The σ-phase precipitation rule in four kinds of typical ultra-low-carbon dual phase stainless steel 00Cr21Ni2Mn5N

00Cr22Ni5Mo3N

00Cr25Ni7Mo3N and 00Cr27Ni7Mo5N solid-solution-treaded at 1 050 ~ 1 120 °C and aged at 500 ~ 1 100 °C and the effect of σ-phase content on pitting corrosion potential of four kinds of ultra-low-carbon dual phase stainless steel are analyzed and studied by Thermo-Calc thermodynamic calculation

metallurgraphy and electrochemical method. Results show that with increasing ageing temperature the a-phase precipitation amount increases at earlier and decreases later

and with chromium-molybdenum content (/% ) in ultra-low-carbon dual phase stainless steel increasing progressive

ly in order of 20. 98-0. 03

22. 41-3. 16

25. 30-3. 46 and 26. 69-4 74

the peak amount of σ- phase precipitation increases progressively in order of 4. 9%

22. 5%

27. 0% and 40. 5%

while the σ-phase complete dissolution temperature increases in order of 660 °C

950°C

1 060 °C and 1 100 °C ； the more amount of σ- phase precipitation

the lower the pitting corrosion resistance of ultra-low-carbon dual phase stainless steel

and the corresponding E

b100

value to σ- phase precipitation peak of four kinds of steel is in order of -94. 0 mV

100. 1 mV

260. 2 mV and 117. 7 mV.