Temper Embrittlement in 2-1/4 Cr-1 Mo Steels After 75,000-Hour Isothermal Aging

A long-term laboratory study has confirmed that temper embrittlement (TE) in 2-1/4 Cr-1 Mo plate, forgings, and weldmetals levels off over time. Fifty-five heats of 2-1/4 Cr-1 Mo steel from several vendors were aged for up to 75,000 hours at 427 to 482°C (800 to 900°F), and extent of embrittlement was determined from shifts in 54 J (40 ft-lb) transition temperature for each heat. Embrittlement levelled off within 35,000 hours at 427°C (800°F) and 454°C (850°F), and within 10,000 hours at 482°C (900°F). Plate material embrittled least, while submerged arc and shielded metal arc weldments embrittled most. Although steel chemistry has previously been used to predict TE susceptibility, our analysis of these 55 heats, and of 23 heats of 2-1/4 Cr-1 Mo in a 1982 API study, shows that a step-cool treatment simulating long-term exposure is a more reliable way to screen susceptible materials.