Effect of Phosphate Coatings on Fatigue Crack Initiation in Quenched and Tempered Low Alloy Steel.

摘要

Fatigue testing was performed on small notched bend specimens of AISI 4335 high strength steel used for cannon barrels, breech rings and blocks. The effect of surface coatings of zinc and manganese phosphate on fatigue life to crack initiation was determined at two levels of applied stress, selected to cause failures in the range of 1000 to 10 000 cycles appropriate to cannon breech mechanisms. Both types of coating drastically decreased life to crack initiation compared with uncoated samples, the degradation being attributed to surface pitting and crevice attack by the phosphating process.