Metallurgical investigation of cryogenically cracked M35 tool steel

Specimens of a complex alloyed high speed tool steel (M35) were hardened at 1200 degrees C, cryotreated at -185 degrees C, soaked for 4-48 h and followed by triple Tempering at 400 degrees C. Material processed in this manner was found to exhibit longitudinal cracking immediately after cryogenic processing. This research work reports and analyzes the results of various characterization techniques such as hardness, wear rate, SEM, and residual stresses for the investigation of the cause of failure. It was found that as-hardened (H) specimen when cryotreated increases hardness and residual stresses. The kinetic of carbides precipitation is found to be governed by the amount of cryosoaking time (4-48 h). It was concluded that excessive accumulation of residual stresses at cryogenic temperature is the prime parameter for the cracking to occur by way of shear fracture and the responsible factors are resolved using the proposed failure mechanism. (C) 2011 Elsevier Ltd. All rights reserved.