Change in the structure and properties of austenitic corrosion-resistant steel under dynamic recrystallization

Institute of Problems of Superplasticity of Metals, Russian Academy of Sciences. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 8, pp. 19–22, September, 1993.     

New grain formation during warm deformation of ferritic stainless steel

Microstructural evolution accompanied by localization of plastic flow was studied in compression of a ferritic stainless steel with high stacking fault energy (SFE) at 873 K (≈0.5 Tm). The structure evolution is characterized by the formation of dense dislocation walls at low strains and subsequently of microbands and their clusters at moderate strains, followed by the evolution of fragmented structure inside the clusters of microbands at high strains. The misorientations of the fragmented boundaries and the fraction of high-angle grain boundaries increase substantially with increasing strain. Finally, further straining leads to the formation of new fine grains with high-angle boundaries, which become more equiaxed than the previous fragmented structure. The mechanisms operating during such structure changes are discussed in detail.     

Recrystallization kinetics of an austenitic high-manganese steel subjected to severe plastic deformation

The evolution of the microstructure and the properties of an austenitic high-manganese steel subjected to severe deformation by cold rolling and subsequent recrystallization annealing is investigated. Cold rolling is accompanied by mechanical structural twinning and shear banding. The microhardness and microstructural analysis of annealed samples are used to study the recrystallization kinetics of the high-manganese steel. It is shown that large plastic deformation and subsequent annealing result in rapid development of recrystallization processes and the formation of an ultrafine-grained structure. A completely recrystallized structure with an average grain size of 0.64 μm forms after 30-min annealing at a temperature of 550°C. No significant structural changes are observed when the annealing time increases to 18 h, which indicates stability of the recrystallized microstructure. The steel cold rolled to 90% and annealed at 550°C for 30 min demonstrates very high strength properties: the yield strength and the tensile strength achieve 650 and 850MPa, respectively. The dependence of the strength properties of the steel on the grain size formed after rolling and recrystallization annealing is described by the Hall–Petch relation.     

Effect of Liquid Hot Isostatic Pressing on Structure and Mechanical Properties of a Sand-Cast A356.02 Alloy

The effect of liquid hot isostatic pressing (LHIP) on the structure and mechanical properties of an A356.02 alloy was examined. It was shown that LHIP provides a porosity decrease from ~0.9 to 0.2 pct due to the elimination of shrinkage voids. As a result, the yield stress (YS) increases from 200 to ~230 MPa, the ultimate tensile strength (UTS) increases from ~275 to 310 MPa, the total elongation increases from ~4 to ~7.5 pct, and the fatigue strength increases from ~88 to ~140 MPa. It was found that the sequence of LHIP and homogenization annealing highly affects the hardness and variability in fatigue strength. LHIP followed by homogenization annealing provides the lowest scattering of fatigue strength and, therefore, the fabrication of the most reliable casting components.