Mr. Qian came to consult me about deep-drawing 1.5mm-thick DC04 sheet metal into cylinders. Initially, he used Cr12MoV with thermal treatment (TD), but the dies didn’t last long and kept developing draw lines. A while back, he spent several thousand yuan per kilogram on YG11 cemented carbide, but the dies started showing draw lines after only two runs. The reason was that material was sticking to the tungsten steel, causing the draw lines on the products. He had wasted several thousand yuan on mold costs and asked me if there was a solution or what type of die steel he should use.
When selecting die steel for drawing operations, you must choose steel with high-quality smelting and no microscopic cracks. Otherwise, material will stick to the die and the product will exhibit stringing—and you won’t even know the cause or how to optimize the die. This can be a real headache.
Using Cr12MoV with thermal treatment (TD) for drawing dies is the wrong material choice. Cr12MoV is a high-carbon, high-chromium cold-work die steel with a carbon content of 1.5%. It suffers from severe segregation and contains a large number of microscopic cracks invisible to the naked eye. Even if you apply a thermal treatment (TD) coating, it won’t cover these microscopic cracks, and you’ll still encounter problems with material sticking to the die and threading. Many people assume that since the die needs a thermal treatment (TD) coating, they can choose a cheaper die steel—and that’s the root cause of your problems.
Using tungsten steel for drawing dies is perfectly fine; tungsten steel drawing dies typically have service lives ranging from tens to millions of cycles. However, in Mr. Qian’s case, his 1.5-thick DC04 cylindrical part experienced stringing after just two products when made with YG11 cemented carbide. This isn’t because tungsten steel is unsuitable; it’s because the tungsten steel he purchased had too coarse a grain size and severe segregation, leading to material sticking. This is a case of selecting the wrong die steel.
There are three solutions to the wire-drawing issues with Mr. Qian’s drawing dies:
First: If your budget allows, continue using tungsten steel. You can purchase tungsten steel with a fine grain size, or you can opt for imported grades. Although tungsten steel has become extremely expensive after tripling in price—making it unaffordable for some dies—if you’re producing long-term molds with high-volume drawing runs, using tungsten steel remains a cost-effective choice.
Second: If you find tungsten steel to be too expensive and cannot afford it, you can switch to powdered high-speed steel, such as PM23, PM30, or PM60. When using powdered high-speed steel to stretch 1.5-thick DC04 cylindrical parts, there will be no sticking or stringing, and no coating is required.
Third, if your mold is relatively large and cannot accommodate powder-metallurgy high-speed steel or tungsten steel, and you wish to apply a coating to reduce mold costs, you must select a die steel with high-quality smelting and a tempering temperature of 530°C to ensure reliability.
High-quality smelting is essential to avoid segregation issues and microcracks, thereby eliminating mold sticking and wire drawing. A tempering temperature of 530°C ensures that the hardness of the mold’s base material does not decrease during thermal treatment (TD), thereby maintaining the mold’s strength. Combined with thermal treatment (TD) to enhance surface hardness and finish, this results in a very long mold service life.
We have a customer who deep draws 1.1mm-thick Q195 casters with a depth of 50–60mm. He said that Cr12MoV cannot be used without thermal treatment (TD); after producing just a few dozen to a hundred pieces, stringing begins to occur. With uncoated 8503 steel, it takes 30,000 pieces before even slight wire marks appear, and after polishing, the die is good to go again. Since this doesn’t happen very often and 8503 isn’t expensive, I’m very satisfied with it.
If you’re willing to coat the dies, using 8503 die steel with a surface coating makes the dies extremely durable. This significantly reduces your costs and avoids the exorbitant prices associated with tungsten steel or powder-metallurged high-speed steel. For non-stick applications, using 8503 for the drawing dies and applying a thermal treatment (TD) surface coating offers the best value for money.
Mr. Qian was deep-drawing 1.5-thick DC04 deep-drawing sheet into cylinders. The Cr12MoV with thermal treatment (TD) surface treatment wasn’t durable enough, and the tungsten steel started sticking to the material and producing stringing after only a few runs. These three solutions are ready to use; you can decide which method to adopt based on your overall mold cost considerations.
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Wu Dejian’s tool steel, the chief of staff of the user, bought everything he had used.