“Our hot forging dies need to be re-surfaced every half day, and each resurfacing takes three hours. The time spent on production is about the same as the time spent on repairs. Is this cost-effective?” Mr. Zhu asks: We are currently using H13 steel for hot forging dies made from 2CrMoA, 20MnCr5, and 20CrMoTiH materials, but it lacks heat resistance. The dies collapse after just half a day of use, and after a single repair, we can’t even produce 3,000 parts. What type of die steel should we use for these hot forging dies?
H13 is used for hot forging dies. Its biggest advantage is its low cost, but its short service life is its biggest drawback. The die surface needs to be reground after every 3,000 strokes, which means repairs are too frequent—we have to stop production for half a day just to repair the die, and that’s a huge waste of time.
When you realize a mold is no longer working properly, you have to remove it from the machine, take it to the machining center to trim the surface, and just the time spent clamping it into the machine takes three hours. Then you have to reinstall the mold on the machine, re-calibrate it, and finally start production. Going through this entire process takes at least three to four hours—the time spent repairing the mold is actually longer than the production time. This kind of cost inversion isn’t worth it. You’ll be exhausted, production will stall, and you won’t make any money.
Instead of constantly repairing molds, it’s better to use the money saved on repairs to buy higher-quality mold steel. This will extend the mold’s service life, reduce the number of repair cycles, and allow you to produce more parts with fewer repairs—so the boss isn’t worn out, and you make a profit.
H13 heat-resistant alloy has a molybdenum (Mo) content of only 1.0%, which is too low to withstand high temperatures. When operating at high temperatures, the mold will quickly anneal, causing its hardness to drop rapidly. This leads to two major problems: mold collapse and cracking—which is also why H13 mold steel is so inexpensive.
For hot forging of iron billets, I recommend the heat-resistant steel 8433. 8433 is a proprietary heat-resistant steel from Yuhui Mold Steel; it far surpasses competing products in multiple metrics—including high heat resistance, fatigue resistance, and thermal conductivity—and its performance is second to none.
The heat resistance and stability of 8433 die steel are 2–3 times that of H13, with a hardness of 50–54 HRC. Throughout its service life, the mold will not anneal, its hardness will not decrease, and its red hardness is guaranteed, eliminating the two major problems of mold collapse and cracking. It is particularly worth emphasizing that the service life of 8433 is not reduced after mold repair; even if the mold is repaired to the point of scrapping, the hardness on the back surface will not decrease.
When Mr. Xing was hot-forging 42CrMo flanges using H13 die steel, the die would crack and collapse after producing 3,000 units. However, when he switched to 8433 heat-resistant steel, he was able to produce 10,000 units each time—a threefold increase in service life. Furthermore, even after four die-surface re-grinding operations, the service life remained unchanged, consistently exceeding 10,000 units per cycle. This means that one 8433 die is equivalent to three H13 dies in terms of usage.
Not to mention the 12 fewer surface-refinishing operations—the savings on machining costs are significant. The time saved from these 12 operations alone is already worth two to three days’ worth of output. These additional savings are enough to offset the cost of purchasing the 8433 heat-resistant steel for the die, effectively making the use of 8433 heat-resistant steel free.
Regarding the hot forging of 2CrMoA, 20MnCr5, and 20CrMoTiH materials mentioned by Mr. Zhu, H13 is no longer heat-resistant—the die collapses after just half a day of forging, and even after a single die repair, it can’t produce more than 3,000 parts. I recommend 8433 heat-resistant steel. When hot forging dies suffer from collapse or cracking, using 8433 die steel is even more satisfying than eating braised pork.
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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 Kyocera has been sourcing our products for seven consecutive years. I have helped over 4,000 companies solve complex challenges related to mold material selection, manufacturing, and usage. If you’re unsure about which mold steel to choose, or if the steel you’re currently using results in short mold lifespans, or if you’re unsure which material to use, feel free to reach out to me. I’m confident I can serve as your trusted advisor in this area and help you avoid costly mistakes. Wu Dejian Mold Steel—your trusted advisor—and customers who’ve tried us keep coming back!