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A D V A N C E D M A T E R I A L S & P R O C E S S E S | N O V E M B E R / D E C E M B E R 2 0 1 8 2 7 deformation also produce more mar- tensite phase transformation in this region. The effective strain value is equiv- alent to the ratio of area difference Fig. 5 — Diffraction peaks (top) andmartensite content (bottom) measured at locations on outer wall of dome-shaped specimen. Fig. 6 — Relationship between effective strain andmartensite content and residual stress at locations on outer wall of dome-shaped specimen after deformation. after forming to the area prior to forming. Values from position 1 through po- sition 6 on the specimen are 0.021, 0.033, 0.015, 0.005, 0.102, and 0.133. Figure 6 shows the relationships be- tween effective strain and martensite content and residual stress of the spher- ical specimen outer wall after deforma- tion. Effective strain in the arc segment of the specimen changes smoothly during forming. The turning point is in the transition section where it quick- ly decreases then rapidly increases in the straight section reaching a maxi- mum value. In the straight section, ef- fective strain is 0.031 higher than in the transition section. Increasing effective strain due to greater material inhomo- geneity enhances martensite phase transformation.Martensitecontent(vol- ume fraction) increased by 0.468 lead- ing to an increase in residual stress of 605 MPa. For austenitic stainless steel, temperature affects the distribution of residual stress. However, in this case, the change in residual stress is essen- tially due to differences in stress caused by the changes in microstructure at dif- ferent temperatures. EFFECTS OF STRAIN-INDUCED MARTENSITE PHASE TRANSFORMATION Deformation-induced martensite phase transformation can be analyzed using the martensite phase-transfor- mation driving force [8-10] . Stress in the straight section of the specimen outer wall is complex and the degree of de- formation is larger (Fig. 7). The greater mechanical force, which drives marten- site phase transformation, increases martensite content resulting in greater microstructural inhomogeneity. There- fore, increasing stress increases de-