Effect of Liquid Carburizing at Lowered Temperature on the Micromechanical Characteristics of Metastable Austenitic Steel

Abstract

The effect of liquid carburizing at a temperature of 780°C on the micromechanical characteristics of the corrosion-resistant chromium–nickel austenitic steel (in wt %: Cr, 16.80; Ni, 8.44) has been studied in this work. According to instrumented microindentation data, it has been established that carburizing leads to the superficial hardening of the studied steel. An average increase in the indentation hardness HIT is nearly 500%. It has been demonstrated that carburizing also leads to an increase in the contact elasticity modulus of the steel E* that grew by 28% on average compared to E* in the quenched state. The carburized steel surface is characterized by an increased resistance to elastoplastic strain as evidenced by an increase in the parameters Re by 1.3–3.5 times, HIT/E* by 2.4–3.5 times, and $${{H_{{{\text{IT}}}}^{3}} \mathord{\left/ {\vphantom {{H_{{{\text{IT}}}}^{3}} {{{E}^{{*2}}}}}} \right. \kern-0em} {{{E}^{{*2}}}}}$$ by 49–109 times. On the contrary, the plasticity index δA decreases by 20% on average from 0.92–0.93 to 0.70–0.74 after carburizing. It has been shown that the instrumented indentation of the steel in the quenched state and after carburizing at different maximum indentor loads provides the possibility to perform a more precise analysis of the micromechanical characteristics of the gradient layer formed by means of carburizing by comparing them with the characteristics of the quenched steel. Based on the results of indentation at different maximum indentor loads, the gradient of properties in the thin carburized layer of up to 4 µm in depth has also been established.