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This report gives the experiences of several steel producers and consumers with vacuum degassing as a melting practice in the manufacture of high-strength steels for critical applications. The parameters involved in determining the effects of melting practice on mechanical properties are outlined. Pertinent melting processes are described and evaluated qualitatively. In presenting the data, vacuum degassing is compared with other melting practices such as conventional air melting and consumable-electrode vacuum-arc remelting (CEVAR). Generally, there is a trend indicating that vacuum degassing is being used in some production applications instead of air-melted or CEVAR material. In terms of higher and more uniform transverse tensile properties and impact strength, longer fatigue life, and improved cleanliness, the CEVAR alloys were the best. Vacuum degassing by any of the various methods resulted in an improvement in properties of air-melted alloys. In some instances it appeared that the quality of CEVAR alloys could be approached when stream degassing or D-H (Dortmund-Horder) treatment was applied to air melts. Recommendations are given for additional investigations on the effects of melting practice on mechanical properties of premium-quality steels. (Author).
This report deals with the deleterious effects of hydrogen gas on steel at elevated temperatures and/or pressures. Hydrogen attack on steels is manifest as decarburization, intergranular fissuring, or blistering. These conditions result in lowered tensile strength, ductility, and impact strength. The reaction of hydrogen with iron carbide to form methane is probably the most important chemical reaction involved in the attack on steel by hydrogen. Attack of steel at elevated temperatures and pressures is limited or prevented by the following measures: (1) use of steel alloyed with strong carbide-forming elements, (2) use of liners of resistant alloy steels, and (3) substitution of resistant nonferrous alloys.
Numerous industrial users were asked for their appraisal of vacuum-degassed steel. Their responses regarding the merits of this vacuum treatment were varied. The producers and users of large forgings reported fewer internal defects, improved toughness, and decreased processing time through shorter hydrogen relief treatments. Improved fatigue life in applications such as bearings was attributed to fewer and smaller nonmetallic inclusions in vacuum-degassed steel. The users of medium and small forgings reported only marginal improvement in properties and little or no change in rejection rates by nondestructive testing. Unfortunately, many of the users could not give a meaningful evaluation because they knew that frequently their suppliers filled orders with vacuum-degassed steels even though such treatment was not specified. Consequently, these users are unable to separate the air melted and the vacuum-degassed steels in their stock for comparison. A more comprehensive study of fully identified steels, steelmaking practice, degassing methods, material properties, and performance in service will be required before a satisfactory evaluation of the merits of vacuum-degassed steels can be made. (Author).
This report presents information dealing with the oxidation of nickel- and cobalt-base superalloys. All of the superalloys will oxidize at high temperatures when oxygen is present in the enveloping atmosphere. The rate of oxidation depends upon alloy composition, temperature, oxygen concentration, oxides formed, diffusion rates of the metals in both base metal and oxide, diffusion rate of oxygen in the oxide, solubility of oxygen in the matrix, and a host of other variables. The effects of oxidation can be beneficial or they can be harmful. The first section of this report deals with the fundamentals of the oxidation of Ni-Cr and Co-Cr alloys. Subsequent sections discuss general surface oxidation, intergranular oxidation, other subsurface oxidation, and the effect of stress on the rate of oxidation. Numerous specific alloys are mentioned in the report; as an aid to the reader, the appendix contains an alloy index of the alloys mentioned in the report along with the compositions of the alloys, and the pages on which mention of the alloys is made.