Effect of low-temperature aging on corrosion resistance of 18Cr--2Mo titanium-stabilized ferritic stainless steel

Corrosion tests were conducted on 18Cr--2Mo titanium-stabilized ferritic stainless steel aged at 6200C for various time periods. Sensitivity to intergranular corrosion was detected in the Streicher test but not in the Strauss or Warren tests. The corrosion resistance in 45 percent boiling formic acid and in dilute chloride solution (600 ppM Cl- + 20 ppM Cu++, 900C) was unaffected by aging at 6200C. Pitting potentials in molar NaCl at 250C were also unaffected by the 6200C heat-treatment. Corrosion tests were also performed with the same 18Cr--2MoTi stainless steel aged at 4750C for 240, 2400, and 4800 h (18Cr--2MoTi steel is embrittled after 240 h at 4750C). The 4750C heat-treatment affected corrosion resistance to boiling formic acid. Corrosion resistance started to deteriorate after 2400 h aging and was seriously impaired after 4800 h aging. Pitting potentials were rendered less noble by the 4750C treatment. The 4750C embrittlement did not result in sensitization to intergranular corrosion in any environment as contrasted to the 6200C treatment which did sensitize the steel to intergranular corrosion in the Streicher test. (U.S.)