Haiyan Yihui Bolt Factory specializes in producing all kinds of cap screws. We produce various DIN 933, DIN 603 and ANSI B18.2.1 products. At the same time, our products are widely praised and loved by our customers.
Haiyan Yihui Has Rich Experience In Manufacturing DIN 603 Bolts
Bolts, screws and studs of class 8.8~12.9 shall be tempered according to the minimum tempering temperature in actual production and kept at 10 °C for 30 min. On the same sample, the difference between the average values of the three points before and after the test shall not exceed 20 HV.
The tempering test can check the incorrect operation due to insufficient quenching hardness and too low temperature tempering to barely reach the specified hardness range, and ensure the comprehensive mechanical properties of the parts. In particular, threaded fasteners made of low-carbon martensitic steel are tempered at low temperatures. Although other mechanical properties can be achieved, the residual elongation fluctuates greatly when measured to ensure stress, much larger than 12.5 um. Moreover, sudden breakage can occur under certain conditions of use. In some automotive and construction bolts, sudden breakage has occurred. This can be reduced by tempering with a minimum tempering temperature. However, special consideration should be given to the manufacture of 10.9 bolts from low carbon martensitic steel.
2. Hydrogen embrittlement inspection
The sensitivity of hydrogen embrittlement increases as the strength of the fastener increases. For the externally threaded fasteners of 10.9 and above or the surface hardened self-tapping screws and the combination screws with hardened steel washers, the hydrogen removal treatment shall be carried out.
The hydrogen removal treatment is generally carried out in an oven or a tempering furnace at 190 to 230 ° C for 4 hours or more to diffuse hydrogen.
Threaded fasteners can be tightened by tightening on a special clamp to maintain the screw with a relatively constant stress, for 48 hours. After the loosening, the threaded fasteners will not break. This method is used as a method of checking for hydrogen embrittlement.
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