why hydrogen embrittlement happen in fastener industryone of customer told us that you got some screws from other screw supplier,and the screws head broken when used.this is always happend in fastener industry especially
8.8,10.9,12.9 high strength screws and bolts,this is because of hydrogen embrittlement.below is the specific details of the reasons;
1.On the whole speaking.the deformation of cold heading process if meets the technical requirements.Special attention should be paid to the boundary between the rod and the head during the cold heading production. Do not displace up and down when over-molding. If there is no absolute guarantee, the head material is allowed to move slightly to the rod, and the rod is never allowed. The material moves slightly to the head, and it is not allowed to move slightly back and forth (the rod length is slightly shorter ); also pay attention to the transition with R at the boundary.
2. The main reason is improper material selection and heat treatment.
The first is to use the unit drawing to mark the error: such as the 8.8 grade hexagonal flange bolt, the material is 35K, and the technical requirement "heat treatment HRC22-32" (the corresponding should be "heat treatment HRC22-25"); another example is the 10.9 grade inner hexagon cylinder Head screws, material 35CrMo (or 40Cr),
technical requirements "heat treatment HRC32-35" (the corresponding should be "heat treatment HRC28-32").
The former JB of the National Ministry of Machinery has guiding standards, bolts: 8.8 ~ material 35K, heat treatment HRC22-25; 10.9 ~ material 35CrMo, 40Cr, heat treatment HRC28-32; 12.9 ~ material 42CrMo, heat treatment HRC35-38; 8.8 level The above are high-strength bolts. Different grades correspond to different materials and heat treatment hardness. Heat treatment of low-level materials to high-level hardness will cause heat treatment hydrogen embrittlement and head fracture hidden dangers. 40Cr (or 35CrMo) cannot be used to produce 12.9 grade screw.
Heatscrew has rich experience about this issue.if you meet some question,welcome to contact us
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