1969 Volume 55 Issue 9 Pages 831-838
A study was made of the effect of alloying elements, carbon, nitrogen, copper, molybdenum and niobium on the properties of precipitation hardenable stainless steels. The results obtained were as follows.
1. The carbon content, the austenite forming element, is required to be lowered. In the case of high carbon content, carbide stabilizing element niobium is necessary to be added a least about five times as much as the carbon content, because carbon stabilizes austenite and lowers Ms temperature to near room temperature.
2. The nitrogen content is also required to be lowered, because this elements has the same behavior as that of carbon.
3. The higher content of copper is desirable, because the element has the remarkable effect on secondary hardening by precipitating e phase. Above 3% of copper, however, lower the Ms temperature remarkably and give harmful influence on the forgeability.
4. Ferrite forming element molybdenum lowers Ms temperature and a large amount of molybdenum added decreases tensile strength of the steel. The higher content of molybdenum is desirable to improve the corrosion resistance, but the efficient value is found to be about 1%, because the improvement effect by molydenum addition becomes gradual above this content.
5. Nb is required as the carbide stabilizer. In the case of niobium-free steel, austenite becomes so stable that it does not transform to martensite by single aging treatment only. In addition, the corrosion resistance of this steel is lowered owing to the precipitation of chromium carbide. Nb is necessary to be contained about five times as much as carbon content.
6. Aluminium addition with molybdenum and copper is beneficial to the improvement of the corrosion resistance of the steel.