Tapping nail is a new type of light structure fastener popular in the world. Compare with general screw, need not drill hole to be able to drill into the steel plate of certain thickness first when using, very convenient. Special cold heading steel for tapping screws is a new generation of cold heading steel with higher requirements developed in the 1970s. Since the 1980s, many factories producing self-tapping screws have been born in China, and these factories began to use all steel. By the end of the 1980s, they have turned to the domestic steel market. In this case, anshan steel also began to develop special cold heading steel for self-tapping screws. The adoption of die casting process, before 2000, angang cancelled after casting, continuous casting technology on how to produce qualified for self tapping screw, cold heading steel is a problem in front of us, this topic is in view of the production of self-tapping screw cold heading steel in continuous casting, rolling and controlled cooling process some of the requirements for the work, implementation using continuous casting billet production of qualified self tapping screw for cold heading steel.
For internal quality of inspection rod, at the same time take test metallographic sample, key inspection organization, non-metallic inclusions, decarburization layer and grain size, test results A, B, C, D class inclusions are less than 0.5, the die casting production inclusions with A magnitude of 1.0 or so commonly, grain size is 8 magnitude, the decarburization layer depth of 0.23 mm, see molded before decarburization layer depth is about 0.1 mm, the commonly used after continuous casting surface decarburization layer depth is about 0.1 mm, the commonly used continuous casting surface decarburization situation has improved in the future. The microstructure of the whole graded cross-section metallographic structure is basically ferrite + pearlite, but some of the microstructure is in the form of wei structure, which is much better than the thick wei structure in the previous casting billet production.