WO2012091069A1 - Method for quenching mold - Google Patents

Method for quenching mold Download PDF

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Publication number
WO2012091069A1
WO2012091069A1 PCT/JP2011/080342 JP2011080342W WO2012091069A1 WO 2012091069 A1 WO2012091069 A1 WO 2012091069A1 JP 2011080342 W JP2011080342 W JP 2011080342W WO 2012091069 A1 WO2012091069 A1 WO 2012091069A1
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Prior art keywords
mold
temperature
cooling
quenching
oil
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PCT/JP2011/080342
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French (fr)
Japanese (ja)
Inventor
仁 片岡
貴司 川上
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日立金属株式会社
小山鋼材株式会社
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Application filed by 日立金属株式会社, 小山鋼材株式会社 filed Critical 日立金属株式会社
Priority to JP2012520604A priority Critical patent/JP5075293B2/en
Priority to CN201180056966.1A priority patent/CN103228802B/en
Publication of WO2012091069A1 publication Critical patent/WO2012091069A1/en

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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D30/00—Cooling castings, not restricted to casting processes covered by a single main group
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C21D1/19—Hardening; Quenching with or without subsequent tempering by interrupted quenching
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/56—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering characterised by the quenching agents
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/56—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering characterised by the quenching agents
    • C21D1/58—Oils
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/0068—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for particular articles not mentioned below

Definitions

  • the present invention relates to a mold quenching method.
  • the mold is required to have high hardness and high toughness, and its characteristics are greatly influenced by the quenching method.
  • a higher quenching temperature is selected so that the crystal grains are not coarsened in order to dissolve the alloy elements to the maximum.
  • rapid cooling is required.
  • rapid cooling increases the distortion and deformation of the mold, and thus it is necessary to appropriately control the cooling rate. For this reason, various proposals have been made in the past, and a method of achieving both low strain and high toughness by adjusting the cooling conditions from the quenching temperature is mainly employed.
  • Patent Document 1 cooling subsequent to heating to the quenching temperature is set to 20 ° C./min to 5 ° C./min in the high temperature region from the quenching temperature to 600 ° C.
  • a marquenching method has been proposed in which the low temperature region from 400 ° C. to 200 ° C. is maintained at 1 ° C./min to 15 ° C./min after being held.
  • the marquenching method is a process in which the cooling during quenching is kept constant at the upper part of the martensite transformation or at a slightly higher temperature to cool after quenching, in order to prevent quench cracking due to rapid cooling. is there.
  • the present applicant has proposed a method for quenching a mold in JP 2009-074155 A (Patent Document 2), focusing on both the temperature raising side condition and the cooling side condition of the quenching temperature. That is, after the quenching and heating step of heating the temperature range from the A1 transformation point to the A3 transformation point at a rate of 100 ° C./h or more, a holding step for holding a temperature range not lower than 1150 ° C. above the A3 transformation point is performed. Next, a high temperature side quenching and cooling process is performed in which the temperature range from the A3 transformation point to 600 ° C.
  • Patent Document 3 discloses techniques related to a quenching method by the same applicant. Specifically, a steel part is rapidly cooled to a temperature just above the martensite transformation start point (Ms point), taken out of the quenching oil, and immediately above the martensite transformation start point (Ms point) by the retained heat of the steel part. This is a technology that maintains a constant temperature until the temperature reaches a nearby temperature.
  • a material having a small internal volume such as a part such as a gear illustrated in paragraph 0002 of cited document 3 or a sharpened portion such as a corner portion of a prism member illustrated in paragraph 0009 of cited document 4, is preferably quenched. it can.
  • Patent Document 3 and Patent Document 4 when the techniques disclosed in Patent Document 3 and Patent Document 4 are applied to a mold having a larger volume than a gear or the like, it is difficult to control the cooling rate, and the surface of the mold is Ms during rapid cooling. The temperature falls below the point. At this time, there is almost no temperature drop inside the mold, and if it is taken out from the quenching oil, the surface temperature again becomes higher than the Ms point due to the retained heat inside the mold, the metal structure becomes unstable, and the mold becomes unstable. Hardness variation will occur. In the case of a heavy mold, if an attempt is made to maintain a constant temperature until it reaches a temperature just above the Ms point, the time required for the mold becomes too long, and the productivity is remarkably deteriorated.
  • An object of the present invention is to provide a quenching method capable of rationally improving the toughness of the mold surface.
  • the present inventor In order to improve the toughness of the surface of the hot mold, the present inventor 1) It is necessary to apply a cooling rate much faster than the cooling rate considering the transformation region of bainite (bainite nose) in order to reliably avoid carbide precipitation at the grain boundaries. and, 2) The adverse effects due to the temperature difference between the surface and the interior due to the application of this fast cooling rate can be reasonably eliminated by appropriately managing the cooling interruption state. And reached the present invention.
  • the present invention A heating / holding step of heating the mold and holding it in a temperature range from the A3 transformation point to 1150 ° C, After the heating / holding step, a first cooling step of immersing the mold in an oil bath and cooling to a temperature at which the surface temperature of the mold is 700 ° C.
  • the mold is lifted from the oil tank to interrupt the oil cooling, and the surface temperature of the mold exceeds the Ms point, and the temperature difference between the mold surface and the inside Improved holding step for holding until the temperature is within 200 ° C.
  • a second cooling step of cooling at a rate of 1 ° C./min to 50 ° C./min until the surface temperature of the mold reaches 200 ° C .
  • the present invention provides the improved holding step in which the mold is lifted from the oil tank and the oil cooling is interrupted, and the immersion and the pulling are performed again in a temperature range where the surface temperature of the mold exceeds the Ms point. You may change to the process repeated until the temperature difference of the surface of a type
  • the mold is quenched by cooling at a rate of 1 ° C./min to 15 ° C./min until the temperature inside the mold drops from 400 ° C. to 250 ° C. More preferably, the second cooling step is oil cooling. More preferably, the environment in the first cooling step, the improved holding step, and the second cooling step is a non-oxidizing atmosphere.
  • the mold toughening method of the present invention can improve the surface toughness of the mold, it can be expected to improve the life of the mold.
  • the temperature of the heating / holding step of the present invention is set to a temperature range not lower than 1150 ° C. above the A3 transformation point. This is because if this temperature is lower than the A3 transformation point, the solid solution of carbides and alloy elements is insufficient, the hardness is low, and the high temperature strength is also low, so heat cracks are likely to occur. Further, when the temperature exceeds 1150 ° C., the carbide pinning the crystal grains also dissolves and the crystal grains grow abnormally. In order to suppress the occurrence of these problems and achieve the refinement of crystal grains, a temperature range from the A3 transformation point to below 1150 ° C. is required. Preferably it is the temperature range of 1010 degreeC or more and less than 1150 degreeC.
  • the cooling process of the present invention will be described.
  • the mold is immersed in an oil tank and cooled until the surface temperature of the mold becomes 700 ° C. or lower (temperature exceeding the Ms point) by oil cooling.
  • a process is performed (FIG. 1 (5)).
  • the reason why the first cooling step is oil-cooled in the present invention is that a region in which carbide precipitates at the grain boundaries can be surely avoided. This oil cooling surely increases the toughness of the mold surface.
  • the reason why oil cooling is selected in the present invention is that if it is oil cooling, the cooling capacity can be suitably adjusted by adjusting the temperature of the quenching oil.
  • the cooling rate is too high, and there is a high risk that the mold surface will undergo martensitic transformation in the first cooling process. This is because there is a possibility that the cooling of the mold surface slows down and passes through the carbide precipitation region.
  • the cooling speed of the mold surface in the first cooling step by oil cooling is approximately 80 ° C / min to 250 ° C / min, depending on the size of the mold, and it is possible to use conventional blast cooling or liquid spraying. Compared with the quenching method of the mold, the cooling rate is much faster. In the first cooling step, cooling until the surface temperature of the mold becomes 700 ° C.
  • the toughness of the mold surface and the vicinity thereof can be improved by the first cooling step by oil cooling described above.
  • an improved holding process is performed. (Fig. 1 (6) and Fig. 2) Since a remarkably fast cooling rate is applied in the first cooling step, the temperature difference between the mold surface and the inside becomes large. In the improved holding process, this is quickly reduced to alleviate the thermal stress. There are two methods for this improved holding process.
  • the first improved holding process is a method of lifting the mold from the oil tank, interrupting the oil rejection, and allowing it to cool.
  • This method a large amount of heat inside the mold is transferred to the mold surface, and the surface temperature rises. Thereby, the temperature difference between the mold surface and the inside is quickly reduced.
  • the second improved holding step is a method of repeatedly immersing the mold in the oil tank and pulling it up from the oil tank.
  • the temperature difference between the mold surface and the inside is quickly relaxed as in the first improved holding step, and the following effects can also be obtained.
  • (1) The amount of heat removed from the mold can be increased, and the cooling rate inside the mold can be increased. As a result, generation of pearlite inside the mold can be prevented more reliably.
  • (2) The cooling rate inside the mold surface and inside the mold is increased, and it is possible to cool the inside of the mold while avoiding the carbide precipitation region.
  • Since the cooling speed of the whole mold is fast, it is particularly suitable for quenching large molds of 200 kg or more.
  • the time required for quenching can be shortened and productivity can be improved.
  • the first time may be raised before the mold surface falls below 400 ° C. This is because the mold is often a heavy object, and if the mold is excessively cooled to the vicinity of the Ms point, the temperature difference between the mold surface and the inside of the mold is widened and the mold is easily deformed.
  • Which one of the first improvement holding process and the second improvement holding process described above is selected is determined, for example, in consideration of the weight and processing time of the mold, and the surface area and volume of the mold. good.
  • the second improved holding process is suitable for processing a mold of 100 kg or more in a short time.
  • the two improved holding steps described above are performed until the temperature difference between the surface and the inside of the mold reaches 200 ° C. or less by oil cooling. This is because if the temperature difference exceeds 200 ° C. and the second cooling step is performed, there is a risk of distortion or deformation due to the thermal stress difference. In order to prevent distortion and deformation more reliably, the temperature difference between the surface of the mold and the inside is preferably within 150 ° C. In addition, since some molds exceed 100 kg and are about 2 tons heavy, if the temperature is kept constant until the temperature is just above the Ms point as in the prior art, the processing time becomes longer and the productivity is significantly reduced.
  • the second cooling step may be performed when the temperature difference between the surface of the mold and the inside becomes 50 ° C. to 200 ° C. (preferably 50 ° C. to 150 ° C.). .
  • a constant temperature holding furnace or a salt bath which has been required in conventional marquenches, can be eliminated.
  • a second cooling step is performed in which the mold is cooled at a rate of 1 ° C./min to 50 ° C./min until the mold surface temperature reaches 200 ° C. (Fig. 1 (7))
  • the cooling rate of this second cooling step suppresses the generation of bainite of the material to be heat-treated (mold) during cooling, and also suppresses temperature unevenness due to rapid cooling, and controls toughness, quenching distortion, and cracking. This is the cooling rate necessary for this.
  • the cooling rate of the surface temperature is less than 1 ° C./min, the suppression of bainite formation is insufficient and the toughness is lowered.
  • a preferable cooling rate of the surface temperature is 10 ° C./min to 30 ° C./min.
  • the cooling rate at the center is also important from the viewpoint of controlling the metal structure, and the region of 400 ° C. to 250 ° C. where bainite is generated is cooled at 1 ° C./min to 15 ° C./min. good. If it is this range, the production
  • this second cooling step it is 5 ° C./min to 15 ° C./min, and the above effect can be obtained more reliably.
  • this second cooling step it is easy to adjust the cooling rate to the above-mentioned temperature range, and in particular, the metal structure inside the heat-treated material is not likely to be a massive bainite structure, and it is easy to obtain a cooling rate, which is oil cooling. Is good.
  • the environment in the first cooling step, the improved holding step, and the second cooling step described above is preferably a non-oxidizing atmosphere.
  • nitrogen, an inert gas, or a vacuum atmosphere (reduced pressure atmosphere) can be applied. This is because the quenching oil burns violently to cause a disaster such as a fire because the first cooling process is a rapid cooling from the quenching temperature to the oil tank.
  • oxidation and decarburization of the heat-treated material can be prevented.
  • the conditions for heating to the above quenching temperature will be described.
  • the low temperature side here means the temperature range below the A1 transformation point.
  • the condition for the low temperature side quenching temperature raising step is preferably a temperature rising rate of 200 ° C./h or less. This is because if the rate of temperature increase is too high, the material to be heat treated may be distorted, or the temperature difference between the surface layer portion and the inside of the material to be heat treated will increase, resulting in variations in crystal grains depending on the part. This is because it becomes higher.
  • a preferred rate of temperature rise is in the range of 50 ° C./h to 150 ° C./h.
  • the temperature holding process which hold maintains temperature more than once in the middle of the above-mentioned low temperature side hardening temperature rising process (FIG. 1 (2)).
  • the temperature holding step By performing the temperature holding step, the temperature unevenness when the heat-treated material is heated is reduced, so that deformation is reduced. Further, the processing residual stress generated at the time of mold manufacture is removed by preheating, and there is also an effect of suppressing abnormal growth of crystal grains using residual strain as a driving force when passing through the transformation point by subsequent heating.
  • the temperature holding step is preferably performed in the temperature range of A1 transformation point ⁇ 200 ° C. to A1 transformation point ⁇ 15 ° C.
  • the temperature range is from A1 transformation point to -70 ° C to A1 transformation point to -20 ° C.
  • the temperature holding time is intended to reduce the temperature unevenness when the heat-treated material is heated as described above, and therefore it is difficult to obtain the effect of reducing the temperature unevenness in a very short time. Therefore, it is preferable to set a time sufficient to reduce the temperature unevenness. Although the time cannot be generally determined depending on the weight and shape of the material to be heat-treated, it is preferable to hold it for about 0.5 to 5 hours from experience. If held for 0.75 hours or longer, the difference between the surface layer temperature and the internal temperature can be kept within 30 ° C., so it is preferable to hold it for 0.75 hours (45 minutes) or longer.
  • the temperature range from the A1 transformation point to the A3 transformation point may be heated at a rate of 100 ° C./h or more as a high temperature side temperature raising step (FIG. 1 (3)).
  • a high temperature side temperature raising step FOG. 1 (3)
  • the non-heat treated member can be adjusted to uniform crystal grains by adjusting the conditions of the temperature raising step up to the heating / holding step.
  • Quenching treatment was performed using the above sample.
  • the temperature conditions up to the heating / holding step are as follows. ⁇ First sample> The first sample was inserted into a quenching furnace, and the temperature increase was started. The conditions of the low temperature side temperature raising step (1) were 150 ° C./h, and the temperature holding step (2) was performed at 800 ° C. for 4 hours. Then, it heated up to 1025 degreeC on 150 degreeC / h conditions as a high temperature side temperature rising process (3), and moved to the heating and holding process (4).
  • ⁇ Second sample> The second sample was inserted into the quenching furnace and the temperature increase was started.
  • the conditions of the low temperature side temperature rising step (1) were 200 ° C./h, and the temperature holding step (2) was performed at 800 ° C. for 2 hours. Then, it heated up to 1025 degreeC on 200 degreeC / h conditions as a high temperature side temperature rising process (3), and moved to the heating and holding process (4).
  • the first improved holding step and measurement temperature applied to the first sample, and the second cooling step, and the second improved holding step and measured temperature applied to the second sample, and the second Table 3 shows the cooling process.
  • the temperature is a result of measuring the vicinity of the surface and the inside (center portion) by forming a drilling hole in the sample and inserting a thermocouple thermometer.
  • the Charpy impact test was a 2 mm U notch test.
  • Table 4 shows the Charpy impact values.
  • the “comparative example” in Table 4 is the “No. This is a test result of 6 alloys (JIS SKD61 equivalent alloy), which is due to cooling by the conventional marquenching method.
  • This comparative example (No. 6 of Patent Document 2) has almost the same thermal history as the example performed this time, and the quenching conditions are as follows. The test piece was heated at 75 ° C./h (low temperature side heating step (1)) and held at 800 ° C. for 1 hour (temperature holding step (2)), and the temperature was increased to 1020 ° C.
  • FIG. 2 shows the measured values of the heat pattern after the first cooling step for the second sample, and the simulation result when the dipping and lifting are performed only once (adopting the first improved holding step). (Corresponding to the result) was plotted. As shown in FIG. 2, it can be seen that the internal (center) cooling rate is faster when immersion and pulling are repeated. It can also be confirmed that the overall cooling rate is fast. From these results, it can be seen that the present invention in which the second improved holding step is particularly suitable for quenching a heavy mold. In addition, as a result of cutting out the test piece for micro observation from the surface side of the 2nd sample and investigating the presence or absence of grain boundary precipitation, as shown in FIG. 3, the grain boundary precipitate could hardly be confirmed. Moreover, the dimensional change amount was about 0.5 mm at the maximum, and it was confirmed that the dimensional change could be suppressed.
  • the mold quenching method of the present invention can improve the toughness of the mold, it can be expected to improve the life of the mold. Therefore, not only the mold but also the other application can be expected as a quenching method capable of improving toughness. In particular, the larger the heat-treated material, the better the improvement effect can be expected.

Abstract

A method for quenching a mold, comprising: a heating/retention step of heating the mold and retaining the mold at a temperature which is equal to or higher than an A3 transformation point and lower than 1150°C; a first cooling step of, subsequent to the heating/retention step, immersing the mold in an oil vessel to cool the mold by oil cooling until the surface of the mold has a temperature which is equal to or lower than 700°C and higher than an Ms point; an improved retention step of, subsequent to the first cooling step, pulling the mold out of the oil vessel to interrupt the oil cooling and retaining the mold until the surface of the mold has a temperature which is higher than the Ms point and at which the difference between the temperature of the surface of the mold and the temperature of the inside of the mold falls within 200°C; and a second cooling step of, subsequent to the improved retention step, cooling the mold at a cooling rate of 1-50°C/min until the surface of the mold has a temperature of 200°C.

Description

金型の焼入れ方法Mold quenching method
　本発明は、金型の焼入れ方法に関する。 The present invention relates to a mold quenching method.
　金型には高硬度、高靭性が要求され、その特性は焼入れ方法により大きく影響される。
　昇温の際には、合金元素を最大限固溶させるため、結晶粒が粗大化しない範囲で高めの焼入れ温度が選定される。また、焼入れの際には、高靭性を得るために、結晶粒を微細化するのと同時に、結晶粒界への炭化物析出を抑え、ベイナイト変態も防止する必要がある。このとき、急冷が求められるが、一方、急冷すると金型の歪み、変形が大きくなるため、冷却速度を適切にコントロールする必要がある。このため、従来から種々の提案がなされており、主として、焼入れ温度からの冷却条件を調整して、低歪みと高靭性の両立を達成するといった方法が採用されている。 The mold is required to have high hardness and high toughness, and its characteristics are greatly influenced by the quenching method.
When raising the temperature, a higher quenching temperature is selected so that the crystal grains are not coarsened in order to dissolve the alloy elements to the maximum. Further, at the time of quenching, in order to obtain high toughness, it is necessary to simultaneously refine the crystal grains, suppress carbide precipitation at the crystal grain boundaries, and prevent bainite transformation. At this time, rapid cooling is required. On the other hand, rapid cooling increases the distortion and deformation of the mold, and thus it is necessary to appropriately control the cooling rate. For this reason, various proposals have been made in the past, and a method of achieving both low strain and high toughness by adjusting the cooling conditions from the quenching temperature is mainly employed.
　例えば、特開２００６－３４２３７７号公報（特許文献１）には、焼入れ温度への加熱に続く冷却を、焼入れ温度から６００℃までの高温領域は２０℃／分～５℃／分とし、次いで恒温保持してから、４００℃から２００℃までの低温領域は１℃／分～１５℃／分となるように実施するマルクエンチ法が提案されている。これにより、焼割れを避けて、低歪みかつ高靱性の金型を得ることができるとされている。マルクエンチ法は、急冷による焼割れを防止するために、焼入れ時の冷却を、マルテンサイト変態の上部、またはそれよりやや高い温度で恒温保持して、各部の温度が均一化した後に冷却する処理である。 For example, in Japanese Patent Application Laid-Open No. 2006-342377 (Patent Document 1), cooling subsequent to heating to the quenching temperature is set to 20 ° C./min to 5 ° C./min in the high temperature region from the quenching temperature to 600 ° C. A marquenching method has been proposed in which the low temperature region from 400 ° C. to 200 ° C. is maintained at 1 ° C./min to 15 ° C./min after being held. Thus, it is said that a mold having low distortion and high toughness can be obtained while avoiding burning cracks. The marquenching method is a process in which the cooling during quenching is kept constant at the upper part of the martensite transformation or at a slightly higher temperature to cool after quenching, in order to prevent quench cracking due to rapid cooling. is there.
　また、本出願人は特開２００９－０７４１５５号公報（特許文献２）において、焼入れ温度の昇温側条件と、冷却側条件との両方に着目した金型の焼入れ方法を提案した。すなわち、Ａ１変態点からＡ３変態点の温度域を１００℃／ｈ以上の速度で加熱する焼入れ昇温工程の後、Ａ３変態点以上で１１５０℃を超えない温度域を保持する保持工程を行い、次いでＡ３変態点から６００℃までの温度域を５℃／分～２０℃／分の速度で冷却する高温側焼入冷却工程を行い、５００℃～４００℃までの温度域にて０．５時間～５時間保持する中断保持工程を経た後、４００℃～２００℃の温度域を１℃／分～１５℃／分の速度で冷却する低温側焼入冷却工程を経る方法である。 In addition, the present applicant has proposed a method for quenching a mold in JP 2009-074155 A (Patent Document 2), focusing on both the temperature raising side condition and the cooling side condition of the quenching temperature. That is, after the quenching and heating step of heating the temperature range from the A1 transformation point to the A3 transformation point at a rate of 100 ° C./h or more, a holding step for holding a temperature range not lower than 1150 ° C. above the A3 transformation point is performed. Next, a high temperature side quenching and cooling process is performed in which the temperature range from the A3 transformation point to 600 ° C. is cooled at a rate of 5 ° C./min to 20 ° C./min, and 0.5 hours in the temperature range from 500 ° C. to 400 ° C. This is a method in which a low temperature side quenching cooling step is performed in which the temperature range of 400 ° C. to 200 ° C. is cooled at a rate of 1 ° C./min to 15 ° C./min after the interruption holding step of holding for ˜5 hours.
　また、特開２００１－１５２２４３号公報（特許文献３）、特開２００２－３０９３１４号公報（特許文献４）は、同一出願人による焼入れ方法に関する技術が開示されている。具体的には、鋼材部品を、マルテンサイト変態開始点（Ｍｓ点）の直上温度まで急冷し、焼入れ油の中から取り出し、当該鋼材部品の保有熱によりマルテンサイト変態開始点（Ｍｓ点）の直上近傍の温度になるまで恒温保持する技術である。これにより、引用文献３の０００２段落に例示される歯車等の部品や、引用文献４の０００９段落に例示される角柱部材のコーナー部などの先鋭部、といった内部体積の小さなものを好適に焼入れ処理できる。 Also, Japanese Patent Application Laid-Open No. 2001-152243 (Patent Document 3) and Japanese Patent Application Laid-Open No. 2002-309314 (Patent Document 4) disclose techniques related to a quenching method by the same applicant. Specifically, a steel part is rapidly cooled to a temperature just above the martensite transformation start point (Ms point), taken out of the quenching oil, and immediately above the martensite transformation start point (Ms point) by the retained heat of the steel part. This is a technology that maintains a constant temperature until the temperature reaches a nearby temperature. Thus, a material having a small internal volume, such as a part such as a gear illustrated in paragraph 0002 of cited document 3 or a sharpened portion such as a corner portion of a prism member illustrated in paragraph 0009 of cited document 4, is preferably quenched. it can.
特開２００６－３４２３７７号公報JP 2006-342377 A 特開２００９－０７４１５５号公報JP 2009-074155 A 特開２００１－１５２２４３号公報JP 2001-152243 A 特開２００２－３０９３１４号公報JP 2002-309314 A
　本発明者らも、マルクエンチ法を検討してきたが、上述した特許文献１および特許文献２に開示される条件では、金型の表面の靭性が不足し、更に改善の余地があることを認識した。 The present inventors have also studied the marquenching method, but under the conditions disclosed in Patent Document 1 and Patent Document 2 described above, it was recognized that the toughness of the mold surface was insufficient and there was room for further improvement. .
　また、特許文献３および特許文献４に開示される技術を、歯車等より一般的に体積が大である金型に適用すると、冷却速度のコントロールが難しく、急冷の際、金型の表面がＭｓ点以下の温度に低下してしまう。このとき、金型内部は殆ど温度低下が見られず、焼入れ油から取り出すと、金型内部の保有熱により再び表面の温度がＭｓ点以上となり、金属組織が不安定となって、金型に硬さのばらつきが生じてしまう。また、重量の大きな金型の場合では、Ｍｓ点直上近傍の温度になるまで恒温保持しようとすると、それに必要な時間が長くなり過ぎ、生産性も著しく悪くなってしまう。 Further, when the techniques disclosed in Patent Document 3 and Patent Document 4 are applied to a mold having a larger volume than a gear or the like, it is difficult to control the cooling rate, and the surface of the mold is Ms during rapid cooling. The temperature falls below the point. At this time, there is almost no temperature drop inside the mold, and if it is taken out from the quenching oil, the surface temperature again becomes higher than the Ms point due to the retained heat inside the mold, the metal structure becomes unstable, and the mold becomes unstable. Hardness variation will occur. In the case of a heavy mold, if an attempt is made to maintain a constant temperature until it reaches a temperature just above the Ms point, the time required for the mold becomes too long, and the productivity is remarkably deteriorated.
　本発明の目的は、特に金型表面の靭性を合理的に改善できる焼入れ方法を提供することである。 An object of the present invention is to provide a quenching method capable of rationally improving the toughness of the mold surface.
　本発明者は、熱間金型の表面の靭性を改善するためには、
１）結晶粒界への炭化物析出を確実に避けるため、ベイナイトの変態領域（ベイナイトノーズ）を考慮した冷却速度よりも遥かに早い冷却速度を適用する必要があること、
　および、
２）この早い冷却速度の適用による表面と内部の温度差による弊害は、冷却中断状態を適正に管理することにより合理的に解消できること、
　を見出し本発明に到達した。 In order to improve the toughness of the surface of the hot mold, the present inventor
1) It is necessary to apply a cooling rate much faster than the cooling rate considering the transformation region of bainite (bainite nose) in order to reliably avoid carbide precipitation at the grain boundaries.
and,
2) The adverse effects due to the temperature difference between the surface and the interior due to the application of this fast cooling rate can be reasonably eliminated by appropriately managing the cooling interruption state.
And reached the present invention.
　すなわち本発明は、
　金型を加熱してＡ３変態点以上から１１５０℃未満の温度範囲に保持する加熱・保持工程と、
　前記加熱・保持工程の後、前記金型を油槽に浸漬し、油冷により金型の表面温度が７００℃以下であってＭｓ点は超えている温度まで冷却する第一の冷却工程と、
　前記第一の冷却工程の後、前記金型を油槽から引き上げて油冷を中断し、前記金型の表面温度がＭｓ点を超える温度域であって前記金型の表面と内部との温度差が２００℃以内となるまで保持する改良保持工程と、
　前記改良保持工程の後、前記金型の表面温度が２００℃となるまで１℃／分～５０℃／分の速度で冷却する第二の冷却工程と、
　を具備したことを特徴とする金型の焼入れ方法である。 That is, the present invention
A heating / holding step of heating the mold and holding it in a temperature range from the A3 transformation point to 1150 ° C,
After the heating / holding step, a first cooling step of immersing the mold in an oil bath and cooling to a temperature at which the surface temperature of the mold is 700 ° C. or less and the Ms point is exceeded by oil cooling;
After the first cooling step, the mold is lifted from the oil tank to interrupt the oil cooling, and the surface temperature of the mold exceeds the Ms point, and the temperature difference between the mold surface and the inside Improved holding step for holding until the temperature is within 200 ° C.,
After the improved holding step, a second cooling step of cooling at a rate of 1 ° C./min to 50 ° C./min until the surface temperature of the mold reaches 200 ° C .;
It is the hardening method of the metal mold | die characterized by comprising.
　また本発明は、前記改良保持工程を、前記金型を油槽から引き上げて油冷を中断し、再度の浸漬および引き上げを、前記金型の表面温度がＭｓ点を超える温度域であって前記金型の表面と内部との温度差が２００℃以内となるまで繰り返す工程に変更しても良い。このとき、引き上げ回数が３回以上であることが好ましい。
　好ましくは、前記第二の冷却工程では、金型内部の温度が４００℃から２５０℃に下がるまで１℃／分～１５℃／分の速度で冷却する金型の焼入れ方法である。
　更に好ましくは、前記第二の冷却工程は、油冷とする。
　更に好ましくは、前記第一の冷却工程、改良保持工程、および、第二の冷却工程における環境は、非酸化性雰囲気とする。 Further, the present invention provides the improved holding step in which the mold is lifted from the oil tank and the oil cooling is interrupted, and the immersion and the pulling are performed again in a temperature range where the surface temperature of the mold exceeds the Ms point. You may change to the process repeated until the temperature difference of the surface of a type | mold and an inside becomes less than 200 degreeC. At this time, it is preferable that the number of pull-ups is 3 or more.
Preferably, in the second cooling step, the mold is quenched by cooling at a rate of 1 ° C./min to 15 ° C./min until the temperature inside the mold drops from 400 ° C. to 250 ° C.
More preferably, the second cooling step is oil cooling.
More preferably, the environment in the first cooling step, the improved holding step, and the second cooling step is a non-oxidizing atmosphere.
　本発明の金型の焼入れ方法により、特に金型の表面靭性を改善することができるため、金型の寿命を向上させることが期待できる。 Since the mold toughening method of the present invention can improve the surface toughness of the mold, it can be expected to improve the life of the mold.
本発明の焼入れ条件の一例を示したヒートパターンの概要図である。なお、改良保持工程は、本図では便宜上直線として表示している。It is the schematic of the heat pattern which showed an example of the quenching conditions of this invention. In addition, the improvement holding process is displayed as a straight line for the sake of convenience in this drawing. 本発明の第一の冷却工程以降の金型冷却時の温度実測値と、シミュレーション結果とを示した図である。It is the figure which showed the temperature measurement value at the time of the metal mold | die cooling after the 1st cooling process of this invention, and a simulation result. 本発明の金型の焼入れ方法を適用し、焼戻しを行った後の顕微鏡写真である。It is a microscope picture after applying the hardening method of the metal mold | die of this invention and performing tempering.
　上述したように、本発明の重要な特徴は、金型の焼入れ方法において、焼入れ時の冷却条件を最適化したことにある。以下に本発明を説明する。
　先ず、加熱・保持工程について説明する（図１（４））。
　本発明の加熱・保持工程の温度は、Ａ３変態点以上で１１５０℃を超えない温度域に設定する。これは、この温度がＡ３変態点未満であると、炭化物や合金元素の固溶が不十分で、硬さが低く、また高温強度も低いためヒートクラックが発生しやすくなるからである。また、温度が１１５０℃を超えると、結晶粒をピンニングしている炭化物も固溶し、結晶粒が異常成長するからである。
　これらの問題の発生を抑制し、結晶粒の微細化を達成するには、Ａ３変態点以上で１１５０℃未満の温度範囲が必要となる。好ましくは１０１０℃以上１１５０℃未満の温度範囲である。 As described above, an important feature of the present invention is that the cooling condition during quenching is optimized in the mold quenching method. The present invention will be described below.
First, the heating / holding step will be described (FIG. 1 (4)).
The temperature of the heating / holding step of the present invention is set to a temperature range not lower than 1150 ° C. above the A3 transformation point. This is because if this temperature is lower than the A3 transformation point, the solid solution of carbides and alloy elements is insufficient, the hardness is low, and the high temperature strength is also low, so heat cracks are likely to occur. Further, when the temperature exceeds 1150 ° C., the carbide pinning the crystal grains also dissolves and the crystal grains grow abnormally.
In order to suppress the occurrence of these problems and achieve the refinement of crystal grains, a temperature range from the A3 transformation point to below 1150 ° C. is required. Preferably it is the temperature range of 1010 degreeC or more and less than 1150 degreeC.
　次に、本発明の冷却工程について説明する。
　本発明では、加熱・保持工程の後、金型を油槽に浸漬し油冷により金型の表面温度が７００℃以下の温度（但し、Ｍｓ点を超える温度）となるまで冷却する第一の冷却工程を行う（図１（５））。
　本発明で第一の冷却工程を油冷とするのは、結晶粒界に炭化物が析出する領域を確実に避けることができるためである。この油冷により、金型表面の靭性が確実に高まる。
　本発明で油冷を選択したのは、油冷であると焼入れ油の温度の調節により、冷却能を好適に調節することも可能であるためである。例えば、冷却能の高い水冷とすると冷却速度が速すぎて、第一の冷却工程で金型表面がマルテンサイト変態する危険性が高く、また、冷却能の低い衝風冷却や液体噴霧では、金型表面の冷却が遅くなって炭化物析出領域を経る可能性があるためである。
　なお、油冷による第一の冷却工程の金型表面の冷却速度は金型の大きさにもよるが、おおよそ８０℃／分～２５０℃／分程度であり、従来の衝風冷却や液体噴霧による金型の焼入れ方法と比較して遥かに速い冷却速度である。
　また、第一の冷却工程において、金型の表面温度が７００℃以下となるまで冷却するのは、７００℃を超える温度領域で油冷を中断すると、結晶粒界に炭化物が析出する可能性があるためである。析出の可能性をなくすためには、金型の表面温度がＭｓ点を超えてＭｓ点＋２００℃の温度範囲に至るまで油冷を行う。なお、表面温度をＭｓ点以下まで冷却すると、金型の表面近傍の金属組織がマルテンサイト変態して、次の改良保持工程時で金属組織が不均一となる。そのため、本発明では表面温度の管理が重要となる。
　本発明では上述した油冷による第一の冷却工程により、特に金型表面とその近傍領域の靭性を向上させることができる。 Next, the cooling process of the present invention will be described.
In the present invention, after the heating / holding step, the mold is immersed in an oil tank and cooled until the surface temperature of the mold becomes 700 ° C. or lower (temperature exceeding the Ms point) by oil cooling. A process is performed (FIG. 1 (5)).
The reason why the first cooling step is oil-cooled in the present invention is that a region in which carbide precipitates at the grain boundaries can be surely avoided. This oil cooling surely increases the toughness of the mold surface.
The reason why oil cooling is selected in the present invention is that if it is oil cooling, the cooling capacity can be suitably adjusted by adjusting the temperature of the quenching oil. For example, if water cooling with high cooling capacity is used, the cooling rate is too high, and there is a high risk that the mold surface will undergo martensitic transformation in the first cooling process. This is because there is a possibility that the cooling of the mold surface slows down and passes through the carbide precipitation region.
The cooling speed of the mold surface in the first cooling step by oil cooling is approximately 80 ° C / min to 250 ° C / min, depending on the size of the mold, and it is possible to use conventional blast cooling or liquid spraying. Compared with the quenching method of the mold, the cooling rate is much faster.
In the first cooling step, cooling until the surface temperature of the mold becomes 700 ° C. or lower is that if oil cooling is interrupted in a temperature range exceeding 700 ° C., carbides may be precipitated at the crystal grain boundaries. Because there is. In order to eliminate the possibility of precipitation, oil cooling is performed until the surface temperature of the mold exceeds the Ms point and reaches the temperature range of Ms point + 200 ° C. When the surface temperature is cooled to the Ms point or lower, the metal structure near the surface of the mold undergoes martensitic transformation, and the metal structure becomes non-uniform during the next improved holding step. Therefore, management of the surface temperature is important in the present invention.
In the present invention, the toughness of the mold surface and the vicinity thereof can be improved by the first cooling step by oil cooling described above.
　続いて本発明では、改良保持工程を行う。（図１（６）および図２）
　第一の冷却工程では著しく早い冷却速度を適用するため、金型の表面と内部の温度差が大きくなる。改良保持工程ではこれを速やかに少なくして熱応力を緩和する。
　この改良保持工程には二つの方法がある。 Subsequently, in the present invention, an improved holding process is performed. (Fig. 1 (6) and Fig. 2)
Since a remarkably fast cooling rate is applied in the first cooling step, the temperature difference between the mold surface and the inside becomes large. In the improved holding process, this is quickly reduced to alleviate the thermal stress.
There are two methods for this improved holding process.
　第一の改良保持工程は、金型を油槽から引き上げ、油却を中断して放冷したままにする方法である。この方法では、金型内部の熱が金型表面に多量に伝達され表面温度が上昇してくる。これにより金型表面と内部の温度差が速やかに緩和されていく。 The first improved holding process is a method of lifting the mold from the oil tank, interrupting the oil rejection, and allowing it to cool. In this method, a large amount of heat inside the mold is transferred to the mold surface, and the surface temperature rises. Thereby, the temperature difference between the mold surface and the inside is quickly reduced.
　第二の改良保持工程は、金型の油槽への浸漬と油槽からの引き上げを繰り返す方法である。この第二の改良保持工程では、第一改良保持工程と同様に金型表面と内部の温度差が速やかに緩和されていく他、以下の効果も得ることができる。
（１）金型の抜熱量を大きくすることができ、金型内部の冷却速度を速めることができる。その結果、金型内部のパーライトの生成をより確実に防止することが可能となる。
（２）金型表面および金型内部の冷却速度が速くなり、金型内部まで炭化物析出領域を避けて冷却することが可能となる。
（３）金型全体の冷却速度が速いことから、特に２００ｋｇ以上の大型の金型の焼入れに好適である。
（４）焼入れに要する時間を短縮でき生産性を向上することができる。
　このうち、特に（１）、（２）及び（４）の効果をより確実に得るには、Ｍｓ点＋２５℃以上の温度範囲で第二の改良保持工程に移行することが好ましい。特に一回目は金型表面が４００℃を下回らないうちに引き上げると良い。これは、金型が重量物であることが多く、過度にＭｓ点近傍まで冷却すると、金型表面と金型内部との温度差が広がって変形し易くなるためである。
　また、金型表面の温度が直近の引き上げ時の表面温度から２００℃（好ましくは１００℃）上昇するまでに次の浸漬を開始すると良い。 The second improved holding step is a method of repeatedly immersing the mold in the oil tank and pulling it up from the oil tank. In the second improved holding step, the temperature difference between the mold surface and the inside is quickly relaxed as in the first improved holding step, and the following effects can also be obtained.
(1) The amount of heat removed from the mold can be increased, and the cooling rate inside the mold can be increased. As a result, generation of pearlite inside the mold can be prevented more reliably.
(2) The cooling rate inside the mold surface and inside the mold is increased, and it is possible to cool the inside of the mold while avoiding the carbide precipitation region.
(3) Since the cooling speed of the whole mold is fast, it is particularly suitable for quenching large molds of 200 kg or more.
(4) The time required for quenching can be shortened and productivity can be improved.
Among these, in order to obtain the effects of (1), (2) and (4) more reliably, it is preferable to shift to the second improved holding step in a temperature range of Ms point + 25 ° C. or higher. In particular, the first time may be raised before the mold surface falls below 400 ° C. This is because the mold is often a heavy object, and if the mold is excessively cooled to the vicinity of the Ms point, the temperature difference between the mold surface and the inside of the mold is widened and the mold is easily deformed.
Moreover, it is good to start the next immersion until the temperature of the mold surface rises by 200 ° C. (preferably 100 ° C.) from the surface temperature at the time of the latest pulling.
　これにより、金型表面のマルテンサイト変態を防止し、抜熱量を大きくして処理時間を短縮することが可能となる。油槽への浸漬回数が増えるほど前述の効果が特に得やすくなり、引き上げは３回以上繰り返すのが良い。特に２００ｋｇを超える大型の金型の場合では、上記のように、最初の引き上げ温度（表面温度）を高めとし、順次引き上げ温度を下げるようにして、浸漬と引き上げの繰り返しの回数を増やすのが好ましい。 This makes it possible to prevent martensite transformation on the mold surface, increase the heat removal amount, and shorten the processing time. As the number of times of immersion in the oil tank increases, the above-described effect is particularly easily obtained, and the pulling up is preferably repeated three times or more. In particular, in the case of a large mold exceeding 200 kg, it is preferable to increase the number of repetitions of dipping and pulling by increasing the initial pulling temperature (surface temperature) and decreasing the pulling temperature sequentially as described above. .
　上述した第一の改良保持工程と第二の改良保持工程の何れを選択するかは、例えば、金型の重量や処理時間、また、金型の表面積と体積とを考慮して判断するのが良い。例えば、１００ｋｇ以上の金型を短時間で処理するには第二の改良保持工程が適している。 Which one of the first improvement holding process and the second improvement holding process described above is selected is determined, for example, in consideration of the weight and processing time of the mold, and the surface area and volume of the mold. good. For example, the second improved holding process is suitable for processing a mold of 100 kg or more in a short time.
　上述した二つの改良保持工程とも、油冷によって金型の表面と内部の温度差が２００℃以内に至るまで行う。温度差が２００℃を越えたまま第二の冷却工程に移ると、熱応力差に起因する歪みや変形のおそれがあるためである。より確実に歪みや変形を防止するには金型の表面と内部の温度差を１５０℃以内とすると良い。
　なお、金型は１００ｋｇを越え約２トン程度の重量物のものもあるため、従来技術のようにＭｓ点の直上近傍の温度になるまで恒温保持すると処理時間が長くなり、生産性を著しく低下させる。そのため、使用の態様により、例えば、金型の表面と内部との温度差が５０℃～２００℃（好ましくは５０℃～１５０℃）となった時点で第二の冷却工程を行っても差し支えない。
　この改良保持工程を採用することにより、従来のマルクエンチで必要とされていた恒温保持炉、あるいはソルトバスを不要とすることができることも本発明の大きな特徴である。 The two improved holding steps described above are performed until the temperature difference between the surface and the inside of the mold reaches 200 ° C. or less by oil cooling. This is because if the temperature difference exceeds 200 ° C. and the second cooling step is performed, there is a risk of distortion or deformation due to the thermal stress difference. In order to prevent distortion and deformation more reliably, the temperature difference between the surface of the mold and the inside is preferably within 150 ° C.
In addition, since some molds exceed 100 kg and are about 2 tons heavy, if the temperature is kept constant until the temperature is just above the Ms point as in the prior art, the processing time becomes longer and the productivity is significantly reduced. Let Therefore, depending on the mode of use, for example, the second cooling step may be performed when the temperature difference between the surface of the mold and the inside becomes 50 ° C. to 200 ° C. (preferably 50 ° C. to 150 ° C.). .
By adopting this improved holding step, it is a major feature of the present invention that a constant temperature holding furnace or a salt bath, which has been required in conventional marquenches, can be eliminated.
　次いで、改良保持工程の後、金型の表面温度が２００℃となるまで１℃／分～５０℃／分の速度で冷却する第二の冷却工程を行う。（図１（７））
　この第二の冷却工程の冷却速度は、冷却中の被熱処理材（金型）のベイナイトの生成を抑制し、また、急冷による温度むらも抑制し、靭性と焼入れ歪み、および、割れを制御するのに必要な冷却速度である。
　表面温度の冷却速度が１℃／分未満では、ベイナイトの生成抑制が不十分となり靭性が低下する。５０℃／分を越えるとマルテンサイト変態中の製品の温度差が大きくなり、冷却中の温度むらにより、歪みが大きくなり易く、焼割れのリスクも大きくなる。好ましい表面温度の冷却速度は１０℃／分～３０℃／分である。
　第二の冷却工程は、金属組織制御の観点から、中心部の冷却速度も重要であり、ベイナイトが生成する４００℃～２５０℃の領域を１℃／分～１５℃／分で冷却するのが良い。この範囲であれば、粗大なベイナイトの生成を抑制し、より確実に靭性を向上させることができる。好ましくは、５℃／分～１５℃／分であり、前記の効果をより確実に得ることができる。
　この第二の冷却工程では、冷却速度を上述の温度範囲に調整するのが容易であり、特に被熱処理材の内部の金属組織が塊状ベイナイト組織となり難い冷却速度を得やすい、油冷とするのが良い。 Next, after the improved holding step, a second cooling step is performed in which the mold is cooled at a rate of 1 ° C./min to 50 ° C./min until the mold surface temperature reaches 200 ° C. (Fig. 1 (7))
The cooling rate of this second cooling step suppresses the generation of bainite of the material to be heat-treated (mold) during cooling, and also suppresses temperature unevenness due to rapid cooling, and controls toughness, quenching distortion, and cracking. This is the cooling rate necessary for this.
When the cooling rate of the surface temperature is less than 1 ° C./min, the suppression of bainite formation is insufficient and the toughness is lowered. If it exceeds 50 ° C./min, the temperature difference of the product during the martensitic transformation becomes large, and due to the temperature unevenness during cooling, distortion tends to increase and the risk of burning cracks also increases. A preferable cooling rate of the surface temperature is 10 ° C./min to 30 ° C./min.
In the second cooling step, the cooling rate at the center is also important from the viewpoint of controlling the metal structure, and the region of 400 ° C. to 250 ° C. where bainite is generated is cooled at 1 ° C./min to 15 ° C./min. good. If it is this range, the production | generation of coarse bainite can be suppressed and toughness can be improved more reliably. Preferably, it is 5 ° C./min to 15 ° C./min, and the above effect can be obtained more reliably.
In this second cooling step, it is easy to adjust the cooling rate to the above-mentioned temperature range, and in particular, the metal structure inside the heat-treated material is not likely to be a massive bainite structure, and it is easy to obtain a cooling rate, which is oil cooling. Is good.
　本発明では、上述した前記第一の冷却工程、改良保持工程、および、第二の冷却工程における環境は、非酸化性雰囲気とするのがよい。具体的には窒素や不活性ガスあるいは真空雰囲気（減圧雰囲気）が適用できる。
　これは、特に、第一の冷却工程が焼入れ温度から油槽への急冷を行うものであるため、焼入れ油が激しく燃焼して火災等の災害が生じる可能性をなくすためである。
　また、非酸化性雰囲気とすると、被熱処理材の酸化や脱炭も防止できる。 In the present invention, the environment in the first cooling step, the improved holding step, and the second cooling step described above is preferably a non-oxidizing atmosphere. Specifically, nitrogen, an inert gas, or a vacuum atmosphere (reduced pressure atmosphere) can be applied.
This is because the quenching oil burns violently to cause a disaster such as a fire because the first cooling process is a rapid cooling from the quenching temperature to the oil tank.
In addition, when the non-oxidizing atmosphere is used, oxidation and decarburization of the heat-treated material can be prevented.
　次に、上述の焼入れ温度まで加熱する条件について述べておく。
　本発明では、焼入れ温度に加熱する条件として、低温側焼入れ昇温工程の昇温条件も併せて調整すると更に好ましい（図１（１））。なお、ここでいう低温側とは、Ａ１変態点以下の温度領域をいう。
　低温側焼入れ昇温工程の条件は、２００℃／ｈ以下の昇温速度とするのが良い。これは、この昇温速度が速すぎると、被熱処理材に歪みが生じたり、被熱処理材の表層部と内部との温度差が大きくなってしまい、部位による結晶粒のばらつきが生じる可能性が高くなるためである。好ましい昇温速度は５０℃／ｈ～１５０℃／ｈの範囲である。 Next, the conditions for heating to the above quenching temperature will be described.
In the present invention, it is more preferable to adjust the temperature raising condition in the low temperature side quenching temperature raising step as the condition for heating to the quenching temperature (FIG. 1 (1)). In addition, the low temperature side here means the temperature range below the A1 transformation point.
The condition for the low temperature side quenching temperature raising step is preferably a temperature rising rate of 200 ° C./h or less. This is because if the rate of temperature increase is too high, the material to be heat treated may be distorted, or the temperature difference between the surface layer portion and the inside of the material to be heat treated will increase, resulting in variations in crystal grains depending on the part. This is because it becomes higher. A preferred rate of temperature rise is in the range of 50 ° C./h to 150 ° C./h.
　上述の低温側焼入れ昇温工程の途中で、１回以上の温度保持をする温度保持工程を行ってもよい（図１（２））。
　温度保持工程を行うことにより、被熱処理材を加熱したときの温度むらが軽減されるため、変形が少なくなる。また、金型製作時に発生した加工残留応力も予熱することで除去され、その後の加熱で変態点を通過する際に残留歪みを駆動力にした結晶粒の異常成長も抑制する効果もある。この効果をより確実に得るには、Ａ１変態点－２００℃～Ａ１変態点－１５℃の温度範囲で温度保持工程を行うとよい。より好ましくはＡ１変態点－７０℃～Ａ１変態点－２０℃の温度範囲である。
　なお、温度保持をする時間は、上述のように被熱処理材を加熱したときの温度むらを軽減することを目的とするため、余りに短時間では温度むらの軽減効果が得難くなる。そのため、温度むらを軽減させるのに十分な時間とするのが良い。被熱処理材の重量や形状によって時間は一概に定めることはできないが、経験上、０．５時間～５時間程度保持するのが好ましい。０．７５時間以上保持すると、表層温度と内部の温度差を３０℃以内とすることが可能となるため、好ましくは０．７５時間（４５分）以上保持するのが良い。 You may perform the temperature holding process which hold | maintains temperature more than once in the middle of the above-mentioned low temperature side hardening temperature rising process (FIG. 1 (2)).
By performing the temperature holding step, the temperature unevenness when the heat-treated material is heated is reduced, so that deformation is reduced. Further, the processing residual stress generated at the time of mold manufacture is removed by preheating, and there is also an effect of suppressing abnormal growth of crystal grains using residual strain as a driving force when passing through the transformation point by subsequent heating. In order to obtain this effect more reliably, the temperature holding step is preferably performed in the temperature range of A1 transformation point−200 ° C. to A1 transformation point−15 ° C. More preferably, the temperature range is from A1 transformation point to -70 ° C to A1 transformation point to -20 ° C.
Note that the temperature holding time is intended to reduce the temperature unevenness when the heat-treated material is heated as described above, and therefore it is difficult to obtain the effect of reducing the temperature unevenness in a very short time. Therefore, it is preferable to set a time sufficient to reduce the temperature unevenness. Although the time cannot be generally determined depending on the weight and shape of the material to be heat-treated, it is preferable to hold it for about 0.5 to 5 hours from experience. If held for 0.75 hours or longer, the difference between the surface layer temperature and the internal temperature can be kept within 30 ° C., so it is preferable to hold it for 0.75 hours (45 minutes) or longer.
　温度保持工程の後、高温側昇温工程として、Ａ１変態点からＡ３変態点の温度域を１００℃／ｈ以上の速度で加熱するとよい（図１（３））。これは、フェライトから新しいオーステナイトの結晶粒が生成するときに、加熱速度が速いと、平衡温度からの過熱効果により、オーステナイトの核生成密度が高く、結晶粒を微細化する作用が得られるためである。
　以上、加熱・保持工程までの昇温工程の条件を調整することで、非熱処理部材を均一な結晶粒に調整できる。 After the temperature holding step, the temperature range from the A1 transformation point to the A3 transformation point may be heated at a rate of 100 ° C./h or more as a high temperature side temperature raising step (FIG. 1 (3)). This is because when a new austenite crystal grain is produced from ferrite, if the heating rate is fast, the austenite nucleation density is high due to the overheating effect from the equilibrium temperature, and the effect of refining the crystal grain is obtained. is there.
As described above, the non-heat treated member can be adjusted to uniform crystal grains by adjusting the conditions of the temperature raising step up to the heating / holding step.
　以下の実施例で本発明を更に詳しく説明する。
　表１に示す組成の熱間ダイス用金型材料から、３００ｍｍ（ｗ）×３００ｍｍ（ｌ）×３００ｍｍ（ｔ）のブロックを切り出して、第一の改良保持工程を施す第一の試料と、第二の改良保持工程を施す第二の資料とを作成した。用意した合金は何れもＪＩＳ－ＳＫＤ６１相当材である。
　この合金のＡ１変態点は８５０℃、Ａ３変態点は８９５℃、Ｍｓ点は３００℃、粒界炭化物析出領域のノーズは、７００℃－２０分である。 The following examples further illustrate the present invention.
From the mold material for hot dies having the composition shown in Table 1, a block of 300 mm (w) × 300 mm (l) × 300 mm (t) is cut out, and a first sample subjected to a first improved holding process, A second material for the second improved holding process was prepared. All the prepared alloys are JIS-SKD61 equivalent materials.
The A1 transformation point of this alloy is 850 ° C., the A3 transformation point is 895 ° C., the Ms point is 300 ° C., and the nose of the grain boundary carbide precipitation region is 700 ° C.-20 minutes.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　上記の試料を用いて焼入れ処理をした。加熱・保持工程までの温度条件は、以下の通りである。
＜第一の試料＞
　第一の試料を焼入れ炉に挿入し、昇温を開始した。低温側昇温工程（１）の条件は１５０℃／ｈとし、８００℃で４時間の温度保持工程（２）を実施した。その後、高温側昇温工程（３）として１５０℃／ｈの条件で１０２５℃まで昇温して、加熱・保持工程（４）に移った。
＜第二の試料＞
　第二の試料を焼入れ炉に挿入し、昇温を開始した。低温側昇温工程（１）の条件は２００℃／ｈとし、８００℃で２時間の温度保持工程（２）を実施した。その後、高温側昇温工程（３）として２００℃／ｈの条件で１０２５℃まで昇温して、加熱・保持工程（４）に移った。 Quenching treatment was performed using the above sample. The temperature conditions up to the heating / holding step are as follows.
<First sample>
The first sample was inserted into a quenching furnace, and the temperature increase was started. The conditions of the low temperature side temperature raising step (1) were 150 ° C./h, and the temperature holding step (2) was performed at 800 ° C. for 4 hours. Then, it heated up to 1025 degreeC on 150 degreeC / h conditions as a high temperature side temperature rising process (3), and moved to the heating and holding process (4).
<Second sample>
The second sample was inserted into the quenching furnace and the temperature increase was started. The conditions of the low temperature side temperature rising step (1) were 200 ° C./h, and the temperature holding step (2) was performed at 800 ° C. for 2 hours. Then, it heated up to 1025 degreeC on 200 degreeC / h conditions as a high temperature side temperature rising process (3), and moved to the heating and holding process (4).
　続く、第一の試料に施す第一の改良保持工程および測定温度、並びに、第二の冷却工程を表２に、第二の試料に施す第二の改良保持工程および測定温度、並びに、第二の冷却工程を表３に示す。なお、温度は、何れも試料にドリルで切削孔を形成して熱電対温度計を挿入し、表面近傍と内部（中心部）を測定した結果である。 The first improved holding step and measurement temperature applied to the first sample, and the second cooling step, and the second improved holding step and measured temperature applied to the second sample, and the second Table 3 shows the cooling process. The temperature is a result of measuring the vicinity of the surface and the inside (center portion) by forming a drilling hole in the sample and inserting a thermocouple thermometer.
Figure JPOXMLDOC01-appb-T000002
  
Figure JPOXMLDOC01-appb-T000002
  
Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000003
　上記工程終了の後、４５ＨＲＣに焼戻しをして、シャルピー衝撃値を評価した。シャルピー衝撃試験は２ｍｍＵノッチ試験を実施した。シャルピー衝撃値を表４に示す。なお、表４の「比較例」は特許文献２のＮｏ．６合金（ＪＩＳ　ＳＫＤ６１相当合金）の試験結果であり、従来のマルクエンチ法による冷却によるものである。この比較例（特許文献２のＮｏ．６）は、今回行った実施例とほぼ同じ熱履歴であり、その焼入れ条件は以下の通りである。
　試験片を、７５℃／ｈで昇温し（低温側昇温工程（１））、８００℃で１時間保持し（温度保持工程（２））、１７５℃／ｈの条件で１０２０℃まで昇温して（高温側昇温工程（３））、加熱・保持工程（４）に移した。その後、Ａ３～６００℃の温度域については１２℃／分の速度で冷却し、４００℃で１時間の保持を行い、４００℃～２００℃の温度域については１０℃／分の速度で冷却を行った。冷却は不活性ガス雰囲気でガス加圧量を制御しながら行ったものである。 After completion of the above steps, tempering was performed to 45HRC and the Charpy impact value was evaluated. The Charpy impact test was a 2 mm U notch test. Table 4 shows the Charpy impact values. The “comparative example” in Table 4 is the “No. This is a test result of 6 alloys (JIS SKD61 equivalent alloy), which is due to cooling by the conventional marquenching method. This comparative example (No. 6 of Patent Document 2) has almost the same thermal history as the example performed this time, and the quenching conditions are as follows.
The test piece was heated at 75 ° C./h (low temperature side heating step (1)) and held at 800 ° C. for 1 hour (temperature holding step (2)), and the temperature was increased to 1020 ° C. under the condition of 175 ° C./h. It was heated (high temperature side temperature raising step (3)), and moved to the heating / holding step (4). Thereafter, the temperature range of A3 to 600 ° C is cooled at a rate of 12 ° C / min, held at 400 ° C for 1 hour, and the temperature range of 400 ° C to 200 ° C is cooled at a rate of 10 ° C / min. went. Cooling is performed while controlling the amount of gas pressurization in an inert gas atmosphere.
Figure JPOXMLDOC01-appb-T000004
Figure JPOXMLDOC01-appb-T000004
　表４に示したように、本発明の焼入れ方法を適用したものは、従来のマルクエンチ法を適用したものより優れた靭性を有することが確認できた。また、試料の大きさと重量が同じであるにも関わらず、第二の試料の内部のシャルピー衝撃値が向上している。これは、金型内部の冷却速度が速まったため、金型内部においても炭化物の粒界析出が抑制できていることを示している。 As shown in Table 4, it was confirmed that the one to which the quenching method of the present invention was applied had toughness superior to that to which the conventional marquenching method was applied. Moreover, although the sample size and weight are the same, the Charpy impact value inside the second sample is improved. This indicates that the grain boundary precipitation of carbides can be suppressed even inside the mold because the cooling rate inside the mold is increased.
　また、図２に、第二の試料について、第一の冷却工程以降のヒートパターンの実測値を示すと共に、浸漬と引き上げを１回のみ行った場合のシミュレーション結果（第一の改良保持工程の採用結果に相当）をプロットした。
　図２に示したように、浸漬と引き上げを繰り返し行ったほうが内部（中心部）の冷却速度が速いことが分かる。また、全体の冷却速度も早いことが確認できる。これらの結果から、特に、第二の改良保持工程を施す本発明は、重量の大きな金型の焼入れに適していることが分かる。
　なお、第二の試料の表面側からミクロ観察用試験片を切り出して、粒界析出の有無を調査した結果、図３に示したように粒界析出物は殆ど確認することができなかった。また、寸法変化量も最大で０．５ｍｍ程度であり、寸法変化も抑制できていることを確認した。 FIG. 2 shows the measured values of the heat pattern after the first cooling step for the second sample, and the simulation result when the dipping and lifting are performed only once (adopting the first improved holding step). (Corresponding to the result) was plotted.
As shown in FIG. 2, it can be seen that the internal (center) cooling rate is faster when immersion and pulling are repeated. It can also be confirmed that the overall cooling rate is fast. From these results, it can be seen that the present invention in which the second improved holding step is particularly suitable for quenching a heavy mold.
In addition, as a result of cutting out the test piece for micro observation from the surface side of the 2nd sample and investigating the presence or absence of grain boundary precipitation, as shown in FIG. 3, the grain boundary precipitate could hardly be confirmed. Moreover, the dimensional change amount was about 0.5 mm at the maximum, and it was confirmed that the dimensional change could be suppressed.
　本発明の金型の焼入れ方法は、金型の靭性を改善することができるため、金型の寿命を向上させることが期待できる。そのため、金型に限らず、靭性を改善可能な焼入れ方法として他の用途への適用も期待できる。特に大型の被熱処理材であるほど、その改善効果が期待できる。 Since the mold quenching method of the present invention can improve the toughness of the mold, it can be expected to improve the life of the mold. Therefore, not only the mold but also the other application can be expected as a quenching method capable of improving toughness. In particular, the larger the heat-treated material, the better the improvement effect can be expected.
１　低温側昇温工程
２　温度保持工程
３　高温側昇温工程
４　加熱・保持工程
５　第一の冷却工程
６　改良保持工程
７　第二の冷却工程
  DESCRIPTION OF SYMBOLS 1 Low temperature side temperature rising process 2 Temperature holding process 3 High temperature side temperature rising process 4 Heating / holding process 5 First cooling process 6 Improved holding process 7 Second cooling process

Claims (6)

  1. 　金型を加熱してＡ３変態点以上から１１５０℃未満の温度範囲に保持する加熱・保持工程と、
    　前記加熱・保持工程の後、前記金型を油槽に浸漬し、油冷により金型の表面温度が７００℃以下であってＭｓ点は超えている温度まで冷却する第一の冷却工程と、
    　前記第一の冷却工程の後、前記金型を油槽から引き上げて油冷を中断し、前記金型の表面温度がＭｓ点を超える温度域であって前記金型の表面と内部との温度差が２００℃以内となるまで保持する改良保持工程と、
    　前記改良保持工程の後、前記金型の表面温度が２００℃となるまで１℃／分～５０℃／分の速度で冷却する第二の冷却工程と、
    　を具備したことを特徴とする金型の焼入れ方法。     A heating / holding step of heating the mold and holding it in a temperature range from the A3 transformation point to 1150 ° C,
    After the heating / holding step, a first cooling step of immersing the mold in an oil bath and cooling to a temperature at which the surface temperature of the mold is 700 ° C. or less and the Ms point is exceeded by oil cooling;
    After the first cooling step, the mold is lifted from the oil tank to interrupt the oil cooling, and the surface temperature of the mold exceeds the Ms point, and the temperature difference between the mold surface and the inside Improved holding step for holding until the temperature is within 200 ° C.,
    After the improved holding step, a second cooling step of cooling at a rate of 1 ° C./min to 50 ° C./min until the surface temperature of the mold reaches 200 ° C .;
    A mold quenching method characterized by comprising:
  2. 　前記改良保持工程を、前記金型を油槽から引き上げて油冷を中断し、再度の浸漬および引き上げを、前記金型の表面温度がＭｓ点を超える温度域であって前記金型の表面と内部との温度差が２００℃以内となるまで繰り返す工程としたことを特徴とする請求項１に記載の金型の焼入れ方法。 In the improved holding step, the mold is lifted from the oil tank to interrupt the oil cooling, and the immersion and the pulling are performed again in a temperature range where the surface temperature of the mold exceeds the Ms point, and the surface of the mold and the inside The method of quenching a mold according to claim 1, wherein the step is repeated until the temperature difference between the temperature and the temperature becomes within 200 ° C.
  3. 　前記改良保持工程における引き上げ回数が３回以上であることを特徴とする請求項２に記載の金型の焼入れ方法。 The method for quenching a mold according to claim 2, wherein the number of pulling times in the improved holding step is 3 or more.
  4. 　前記第二の冷却工程では、金型内部の温度が４００℃から２５０℃に下がるまで１℃／分～１５℃／分の速度で冷却することを特徴とする請求項１乃至３の何れかに記載の金型の焼入れ方法。 4. The method according to claim 1, wherein in the second cooling step, cooling is performed at a rate of 1 ° C./min to 15 ° C./min until the temperature inside the mold is lowered from 400 ° C. to 250 ° C. The method of quenching the described mold.
  5. 　前記第二の冷却工程は、油冷であることを特徴とする請求項１乃至４の何れかに記載の金型の焼入れ方法。 The mold quenching method according to any one of claims 1 to 4, wherein the second cooling step is oil cooling.
  6. 　前記第一の冷却工程、改良保持工程、および、第二の冷却工程における環境は、非酸化性雰囲気とすることを特徴とする請求項１乃至５の何れかに記載の金型の焼入れ方法。
          The mold quenching method according to any one of claims 1 to 5, wherein the environment in the first cooling step, the improved holding step, and the second cooling step is a non-oxidizing atmosphere.
PCT/JP2011/080342 2010-12-29 2011-12-27 Method for quenching mold WO2012091069A1 (en)

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JP2016194132A (en) * 2015-04-01 2016-11-17 トヨタ自動車東日本株式会社 Method for quenching steel sheet

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JP2014101576A (en) * 2012-10-23 2014-06-05 Hitachi Metals Ltd Hardening method for metal mold
JP2016194132A (en) * 2015-04-01 2016-11-17 トヨタ自動車東日本株式会社 Method for quenching steel sheet

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