EFFECT OF SOLUTION TEMPERATURE ON MICRO- STRUCTURE AND PITTING CORROSION RESISTANCE OF S32760 DUPLEX STAINLESS STEEL
Yulai CHEN1,Zhaoyin LUO2,Jingyuan LI2()
1 Metallurgical Engineering Research Institute, University of Science and Technology Beijing, Beijing 100083 2 School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083
In order to obtain the optimal corrosion resistance, the characteristics of microstructure and alloy elements distribution of S32760 duplex stainless steel were studied after solid solution treatment at various temperatures from 1000 ℃ to 1300 ℃ by means of OM, EPMA, SEM, EDS and TEM. In addition, the pitting corrosion resistance was measured by the electrochemical workstation. The results show that the N atoms diffused into d phase from g phase during solution treatment when the temperature was higher than 1080 ℃. N atoms migrated back into g phase when the subsequent cooling was slow enough. However, Cr2N phase in situ precipitated during quenching because there was not enough time for the N atoms to diffuse back into g phase. Cr2N particles increased with the solution temperature increasing. Furthermore, s phase precipitated when the tested sheet was heat treated at or below 1040 ℃ due to the high content of N. Thus it is obvious that the solution temperature range of the S32750 duplex stainless steel is quite narrow, which is between 1040 ℃ and 1080 ℃, and it is confirmed that the optimal temperature is 1060 ℃. After treated at 1060 ℃ for 60 min, the Brinell hardness of S32760 steel is 249 HBW, pitting potential is up to 1068 mV and the passive current density is as low as 1.48×10-4 A/cm2.