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    • Difficulties in hardness testing of metal stamping parts

    In order to obtain high surface hardness and wear resistance, many molds and stamping die accessories need surface heat treatment, such as surface nitriding. For such a mold, people are very concerned about its surface hardness and depth of hardened layer. When testing the hardness of die steel of stamping parts after surface heat treatment, there is a wrong practice that is worth correcting. This is the improper use of the Leeb hardness tester on this occasion. This is determined by the principle of the Leeb hardness tester. The three commonly used hardness testers, Bu, Luo and Wei, all adopt the static testing principle, which is to slowly press a hard indenter into the surface of the sample, and then test the depth or size of the indentation to determine the hardness value. The Leeb hardness tester adopts the dynamic testing principle.


    It is to determine the hardness value of the sample by impacting the surface of the sample with a ball of specified mass at the specified speed and testing the difference between its initial speed and the speed after rebound. To understand this, just look at how thick the standard hardness block of the Leeb hardness tester is. It is obvious that the hardness value measured by it is not the hardness of the nitriding layer or the hardness of the base material, but the result of the joint action of the two. Because the thickness of the surface layer of the stamping part is different, different results will inevitably be obtained.

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