Hot Deformation and Cracking during Compression of 21-4N Steel

Abstract

Hot compressive deformation and cracking behaviors of cast 21-4N steel were investigated over a temperature range between 900°C~1250°C. The strength of the specimen at the outer surface of ingot is greater than that in the inner part because of the initial rapid solidification and corresponding fine structure at the outer surface. The initial flow stress hump in the stress-strain curves can be attributed to the dynamic recrystallization, which requires the initial strain energy build-up before the activation of grain nucleation process. With increase of temperature the critical stain for dynamic recrystallization decreases and at high enough temperatures, no critical strain for the build-up of strain energy is needed. At temperatures between 1000°C and 1200°C, homogeneous deformation occurred and no cracks were observed even after 50% strain. The cracks observed below 1000°C could be associated with the more difficult plastic flow in the presence of carbides and nitrides. The presence of fatal crack at 1250°C and the loss of hot ductility can be attributed to the partial melting in austenite grain boundaries at high temperatures.

Effect of magnesium on the morphology of carbides and on M7C3→M23C6 carbides transformation in the 21-4N heat-resistant steel

“…Heat-resistant steel 53Cr21Mn9Ni4N (21-4N steel) has been widely used for engine exhaust valves because it has excellent strength and toughness at high temperatures, as well as strong corrosion resistance in extreme working environments [1]. In the past decades, 21-4N steel has attracted the attentions of scientists and engineers [2][3][4][5][6].…”

Crack formation of steel reinforced concrete structure under stress in construction period

“…In construction, core tube and external framework will both deform under the effects of their own weights and construction loading; due to the compression of structure, the height of buildings will decrease [15]. To solve the problem, construction leveling is adopted in actual construction to make up the loss caused by vertical compressive deformation [16,17]. The following two methods are usually adopted to perform construction leveling.…”