Treatment of spiral steel pipe to avoid these defects

Spiral steel pipe has a very important role in our life, the following is based on the heat treatment process of spiral steel pipe, introducing the common defects of each process.

(1) Defects arising from the heating process. For the heating process, heat treatment heating equipment and heating medium must be selected. What occurs or is prone to occur here is that the surface of the part is affected by the oxidizing heating medium and the heating temperature exceeds the process requirements. The austenite grain is too coarse, or even the grain boundary melting, which will seriously affect the appearance and internal quality of the parts. Therefore, in the actual process, feasible measures should be taken for the analysis of such defects.

(2) Defects produced during the quenching of small diameter spiral pipe. The parts are cooled after heating and austenite homogenization to obtain the desired structural and mechanical properties. At this point, should be based on the material and specific hardness of the part, you need to choose the ideal cooling medium, the ideal cooling medium is to cool quickly at high temperatures and slowly at low temperatures (3o0 ° C).

Usually the cooling medium is air, water, oil (mineral oil, vegetable oil, etc.) 5% ~ 10% brine, 5% ~ 15% alkaline water, synthetic coolant, water quenching oil cooling, water quenching nitrate cooling, alkaline bath, nitrate bath, chloride salt bath, etc. The cooling performance of these cooling medium has a great difference, especially for brine, alkaline water, oil, alkaline bath, nitrate bath, chloride salt bath, etc.. If there is a problem with the cooling medium performance will be degraded (aging), if not detected in time, it will become an important source of defects. Insufficient hardness, soft spots, quench cracks and poor distortion of quenched parts are common heat treatment defects.