Part 1: Postweld Heat Treatment Cracking In Chromium-Molybdenum Steels

The postweld heat treatment (PWHT) cracking susceptibility of standard and modified 2¼Cr-lMo and 3Cr-1 and 1½Mo steels has been investigated. The modified steels tested include three heats of 3Cr-1½Mo-0.1V, a heat of 3Cr-1½Mo-½Ni and a heat each of V-Ti-B modified 2¼Cr-1Mo and 3Cr-1Mo. Tests used to evaluate PWHT cracking susceptibility were Gleeble simulation and a "C-Ring" test adapted from that described in ASTM G-38 (used to evaluate stress corrosion cracking susceptibility).

The results of the tests indicate that the susceptibility to PWHT cracking is synergistically dependent on the compositional effects of major and minor alloying elements. Both the V-Ti-B heats were relatively susceptible to PWHT cracking whereas the susceptibility of the vanadium alone heats was apparently dependent on the presence of grain boundary embrittling elements (phosphorus). Transmission electron microscopy of carbide extraction replicas leads to the general conclusion that elements (such as V, Si) that contribute to the stability of coherent matrix precipitates of the MC, M₂C or M₄C₃ type lead to enhanced susceptibility of PWHT cracking. The presence of elements such as nickel that will drive the precipitation process faster towards equilibrium reduces susceptibility to PWHT cracking.

Part 2: Postweld Heat Treatment Cracking In High Strength Low Alloy Steels

The evaluation of the postweld heat treatment (PWHT) cracking susceptibility of several HSLA, pressure vessel and structural steels is described. Gleeble simulation tests were conducted to gain an initial assessment of the PWHT cracking susceptibility. This was followed by C-Ring and Y-Groove tests on three of the HSLA steels. The C-Ring test has been adapted from one that is conventionally used to evaluate stress corrosion cracking susceptibility and is described in ASTM Standard G-38. The results of the Gleeble tests indicate that steels of the quenched and tempered (also quenched and precipitation hardened) variety have a potentially greater susceptibility to PWHT cracking. The C-Ring and Y-Groove tests confirmed the potentially greater susceptibility of HSLA steel A 710 Gr A Cl 3 when compared to HSLA steels, A 808 and A 572 Gr 50.