A process-structure-property model for welding of 9Cr power plant components: The influence of welding process temperatures on in-service cyclic plasticity response

Abstract

A process-structure-property methodology is presented for welding of 9Cr steels under representative flexible operating conditions for a typical thermal power plant girth-welded pipe. The welding-induced evolution of microstructural variables is represented via (i) a solid-state phase transformation model for martensite-austenite transformation and (ii) empirical equations for prior austenite grain size, martensite lath width, hardness and M23C6 precipitate diameter and area fraction, calibrated from published heat treatment data.The temperature-dependent, physically-based, unified viscoplastic constitutive model, which includes a fatigue damage initiation criterion, is based on dislocation density evolution and is validated against high temperature cyclic plasticity data at a range of relevant temperatures for parent material P91, including combined isotropic-kinematic hardening effects. This model is shown to successfully predict weld-life reduction factor for cross-weld tests. The effects of key welding process variables on the microstructure gradient in the heat-affected zone, and associated thermo-mechanical, cyclic plasticity response are assessed. The inter-critical and fine-grained heat-affected zones are identified as the critical regions, consistent with observed plant experience. Increasing post-weld heat-treatment temperature from 760 o C from 780 o C is predicted to be detrimental due to increased precipitate coarsening. In contrast, increasing preheat and interpass temperature from 350 o C to 400 o C is predicted to be beneficial due to increased hardness in the critical regions.

A review of thermal, microstructural and constitutive modelling of 9Cr steel for power plant applications: Towards a through-process model for structural integrity of welded connections

“…This, combined with the microstructure evolution models discussed previously, should enable (future) more accurate predictions of the weld-region microstructure, which together with physically-based continuum structural models, should, in turn, facilitate more accurate predictions of in-service performance of welded components, e.g. along the lines of recent work by Mac Ardghail et al [99].…”

“…The work of Galindo-Nava, for example, is highly physically-based whereas other authors have used more empirical approaches with fitting-parameters, e.g. [99]. The ability to predict microstructure evolution with precision is important in the context of physically-based constitutive modelling.…”

Material Characterisation and Computational Thermal Modelling of Electron Beam Powder Bed Fusion Additive Manufacturing of Ti2448 Titanium Alloy

“…They caused a gradient along sample height and a gradient along the sample radius in α phase content and in grain size. This work could be further developed into an integrated through-process thermal history based microstructural evolution model, similar to recent computational PBF-LB [ 59 , 60 ] and weld [ 61 , 62 ] simulation tools. Such tools can be used by experimentalists and in industry to optimise the design of PBF-EB process parameters to achieve optimal material microstructures in order to benefit in-service mechanical performance.…”

Corrosion behavior of T24, T92, VM12, and AISI 304 steels exposed to KCl–NaCl–K2SO4–Na2SO4 salt mixtures

“…The T24 steel, with 2.4‐wt% Cr, has a maximum service temperature limited to 575°C according to ASME Code Case 2540. Otherwise, the T92 and VM12 steels, with 9‐ and 12‐wt% Cr, [ 12,13 ] have a maximum operating temperature of 600°C and 620°C, respectively. These ferritic steels have been described deeply in previous works.…”