40CR SMLS Pipe Working Characteristics

As the 40cr smls pipe is characterized by strong impact load and alternating load, the working environment is poor, so the bearing steel with high and uniform hardness, high contact fatigue strength, good toughness and a certain degree of hardenability. Recently, a steel mill in the daily inspection found that individual GCr15 bearing steel samples crack, in order to find out the reasons for the crack, the researchers conducted a detailed analysis and discussion for the actual production provides a theoretical basis.

The chemical composition of 40cr smls pipe, hot-rolled tissue is fine flaky pearlite and carbide (Fe, Cr) 3C, generally need to be balloon annealing, quenching and low temperature tempering heat treatment, after heat treatment, the organization is small cryptocrystalline martensite and cementite particles.

The crack samples of 40cr smls pipe were cut and sampled, polished with standard grinding and grinding machine, and the crack defects were observed in plane and cross section with Nippon Electronic JSM-6490 scanning electron microscope. Oxford instrument OXFORD was used to carry out the crack and the microstructures of the microstructures were analyzed by elemental analysis, and then the microstructure of the crack was observed by 4% nitric acid.

Metallic theory is usually considered grain boundary is to strengthen the element, that is, the grain boundary bonding force is higher than the crystal, only in the grain boundary is weakened will occur along the crystal brittle fracture. In general, there are several reasons for the grain boundary weakening: First, the intergranular fracture caused by the grain boundary sedimentation is caused by the inclusion of the grain boundary and the precipitation of the second phase. The precipitated phase on the grain boundary is usually continuous, spherical, rod or dendritic, sometimes covered with more than 50% grain boundary area, the more grain boundary precipitation, the lower the fracture stress. Second, the impurity elements in the grain boundary segregation caused by crisp crisp, mainly the periodic table of?,?,? family of elements such as Ge, P, As, Sb, Bi, S, Se, Te, etc. The Third, the erosion of environmental media caused by the intergranular fracture, such as copper crisp, cadmium crisp and so on. Fourth, the high temperature of the intergranular fracture, mainly welding hot cracks, grinding cracks, creep rupture.

A worker from a steel pipe company, which is located in China.