Wear and corrosion resistance of pack chromised carbon steel F. A. P. Fernandes* 1 , S. C. Heck 1 , C. A. Picon 2 , G. E. Totten 3 and L. C. Casteletti 1 Pack chromising treatment is an environmentally friendly alternative to hard chromium to form wear and corrosion resistant surface layers. In this work, samples of AISI 1060 steel were pack chromised for 6 and 9 h at 1000 and 1050uC using different activator concentrations. Wear tests were performed in dry conditions and corrosion tests in natural sea water for the pack chromised samples and hard chromium. Pack chromising yielded the formation of layers with high chromium concentrations, high hardness and wear resistance. Increasing activator concentration causes no significant change on the morphology and thickness of the layers. The layers produced at 1050uC yielded only a (Cr,Fe) 2 N 12x phase, and those obtained at 1000uC are composed of a carbide mixture with (Cr,Fe) 2 N 12x . The sample treated at 1050uC for 9 h resulted in an optimum condition by means of better wear resistance and corrosion properties, which were close to that exhibited by the hard chrome, indicating that pack chromising is a promising alternative. Keywords: Chromising, Steel, Wear, Corrosion Introduction Surface coatings are one of the most versatile ways to improve the performance of components with res- pect to wear and/or corrosion. Historically, the most frequently used industrial coating for this purpose is the electrolytically formed hard chrome. 1–4 However, the electrolytic deposition of the hard chrome coating involves the presence of hexavalent chromium, which is highly carcinogenic and has resulted in increasing limitations of its use. Because of this, several alter- native chromising processes have been developed, such as solid (pack) chromising 5–7 in bath of molten salt 8 and vacuum. 9 The coating is obtained by diffusion of atoms of chromium into the substrate, which produces a chromium rich layer. The chromising of steel and ferrous alloys produces a surface layer composed mainly of Cr, Fe and C, which significantly increase the hardness, wear and corrosion resistance of the substrate. 7,10 The powder process (pack) is an inexpensive and relatively easy way to obtain chromising coatings with the possibility of processing pieces with different geometries. 9 The process involves placing the substrate in a powder mixture containing a source of chromium (pure Cr or Fe–Cr), an inert element (usually Al 2 O 3 ) and an activator. The package containing the mixture and the sample is heated to 1000–1300uC for up to 12 h to form the coating. 7 The objective of this study is to evaluate the influence of pack chromising parameters (temperature, time and activator concentration) on AISI 1060 steel, to study the morphology and composition of the produced layers and to examine its wear and corrosion resistance. These properties are compared with those obtained for a hard electrolyte chromium coating. Materials and methods Initially, samples with 2062065 mm of AISI 1060 steel were cut and ground using 600 mesh sandpaper. The chemical composition of the steel was Fe–0?57C–0?78Mn– 0?036P–0?024S–0?21Si–0?046Ni–0?034Cr–0?003Mo (wt-%). The steel was then cleaned and pack chromised in steel crucibles for 6 and 9 h at the temperatures of 1000 and 1050uC. The composition of the powder was 25% of pure Cr (.150 mesh), 69%Al 2 O 3 and 6 and 12%NH 4 Cl. The hard chromium coating was obtained using the traditional electrolytic process, which was performed by a company specialised in these types of treatments using an AISI 1045 steel plate. A layer thickness of 0?7 mm was obtained after grinding. All the studied samples were subjected to analysis by optical and electron mi- croscopy, microhardness measurements, X-ray diffrac- tion, wear and corrosion testing. Measurements of Vickers microhardness were made on a digital Buehler equipment with a load of 50 gf and an application time of 10 s. The X-ray diffraction patterns were obtained on the surface of the samples in a Geigerflex Rigaku equipment with a scanning angle from 20 to 100u. The tests were performed using copper radiation and continuous scanning with a speed of 2u min 21 . 1 Department of Materials, Aeronautical and Automotive Engineering, Sa ˜o Carlos School of Engineering, University of Sa ˜ o Paulo, Av. Trabalhador Sa ˜ ocarlense, no. 400, Sa ˜ o Carlos, Sa ˜ o Paulo 13566-590, Brazil 2 Department of Physics and Chemistry, Engineering School of Ilha Solteira, Av. Brasil, no. 56, Ilha Solteira, Sa ˜ o Paulo 15385-000, Brazil 3 Department of Mechanical and Materials Engineering, Portland State University, PO Box 751, Portland, OR 97207-0751, USA *Corresponding author, email codoico@gmail.com ß 2011 Institute of Materials, Minerals and Mining Published by Maney on behalf of the Institute Received 26 April 2011; accepted 27 September 2011 DOI 10.1179/1743294411Y.0000000079 Surface Engineering 2011 VOL 000 NO 000 1