Effects of Straining, Aging, and Stress-Relieving on Mechanical Properties of Steels for Arctic Service

The effects of straining, straining + aging, and straining + aging + stress-relieving on tensile and Charpy V-notch impact properties were determined for several candidate arctic pipe and fitting steels. Possible compositional and processing means to maintain high as-rolled energy levels in strained + aged pipe are discussed. Heat treatment of 787 and Mn-Mo-Cb, as would be necessary in fittings, increased toughness to the level that degradation due to straining + aging was readily accommodated even at −80°F (−62°C) test temperatures. For fittings designed to −20°F (−29°C) or higher service temperatures, Armco VNT-QT with restricted carbon content and sulfide shape control provided adequate toughness in the strained + aged condition. After stress-relieving, the impact properties improved enough to allow use of this grade at −80°F (−62°C).