Optimized warm peening of the quenched and tempered steel AISI 4140

Using a modified air blast shot peening machine with an upgraded air flow heater system, warm peening at 20 less than or equal to T less than or equal to 410 degreesC was feasible. An optimized peening temperatures of about 320 degreesC was identified for quenched and tempered steel AISI 4140 by analyzing the stability of the shot peening induced residual stress states during cyclic loading. Additionally, the quasi-static surface compressive yield strength as well as the cyclic surface yield strength of optimally peened states were determined from residual stress relaxation tests. At these peening temperatures, the Bauschinger effect common in quenched and tempered steels was overcompensated by dynamic and static strain aging effects resulting in stabilized dislocation structures. Finally, the effect of warm peening on the fatigue behavior at alternating bending will be discussed. (C) 2002 Elsevier Science B.V. All rights reserved.