Tungsten hot die steel performance characteristics

The commonly used hot extrusion die steels are tungsten hot die steels, and hot die steels such as chromium-molybdenum, tungsten-molybdenum, and chromium-tungsten-aluminum, as well as matrix steels.

The typical steel of this type is the traditional 3Cr2W8V steel. Due to its poor thermal fatigue resistance, the application in hot extrusion die will gradually decrease, but there are more applications in die casting moulds. The steel is used in die casting. Die steel will be introduced in detail.

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Tungsten hot work die steel is characterized by high thermal stability, W can improve thermal stability and wear resistance, the higher the W content, the higher the thermal stability. Cr can increase the hardenability of the steel, so that the mold has better oxidation resistance. 3Cr2W8V steel due to the addition of a large number of alloying elements, so that the eutation point greatly left, so the carbon content is not high, but it belongs to hypereutectoid steel. The carbide forming elements W and Cr increase the critical point of the steel, thus improving the thermal fatigue resistance, and at the same time have higher strength and hardness at the high temperature than the low alloy hot work die steel. Tungsten hot work die steel is mainly used for making small-size hot forging die, aluminum and copper alloy die-casting die, hot extrusion die for steel and copper alloy, and forging die.

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Forging and heat treatment process (taking 3Cr2W8V steel as an example):

1) Forging. The initial forging temperature is 1080 to 1120°C and the final forging temperature is 900 to 850°C. Slow cooling after forging.

2) Annealing. Annealing temperature is 830 ~ 850 °C, heat 3 ~ 4h, 40 °C / h speed furnace cooling to 400 °C, baked air cooling. The annealed state is organized on the ferrite matrix with M2C and M23C6.

3) Quenching. General use of 1080 ~ 1150 °C quenching heating, such as the requirements of high temperature mechanical properties (such as die-casting mold), then the upper heating temperature, so that the alloy carbides fully dissolved to ensure high hardness and high thermal hardness; for a certain load, For hot die forgings with better toughness, the lower quenching temperature is used. The quenched structure is martensite and excess carbides (about 6% mass fraction) and retained austenite. Hardness is 50～55HRC.

4) Tempered. Tempering temperature is generally 560 ~ 600 °C, tempering the organization for the tempered martensite + excess carbide, hardness 40 ~ 48HRC.