敏化温度对SAF2304双相不锈钢耐局部腐蚀性能的影响

THE INFLUENCE OF SENSITIVE TEMPERATURE ON THE LOCALIZED CORROSION RESISTANCE OF DUPLEX STAINLESS STEEL SAF2304

用双环电化学动电位再活化法(DL EPR)和临界点蚀温度(CPT)分别评价了在不同温度(600—950℃)下敏化处理2 h对SAF2304双相不锈钢的耐晶间腐蚀性能和耐点蚀性能的影响、并通过电化学蚀刻技术结合SEM对材料的微观组织演变进行了表征.结果表明,随着敏化温度的升高,SAF2304双相不锈钢的耐晶间腐蚀性能和耐点蚀性能都是先变差后增强,在700和750℃下敏化处理2 h后其耐局部腐蚀性能最差.对材料微观组织形貌的表征显示,Cr_2N的析出及其周边贫Cr区的形成是导致材料耐蚀性能下降的主要原因.

Duplex stainless steels （DSS）, characterized by a two-phase microstructure of ferrite （α） and austenite （r）, have an attractive combination of mechanical strength and corrosion resistance in various aggressive environment. DSS SAF2304 shows wide application potential due to its lower cost compared with conventional DSS and better corrosion performance than austenite steel. However, precipitations of detrimental phases inevitably occur when DSS is heated to temperatures ranging from 300 ℃ to 1000 ℃during manufacturing and welding procedures. These precipitations will lead to the reduction of corrosion resistance of DSS due to the presence of chromium-depleted zones around them. This work investigates the influence of sensitive temperature on the localized corrosion resistance of DSS SAF2304. The resistances to intergranular corrosion and pitting corrosion of DSS SAF2304 annealed at various temperatures ranging from 600 ℃ to 950 ℃ for 2 h were investigated by means of double loop electrochemical potentiodynamic reactivation （DL-EPR） technique in a solution of 1 mol/L H2SO4＋1 mol/L HCI＋0.2 mol/L NaC1 at 30 ical pitting corrosion temperature （CPT） technique in ℃ with a scanning rate of 1.667 mV/s and crit- a solution of i mol/L NaC1 with a rising rate of 1 ℃/min, respectively. The morphologies and microstructures of the specimens after electrolytic etching in 30%KOH, oxalic acid and potassium metabisulfite were characterized by OM and SEM techniques. A same trend was observed by the different evaluating techniques, which suggested thatboth of the resistances of intergranular corrosion and pitting corrosion of DSS SAF2304 decreased with the annealing temperature increased from 600 ℃ to 700 ℃, while a contrary trend was found from 750 ℃ to 950 ℃. In particular, the samples annealed at 700 and 750 ℃ suffered the severest corro- sion. The relationship between microstructure and localized corrosion resistance was revealed by the evolution of the microstructure, and it was found that the deterioration of the resistance to localized corrosion was due to the formation of chromium depleted zones around the precipitation of Cr2N.