General expression of the Zener-Hollomon parameter as a function of the chemical composition of low alloy and microalloyed steels

Concepts derived from phase diagram studies for the strengthening of Fe–Al-based alloys

In order to improve the understanding of the dynamic and post-dynamic recrystallization behaviours of AISI 304 austenitic stainless steel, a series of hot torsion test have been performed under a range of deformation conditions. The mechanical and microstructural features of dynamic recrystallization (DRX) were characterized to compare and contrast them with those of the post-dynamic recrystallization. A necklace type of dynamically recrystallized microstructure was observed during hot deformation at 900 °C and at a strain rate of 0.01 s−1. Following deformation, the dependency of time for 50% recrystallization, t50, changed from “strain dependent” to “strain independent” at a transition strain (ɛ*), which is significantly beyond the peak. This transition strain was clearly linked to the strain for 50% dynamic recrystallization during deformation. The interrelations between the fraction of dynamically recrystallized microstructure, the evolution of post-dynamically recrystallized microstructure and the final grain size have been established. The results also showed an important role of grain growth on softening of deformed austenite.

Recrystallization in AISI 304 austenitic stainless steel during and after hot deformation

The hot deformation behavior of a 304 austenitic stainless steel was investigated to characterize the evolution of the dynamically recrystallized structure as a starting point for studies of the postdeformation recrystallization behavior. The effect of different deformation parameters such as strain, strain rate, and temperature were investigated. The flow curves showed typical signs of dynamic recrystallization (DRX) over a wide range of temperatures and strain rates (i.e., different Zener–Hollomon (Z) values). However, under very high or very low Z values, the flow curves’ shapes changed toward those of the dynamic recovery and multiple peaks, respectively. The results showed that while DRX starts at a strain as low as 60 pct of the peak strain, a fully DRX microstructure needs a high strain of almost 4.5 times the initiation strain. The DRX average grain size showed power-law functions with both the Zener–Hollomon parameter and the peak stress, although power-law breakdown was observed at high Z values.

https://ro.uow.edu.au/cgi/viewcontent.cgi?article=2012&context=engpapers

Hot deformation and recrystallization of austenitic stainless steel. Part I: dynamic recrystallization

The dynamic recrystallization (DRX) of AISI 304 stainless steel was studied with torsion test in the temperature range of 900–1100°C and the strain rate range of 5.0×10 −2 –5.0×10 0 s −1 . The initiation and evolution of DRX were investigated with microstructural analysis and then the critical strain for DRX initiation could be confirmed by analysis of flow stress. The volume fraction of DRX ( X DRX ) as a function of processing variables, such as strain rate ( e ), temperature ( T ), and strain ( e ) were established. For the exact prediction of X DRX , the variation of flow stress with strain was analyzed in detail. The calculation of grain size was based on X DRX and the investigated microstructure at a few points. It was found that the calculated results agreed with the microstructure of the alloy at any deformation conditions.

Dynamic recrystallization behavior of AISI 304 stainless steel

By collaborative work the Sheffield Leicester Integrated Model for Microstructural Evolution in Rolling (SLIMMER) has been developed for hot rolling of flat products. The background physical metallurgy is presented together with the expressions used to describe microstructure evolution for a range of ferrous and non-ferrous metals. The finite difference thermal model at the heart of SLIMMER computes heat loss to air, descalers, rolls and water cooling while allowing for oxidation and deformation heating. The use of temperature compensated time enables isothermally determined equations for microstructure evolution to be applied to practical non-isothermal conditions. Rolling loads and torques are calculated using Sims theory with an accurate prediction of mean flow stress. Examples of rolling niobium microalloyed steel plate and the effect of initial grain size illustrate the capabilities of SLIMMER and show some of the validation of the predictions.

Modelling Microstructure and Its Effects during Multipass Hot Rolling

Recent work on the ordered Fe-Al based intermetallics (B2-FeAl and D03-Fe3Al) for potential high temperature applications is reviewed with emphasis on improvements in mechanical properties achievable by processing and compositional control. Constitution and microstructure as well as the role of crystalline defects, including vacancies, dislocations, tubes, antiphase boundaries and grain boundaries are discussed. The influence and behaviour of these defects with respect to strength, work hardening, ductility and fracture are analysed. Proposed mechanisms for deformation and recent investigations on creep and fatigue of these materials are also reviewed. Current literature on ternary additions, multi-phase alloys and non-equilibrium processing is discussed.

C. Michael Sellars

Papers

Modelling Microstructure and Its Effects during Multipass Hot Rolling

Structure and Properties of Ordered Intermetallics Based on the Fe-Al System