Microstructual Investigations Of The Shot Peened Steel 42 Crmo 4 In Diff.heat Treat Cond.by Aid Of X-ray Profile Analysis

Author:  Burgahn, Vohringer, Macherauch
Source:  Conf Proc: ICSP-4, (p.199-208)
Doc ID:  1990042
Year of Publication:  1990
The dislocation density in the surface layers of shot peened materials changes in a characteristic way with the distance from surface and the hardness of the material. The determination of the dislocation density p(t)-values, with the transmission electron microscopy is very difficult. However, the X-ray interference profile analysis allows this determination in an integral manner. Therefore, it is necessary to separate from a real profile the physical profile f using a standard specimen of the instrumental broaded profile h. The profiles are approximated with the Voigt-function, a convolution of Gauss- and Cauchy-functions. Then, the physical profile f is set to calculate the mean microstrain <&(2)>(1/2) and the domain size D. In special circumstances, it is possible to estimate the dislocation density p(t), because p(t) - <&(2)>(1/2)D. Results of a single line analysis will be presented for the shot peened steel 42 CrMo 4 (A1S1 4140) in different heat treatment conditions. The microhardness, the macro residual stresses, the mean microstrain and the domain sizes versus distance from surface were evaluated. Shot peening causes an increase in the mean microstrain near the surface (workhardening) for materials with a microhardness lower than 400 HV).3 in the unpeened condition. Materials with a microhardness larger than 500 HV0.3 worksoften as a result of shot peening induced changes in the microstructure. Shot peening causes a decrease of the domain size in material states with low hardness. At high hardness, the domain size will be not influenced. These findings will be discussed together with shot peening induced changes in the microstructure. Descriptors: Residual stress; Half width; Dislocation density; Microstrain; Domain size; Profile analysis; Workhardening; Worksoftening

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