For stamping solid chain links, I still recommend PM23 powdered high-speed steel, which is of high smelting quality, free of microscopic cracks, and offers high hardness and good wear resistance. Mr. Zhou asked what die steel to use for stamping 0.5mm-thick nickel strips. He is currently using SKH-9 high-speed steel, but after stamping 5,000–6,000 parts, the punch becomes coated with metal debris, resulting in significant burrs, rendering it unusable.
Nickel material may seem soft, but it is prone to sticking to the die. If the die steel you choose has segregation or microscopic cracks in its microstructure, it is prone to adhesive wear caused by adhesion to the cracks during the stamping process, resulting in burrs on the product. Previously, this type of adhesive wear caused by material sticking would occur right at the start of stamping, which is due to the poor metallurgical quality of the die steel.
SKH-9 is a tungsten-molybdenum high-speed steel with a hardness of 62–64 HRC. It offers excellent wear resistance. When used to punch 0.5-thick sheet metal, it should not develop burrs after only 4,000–5,000 punches. In such cases, the issue is generally caused by adhesive wear resulting from material sticking. I provided him with two solutions.
The first is to apply a coating. After coating, the fine cracks will be partially covered, and the sticking issue will improve slightly.
He then said that he had already tried coating, but it didn’t work—the material still stuck to the die after only a few stamping cycles. This further confirms that the SKH-9 he purchased was of very poor metallurgical quality, with too many microcracks—so many that even the coating couldn’t cover them, rendering the coating ineffective. The only solution is to switch to a different die steel.
If the budget allows, tungsten carbide is the best option. With a hardness of 86–89 HRA, it offers excellent wear resistance. If you can source tungsten carbide with fine grain size, it won’t stick to the die when punching 0.5mm-thick pure nickel strip. It’s highly durable and can even be used continuously without requiring die repairs.
When punching 0.5mm-thick nickel strip, SKH-9 currently develops burrs after just 5,000–6,000 punches. Considering both the performance requirements for the die and cost-effectiveness, I still recommend PM23 powdered high-speed steel.
PM23 is also a general-purpose high-speed steel with a hardness of 64–66 HRC. Its wear resistance is sufficient for this application. Most importantly, the powder metallurgy process eliminates segregation and removes microscopic cracks, preventing material sticking to the die. When you use PM23 to stamp pure titanium or nickel materials, it won’t suffer from adhesive wear caused by material sticking, and the die will have a very long service life—all at a cost significantly lower than that of cemented carbide.
In terms of value for money, PM23 is the best choice for stamping 0.5mm-thick pure nickel strips. It solves the adhesion problem, ensures wear resistance, and is cheaper than tungsten carbide. This allows us to achieve high efficiency, long service life, and low costs.
In mold making, improper material selection renders all your efforts futile. SKH-9 is also a high-speed steel and isn’t cheap, but it develops burrs after only 5,000–6,000 cycles, forcing you to polish the mold. If you keep having to rework the mold like this, the apparent low cost of the mold steel actually results in exorbitant operating costs. Choosing the right mold steel means achieving twice the result with half the effort. With PM23, you’ll have nothing to worry about.
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Wu Dejian’s tool steel, the chief of staff of the user, bought everything he had used.