摘要
Abstract
The tubesheet is a critical pressure-bearing component in heat exchangers,typically thick and predominantly made from carbon steel or low-alloy steel.To enhance corrosion resistance,corrosion-resistant alloys are often surfacing-welded onto the tubesheet.Duplex stainless steel is widely used in the surfacing of heat exchanger tubesheets due to its high strength and exceptional resistance to stress corrosion cracking.The selection of appropriate welding materials and surfacing processes is key to achieving a balanced austenitic(γ)and ferritic(δ)two-phase structure in the duplex stainless steel surfacing layer.Because of the high ferrite content in duplex stainless steel,harmful phases may precipitate from the ferrite at elevated temperatures,significantly degrading the material's overall performance.Therefore,conventional stress relief heat treatments in the range of 600℃to 900℃cannot be applied to duplex stainless steel surfacing layers.When the tubesheet material has high hardenability and post-welding heat treatment is required,austenitic stainless steel should be used as a transition layer,and heat treatment should be performed after the transition layer is surfacing-welded.The linear expansion coefficient of duplex stainless steel is similar to that of carbon steel or low-alloy steel,allowing for direct surfacing welding onto tubesheets with good weldability.In such cases,no transition layer or conventional stress relief heat treatment is needed.Experimental comparisons and practical applications demonstrate that both welding processes with and without a transition layer are suitable for tubesheet surfacing.If the process parameters are properly selected,a surfacing layer with a ferrite content of over 40%can be achieved,ensuring excellent overall performance.Notably,the surfacing process without a transition layer offers significant advantages and should be prioritized whenever conditions permit.关键词
双相不锈钢/管板/带极堆焊/电渣堆焊/过渡层/热处理Key words
duplex stainless steel/tubesheet/strip surfacing welding/electroslag welding(ESW)/transition layer/heat treatment分类
机械制造
