An Incremental Physically-Based Model of P91 Steel Flow Behaviour for the Numerical Analysis of Hot-Working Processes

Alberto Murillo-Marrodán,Eli Puchi-Cabrera,Laurent Dubar,Mirentxu Dubar,Eduardo García,Fernando Cortés

doi:10.3390/met8040269

Abstract

This paper is aimed at modelling the flow behaviour of P91 steel at high temperature and a wide range of strain rates for constant and also variable strain-rate deformation conditions, such as those in real hot-working processes. For this purpose, an incremental physically-based model is proposed for the P91 steel flow behavior. This formulation considers the effects of dynamic recovery (DRV) and dynamic recrystallization (DRX) on the mechanical properties of the material, using only the flow stress, strain rate and temperature as state variables and not the accumulated strain. Therefore, it reproduces accurately the flow stress, work hardening and work softening not only under constant, but also under transient deformation conditions. To accomplish this study, the material is characterised experimentally by means of uniaxial compression tests, conducted at a temperature range of 900–1270 °C and at strain rates in the range of 0.005–10 s−1. Finally, the proposed model is implemented in commercial finite element (FE) software to provide evidence of the performance of the proposed formulation. The experimental compression tests are simulated using the novel model and the well-known Hansel–Spittel formulation. In conclusion, the incremental physically-based model shows accurate results when work softening is present, especially under variable strain-rate deformation conditions. Hence, the present formulation is appropriate for the simulation of the hot-working processes typically conducted at industrial scale.

Highlights

The P91 steel grade is a widely used material in power-plant header applications, such as heavy-section boiler components, heat exchangers, piping and tubing, etc
Under temperatures higher than 950 ◦ C, both dynamic recovery (DRV) and DRX dynamic restoration mechanisms are present depending on the strain rate conditions under which the deformation is conducted
The industrial manufacturing of different components by hot-metalworking operations, is mostly conducted under transient deformation conditions and, the prediction of the flow stress, work-hardening and work-softening rate must be carried out based on valid state parameters

Summary

Introduction

The P91 steel grade is a widely used material in power-plant header applications, such as heavy-section boiler components, heat exchangers, piping and tubing, etc. The interest in this ferritic–martensitic steel arises mainly due to its high creep strength and toughness at elevated temperatures, enhanced oxidation and corrosion resistance, low thermal expansion coefficient and low cost as compared to other high-temperature alloys [1]. One of the aspects which has been investigated to a much lesser extent is that concerning the formulation of the constitutive description of this material during deformation under hot-working conditions Such relationships are of fundamental importance in numerical behaviour and the optimisation of industrial hot-working operations employed in the manufacturing of high-temperature components by means, for example, of the Mannesmann process for the production of seamless tubes

Objectives

Methods

Results

Discussion

Conclusion