Viscoplastic behaviour of steels during phase transformations

Abstract

That contribution to transformation plasticity of steels arising from the so-called Greenwood-Johnson mechanism is often described using the model developed by Leblond and coworkers. This model made the assumption of purely plastic behaviour. It is extended here to incorporate viscous effects, which are present during some transformations, especially at high temperatures. The predictions of the original and extended models are compared to experimental results for a material for which the second contribution to transformation plasticity, due to the so-called Magee mechanism, is known to be negligible, and it is shown that the incorporation of viscous effects into the model significantly improves its predictions.

Comparison of different approaches to transformation‐induced plasticity in steel

“…In [20], elasto-viscoplastic behaviour of austenite was included. As this does not change the essentials of the model, we drop this here.…”

Simplified method for establishing constitutive equations and flow stress data for welding stress modelling

“…If the temperature reaches T 0 , w is reset to zero. The parameters F i (T), w 0 i (constant) and n i (T) have been obtained by fitting equation (10) to data found in Ref. 12.…”

“…In order to address these differences in more detail, Fig. 8a and b display respectively the temperature development and hardening parameter w in equation (10) in points A, B, and C versus time. It is revealed that the material points just outside the HAZ, which exhibit the largest deviations, neither experience a phase transformation (point A experiences a partial phase transformation) nor reach the relaxation temperature T 0 of 900uC above which the hardening parameter w is reset to zero.…”

“…8b, the hardening parameter w in equation is zero and about 0?0052 at the beginning and by the end of the first pass respectively. Equation (10) with the given parameters inserted then gives flow stresses of 421 and 539 MPa at room temperature respectively.…”

Viscoplastic behaviour of steels during welding

“…24,25 These parameters have been measured between 400 and 700uC for bainite and martensite and between 700 and 1100uC for austenite. For example, the left part of Fig.…”