ASME SA645 in the standard SA-645/SA-645M is a kind of Ni alloy steel plates material used to fabric high temperature pressure vessels, the composition of Ni is 5%. jwvivian98 (at) yahoo (dot) com Skype jw-vivian (at) hotmail (dot) com ASME SA645 need to be done the special heat-treatment to meet the property requirement in the standard ASTM SA-645/SA-645M.