In order to obtain high surface hardness and wear resistance, many metal stamping die and metal stamping die accessories must undergo surface heat treatment, such as surface nitriding. For such a mold, people are very concerned about its surface hardness and hardened layer depth.
When testing the hardness of stamping die steel that has undergone surface heat treatment, there is a wrong approach worthy of correction. This is the improper use of the Leeb hardness tester in this situation. This is determined by the principle of the Leeb hardness tester. The three commonly used hardness testers of cloth, Luo, and Wei all adopt the static test principle, in which a hard indenter is slowly pressed into the surface of the sample, and then the depth or size of the indentation is tested to determine the hardness value. The Leeb hardness tester uses the principle of dynamic testing.
It is to impact a sphere of specified mass on the surface of the sample at a specified speed, and test the difference between its initial speed and the rebound speed to determine the hardness value of the sample. To understand this, just look at how thick the standard hardness block of the Leeb hardness tester is. Obviously, the measured hardness value is neither the hardness of the nitride layer nor the hardness of the base material, but the result of the interaction of the two. Because the thickness of the surface layer of the stamping part is different, different results will inevitably be obtained.
The main material of stamping parts molds is tool steel (including tool steel and high-speed steel), and sometimes hard alloy stamping parts molds are usually required to have high hardness and wear resistance, and heat treatment is essential.