Probing true creep-hardening interaction in weld simulated heat affected zone of P91 steels

Abstract

The inducement of this paper was to discuss the novel perspective in establishing true creep-hardening interaction at room temperature by hardness and at high temperature by impression creep testing in two boron modified P91 steels. Different sub-heat affected zones(HAZs)were physically simulated. Their creep-strengths were governed by heat treatment,grain-size,hardness,boron addition,and microstructural stability. Post weld heat treatment resulted inreduction in hardness by 50%whereas, impression creep testing showed enhanced creep-strength (50–77%) and the narrow band of creep-damage (∼57%) in P91B steel than P91 steel. An increase in creep-rate with the increase inprior-austenitegra in size show edgra in boundary embrittlement in P91 steel. Whereas, with an increase in creep-rate and the corresponding decrease in prior-austenite grain size show edgra in boundary and sub-grain boundary hardening in P91B steel.Further more,type-IV(fine-grain HAZ) and type-III (coarse-grain HAZ) failures were observed depending upon critical prior-austenite grain size of 17μm in P91 and P91B samples respectively.Based on prior-austenitegra in size and creep-strength,sub-HAZs were classified into different classes pursuant to the nature of creep-damage and discussed systematically.Grain boundary hardening was ineffective for both coarse + finegra in HAZ(CF)and B-CF due to the lock in gmovement of fine-grains.However,the formation of soft ferrite grain sweakens both coarse+inter-critical HAZ(CI) and B-CI.ThisstudyprovidedbetterunderstandingoffailuremechanismsinP91andP91Bsteelsthatresultsin the delay of failures of power plant components.