure, it can be seen that the turning ring to which the method of the present invention is applied has improved roundness after intermediate tempering compared to the first invention, and as a result, the finished product.

Compared to the case where the first invention follows the conventional method, the amount of distortion is approximately 30
It became clear that the effect of reducing the roundness by 50 to 55% was even greater than that of the reduction in roundness by 50 to 55%, and it was possible to achieve extremely high roundness, demonstrating the remarkable effectiveness of the method of the present invention.

Furthermore, it is shown that the roundness exhibited by the turning ring treated by applying the heat treatment method of the present invention completely eliminates the need for a straightening process after the heat treatment.

(Accuracy test) The present inventor has developed a second method that succeeded in eliminating the need for a straightening process.
In the slewing ring in which the invention was implemented, since the restraint using the bridge member was biased in the height direction during hardening of the race groove, the tooth profile deformation was measured due to concerns that the diameter in the unrestricted direction would expand and the tooth profile would be deformed. The test was conducted. In addition, various tests were conducted to confirm whether desired mechanical properties were imparted to the race grooves and teeth. The results of these tests are disclosed below.

☆Tooth profile deformation measurement test ○Test method: For specimens 1 and 2 in Table 4, in the 90° direction shown as x-x' and Y-Y' in (a) of Figure 5, as shown in (b) The diameters between the end faces of the lower restrained side and the upper non-restricted side were measured and the difference value was determined to investigate the falling deformation of the tooth profile.

○Test results: Table 5 shows the measurement results at each measurement position. From the same table, it was confirmed that there was only a slight amount of collapse and deformation, and that the heat-treated finish did not cause any problems during use.

☆Surface hardness test ○Test method: For each specimen 1 to 5, (a
) The surface hardness of the race grooves and teeth at four locations in the X-X" and Y-Y' directions shown in
s). The measurement positions of the race groove are two places shown as A and Mouth in Figure 6 (a), and the measurement positions of the tooth part are three places on the top of the tooth and three places on the bottom of the tooth as shown in (b). The average value was taken as the measured value at the relevant position. The above three locations are 5mm from each end face.
These are points a and c on the top of the tooth near the center, points d and f on the bottom of the tooth, and points 8 on the top of the tooth in the center and 8 points on the bottom of the tooth.

○Test results: Table 6 shows the measurement results at each measurement position. From the same table, the surface of the race groove shows a hardness of Hs 75 to 79, and the surface hardness required for the race groove is Hs 74 to 8.
It was confirmed that the surface hardness of the tooth surface was within the range of Hs 73 to 80 for both the top and bottom of the tooth, and that the surface hardness was within the range of Hs 69 to 81 required for the tooth. .

☆ Hardness test of hardened layer ○ Test method: Specimen 3 in Table 4 was cut at a predetermined position to prepare a specimen.
), and the hardness of the cross section along the line shown as A-D is shown in FIG. The cross-sectional hardness along the line indicated by ~■ was measured using a Vickers hardness meter.

○Test results: Figure 8 (a) shows the race groove.

(b) shows the measurement results of the teeth.

From Figure 8(a), all lines A-D are at a distance of 3 from the surface.
．． The present invention shows an HRc of 43 or more up to 2 mm, and the present invention meets the above-mentioned effective depth requirement for the race groove (3.1 mm to 2 mm).
4.3 mm is HRc43 or more).

In addition, from Fig. 8(b), the lines I~■ all passing through the top of the tooth show a hardness of Hs50 or less before reaching 20 mm from the surface, and all the lines ■~■ passing through the tooth bottom show hardness at least from the surface. I] Rc51 at a distance of 2.5 mm or more
The above is shown above, and the above-mentioned effective depth requirement value for the crest (the top of the tooth must be Hs50 or less at 20 mm or more from the surface).

and the bottom of the tooth must have an HRc of 45 or higher within 1 to 3 mm from the surface. In other words, the above result shows that the tooth profile is not hardened, a tough heat-affected transition zone is left in the core, a hardening pattern H is formed in the base that preserves the material quality, and the tooth bottom is hardened. This proves that the hardened layer H was reliably formed to the required depth.

Odd tissue microscopic observation test ○Test method: A specimen was prepared from the center between both end faces at a predetermined position in the circumferential direction of specimen 3 shown in Table 4, and subjected to a tissue microscopic observation test (magnification: 400). The specimen sampling positions are shown in FIG. 9 as (a) to (e).

- Test results: Figures 10(a) to (e) are micrographs of metallographic structures of specimens with the same symbols.

Photographs (a) to (d) of specimens taken from the quenched hardened layer
are all tempered martensitic structures.
In addition, the photograph (e) of the specimen taken from the core of the member shows that the annealed ferrite + pearlite structure of the base material is intact, and the test results indicate that the heat treatment according to the method of the present invention or the race groove and tooth portion, respectively. This shows that the desired hardened layer was reliably formed.

Regarding the second invention, the results of the roundness measurement test and the results of each accuracy test are as follows. It has been proven that it is guaranteed.

Moreover, each confirmation test result for the second invention described in -Y confirms the mechanical properties of the first invention, which has been omitted since the description would be redundant.

(Other Examples) In each of the above experimental examples, the present invention was explained using a rotating ring of the same size as a specimen for convenience of comparison. The method of the present invention is also applicable to various types of swing wheels having different dimensions, wall thickness, etc. In this case, if the input energy relationship in the [heat treatment conditions] is changed depending on the size and shape of the target material, but if the [heat treatment step] is carried out in accordance with the first invention of the present application, and furthermore with the addition of the second invention of the present application, It has been confirmed that exactly the same results as in each of the above experimental examples can be obtained.

(Effects of the Invention) The heat treatment method of the present invention reliably imparts desired mechanical properties to a rotating ring having teeth on the inner peripheral side, and eliminates the need for a straightening process after heat treatment. Therefore, productivity is greatly improved, and the mechanical properties obtained through heat treatment remain unchanged over a long period of time, which greatly contributes to quality reliability.Furthermore, compressive residual stress in the treated part, which is expected to be an effect of heat treatment, is reduced. It does not deteriorate like conventional mechanically straightened products and contributes to the fatigue strength and wear resistance of the product, contributing to the durability of the product, etc. = 21
− It has a great effect.

[Brief explanation of the drawing]

Fig. 1 (a), (b) and ('c) are the measured values at the same circumferential positions in the roundness measurement test during the heat treatment process according to the conventional method, the first invention method of the present application, and the second invention method of the present application, respectively. Figures 2 (a), (b), and (C) are diagrams showing the differences from the standard dimensions of the specimens, respectively. Fig. 3 is a diagram showing the roundness transition during the heat treatment process of the specimens to which the conventional method, the first invention method, and the second invention method were applied, respectively. A front view and a plan view showing the restrained state of the slewing ring during hardening of the race groove of the slewing ring in the invention method,
5(a) and (b) are a plan view and a cross-sectional front view showing the measurement position and measurement method in the tooth profile deformation measurement test of the specimen to which the second invention method is applied, and FIGS. 6(a) and (b) are the A partial cross-sectional view and a partial perspective view showing measurement positions in the surface hardness test of the specimen to which the second invention method was applied, Figure 7 (2) and -22= (b) show the hardness of the hardened layer of the specimen to which the second invention method was applied. A cross-sectional view showing the measurement lines of the race groove and the peak in the test, and FIGS. 8(a) and 8(b) respectively show the hardness test results of the hardened layer of the race groove and the tooth of the specimen to which the second invention method was applied. Fig. 9 is a cross-sectional side view showing the metallographic micrograph sample collection position of the specimen to which the second invention method was applied, and Fig. 10 (
Each of a) to (e) is a metallographic micrograph. Patent applicant Koshuha Netoren Co., Ltd.

Claims (1)

[Claims] 1. When heat treating a turning ring in which teeth are formed on the inner periphery and race grooves are formed on the outer periphery, the race groove is surface hardened and subjected to intermediate tempering, and then the above-mentioned A low-distortion heat treatment method for a swing ring, characterized by hardening and tempering the teeth. 2. Claim 1 characterized in that, when the race groove is hardened, a plurality of bridge members are brought into contact with the circumferential surface on which the race groove is formed from directions spaced at equal angles, thereby placing the turning ring in a restrained state. The described low distortion heat treatment method for a turning ring.