Effect of chromium plating on the endurance limit of steels used in aircraft

Abstract

Chromium plating reduced the endurance limits of both normalized and hardened (quenched and tempered) SAE X4130 steels; the reduction was larger for the harden ed steel. The endurance limits for steel of a given hardness decreased with increased plating bath temperatures. Baking of the plated steel, at temperatures up to 350 0 C, reduced the endurance limit; baking at 440 0 C increased the endurance li mit of the p lated steel. However (for hardened steel) baking did not restore the endurance limi t to that of the unplated steel. Damaging effects of chromium on the endurance limits of plated teel are attributed to stresses in the chromium and /or steel, which are increased by low te mperature baking but are relieved in part by baking at 400 0 to 440 0 C.