JP4783032B2 - Sintered high speed steel, its manufacturing method and sliding parts made of the sintered high speed steel - Google Patents

Description

  The present invention relates to a method for producing sintered high-speed steel suitable as a material for wear-resistant sliding members, and more specifically, to produce sintered high-speed steel excellent in wear resistance at a low cost while suppressing deterioration of dimensional accuracy. And a sintered high speed steel obtained by the method and a sliding part made of the sintered high speed steel.

As an iron-based sintered vane for compressors that has excellent wear resistance and low attack resistance, the present applicant has uniformly dispersed hard carbides having an average particle size of 5 μm or less in an iron-based matrix. theoretical density ratio 80-90%, has proposed a vane Rockwell hardness is formed by sintering high speed steel of _H R _C10~45 by Patent Document 1 below.
Japanese Patent Publication No. 7-26629

  This compressor-based iron-based sintered blade is quenched and tempered after sintering in order to improve wear resistance. However, the conventional heat treatment has a cooling rate that is too fast (for example, quenching with oil) When the cooling rate is 10 ° C./sec or more), there is a problem in that large distortion occurs in the product, resulting in poor dimensional accuracy, particularly flatness.

  Moreover, since the amount of retained austenite in the material increases due to rapid cooling (30 wt% or more), there is a problem that the tempering conditions become severe.

  For example, a compressor component for a refrigerator is used in an extremely low temperature environment that reaches as high as −60 ° C. For such a special purpose component, the residual austenite is transformed into martensite at a low temperature and expands. In order to prevent rocking phenomenon during use due to the fact that the sliding clearance cannot be secured for that reason, the amount of retained austenite in the high-speed steel of the material is made as close to 0% as possible. It is desired to be (1 wt% or less). Further, high-speed steel for general use used at a temperature of 0 ° C. or higher as a chiller part or a dehumidifier part is also desired to have a retained austenite amount of 5 wt% or less.

  In order to reduce the austenite remaining at 30 wt% or more to a point where the above-mentioned requirement can be met, it is necessary to perform tempering 2-3 times in the conventional method. In addition to this, in the conventional tempering process, the heating process and the process of cooling to room temperature after the heating are repeated, and for this reason, the time for the heat treatment becomes longer.

  In addition, tempering is performed while the work is taken out from the furnace once, and the parts to be processed must be aligned and introduced into the furnace for uniform heating and cooling. The amount of the heat treatment was small, and the heat treatment efficiency was not good.

  In addition to this, since the heat treatment of further tempering and tempering is performed after sintering, the thermal efficiency and productivity are poor, the manufacturing cost is increased, and dimensional accuracy is achieved by cooling with water or oil. In particular, there is a problem that the flatness is deteriorated and the product is cracked in an extreme case.

The above Patent Document 1, although stated to carry out N ₂ gas quenching from 1150 ° C. After sintering, the above problems have occurred also employ the gas quenching method.

  The present invention provides a production method capable of producing a sintered high-speed steel having the composition disclosed in Patent Document 1 without generating a large strain, and a production method capable of realizing a reduction in the amount of retained austenite by reducing the number of tempers. It is an object of the present invention to provide a sintered high-speed steel with high hardness and low strain produced by these methods, and a sliding part with good dimensional accuracy formed from the sintered high-speed steel.

In order to solve the above-described problems, in the present invention, a steel material (high speed steel, hereinafter also referred to as a product) sintered during cooling after sintering is 0.3 ° C./sec or more and 3.5 ° C./sec or less. speed, more preferably 0.3 ° C. / sec or higher, have rows quenching by cooling at a rate 2.0 ° C. / sec upon cooling after sintering, further tempered after the hardening And the number of times of tempering is set to 2 and the cooling temperature in the first tempering is 100 ° C to 180 ° C, more preferably 100 ° C to 150 ° C. A manufacturing method is provided.

By this method, the sintered high speed steel of the present invention is produced. Note that sintered high-speed steel having a retained austenite amount of 1 to 5 wt% can be suitably used as a material for sliding parts for general use (for example, parts for chillers and dehumidifiers), and the retained austenite amount is 1 wt%. The following sintered high speed steel can be suitably used as a material for sliding parts for special applications (for example, sliding parts for refrigerators) used at a temperature of 0 ° C. or lower.

  The product after sintering is preferably cooled with an inert gas such as nitrogen gas or argon gas. A gas in which hydrogen is included in an inert gas may be used. However, since hydrogen is expensive, the upper limit of the amount of hydrogen used is preferably about 5%. The cooling with the inert gas is preferably performed using a production facility having an independent cooling zone having no heat source.

The present invention has a degassing zone, a sintering zone, and a cooling zone that does not have a heat source independent of the degassing zone and the sintering zone, and the introduced high-speed steel is an inert gas in the cooling zone, or Production of sintered high-speed steel that can be cooled at a rate of 0.3 ° C./sec or more and 3.5 ° C./sec or less using a mixed gas containing 5% or less of hydrogen in an inert gas Also provided is a sintered high speed steel produced by the above method using equipment and having a hard carbide having an average particle size of 5 μm or less uniformly dispersed in the matrix. The sintered high speed steel has a weight ratio of C: 0.7 to 1.5%, Cr: 3.0 to 5.0%, Mo: 0 to 10%, W: 1 to 20%, V: 0 0.5 to 6.0%, Co: 0 to 15%, balance Fe and inevitable impurities, the theoretical density ratio is 80 to 90%, and the Rockwell hardness is HRC20 to 45.

  The invention also provides a sliding part made of the sintered high speed steel.

  If the cooling rate during the heat treatment is too fast, the heat distribution of the product becomes non-uniform, and there is a difference in the amount of expansion and contraction of each part, resulting in distortion.In this invention, the high-speed steel is sintered, Since quenching is performed at a cooling rate of 3.5 ° C./sec or less after the sintering, variation in product heat distribution is suppressed, and a product with good dimensional accuracy can be obtained.

In addition, the product which satisfy | fills a desired characteristic (for example, hardness is HRC20 or more) is obtained by setting a cooling rate to 0.3 degrees C / sec or more. Further, the dimensional accuracy of the product that sufficiently high by the cooling rate 3.5 ° C. / sec or less.

If the high-speed steel to be processed is a sintered material having a structure in which fine hard carbides having an average particle size of 5 μm or less are uniformly dispersed in the matrix, quenching is performed at the above cooling rate. Thus, a material having a Rockwell hardness of H _R C20-45 can be obtained.

  According to the method of the present invention, since quenching is performed after the sintering and cooling, it is not necessary to reheat the product once cooled after the sintering. As a result, the thermal efficiency is improved, the process is shortened, and the product cost can be reduced.

Furthermore, according to the method of cooling after sintering with an inert gas or a gas containing 5% or less of hydrogen in an inert gas, oxidation of the product can be prevented. Moreover, if it is gas cooling, it is easy to control a cooling rate to a required range.

Further, when the sintered high speed steel is quenched by the method of the present invention, the amount of retained austenite is reduced as compared with the conventional case, and therefore, the number of times of tempering can be reduced. Conventionally, had conducted back its tempered three times when forming the residual austenite amount less 1 wt%, the amount of retained austenite having been subjected to the quenching in a way, that was conventionally 30 wt% or more of the invention Therefore , the amount of retained austenite can be reduced to 1 wt% or less by tempering twice .

Further, tempering twice row Utame, first bake is not necessary to lower to room cooling temperature in the return, the effect of reducing the processing time more remarkable. As for the cooling temperature in the first tempering, if the cooling of the part is made uniform, the martensitic transformation occurs even if the temperature of the highest temperature part in the part is 180 ° C. However, depending on the quenching conditions (such as quenching method and part shape), heating and cooling may vary. Therefore, it is preferable to set the cooling temperature lower in consideration of this. For example, when the parts are packed and quenched, heating and cooling are particularly likely to vary, but even in such a case, if the parts are cooled to about 120 to 150 ° C., stable tempering can be performed. Note that if the cooling temperature in the first tempering is lowered unnecessarily, the effect of shortening the processing time is diminished, so the lower limit of the cooling temperature is preferably limited to about 100 ° C.

  The sintered high-speed steel produced by the method of the present invention has high hardness and excellent wear resistance, and has small distortion during heat treatment and excellent dimensional accuracy.

  In addition, the sliding parts made of this high-speed steel exhibit excellent durability while being low in attacking the other party. Furthermore, because the dimensional accuracy is improved, the machining allowance during machining is small. There are also benefits.

Example 1
By weight ratio, C: 1.1%, W: 6.1%, Mo: 5.0%, Cr: 4.0%, V: 2.0%, the average particle size consisting of the balance Fe and inevitable impurities is 100 The mesh alloy powder was mixed with 0.8% zinc stearate as a forming aid, formed at a pressure of 882 MPa, and the formed body was degassed and sintered in vacuum at 1180 ° C. for 1 hour. .

  Next, cooling after sintering is performed using an inert gas, cooling oil, and cooling water at 0.15 ° C./sec, 0.30 ° C./sec, 1.75 ° C./sec, 2.0 ° C./sec, 3 ° C. .5 ° C./sec, 20-80 ° C./sec, 80-140 ° C./sec, then tempered twice at 580 ° C. to obtain a test piece of 33 mm length × 30 mm width × 5 mm thickness . The atmosphere of tempering is preferably in an inert gas considering the brightness of the product, but there is no problem even in the air.

  As shown in FIG. 1, the degassing treatment, sintering, and cooling after sintering of the molded body is a three-tank structure in which a degassing zone 1, a sintering zone 2, and a cooling zone 3 without a heat source are independent from each other. The furnace was used. As in this furnace, when the cooling zone 3 is cooled with an inert gas as an independent zone having no heat source, sintered high-speed steel can be manufactured at low cost. In FIG. 1, 4 is a vacuum pump, 5 is a cooling gas, 6 is a cooling fan, 7 is degassing, and 8 is a carrier gas. Here, the cooling zone is provided independently, but the independent meaning here is that the sintering zone and the cooling zone may be insulated from each other. For example, the sintering zone and the cooling zone are insulated by a heat insulating material. You may form continuously.

  The flatness and Rockwell hardness of each test piece having a theoretical density ratio of 85% thus obtained were measured.

  For flatness, the amount of warpage of the end face of the test piece was determined. The results are summarized in Table 1.

As can be seen from Table 1, which was cooled with satisfying rate of the present invention, _H R C20 or higher hardness is obtained as a target, also the cooling rate of .30-2.0 ° C. / sec Especially in the range, the flatness is much better than that exceeding 20 ° C./sec.

-Example 2-
A sintered high-speed steel having the same composition was produced under the same conditions as in Example 1, and then cooling after sintering was performed at a rate of 3.5 ° C./sec using an inert gas so that the amount of retained austenite was about 10 wt% of Invention I was obtained. In addition, comparative products I and II in which a sintered material (same composition as that of Invention Product I) manufactured by gradually cooling to room temperature after sintering by the conventional method was heated to 1150 ° C. and then cooled and quenched were also obtained. Got ready. Comparative product I is cooled by quenching at a rate of 3.5 ° C./sec or more using an inert gas, and comparative product II is cooled by quenching at 10 ° C./second using oil. Each was performed at a speed of at least sec. In these comparative products I and II, the amount of retained austenite was 30 wt% or more. The amount of retained austenite was measured with an X-ray diffractometer.

  Next, the invention product I and the comparison products I and II were tempered. Tempering was performed once and twice for the inventive product and twice and three times for the comparative product. The heating temperature during tempering was 580 ° C., and the heating temperature was held for 1.5 hours. The comparative product was cooled to room temperature in each tempering, while the second tempering of the invention product was set to 120 ° C. and then again to 580 ° C. Heated and then cooled to room temperature. Cooling is performed by natural cooling, the temperature rising time from room temperature to 580 ° C. is 1 hour, the temperature rising time from 120 ° C. to 580 ° C. is 0.8 hours, the cooling time from 580 ° C. to room temperature is 3 hours, 580 ° C. The cooling time from 120 ° C. to 120 ° C. was about 1.5 hours. The results of the comparative test are summarized in Table 2.

  As can be seen from Table 2, when quenching is performed by the method of the present invention, the amount of retained austenite of the workpiece at the quenching stage is greatly reduced as compared with the conventional method. In addition, the amount of retained austenite is 5 wt% or less after two tempers in the conventional method, and 1 wt% or less after three tempers, whereas the amount of retained austenite is 5 wt% or less after one tempering. The number of steps and heat treatment time can be shortened by reducing the number of steps to 1 wt% or less by tempering twice. Further, in the conventional method, it was necessary to perform tempering by arranging the workpieces on a pallet for uniform cooling. However, in the method of the present invention, the workpieces are packed on the pallet at a double density and baked. It was possible to return, and productivity was greatly improved. Nevertheless, the workpiece after quenching and tempering has a hardness that is not significantly different from the conventional method.

-Example 3-
FIG. 2 shows that the cooling temperature at the first tempering is 120 ° C. and the conventional method in which the cooling at each tempering is performed to room temperature, and each tempering is performed twice. Comparison time is shown. The heating temperature in tempering, the temperature holding time after heating, the cooling time to room temperature by natural cooling, and the cooling time to 120 ° C. are the same as in Example 2.

  In this comparative test, the processing time for tempering in the conventional method was 11 hours, whereas in the method of the present invention, the processing time was reduced to 9.3 hours. In the conventional method, when the amount of retained austenite is 1 wt% or less, tempering is required three times, so the total time required for tempering is 16.5 hours. Therefore, if sintered high-speed steel having substantially the same characteristics is produced using the same furnace, the processing time in the method of the present invention is almost halved compared with the conventional method.

The sintered high speed steel produced by the method of the present invention is not limited to the composition shown in the examples. C: 0.7 to 1.5%, Cr: 3.0 to 5.0%, Mo: 0 to 10%, W: 1 to 20%, V: 0.5 to 6.0% by weight ratio, Co: 0 to 15%, balance Fe and inevitable impurities, powder forming is performed at a pressure of 490 to 980 MPa (5 to 10 Tonf / cm ² ), for example, and the theoretical density ratio after forming is 80 to 90%. If the steel is cooled at a speed within a specified range at the time of cooling after sintering, preferably sintered, a high-speed sintered steel having high hardness and excellent dimensional accuracy can be obtained.

  In addition, the sliding part formed of the sintered high speed steel of the present invention has excellent wear resistance and can withstand long-term use. Further, the opponent's aggression is low, and wear of the opponent sliding part is suppressed. Furthermore, since the dimensional accuracy is increased, the machining allowance at the time of machining is less than that of the conventional product, so that the processing efficiency can be improved and the cost can be reduced accordingly. Therefore, it is suitable for a sliding part for a compressor such as a vane.

The figure which shows an example of zone arrangement | positioning of the manufacturing equipment of this invention The figure which compared the time required for twice tempering by the method of this invention and twice tempering by the conventional method

Explanation of symbols

1 Degassing Zone 2 Sintering Zone 3 Cooling Zone 4 Vacuum Pump 5 Cooling Gas 6 Cooling Fan 7 Degassing 8 Carrier Gas

Claims (6)

The sintered high speed steel during cooling after sintering 0.3 ° C. / sec or higher, have rows quenching by cooling at a rate 3.5 ° C. / sec, further, after the hardening Tempering is performed, the number of times of tempering is set to 2 times, and the cooling temperature in the first tempering is set in a range of 100 ° C. to 180 ° C. A method for producing sintered high-speed steel, characterized in that it is obtained .   The method for producing a sintered high-speed steel according to claim 1, wherein the high-speed steel after sintering is cooled at a rate of 0.3 ° C / sec to 2.0 ° C / sec.   Using a production facility comprising a degassing zone, a sintering zone, and a cooling zone that does not have a heat source independent of the degassing zone and the sintering zone, cooling of the steel material in the cooling zone after sintering is performed using an inert gas, Or the manufacturing method of the sintered high speed steel of Claim 1 or 2 performed by the mixed gas which contained 5% or less of hydrogen in the inert gas.   The method for producing a sintered high speed steel according to any one of claims 1 to 3, wherein a cooling temperature in the first tempering is in a range of 100C to 150C.   A sintered high-speed steel having a Rockwell hardness of HRC 20 to 45 obtained by the production method according to any one of claims 1 to 4, wherein hard carbides having an average particle size of 5 µm or less are uniformly dispersed in a matrix.   A sliding part made of the sintered high speed steel according to claim 5.

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