The original csk self drilling screw factory are hydrogen-induced cracks. No oxidation corrosion. With the help of a metallographic analyzer, observe the metallographic structure near the core and fracture of the intact part and the 1# fractured part, and conduct a comparative analysis of 5% in combination with heat treatment knowledge. Figure 3
The metallographic structure of the core of the intact part and the 1# fractured part (3) Hardness analysisThe hardness test was carried out on the intact part and the fractured part. Figure 1 below shows the broken parts, simulated broken parts and intact parts; Figure 2 shows the macroscopic morphology of the fractured parts. According to ‘JISG4053-2008’, its chemical composition meets the requirements for SCM435 steel in the standard. As shown in Figure 3.
The hydrogen comes from pickling before oxidation and blackening. To this end, according to its process, combined with material knowledge, analysis of metallography and hardness using magnifying glass, microscope and other aspects. This structure is easy to produce a larger internal stress at the bottom of the inner hexagon when the external thread is rolled; the part is in After the external thread is rolled, pickling is used to remove oil and rust during the surface oxidation treatment, which leads to hydrogen infiltration into the parts (according to the hydrogen content detection, the hydrogen content of the nut is as high as 6~7ppm), and the hardness of the broken parts is relatively high.
Through analysis and observation, it is uniform tempered sorbite, no abnormality. Too high hydrogen content can easily lead to hydrogen embrittlement. (4) Chemical composition analysis. Due to the presence of oxidation corrosion on the section3, it is impossible to determine whether there is chicken claw-shaped hairline on the surface; the microscopic morphology of the outer edge of the fracture4 is a dimple morphology, and this area is the terminal zone.9 fasteners. The surface hardness of the fractured part is too high, which does not meet the level of 12
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