Strength metallurgical factors

K scc depends on metallurgical factors (it usually decreases as the strength of the steel increases, even though it also depends on the microstructure of the material, e. g. it is lower in quenched and tempered steel than in cold-worked steels) and on environmental factors (for instance, in alkaline environments and in the absence of chlorides, Kfscc so high that normal mechanical failure takes place before stress corrosion cracks can develop). 

Metallurgical factors such as alloy composition microstructure and yield strength (4). 

METALLURGICAL FACTORS. Typical metallurgical factors influencing ductile—brittle behavior are temper, microstructure, and welds. In general, the stronger the condition of a given alloy, the more susceptible it becomes to brittle behavior. As strength increases, ductility decreases. There are some exceptions... 

Material factors. The main metallurgical properties of importance are alloy composition, distribution of alloying elements and impurities, microstructure and crystal structure, heat treatment, mechanical working, preferred orientation of grains and grain boundaries (texture), mechanical properties (strength, fracture toughness, etc.).31... 

Factors that influence SCC response will generally affect one of four basic variables in the process the material or alloy system, the chemical service environment, the electrochemical state of the system relative to surroundings, and the state of mechanical stress. Nearly all structural alloy systems can be found susceptible to SCC under certain alloy chemistry, metallurgical condition, and service environmental conditions. SCC behavior relative to alloy system was detailed in an American Society for Metals (ASM) publication [6], for a broad range of structural alloys, and has also been covered extensively for aluminum, titanium, and high-strength steels [8]. 

The appendix states that extrapolations by more than a factor of 3 will require metallurgical justification for metastable alloys such as the creep strength-enhanced ferritic-martensitic steels. When the maximum rupture time experimentally obtained is less than 166,667 h, for example, in order to achieve a 60-year design, an extrapolation of factor of 3 would be necessary. If we follow the guidelines, metallurgical justification would be required. 

Strength properties, corrosion resistance, and metallurgical stability. Therefore, it is necessary to choose the optimum steel, considering these factors at anticipated metal temperatures. 

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