In view of the main causes of the above cracks, we have taken corresponding measures.
1 Strengthen the strict inspection of incoming materials and control the quality of incoming materials. The inspection includes two aspects: macro aspect, mainly checking the appearance quality and surface defects such as micro crack folding; micro aspect, mainly testing the material composition, testing the internal defects such as segregation and white spot.
2 Establish strict forging system to control the uniformity of deformation degree. The forging method of “two light and one heavy” is adopted to reduce the deformation stress and internal defects.
3 The white spot and residual stress are controlled in the cooling process after forging.
(1) For large-scale parts, because of the complex structure and serious segregation of multi-element alloy steel, the decomposition transformation of austenite is not complete and there are too many retained austenite during the cooling after forging. Therefore, the recrystallization fluctuation isothermal cooling process with secondary subcooling can be used to make hydrogen have sufficient time to spread out and prevent white spots.
(2) For small parts, the method of slow cooling after forging can be used. For details, stack and cover insulation materials (such as insulation blanket or ash cooling in slow cooling pit, etc.).
For some workpieces with poor original state and many defects, heat treatment after forging should be carried out in time, and strict quenching and tempering process should be formulated to avoid cracking due to excessive quenching stress. Secondly, we should pay attention to prevent the influence of the “wind in the cold winter season”.
Based on the qualitative analysis of the causes of the cracks, the technological measures to control the cracks are formulated. The implementation process shows that these measures are effective and basically control the finished product defects of the gear shaft and gear of s17cr2ni2mo hard tooth surface reducer.