Measurement of retained asutenite by using x-ray diffraction method and residual stress by indentation technique in steels

Retained austenite and residual stress after various production stages such as welding, casting, surface processing and heat treatment processes remain in the parts. X-ray diffraction is considered to be the most accurate method of determining the amount of retained austenite in steels. By utilizing instrumented sharp indentation which is a semi-destructive technique, residual stresses produced by various different processes on material surfaces can be directly measured. It?s evident through current studies that results obtained by using this technique are robust enough to compare its results with those of other methods. As a fast and reliable means of residual stress evaluation, it?s believed that this technique will become a common practice in the foreseable future.In this research, heat treated AISI 5115 (16MnCr5) cementation and AISI 52100 roller bearing steels were investigated. Specimens with and without residual stresses that were sectioned by wire-erosion machine. Specimens were properly sanded and polished to get smooth surfaces. Optical micrographs of each specimen were taken by a Nikon Eclipse ME 600 metallographic microscope. Their retained austenite content was determined by the X-ray diffraction technique. These specimens were then examined by using a Dynamic Ultra Micro Hardness (DUH) tester under the maximum loads of 200, 400, 600, 800 and 1000 mN. Specimens with and without residual stresses that were subjected to loading-unloading cycles under the same amount of maximum load and their load vs. penetration depth curves were plotted. By comparing the resultant loading-unloading curves, the type of the residual stresses present in the specimens was determined. Seperate calculations were made for tensile and compressive residual stresses to obtain the residual stress values.