Articles written in Bulletin of Materials Science
Volume 25 Issue 5 October 2002 pp 361-366 Alloys and Steels
Microstructure, precipitates and fracture morphology in the coarse grained heat-affected zone (CGHAZ) of a new high-purity 0Cr18Mo2Ti ferritic stainless steel were studied by means of optical metallography, SEM, TEM, X-ray diffractometer, etc. Experimental results indicated that grain coarsening resulted in brittle fracture in the CGHAZ of 0Cr18Mo2Ti steel. The reduction of impact toughness in the CGHAZ due to change of cooling rate can be attributed to the increase of nitrides (TiN, Cr2N, etc). These nitrides in the CGHAZ promote initiation and propagation of brittle cracks. The precipitated Cr2N nitrides in the grain boundaries decrease impact toughness in the CGHAZ of 0Cr18Mo2Ti steel by promoting crack initiation. In practical applications, the welding heat input (𝐸) should be as low as possible to prevent toughness reduction in the CGHAZ.
Volume 25 Issue 7 December 2002 pp 635-639 Alloys and Steels
The fine structure in the Fe–Al alloy layer of a new hot dip aluminized steel (HDA) was examined by means of X-ray diffractometry (XRD), electron diffraction technique, etc. The test results indicated that the Fe–Al alloy layer of the new aluminized steel mainly composed of Fe3Al, FeAl and 𝛼-Fe (Al) solid solution. There was no brittle phase containing higher aluminum content, such as FeAl3 (59.18% Al) and Fe2Al7 (62.93% Al). The tiny cracks and embrittlement, formerly caused by these brittle phases in the conventional aluminum-coated steel, were effectively eliminated. There was no microscopic defect (such as tiny cracks, pores or loose layer) in the coating. This is favourable to resist high temperature oxidation and corrosion of the aluminized steel.
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