Analysis of the Low Service Life of a Planing Knife – A Case Study

The presented work deals with an analysis of causes of the very low service life of the new version of hand woodworking planing knife, which has replaced the original version of a planing knife. Based on the performed experimental works, chemical analysis, macroscopic and microscopic observation, SEM, diffractometric analysis, and Vickers hardness test it was concluded that the cause for the very low service life (practically the nonexistent one) of the new version of a planing knife are significant features of overheating. During the heating to the hardening temperature used steel was overheated, the cementite carbides dissolved, and the austenitic grains became coarse. The final microstructure of the used steel after hardening and tempering consists of brittle coarse martensitic needles, without any presence of the fine globular cementite carbides, accompanied by a very high amount of retained austenite. Thus, the chipping of the knife's cutting edge took place and the planer was unusable.