High Chromium Heat Resistant Steel Strengthening Method Based On M₂₃C₆ Component Design

High-chromium heat-resistant steel undergoes creep degradation in actual service.This kind of degradation is closely related to the evolution of precipitates.Therefore,precipitation strengthening is one of the strengthening methods of heat-resistant steel.Based on the elemental composition of the precipitation phase M₂₃C₆,this paper explores the effects of two elements W and B on the microstructure and high-temperature creep properties of the precipitate M₂₃C₆,after which the relationship among the W,B content,the microstructure and the creep properties of the M₂₃C₆will be established,providing an idea for the strengthening of high-chromium heat-resistant steel.Besides,JMatPro was used to perform thermodynamic simulation to determine the element ratio and thermal process parameters of five groups of experimental steels,and to predict the changes of ferrite,austenite matrix and precipitate M₂₃C₆,respectively.Additionally,the microstructures of high-chromium heat-resistant steels with different W and B contents after tempering and aging for 3000h were studied,which determines that the matrices always are martensite and retained austenite,and the precipitate is M₂₃C₆ with the heat-resistant steels of different B contents were tempered after 3000h.Besides,heat-resistant steels with different W contents are ferrite and martensite after tempering,and martensite after aging for 3000 hours,with precipitate M₂₃C₆.At the same time,it was found that both W and B could both inhibit the coarsening of M₂₃C₆.With the increase of W and B content,the number of M₂₃C₆increased,and the area fraction increased but the size of average particle decreased.At the same time,the W and B elements have the effects of refining grains and martensite laths.The W and B elements can improve the creep properties of high-chromium heat-resistant steel.As the W and B content increases,the minimum creep rate decreases,and the accelerated creep delay.Meanwhile,the fracture time of the high-chromium heat-resistant steel increases,and the strain and elongation decrease.Element B improves the creep performance by suppressing the coarsening of M₂₃C₆,strengthening the martensite stability,and facilitates the Orowan stress of dislocations;element W improves the creep performance by precipitation phase strengthening,solution strengthening,and dislocates strengthening.It was found that the Power law fits the rate curve of the creep deceleration stage of the high chromium heat-resistant steel best,and the law of Exponential fits the rate curve of the creep acceleration stage best.Lastly,the global constitutive equation that describes the entire creep process is derived.