The chemical composition of the 42CrMo continuous casting rolls meets the requirements, but longitudinal cracks are found in the large neck position after finishing the car. The rough fracture is a brittle fracture, and there is a small facet that emits light. The crack source expands to the periphery of the fracture, and the expansion stress decreases. Microscopically, it was found that the crack source originated from the weak parts of non-metallic inclusions, coarse lamellar pearlite, Wei's structure, and stress concentration.
Causes of cracks in 42CrMo continuous casting rolls:
1. The content of non-metallic inclusions is more, reaching D3 level; improper forging, retaining the as-cast morphology, low-melting inclusions between dendrites, chemical composition segregation and as-cast defects; quenching and tempering treatment temperature is too high or holding time is higher Long, forming the Wei's structure, reducing the mechanical properties of the continuous casting rolls.
2, the rough car eats a large amount of the knife, the machined surface is subject to large tensile stress, and the formation of a large tensile stress on the surface is an external cause of cracking.
3. The large neck is the stress concentration part, which is a weak link and there is stress concentration.
Therefore, the control measures are:
1. Before entering the factory, the raw materials should be tested for high and low-fold microstructure, non-metallic inclusion content and microstructure.
2, the forging process should be carefully implemented, forging ensures sufficient compression ratio to break the cast dendrites, and truly plays a role in uniform organization to eliminate chemical composition segregation and as-cast defects.
3. Appropriately reduce the quenching temperature in the quenching and tempering treatment so that it is controlled at 30~50 °C above Ac3, the holding time should not be too long, and the cooling rate is appropriate.
4. Under the premise of not affecting the processing efficiency, the amount of the knife should be smaller, reduce the machining stress, and avoid machining cracks.
5, without affecting the roller work, the size of the large neck should be designed to reduce the stress concentration
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