Quench cracking along a line of aluminum oxide dross particles in a hex head capscrew. The aluminum oxide particles were probably added as a "killing" agent in the steeling practice. The gray material in the crack interior is high-temperature oxide formed during tempering. The microstructure is 44 HRC quench and tempered martensite. 2% Nital Etch, 200X
The Hendrix Group, Inc. | 15823 N. Barkers Landing | Houston, Texas 77079 | Phone: (281) 556-8774 | Fax: (281) 870-0659