20th International Forgemasters Meeting - IFM 2017

Pressure Vessel components, during manufacturing, undergo several heat Treatments that aim to confer the required properties on the entire equipment, including welds and base metal. Quality Heat Treatments (QHT) typically comprise of normalizing and tempering, or hardening and tempering, as per customer requirements. Usually, these QHTs are followed by Post weld heat treatments (PWHT). The aim of a PWHT is to ensure good behaviour of welded zones in terms of residual stresses and properties such as toughness. In view of enhanced customer demands, increasingly stringent requirements are now encountered often, which stipulate higher tempering temperatures followed by very high PWHT’s. Such high PWHT requirements, for increasing the toughness in the weld metal, leads to deterioration in the properties of the base metal. This paper presents the study carried out on forgings of two grades of pressure vessel steel and the resulting data. The cumulative time-temperature effect of various heat treatments have been made comparable using the Larson-Miller tempering Parameter. The corresponding effect on the steel has been measured via standard Tensile and Charpy V-notch tests. The data shows a decline in properties beyond a point, as one progresses to higher Larsen Miller Tempering Parameters.