fracture behaviour of p/m cr-v ledeburitic steel with different surface roughness

The samples made from the Vanadis 6 PM ledeburitic tool steel were surface machined to different quality and heat treated by standard regime of the processing. Three point bending tests were carried out on processed samples. It was found that the flexural strength decreased with decreasing surface quality. The lowering of flexural strength has been accompanied with the decrease of the plastic component of plastic straining preceeding to fracture initiation (work of fracture) of the material. It indicates that the surface roughness leads to the crack initiation before a larger plastic deformation of the material can be developed. Based on the results it can be suggested that to prevent the cracking of tools in the practice it is essential to make a surface machining (grinding, lapping, polishing) to as high quality as possible.