ATI corrosion resistant engineering alloy, JS700®, is a high-alloy, fully austenitic, superaustenitic stainless steel. This alloy is a proven problem-solver in many applications where corrosive conditions are too severe for standard grades of stainless steel. It has also provided a cost-effective alternative to more expensive nickel-base and titanium-base alloys.

JS700 stainless steel is more highly alloyed than standard stainless steels. It contains nominally 25% nickel, 20% chromium and 4.5% molybdenum. The high molybdenum content is particularly important to the corrosion resistant properties. Molybdenum is used in many stainless steels to improve resistance to both localized and general corrosion. It enhances development of the passive film responsible for the corrosion resistance of stainless, and makes the alloy more noble so that corrosion resistance is improved even under conditions which tend to destroy passivity. The molybdenum content of JS700 steel, at 4.3 to 5.0%, is more than twice the level usually found in the widely-used Type 316 stainless steel.

The chromium content of the JS700 alloy is essential to corrosion resistance. Since chromium contributes to sigma formation, the 20% level was chosen as a satisfactory compromise. The high nickel content not only minimizes sigma, but also contributes markedly to corrosion resistance. The effects of higher nickel are believed to relate more to corrosion propagation than to initiation. As shown in the tabulated corrosion test results, JS700 steel far outperforms Type 317LM, a steel with similar molybdenum content and only slightly lower chromium, but much lower nickel.

The combination of the three major alloying elements gives JS700 stainless steel a high degree of resistance to stress corrosion cracking. No field service failures from stress corrosion cracking in JS700 alloy have been reported to date.

JS700 steel has a relatively low carbon content, plus columbium stabilization to tie up the remaining carbon. This stabilization guards against intergranular corrosion due to carbide precipitation (sensitization) in areas such as weld heat affected zones even more effectively than with a 0.020% carbon level without stabilization. JS700 alloy will, in fact, pass a demanding Huey test in the furnace sensitized condition.