After the heat treatment of the fastener cold heading die, the surface must have high hardness and the core must have good toughness, so that the surface has a certain compressive stress to offset the stress during the cold rolling process.
It is used to produce cold heading die with small batch size. Generally, carbon tool steel or low alloy cold working die steel is selected to partially quench the surface of the mold cavity, so that the surface hardness of the cavity reaches about HRC60, and the hardness of the mold core 5 is HRC 35~45 or so. According to the section size of the mold, the mold steel with certain hardenability should be selected to obtain the ideal depth of the hardened layer. The hardened layer is too shallow, which may cause the use of the medium cavity to collapse; the hardened layer is too deep, which may cause cracking of the mold during use.
For cold heading molds with long service life, high alloy die steel (such as Cr5Mo1V, Cr12, Cr12MoV, 7CrMo2V2Si, etc.), high speed steel (such as W6Mo5Cr4V2, W18Cr4V, powder high speed steel, etc.), steel bonded carbide or cobalt content Made of cemented carbide with higher toughness. In order to make the mold can withstand high impact loads, a modular mold structure is generally used. The mold jacket is made of high-toughness alloy structural steel or hot work die steel such as 4Cr5MoSiV1. The hardness after heat treatment is about HRC45. The fasteners of the fasteners are made of high-alloy mould material, which are inlaid into the jacket by cold pressing or hot pressing, so that they are in close contact with each other. The jacket causes a certain compressive stress on the inner sleeve to improve the service conditions of the mold and prolong the tightening. The firmware cools the life of the mold.