THE EFFECT OF TRACE IMPURITIES ON THE STRESS-CORROSION CRACKING SUSCEPTIBILITY AND FRACTURE TOUGHNESS OF 18 Ni (300 GRADE) MARAGING STEEL
Final technical rept.
CARNEGIE-MELLON UNIV PITTSBURGH PA DEPT OF METALLURGICAL ENGINEERING AND MATERIALS SCIENCE
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A series of 18 Ni 300 grade maraging steels of overall commercial purity but containing also deliberate impurity additions of sulphur, phosphorus, carbon, chromium and silicon plus manganese was studied. The fracture toughness and stress-corrosion resistance determined using plane-strain fatigue- precracked specimens tested in 3.5 sodium chloride solution of these steels was compared to the fracture toughness and stress-corrosion resistance of a commercial purity 18 Ni 300 grade maraging steel with no deliberate impurity additions, and to a similar steel prepared from special high-purity melting stock. The most important conclusions reached are that i Ultra-high purity steels do not have significantly improved stress-corrosion resistance, but show useful increases in fracture toughness when the carbon content is less than 0. 005 ii Simultaneous additions of Mn plus Si result in extremely low fracture toughness values iii High carbon contents greater than 0.03 result in marginally improved stress-corrosion resistance iv High Cr contents result in rather poor stress-corrosion properties. These results were correlated with the electron transmission microstructure of the steels and the results of a fractographic analysis of the fracture surfaces.
- Properties of Metals and Alloys