Reverse-punch die, carbon steel blank, temperature 1200 degrees. H13 cracks after only 100 pieces. Do you have any mold steel recommendations?
The reverse extrusion process is carried out using hydraulic presses, which operate at a very slow stroke rate. Since the punch remains in contact with parts at a high temperature of 1200°C for an extended period, it is prone to red-hot annealing and annealing-induced deformation. Therefore, the die steel must have excellent heat resistance and thermal stability; otherwise, the punch will deform or crack due to annealing. H13, for example, suffers from poor heat resistance, leading to punch swelling and deformation, as well as thermal fatigue cracking caused by annealing.
Reverse extrusion parts undergo significant deformation, causing severe thermal wear on the punch; therefore, a high-hardness die steel must be selected. At the same time, toughness must be ensured to prevent punch fracture.
Based on the four key performance requirements for reverse extrusion punches—heat resistance, thermal stability, high hardness, and high toughness—we recommend the following three mold steels.
The first is 8566 die steel, with a hardness of HRC 58–60. 8566 offers heat resistance comparable to that of high-speed steel SKH51, with four times the toughness of SKH51. 8566 die steel strikes the perfect balance between high heat resistance, high hardness, and high toughness—a feat other die steels cannot achieve. It delivers excellent thermal wear resistance and a long service life when used as a hot extrusion punch.
Mr. Du is hot-stamping motor housings made of No. 10 steel. The cavities are quite deep—over 100 mm. Previously, he used HD punch steel with a hardness of HRC 50, but the punch developed corner cracks after just a few thousand strokes. When the hardness was increased to 54, the tip began to chip off. Now, using 8566 punch steel, a single punch has a total service life of 200,000 strokes, representing a significant improvement in performance.
The second option is YXR33 die steel, with a hardness of HRC 58–60. This material contains tungsten and offers good heat resistance, but its toughness is inferior to that of 8566. There is a risk of fracture in small punches, and its resistance to cracking is slightly lower. It is also more expensive than 8566.
The third option is W360 die steel, with a hardness of HRC 56–58. Its heat resistance and resistance to thermal wear are inferior to those of 8566 and YXR33, and the tip is prone to rounding due to wear. However, because it has a lower total alloy content and lower hardness, it offers better toughness.
Regarding the carbon steel being cold-formed at 1200°C mentioned by this user—where an H13 punch cracked after only 100 pieces—based on the performance requirements for the punch and cost considerations, I would prioritize 8566 die steel, followed by YXR33, and finally W360 die steel.
*************
Wu Dejian’s tool steel, the chief of staff of the user, bought everything he had used.