Mr. Chen asked for recommendations on mold steel materials for thinning and drawing dies used on 3–5 mm thick material.
Upon further inquiry, it was learned that he is performing thinning and drawing operations on 3–5 mm thick Q235 pickled material, with a drawing height of 100 mm and no blankholding. He is currently using Cr12MoV for the die, but it is prone to drawing marks—scratches appear after just a few draws.
The formation of drawing lines on drawn products is caused by adhesive wear resulting from material adhesion. The root cause lies in microscopic cracks in the microstructure of the selected die steel that are invisible to the naked eye. During the drawing process, these microscopic cracks adhere to the material, leading to the formation of drawing lines on the product.
Using Cr12MoV for drawing dies is a mistake in material selection. Cr12MoV is a high-carbon, high-chromium cold-work die steel with a carbon (C) content of 1.5%. It suffers from severe microstructural segregation and contains a large number of microscopic cracks invisible to the naked eye. Therefore, using Cr12MoV for drawing dies will inevitably result in adhesive wear caused by material adhesion—no amount of polishing will help. Stringing will appear after just a few products are made, and even a coating cannot cover it up. The fact that scratches are already appearing on the products after just a few runs further confirms this. There is no remedy for this; the only solution is to change the material.
The material used for drawing dies for iron products is the ultimate test of a die steel’s non-stick properties. Improper material selection will result in sticking, causing the product to develop stringing. Scratches on drawn products are the most frustrating issue with drawing dies and also the most common problem. You must prioritize non-stick properties when selecting your die steel; this is the key to preventing string marks on the product. A hardness of 58–62 HRC is actually sufficient for drawing iron materials.
Mr. Chen asked for a material recommendation for a drawing die used in 3–5 mm thin-wall drawing. I recommend 8503 die steel, which is non-stick.
8503 is a proprietary non-stick mold steel from Wudejian Mold Steel. It has twice the toughness of DC53 and a hardness of 59–61 HRC. Compared to DC53, its performance is doubled without a corresponding increase in price, and it offers the added benefit of non-stick properties. This non-stick characteristic is particularly advantageous for drawing dies.
Mr. Cheng said that when drawing 1.1mm-thick Q195 cold-rolled steel sheet for casters, Cr12MoV without a coating simply won’t work—scratches will appear before you can produce even 100 units. The non-stick 8503 steel you bought last time produced about 30,000 units before showing any signs of material sticking, making it much better than Cr12MoV.
Therefore, for Mr. Chen’s thinning and stretching dies for 3–5 mm Q235 pickled sheet, using Cr12MoV is prone to causing wire marks. I recommend using the non-stick 8503 die steel; the products won’t develop wire marks as quickly. If you’re willing, adding a coating will yield even better results.
*************
Wu Dejian’s tool steel, the chief of staff of the user, bought everything he had used.