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Banuta M.,SGS Canada Inc. Materials Engineering | Tarquini I.,SGS Canada Inc. Materials Engineering
Journal of Failure Analysis and Prevention | Year: 2010

Steak knives from three different suppliers were brought to our facility to conduct a comparative analysis of their metallurgical properties. Although they have allegedly been used and cleaned in similar conditions in several restaurants across North America, only knives coming from one supplier showed signs of premature corrosion. Our investigation found that even though they have similar chemical and mechanical properties, and had been submitted to the same heat treatment, major microstructure discrepancies made some of these knives prone to rapid corrosion. As per our examination, the prematurely corroded knives experienced extensive chromium carbides precipitation during heat treatment, which determined a massive chromium depletion of the matrix and lowered their corrosion resistance. On the contrary, the knives that never corroded kept all their chromium content inside the matrix, thus contributing to better corrosion resistance. © 2010 ASM International.


Banuta M.,SGS Canada Inc. Materials Engineering | Tarquini I.,SGS Canada Inc. Materials Engineering
Journal of Failure Analysis and Prevention | Year: 2012

The drive shaft in the propulsion system of a boat broke, while the vessel was sailing along the Western Canadian coast. This part was made from a low-alloy steel grade 4340 quenched and tempered. Fractographic investigation at macro scale revealed that the shaft failed under low rotating-bending variable stress. Fatigue propagation occurred on about 95% of the total cross section of the shaft, under both low-cycle and high-cycle fatigue mechanisms. It was found that the fillet radius present at the fracture's origin was smaller than the one provisioned by design. This situation has raised the stress level at this location higher than the one taken into consideration at the moment of the design calculations and caused the initiation of the cracking. Moreover, although the shaft has been quenched and tempered, its actual hardness did not have the optimal value for long-life fatigue strength. © ASM International 2012.

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