Advanced Materials & Processes

FEB 2015

Covers developments in engineering materials selection, processing, fabrication, testing/characterization, materials engineering trends, and emerging technologies, industrial and consumer applications, as well as business and management trends

Issue link: http://amp.digitaledition.asminternational.org/i/466012

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not present). If free ferrite is present, the free-ferrite layer's maximum depth (ofen variable) plus the depth of partial decarburization to the unafected core is measured. This total—FFD + PDD—is called maximum afected depth (MAD). These depths are not uniform and can vary substantially, leading to measure- ments of average FFD, PDD, and MAD, as well as maximum values for each. ASTM E1077 covers decarburization measurement. In practice, decarburization should be evaluated on a plane transverse to the hot working axis, as depth variation is greater around the bar on the transverse plane than at a specific constant position along a longitudinal plane. Decarburiza- tion depth can vary substantially around the periphery of a bar, as shown in Fig. 1. Qualitative measurements can be sub- jective and biased. Free-ferrite depth can also be erratic, even over a small sur- face area, as shown in Fig. 2. Corners of square or rectangular sections normally exhibit greater decarburization depths than planar surfaces. Sampling schemes for large cross-sections are also illustrat- ed in ASTM E1077. To obtain good data, edge reten- tion must be perfect—the surface must be perfectly flat to the extreme edge. If edges are rounded, the exact location of the outer surface is difficult to define with precision and depth measurement accuracy suffers. Good edge retention requires mounting of the specimen in a resin, such as DuroFast, that does not ex- hibit shrinkage gaps between the mount and specimen after polymerization. Grinding and polishing procedures must emphasize maintaining flatness. While Fig. 3 — Decarburization of 5160 modified spring steel defined by surface hardness and incremental turnings analyzed chemically for carbon content as a function of whether or not the surface was descaled or was covered by mill scale, and austenitizing at 1600°F for 80 minutes. A D V A N C E D M A T E R I A L S & P R O C E S S E S | F E B R U A R Y 2 0 1 5 2 3

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