Mr. Chen asked which tool steel is best for hot-forged stainless steel punches. Currently, the SKH-9 steel wears down very quickly—the tip wears out after just a few dozen uses—while the M42 steel breaks at the tip after only a few uses.
Hot-forging dies for stainless steel operate at high temperatures, so the die steel must have good red hardness. However, in addition to good red hardness, it must also possess toughness; otherwise, the punch is prone to fracture. Only high-toughness hot-work tool steels can meet the thermal fatigue performance requirements of hot-forging dies subjected to rapid cooling and heating.
SKH-9 and M42 are tungsten- and cobalt-containing high-speed steels that offer excellent red hardness but suffer from poor toughness and thermal conductivity. They are unsuitable for hot forging dies; if used, they will either crack or fracture.
No single property can meet the harsh operating conditions of hot forging dies, which involve both high temperatures and rapid cooling and heating. Only mold steel with excellent comprehensive properties—high heat resistance, high hardness, and high toughness—can meet the demands of hot forging dies.
You are currently using SKH-9 high-speed steel, which wears out after just a few dozen strikes, indicating that it lacks wear resistance and will quickly develop surface cracks. M42, with 8.5% cobalt, breaks after just a few uses, indicating that its toughness is too poor. This is a mistake in material selection; you should use 8566 die steel.
8566 is a proprietary product of Yuhui mold Steel. Its heat resistance is comparable to that of high-speed steel SKH51, with a hardness of 58–60 HRC, and its toughness is four times that of SKH51. 8566 die steel perfectly balances high heat resistance, high hardness, and high toughness. When used for hot forging of stainless steel, it prevents mold collapse, cracking, and wear, ensuring a long service life—something other mold steels cannot achieve.
Mr. Zhang, who uses 304 stainless steel for red forging, gave 8566 a five-star review, noting that the product has excellent surface finish and, once finished, looks just like it was made from a tube.
Mr. Chen uses SKH-9 for the punches in his hot-forged stainless steel process, but they wear out after just a few dozen strikes, and the M42 ones break after only a few uses. This is a mistake in material selection—he only considered red hardness and didn’t take toughness into account. You need to use 8566 die steel.
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Wu Dejian’s tool steel, the chief of staff of the user, bought everything he had used.