The Effects of Steel Cleanliness and Inclusions on the Sulfide Stress Corrosion Cracking of AISI 4137-H Steel

The effects of cleanliness of the steel and calcium-aluminum deoxidation practice on the sulfide stress corrosion cracking (SSC) behavior of quenched and tempered AISI 4137-H steel were studied using the NACE test on smooth tensile specimens. Time to failure vs loading (applied) stress plots were made for three commercially produced heats of steel corresponding to open-hearth quality, aircraft quality, and calcium-aluminum deoxidized steel. This comparative SSC study was conducted at a hardness of 33 HRC achieved by tempering at two different temperatures. Scanning electron microscopy (SEM) and optical metallographic techniques were used to characterize the hydrogen fracture morphology while the transmission electron microscopy (TEM) technique was used to study the tempering response of the specimens. The study indicated that all three heats of the steel exhibited superior performance in the SCC tests when tempered at 685 C compared to 565 C temper as a result of the changes that occurred in the specimen substructure as revealed by the TEM study. The study also indicated that while the use of cleaner steels certainly improves the SSC resistance of the steel, calcium-aluminum deoxidation practice helps to improve the SSC resistance of the steel as well.