Statistical Analyses of Mechanical Properties and Slow-Strain Rate Test Results in Air and Corrosive Environment to Compare Alloy 718 from Additive Manufacturing with Bar Stocks from Established and Newer Mills

摘要

Alloy 718(UNS N07718)bar stocks,as per API6CRA,are being produced by an increasing number of mills worldwide;similarly,Alloy 718 powders of various origins are currently offered to serve a multitude of Additive Manufacturing(AM)processes.Today,there are needs to compare,evaluate,and qualify Alloy 718 from established mills,newer mills,and AM.Due to concerns over oilfield service performances,statistical analyses of tensile properties and environmentally-assisted cracking(EAC)test results were applied onto a large database of mill certificates,third-party mechanical test reports,and EAC test results at the NACE MR0175/IS015156 sour service limit of UNS N07718 of 300 °F(149 °C).The analyses demonstrate that(1)718 bar stocks(including newer mills)consistently outperform their AM counterparts,(2)AM 718 properties vary greatly from vendor-to-vendor despite the use of a standardized post-AM process in line with API6CRA,and(3)more research is needed to better balance and optimize AM 718 properties.Despite inferior properties and greater property variability,AM 718 is found to be consistently environmentally-cracking resistant at the NACE MR0175/IS015156 condition analyzed.For an oilfield user perspective(especially for service equipment),AM 718 questionably requires all its properties to match that of API6CRA bar stocks;however,both yield strength and impact toughness values of AM 718 products should closely match the minimum values of API6CRA.