After several days of deliberation, Mr. Du’s order for 8566 round bars was finally placed. This is a classic and successful case study: hot-forging No. 10 steel motor housings, hot-forged motor housings made from 10 steel, with hot-forging punches made from 8566 die steel—each punch has a total service life of over 200,000 strokes. In contrast, the original punches made from HD mold steel would collapse, crack, or chip after just a few thousand to ten thousand strokes. This represents a more than tenfold increase in service life. The service life of these 8566 hot-forging punches provides valuable guidance and reference for material selection in hot forging, which is why I take this matter very seriously.
A couple of days ago, Mr. Du inquired about the price of 8566 round bars and expressed his intention to purchase 50 pieces for use as hot-forging punches for his motor housings. He also told me that with the current 8566 material, a single punch can produce over 200,000 units, representing a significant improvement in performance.
I was very pleased to hear this good news. Mr. Du’s mold is used for hot stamping motor housings made of No. 10 steel, and the cavities are somewhat deep. Previously, the punches were made of HD mold steel with a hardness of 50 HRC, but they developed cracks at the fillet after just a few thousand strokes; when the hardness was increased to 54 HRC, the tips began to chip off. Now, with the 8566 hot stamping punches, each punch has a total service life of 200,000 strokes, representing a significant improvement in performance.
At the time, I asked him further: “How many products can the 8566 punch produce in a single cycle?”
He replied, “I haven’t calculated the lifespan per cycle, but the 8566 punch can still be used after the striking surface wears down. The total lifespan of a single punch is over 200,000 cycles. Compared to the previous HD model, the lifespan has improved significantly. Now I have to replace punches less often, which boosts efficiency. Since the 8566 punches a lot and isn’t expensive, I’ll be using 8566 for all my hot punches from now on.”
Hot-forging punches demand extremely high resistance to thermal wear; they must not only have excellent heat resistance but also high hardness. Otherwise, the punches are prone to corner collapse or cracking, resulting in a short service life—a common issue with current hot punches and a major pain point for hot-forging molds.
Mold steel with good heat resistance ensures that hardness is not lost through annealing—this is the foundation for ensuring punch life. Combined with high hardness, this is what guarantees excellent thermal wear resistance, which is the key to ensuring a long punch life. HD punches tend to develop rounded corners precisely because HD has such poor heat resistance; its hardness is lost through annealing, resulting in a loss of red hardness, which leads to the corners becoming rounded. However, 8566 does not lose its hardness through annealing, so the punch naturally has a longer service life.
However, with today’s 8566 die steel, a single punch can achieve a total service life of over 200,000 cycles—even in applications with deep cavities where the punch is in prolonged contact with high-temperature components and features small protrusions on its head (the areas most prone to corner collapse and cracking). Under such grueling and harsh operating conditions, 8566 can still achieve a service life of over 200,000 cycles—more than 20 times that of HD. I believe this is something worth boasting about.
Crucially, these operating conditions provide valuable reference and insights for those in the hot forging industry. If you’re facing short punch lifespans in the future and aren’t sure which mold steel to use, you should definitely give 8566 die steel a try.
8566 die steel offers the same heat resistance as SKH51 high-speed steel, with a hardness of 58–60 HRC and four times the toughness of SKH51. 8566 die steel strikes the perfect balance between high heat resistance, high hardness, and high toughness—a combination that other mold steels cannot match. When used for hot forging of stainless steel at extremely high temperatures, for multi-directional forging punches that remain in contact with high-temperature parts for extended periods, or for punches in hot-forging molds requiring high hardness, 8566 die steel resists mold collapse, cracking, and wear, ensuring a long service life.
As Mr. Zhang mentioned, when hot forging 304 stainless steel, 8566 earned a five-star rating—the product’s surface finish is excellent, and the finished product looks just like one made from tubing. Today, Mr. Du used 8566 die steel to hot forge motor housings, with a single punch lasting over 200,000 strokes, which once again confirms this point: 8566 is indeed durable when used as punches for hot forging molds.
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I am Wu Dejian, the “King of mold Steel,” from Dongguan Yuhui mold Steel. Yuhui mold Steel is used by three Fortune 500 companies and seven of China’s Top 500 companies; Kyocera has been sourcing Yuhui mold Steel for seven consecutive years. I have helped over 4,000 companies resolve complex issues related to mold material selection, manufacturing, and usage. If you’re unsure about which mold steel to choose, or if the mold steel you’re currently using results in short mold lifespans and you’re unsure which material to use, feel free to reach out to me. I’m confident that when it comes to mold material selection and application, I can serve as your chief advisor and help you avoid costly trial-and-error. Wu Dejian Mold Steel—the users’ trusted advisor. Everyone who’s tried it is satisfied!