Structural strength and plasticity of metastable austentic steels

Conclusions

• 1. In hardened austenitic Kh12N19T3 steel exposed to tension at temperatures t_test=20 and −196°C, the stress concentration produced by annular notches of various depth causes a reduction in relative elongation. The course of martensite γ → α-transformation during the process of specimen stretching at t_test=−196°C helps to obtain a higher level of plasticity than at a temperature t_test=20°C, at which Kh12N18T3 steel has a structure of stable austenite.

• 2. In hardened austenitic 10Kh18AG21 and 55Kh4G18F steels on iron-manganese base after tension at 20 and 300°C the stress concentration produced by annular notches of various depth causes a reduction of relative elongation. The course of martensite γ → DD → ε- transformation at t_test=20°C does not lead to an increase of their plasticity as compared with the plasticity of specimens tested at t_test=300°C which have the structure of stable austenite. The more packets DD+ε are formed during stretching the smaller is the relative elongation.

• 3. Viscous failure in iron-nickel 10Kh12AG21 steel is observed at t_test≥−196°C, while in iron manganese 10Kh12AG21 and 55Kh5G18F steels it is observed at t_test≥20°C. In the case of viscous fracture the values of coefficients${\text{K}}_{\text{1}} ^{\text{T}} \sigma _{\text{u}} ^{{\text{nt}}} /\sigma _{{\text{0}}{\text{.2}}}$ and${\text{K}}_{\text{2}} ^{\text{T}} = \sigma _{\text{T}} ^{{\text{nt}}} /\sigma _{{\text{0}}{\text{.2}}}$ is higher in hardened iron-nickel steel than in iron-manganese steels.