Duplex stainless steel

A duplex ferritic austenitic TRIP stainless steel having a proportion of austenite phase in a microstructure of the duplex stainless steel of 55-70 volume %, the rest being ferrite, having undergone heat treatment at a temperature range of 900-1200° C., wherein:

• the duplex ferritic austenitic TRIP stainless steel includes greater than 0 and less than 0.04 weight % carbon, 0.2-0.8 weight % silicon, greater than 0 and less than 2.0 weight % manganese, 16.5-19.5 weight % chromium, 3.0-4.7 weight % nickel, 1.5-4.0 weight % molybdenum, greater than 0 and less than 3.5 weight % tungsten, greater than 0 and less than 1 weight % copper, 0.13-0.26 weight % nitrogen, the rest being iron and inevitable impurities occurring in stainless steels;
• the duplex ferritic austenitic TRIP stainless steel includes 16.9<(Si+Cr)<19.5, 2.0<(Cu+Mo+0.5W)<4.0, 0.16<(C+N)<0.29, 3.0<(Mn+Ni)<5.5, wherein Si, Cr, Cu, Mo, W, C, N, Mn and Ni are expressed in weight %;
• the duplex ferritic austenitic TRIP stainless steel has a measured Md30 temperature greater than 10° C. and less than 60° C.;
• the measured Md30 temperature defined as the temperature at which 0.3 true strain yields 50% transformation of the austentite to martensite, the fraction of the transformed martensite measured with Satmagan equipment;
• and
• the duplex ferritic austenitic TRIP stainless steel has a pitting resistance equivalent value (PRE) of the duplex stainless steel is 30-36, the PRE calculated as follows:
• PRE=Cr+3.3(Mo+0.5 W)+30 N—Mn, wherein Cr, Mo, W, N and Mn are expressed in weight %;
• the duplex ferritic austenitic TRIP stainless steel has a critical pitting temperature CPT in the range of 34-45° C., where the CPT is measured in a 1 M sodium chloride (NaCl) solution according to ASTM G150 test.