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High Speed Steel Oil Quenching
1. Typical High-speed Steel
At present, there are about dozens of types of high-speed steel at home and abroad. High-speed steel can generally be divided into two categories,-type is general-purpose high-speed steel, and can be further divided into tungsten, molybdenum and tungsten-molybdenum series. Typical steel grades are W18Cr4V (18-4-1), W2Mo9Cr4V2 and W6Mo5Cr4V2 (abbreviated as 6-5-4-2).
2. High Speed Steel Oil Quenching
The superiority of oil-quenched high-speed steel can only be brought into play after correct oil-quenching and tempering. The oil quenching temperature-generally lower alloy cutting tool steel is much higher. For high-speed steel, the higher the oil quenching heating temperature, the more alloying elements are dissolved into austenite, and the higher the alloying elements of martensite after oil quenching. Only martensite with a high content of alloying elements has high red hardness. The alloying elements (W, Mo, V) that have the greatest effect on the red hardness of high-speed steel only increase sharply when the temperature is above 1000C. When the temperature exceeds 1300°C, although the content of these alloying elements can continue to increase, at this time The tensite grains grow up sharply, and even local melting occurs at the grain boundaries. Therefore, the toughness of oil quenched steel is greatly reduced. Therefore, for the oil quenching heating temperature of high-speed steel, as long as the oil quenching temperature of high-speed steel does not occur overheating, the higher the oil quenching temperature, the better the red hardness. Commonly used high-speed steel.The oil quenching heating temperature is shown in Table 1.
Table 1 Oil quenching heating temperature of commonly used high-speed steel/°C
Because high-speed steel has poor thermal conductivity and extremely high oil quenching temperature, it is often heated in two or three stages, that is, preheated at 800~850°C, and then heated to the oil quenching temperature. Large blades (tools) and complex blades (tools) should be preheated twice (three-stage heating), the first time at 500~600°C, and the second time at 800~850C. In addition, the use of high-speed steel preheating can shorten the residence time in high temperature treatment, which can reduce the risk of oxidative decarburization and overheating.
The supercooled austenite transformation curve of W18Cr4V steel is shown in Figure 1. Due to the high degree of austenitic alloy, the decomposition rate is relatively slow. The pearlite transformation interval is between A1 and 600°C, and the fastest time from the beginning to the end of the transformation is 1.0-10h. From 600°C to B, (360°C) It is the medium temperature stable zone of supercooled austenite, B, 175°C is the bainite transformation zone, but the transformation does not proceed to the end. M, below (220°C) is the martensite transformation range. After oil quenching, it contains about 70% cryptocrystalline martensite and 20% to 25% retained austenite. During the cooling process, if the temperature stays at the middle temperature or is slowly cooled, the austenite thermal stabilization will occur, which will reduce the M point and increase the amount of retained austenite.
Fig 1 CCT diagram of W18Cr4V high-speed steel heated to 1300°C
Shanghai Geheng Vacuum Technology Co., Ltd. is a vacuum heat treatment furnace manufacturer with many years of experience in design, manufacturing and production. Mainly produce vacuum heat treatment furnace, vacuum sintering furnace, vacuum brazing furnace, New Energy And Environmental Protection Equipment and other vacuum equipments.Provide customized services, equipment work area can be based on customer output.
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