Last time we spoke about the "steel quenching cracks, this is why, we analysis according to the analysis, the reasons are found out, but still can not find the real reason of steel quenching crack. Well, we need to analyze the quenching process further. 1. quenching temperature caused by improper quenching of two (1) the instrument indicating temperature lower than the actual temperature of the furnace, so that the actual quenching temperature is high, resulting in overheating quenching, resulting in cracking of parts. In the microstructure of overheating quenching cracking, there are coarse and coarse martensite, and the cracks mainly exist in the form of intergranular. (2) the actual carbon content is higher than that of steel casting steel grades by the provisions of the content, according to the original brand as the normal process of quenching, quenching temperature is equal to the increase of the steel, so easily lead to parts overheating and grain growth, increase may cause stress to quenching crack quenching. 2. quenching caused by improper cooling, quenching due to improper cooling, but also parts will cause quenching cracks. For example, steel No. 45 has a tendency to form a hardening crack during quenching. Especially when the carbon content is in the upper limit and the diameter of parts is between 7 and 8mm, it is easy to crack. Therefore, it is very important to choose suitable cooling medium when quenching. In addition, some parts of the structure is more complex, cross section size change is larger, if the coolant selection is improper, thin wall parts easily cause stress concentration and cause quenching crack. 3 of machining defects lead to quenching crack due to mechanical processing, left deep marks and thick on the surface of parts, on quenching, the stress concentration caused by crack.
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