During the 295th live stream, a viewer asked: “What type of die steel is best for single-step precision punching of 8mm-thick S500MC high-strength steel?”
Precision stamping 8mm-thick S500MC high-strength steel involves stamping thick, hard material. To ensure a bright edge, the die clearance is very small, and the material is forced in tightly. Since this is a single-step process, the requirements for crack resistance are even higher. The die must balance crack resistance with anti-welding properties and high wear resistance. For thick-sheet fine blanking dies, crack resistance is a top priority. Based on the required die performance and past case experience, I recommend 8566 anti-crack steel.
The crack resistance of 8566 die steel is four times that of high-speed steel SKH-9 and twice that of D2, with a hardness of 58–60 HRC. It is primarily designed to address cracking issues that high-hardness die steels such as D2, DC53, and SKH-9 cannot resolve. In particular, for stainless steel stamping, thick-sheet stamping, and fine-blanking dies—especially in narrow-edge conditions where the punch width is smaller than the sheet thickness and the overlap is minimal—cracking issues that standard die steels cannot resolve are effectively addressed using 8566 anti-cracking steel.
Mr. He was performing a single-step fine blanking of 7mm 45 steel gears. Initially, he used DC53 without noticing any issues; the hardness was achieved at 58–60 HRC. However, after only 2,000 products, the gear tips would chip off, with each chip measuring 3–5 mm. Every time the die needed repair, a section of the punch had to be cut off and then ground down to restore it. He said, “I invested in a fine-blanking machine, but having to repair the punch after just 2,000 parts means I can’t scale up production, and I can’t afford the machining costs either, since fine-blanking punches are made using slow-wire EDM, which is very expensive.”
Later, he switched to LD die steel to lower the hardness, but the teeth still chipped after 5,000 pieces—losing 2–3 mm each time—and he still had to cut off a section of the punch to repair it. Since constantly repairing the punch was such a hassle, he decided to try a die steel with higher toughness. He also tried W360 die steel, which has even better toughness, but it was ridiculously expensive and had poor wear resistance—it couldn’t even last for 5,000 products. After he contacted me, I recommended he use 8566 anti-chipping steel.
Once he started using 8566, the service life increased fivefold. He said that with 8566, the punch doesn’t chip. Typically, after punching 25,000 parts, the punch shows some wear, but I can simply flip it over and use it again, or grind it down to restore it. Since the punch doesn’t chip this way, I can plan production effectively. 8566 increased the punch lifespan from the previous best of 5,000 cycles to 25,000 cycles—a fivefold improvement.
Given Mr. He’s successful case of fine-blanking 7mm 45 steel gears, I also recommend using 8566 anti-chipping steel for the 8mm S500 material mentioned by this user.
Precision punching 8mm S500 high-strength steel—which is a harder variant of the S500MC high-strength steel used in single-step precision punching—is prone to punch chipping as the primary failure mode. When selecting die steel, you must prioritize chip resistance.
Youqin would like to remind you: under no circumstances should you use Cr12MoV, SKD11, or D2—these high-carbon cold work tool steels will chip immediately upon use. At most, you can use mold steels from the Cr8Mo2VSi series, such as DC53, or the 7Cr7Mo2V2Si LD mold steel. If these two types of mold steel still crack, don’t overthink it—just go straight to 8566 anti-cracking steel. Using 8566 die steel for punch cracking is like night and day.
Of course, if your budget allows and you prefer not to use 8566 anti-chipping steel, you can opt for V4E powder metallurgy tool steel at three times the price. This tungsten-free powder-sintered tool steel features excellent microstructural uniformity with no segregation. It offers the strength of die steel combined with 4.0% vanadium (V), delivering both the wear resistance of high-speed steel and the chipping resistance of die steel. However, its hardness is limited to 58–60 HRC; if the hardness is too high, it will chip. If a punch costing several hundred yuan per kilogram chips, the loss is significant.
Regarding the user’s question about which die steel is best for single-step fine blanking of 8mm-thick S500MC high-strength steel: 8566 anti-chipping steel is the top recommendation, with V4E powder tool steel as an alternative. The use of Cr12MoV, SKD11, and D2 die steels is strictly prohibited. Those who ignore this advice may use DC53 or LD—but they’ll have to learn the hard way.
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Wu Dejian’s tool steel, the chief of staff of the user, bought everything he had used.