When I saw six pieces of 8566 die steel ordered by a stainless steel hot-forging plant in the workshop, it occurred to me that H13 wears out too quickly for stainless steel hot-forging dies, so more and more people are switching to 8566 die steel. His stainless steel hot-forging dies originally used H13, and other die steels he could find on the market all suffered from excessive die collapse, making mass production impossible. After much trial and error, he began using 8566 die steel, which offers high heat resistance, high hardness, and high toughness. After testing it, he started purchasing it frequently, and this time he bought six more pieces.
For smaller-sized stainless steel hot forging applications where the die has an outer sleeve and you want a long die life, you can use 8566 die steel.
8566 has the same heat resistance as SKH-51 high-speed steel, achieves a hardness of 58–60 HRC, and has four times the toughness of SKH-51 high-speed steel. 8566 strikes the perfect balance between high heat resistance, high hardness, and high toughness—a combination that other die steels cannot achieve. High heat resistance is the foundation for preventing die collapse; high hardness is the key to ensuring a long service life; and good toughness ensures the die won’t crack.
Yesterday, a customer I hadn’t been in touch with for many years called me four times in a row. He specializes in the hot forging of 304 and 201 stainless steel. Currently, he’s using V8 die steel purchased from Zhejiang, which achieves a hardness of 60 HRC. However, his dies can only produce 1,000 parts before they split in half. Attempts to use other die steels have failed, leaving him with no other option but to contact me to ask which die steel he should use.
During the hot forging of stainless steel, the material is heated to 1100°C, and the die must withstand extremely high temperatures. Die steels with poor heat resistance are prone to annealing, causing the die to collapse. The customer assumed the problem was insufficient hardness, so he increased it to 60–61 HRC. However, the die still collapsed and cracked after producing only 1,000 parts, leaving him in a very difficult situation.
For hot-forging dies, heat resistance must be your top priority. Only with excellent heat resistance will the die avoid annealing and hardness loss, ensuring its red hardness and preventing collapse and cracking. Good heat resistance is the foundation for preventing die collapse in hot-forging applications.
Second, higher hardness improves thermal wear resistance and high-temperature strength, which ensures a longer service life for your die.
Good toughness is also crucial, as hot-forging dies require water cooling and are subjected to rapid thermal cycling. Die steels with poor toughness and low thermal conductivity are prone to cracking. For example, high-speed steel (HSS) has excellent red hardness and high hardness, but its toughness and thermal conductivity are very poor; water cooling causes it to crack, so it cannot be used for stainless steel hot forging.
For hot-forging dies for stainless steel, if you’re currently using H13, HD, or V8—which are prone to die collapse and cracking—and you’re unsure which die steel to choose, then 8566 is the best option for hot-forging stainless steel. As Mr. Zhang from Zhejiang puts it, when hot-forging 304 stainless steel, 8566 earns a five-star rating—the finished product has excellent surface finish, looking as if it were made from a tube.
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Wu Dejian’s tool steel, the chief of staff of the user, bought everything he had used.