KR100343856B1 - A Heat Treatment Method of Forming Punch made of P/M High-speed Steel - Google Patents

Abstract

The present invention relates to a heat treatment method of a forming punch made of powder high speed tool steel. For this purpose 1.0 to 2.5 wt% carbon (C), 3 to 6 wt% chromium (Cr), 0.2 to 7.0 wt% tungsten (W), 1.0 to 7.2 wt% molybdenum (Mo), 2.5 to 11 wt% A heat treatment method for a forming punch made of vanadium (V), 0 to 11 wt% cobalt (Co) and the remainder of powder high speed tool steel composed of iron (Fe), wherein the forming punch is subjected to vacuum furnace, inert gas atmosphere, or salt bath. Heat-treat the forming punch made of powder high-speed tool steel, which is charged and held at 1020-1200 ° C. for 3 minutes to 2 hours, then quenched and tempered at least once every 30 minutes to 5 hours in the temperature range of 580-680 ° C. Provide a method. Powdered high speed tool steel punches using this heat treatment method are not easily broken during use, so they have a long service life and can significantly reduce punch requirements, resulting in significant cost savings in punch material costs, punch processing costs, and heat treatment costs. The economic effect is very large.

Description

A Heat Treatment Method of Forming Punch made of P / M High-speed Steel}

The present invention relates to a heat treatment method for forming punches made of powder high speed tool steel, and in detail, by performing austenite treatment of the powder high speed tool steel punch at 1020 to 1200 ° C, and then performing high temperature tempering at a temperature range of 580 to 680 ° C. The present invention relates to a heat treatment method in which chipping or breakage caused by high pressure and repetitive stress is suppressed, thereby greatly increasing the life of the punch.

Casting high speed tool steels manufactured by a series of processes such as casting, hot forging, and rolling after melting the material have become a problem due to unevenness of the structure, coarse grains and orientation due to segregation during melting and casting. The powder high speed tool steel produced by the powder metallurgy method is a process of hot isostatic pressing, hot forging or rolling after melting a material, filling powder made by gas spraying with a metal can, degassing and sealing it. It is manufactured through.

Unlike conventionally cast high speed tool steels, such powder high speed tool steels can obtain a uniform microstructure without segregation, and have excellent characteristics such as stability of heat treatment as well as improved wear resistance due to formation of various carbides and supersaturated solid solution of elements. It is used in molds, end mills, forming punches and the like.

Currently used powder high speed tool steels are 1.0 to 2.5 wt% carbon (C), 3 to 6 wt% chromium (Cr), 0.2 to 7.0 wt% tungsten (W), 1.0 to 7.2 wt% molybdenum (Mo) ), 2.5 to 11 wt% vanadium (V), 0 to 11 wt% cobalt (Co), and the remainder is composed of iron (Fe).

For example, 1.28 wt% carbon (C), 4.20 wt% chromium (Cr), 6.4 wt% tungsten (W), 5.0 wt% molybdenum (Mo), 3.1 wt% vanadium without cobalt (V) and powder high speed tool steels (trade name ASP 23), the remainder of which is iron (Fe), are used in cold forming punches and the like because they have appropriate toughness and wear resistance. This powder high speed tool steel has a high service life when applied to a high-pressure forming punch than a material produced by a conventional casting method, and is used a lot.

In particular, when various metal powders are molded at high pressure to produce iron, stainless, and copper sintering machine parts, the punch itself often has sharp edges due to the complicated shape of the machine parts. In this case, chipping breakage tends to occur at sharp portions due to repeated loads.

On the other hand, the heat treatment method of the powder high-speed tool steel for high-pressure molding is usually maintained at 1020 ~ 1200 ℃ for 3 minutes to 2 hours, then quenched, and 30 minutes to a temperature range of 530 ~ 560 ℃ to maximize the drag force or hardness Many heat treatment methods which temper at least once every 3 hours are used.

However, when using the high-pressure molding punch, the edge near the sharp edges during use, the end of life due to the cracks are broken, frequent replacement is inevitable, and the manufacturing cost (material cost, processing cost, heat treatment cost) of the punch is high. This problem occurs because the fatigue cracks are generated in the material when the punch is repeatedly subjected to high pressure, and the propagation of the fatigue cracks is rapid.

The present invention has been made to improve the problem of the conventional powder high speed tool steel heat treatment as described above, and provides a heat treatment method for increasing the life of the punch for forming made of the powder high speed tool steel by significantly increasing the fatigue life of the powder high speed tool steel. Has its purpose.

Hereinafter, the configuration of the present invention in detail as follows.

The present invention is 1.0 to 2.5wt% carbon (C), 3 to 6wt% chromium (Cr), 0.2 to 7.0wt% tungsten (W), 1.0 to 7.2wt% molybdenum (Mo), 2.5 to 11wt% A heat treatment method of a forming punch made of powder high speed tool steel composed of vanadium (V), 0-11 wt% of cobalt (Co), and the remainder of iron (Fe), wherein the forming punch is a vacuum furnace, an inert gas atmosphere, or a salt bath. It is charged to and then quenched after holding for 3 minutes to 2 hours at 1020 to 1200 ℃, characterized in that the tempering at least once every 10 minutes to 5 hours in the temperature range of 580 to 680 ℃.

In the above description, the austenite treatment temperature range is limited to 1020 to 1200 占 폚, since carbides are not sufficiently dissolved when the austenite treatment temperature is 1020 占 폚 or less, so that sufficient hardening heat treatment effect cannot be obtained even after rapid cooling after austenite treatment. This is because grain growth is likely to occur at a temperature of 1200 ° C. or higher, making it brittle.

In addition, limiting the heat treatment time between 3 minutes and 2 hours is that if the heat treatment time is shorter than 3 minutes at the austenite treatment temperature, the temperature in the furnace is not uniform and a difference in the heat treatment temperature for each position of the punch occurs. This is because when it is long, grain growth and carbide growth occur and become vulnerable.

Therefore, it is most preferable to hold the austenite treatment at 1020 to 1200 DEG C for 3 minutes to 2 hours and then quench with high pressure gas or cooling oil.

On the other hand, the tempering temperature range is also limited to 580 to 680 ° C. If the tempering temperature is low at 580 ° C or lower, fine secondary carbides are precipitated in the matrix and martensite does not completely decompose so that the matrix is hardened. It is easy to propagate, and the fatigue crack propagates easily during high pressure molding, and the life of the punch is lowered. If the tempering temperature is over 680 ° C, the hardness is severely reduced and plastic deformation of the punch edge occurs during high pressure molding. This is because local deformation is more likely to occur than breakage, and the punch dimensions change and become poor.

Further, the reason for limiting the tempering holding time to 10 minutes to 5 hours is that if the tempering holding time is too short, less than 10 minutes, the time for decomposing martensite in the known phase is insufficient, and if the holding time is longer than 5 hours, it is uneconomical. This is because the punch surface tends to be decarburized, which is not good.

Hereinafter, Example 1 in which the fracture resistance test (triple point bending fatigue test) for the repeated load of the specimen tempered and austenitic at various temperatures will be described.

Powder high speed tool steel mainly used as high pressure powder forming punch material (composition: 1.2wt% carbon (C), 4.0wt% chromium (Cr), 4.9wt% molybdenum (Mo), 6.2wt% tungsten (W)) , 2.9 wt% vanadium (V), and the rest of the iron (Fe)) charged gas-discharged powder into the can and degassed, and then hot at 1000 atmosphere pressure for 1 hour at 1150 ℃ under nitrogen atmosphere. After isostatic pressing, it was prepared by hot working at 1100 ° C.

After inserting the powder high speed tool steel punch made of the above material into the vacuum heat treatment furnace, it is made into a vacuum state, heated to 850 ° C. at a heating rate of 10 ° C. per minute, and maintained for 20 minutes, followed by austerus at a heating rate of 15 ° C. per minute. It was heated to 1020 ~ 1200 ℃ nitrite temperature, and then quenched with 10 bar of nitrogen gas.

Subsequently, it was heated to a tempering temperature zone of 500 to 620 ° C. at a heating rate of 10 ° C. per minute and maintained for 1 hour, followed by cooling with 2 bar of nitrogen gas, followed by two tempering treatments under the same tempering conditions, for a total of three times. Tempering treatment was performed.

A test piece of polished 2.3 × 2.3 × 17mm size was mounted on a test jig (10mm between specimen points) with a triple point bending fatigue, and repeatedly applied a constant load of 215kg once per second to give the fatigue life until the specimen was destroyed. Obtained. The tensile strength test specimen was ground by 5.0 × 5.0 × 30.6mm, loaded on the support point of 25.4mm, and then tested for the tensile strength and hardness test was also performed. The results are shown in Table 1 below.

From Table 1, when the tempering temperature is low, such as 500 ℃, 540 ℃, chipping breakage easily occurs when repeated load is applied, and fatigue life is low when cracking occurs easily when applied to the actual forming punch, and the life is shortened. It can be seen that when the tempering temperature increases above 580 ° C., fatigue life and punch life increase.

Next, as a second example, the results of application to the powder forming punches tempered and austenitic at various temperatures will be described.

In the same manner as in Example 1, the specimen was manufactured to fabricate a punch for forming a flange-shaped iron-based powder metallurgy product as a vehicle part, and heated to 850 ° C. at a heating rate of 10 ° C. per minute in a vacuum heat treatment furnace for 20 minutes. After maintaining, the mixture was heated to 1175 ° C., which is an austenite treatment temperature at a heating rate of 15 ° C. per minute, and maintained for 10 minutes, and then quenched with 10 bar of nitrogen gas.

Subsequently, it was heated to a tempering temperature zone of 530 to 610 ° C. at a heating rate of 10 ° C. per minute, maintained for 1 hour, cooled with 2 bar of nitrogen gas, and then tempered twice with the same tempering conditions for a total of three times. After finishing the punching, powder molding was performed at a pressure of 6 tons per cross section of the molded body. The life of the punch was determined by measuring the number of molded products until chipping failure occurred at the sharp edges of the powder forming punch. The results are shown in Table 2.

In Table 2, when the tempering temperature is low as 500 ℃ and 530 ℃, when applied to the actual high-pressure molding punch, cracks easily occur and the service life is reduced, and when the tempering temperature increases above 580 ℃ and 610 ℃, chipping occurs. It can be seen that the punch life is increased rapidly.

According to the heat treatment method of the present invention having the above object and configuration, after forming austenite punched molding punch made of powder high speed tool steel, the tempering temperature is increased to 580 to 680 ° C, and the punch repeatedly applied to the load is easily used. As the service life is greatly increased since it is not damaged, the number of punches required for the same production amount is reduced, and the overall cost such as punch material cost, punch processing cost, and heat treatment cost is greatly reduced.

Claims (2)

1.0 to 2.5 wt% carbon (C), 3 to 6 wt% chromium (Cr), 0.2 to 7.0 wt% tungsten (W), 1.0 to 7.2 wt% molybdenum (Mo), 2.5 to 11 wt% vanadium ( V), in the heat treatment method of the forming punch made of powder high speed tool steel composed of cobalt (Co) of less than 11wt%, and the rest of iron (Fe), The molding punch is charged into a heat treatment furnace, held at 1020 to 1200 ° C. for 3 minutes to 2 hours, quenched, and tempered at least once for 10 minutes to 5 hours at a temperature range of 580 to 680 ° C. Heat treatment method of forming punch made of tool steel. 1.0 to 2.5 wt% carbon (C), 3 to 6 wt% chromium (Cr), 0.2 to 7.0 wt% tungsten (W), 1.0 to 7.2 wt% molybdenum (Mo), 2.5 to 11 wt% vanadium ( V), in the heat treatment method of the forming punch made of powder high speed tool steel, the remainder is iron (Fe), the remainder is iron (Fe), The molding punch is charged into a heat treatment furnace, held at 1020 to 1200 ° C. for 3 minutes to 2 hours, quenched, and tempered at least once for 10 minutes to 5 hours at a temperature range of 580 to 680 ° C. Heat treatment method of forming punch made of tool steel.