EFFECT OF MATRIX CONSTITUTIVE BEHAVIOR AND INCLUSIONS ON FORMING LIMITS OF FE-42 PCT NI-ALLOY SHEET

The effects of matrix constitutive behavior and nonmetallic inclusions on forming limit strains have been examined with five laboratory heat s of Fe-42 pet Ni alloy. The inclusion volume fi-action was varied bet ween approximately 0.01 and 1.59 pct by proper selection of Mn, S, and O contents. Each ingot was processed into 0.38-mm-thick sheets and he at treated to the recovered or the recrystallized condition. Forming l imit strains were obtained from uniaxial tensile, plane-strain tensile , and hydraulic bulge tests by circle grid analysis. In any strain pat h, the limit strain increased with increasing the strain hardening exp onent, n. The forming limit strains on the right-hand side of the form ing limit diagram (FLD) decreased with inclusion volume fraction, whil e no effects of the inclusion volume fraction were observed on the lef t-hand side. A decrease in the slope of the FLD on the right-hand side due to an increase in the inclusion volume fraction qualitatively agr ees with the theoretical calculation by Graf and Hosford, which was co nducted on the basis of the Marciniak-Kuczynski (M-K) theory.