Fatigue of Autofrettaged Thick Tubes: Effect of Thermal Shock, Electropolishing, and Tempering

Abstract

Thick tubes of 32.3 mm (1.27 in.) ID and wall ratio of 2.5 for SAE 4333 steel were subjected to fatigue testing after the following treatments: normal autofrettage followed by thermal shock; electropolishing; electropolishing then normal autofrettage; electropolishing then normal autofrettage then thermal shock; electropolishing then open-ended autofrettage; tempering from Rc 36 down to Rc 29. Results showed a thermal shock of 600°C for 3 s reduced the fatigue strength of autofrettaged specimens 6 to 8 percent. Electropolishing reduced the fatigue strength 13 percent for as-received bores and 6 percent for autofrettaged bores. Double tempering to Rc 29 reduced the fatigue strength 57 percent compared to Rc 36.