Hydrogen embrittlement in an AISI 1045 steel component of the sugarcane industry

This paper will present a failure analysis of a chain component, manufactured with AISI 1045 steel and used for sugarcane transport. During the fabrication process, this component is submitted to induction hardening, just on one surface, before the galvanizing process. The occurrence of surface cracks, during storage, disables the usage of these components. Chemical and metallographic analyses, tensile, fracture toughness, and hardness tests, and fractography were conducted in order to determine the causes of failure. The steel chemical composition was in accordance with AISI 1045. The metallographic analyses and fractography did not exhibit the presence of zinc into the cracks; this is an indication that the cracks occurred after the galvanizing process. Tensile and fracture toughness test results are as expected. The crack surface and the fracture toughness specimen surfaces showed two different fracture micromechanisms: dimples and intergranular. The delayed fracture associated with the predominance of intergranular fracture micromechanism at the induction hardened layer and the high hardness level is a clear indication of the hydrogen embrittlement. (c) 2008 Elsevier Ltd. All rights reserved.

Comparative study of Cr3C2-NiCr coatings obtained by HVOF and hard chromium coatings

In the present work the corrosion resistance of micro-cracked hard chromium and Cr3C2-NiCr (HVOF) coatings applied on a steel substrate have been compared using open-circuit potential (E-OC) measurements, electrochemical impedance spectroscopy (EIS) and polarization curves. The coatings surfaces and cross-section were characterized before and after corrosion tests using optical microscopy (OM) and scanning electron microscopy (SEM). After 18 h of immersion, the open-circuit potential values were around -0.50 and -0.25V/(Ag vertical bar AgCl vertical bar KClsat) for hard chromium and Cr3C2- NiCr, respectively. The surface analysis done after 12 h of immersion showed iron on the hard chromium surface inside/near surface cracks, while iron was not detected on the Cr3C2-NiCr surface even after 18 h. For longer immersion time hard chromium was more degraded than thermal sprayed coating. For hard chromium coating a total resistance values between 50 and 80 k Omega cm(2) were measured and two well-defined time constants were observed, without significant change with the immersion time. For Cr3C2-NiCr coating the total impedance diminished from around 750 to 25 k Omega cm(2) as the immersion time increased from 17 up to 132 h and two overlapped time constants were also observed. Polarization curves recorded after 18 h of immersion showed a lower current and higher corrosion potential for Cr3C2-NiCr coating than other samples studied. (c) 2005 Elsevier Ltd. All rights reserved.

Influência da deformação do encosto e do alojamento no campo de tensões em bronzinas

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Caracterização do defeito tipo trinca de laminação, ocorrido no processo de laminação de barras de aço

The mechanical forming processes are the main means of transformation. Among all processes, the most used is rolling and broken down into flat and non-flat products. In the flat products are classified plates, and products no plans bars and profiles. Thus laminating products, mostly, are the raw materials for other processes of transformation, as stamping, forging, machining, bending and more. This work has focused on non-flat products, classified as bars and rods, watching a key point in the proceedings that is the product quality. Here is demonstrated through metallographic analysis of steel bars, hot-rolled, the characteristics of surface cracks in these bars

An investigation of electrolytic surface damages and electroplated crhomium effects on fatigue behavior of high strength steel

Fatigue crack initiation occurs at the surface, although sub surface nucleation has also been reported. Localized imperfections like inclusions close to surface and surface small pits can result in crack sources. Coatings are not always beneficial by fatigue point of view too. Mechanical properties of the covering material can change considerably the fatigue behavior of base metal due to residual surface stresses, to micro cracks or to hydrogen embrittlement. This paper is concerned with analysis of electrolytic etch on the fatigue resistance of a 35NCD16 high strength steel in a mechanical condition of (1760 - 1960) MPa, and analysis of electroplated hard chromium effects on the fatigue resistance in a strength condition of 989 MPa. Hardness impression was used as a reference parameter in case of electrolytic etch. In both cases, experimental data showed that fatigue strength of 35NCD16 steel was considerably reduced. Copyright © 2001 Society of Automotive Engineers, Inc.

Comparison surface characteristics and chemical composition of conventional metallic and Nickel-Free brackets

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)