Recrystallization-thermal etching of local plastic strain in heat resistant alloys

Abstract

A recrystallization-thermal etching technique used with heat resistant alloys (Type 304, 2.25Cr-lMo and HastelloyX) has been developed, by which the measurement of the plastic zone and plastic strain around notch or crack at elevated temperatures can by quantitatively made. The optimum annealing conditions are in a vacuum in the range of 2.7 × 10−3 to 1.3 × l0−4 Pa for 86.4 ks at 1223 K (Type 304), at 1098 K (2.25Cr-lMo) and at 1248, 1303 and 1343 K (HastelloyX). Detectable critical strain is 0.02 for Type 304, 0.2 for 2.25Cr-lMo and 0.2 ∼ 0.03 for HastelloyX. The plastic zones in notched tensile specimens loaded to the ultimate tensile strength at temperatures from 298 to 1273 K were successfully observed with the technique. Local plastic strain near the crack was also measured. The effect of the work hardening characteristic on the strain gradient is shown.