Effects of Intercritical Heat Treatment on the Temper Embrittlement of SA508 Gr.4N Ni-Cr-Mo High Strength Low Alloy Steels for Reactor Pressure Vessels

To analyze the effects of intercritical heat treatment on temper embrittlement SA508 Gr.4N steels, two model alloys with different phosphorus (P) contents were fabricated. Each sample was treated by applying a conventional process (quenching-tempering) with/without an (IHT) and step-cooling for embrittlement. Then their microstructure mechanical properties evaluated. The alloy composed tempered lower bainite martensite, nano-sized precipitates formed both inside at boundaries. grain size reduced when IHT applied. There small difference in tensile according to heat-treatment conditions P contents, but Charpy impact large. (TE) increased transition temperature, very significant increase observed steels high content. temperature owing TE fractograph analysis fractured specimens temperatures showed that intergranular fracture main reason TE, formation fracture. AES results P-Ni segregated boundaries, level segregation IHT. This occurred because prior austenite boundaries dispersed amount segregation.