leometwu的部落格

紅十字, JIS SCM440, induction hardened. Corner locally over-heated,  coarse grains obtained and workpiece cracked on quenching.  These beautiful photos of Martensite are obtained by color etching, with a bit of luck and lots of labor. If you look closely, you will find grain diameter  is the largest at the bottom of the photo because it is the edge of a hole where induction heat concentrates. Crack is not shown here but it initiated from the corner of  the  hole.    At the bottom, grain diameter is about  50~90 um which is too coarse, therefore workpiece cracks readily on quenching.