Cyanide in salt bath Applied to ASTM A-517 Steel Effects on Hardness Wear and Microstructure

Abstract

The effects of the cyanide treatment (CN) in a salt bath at elevated temperatures on the hardness; adhesive and abrasive wear; of ASTM A-517 steel, were investigated. For abrasive wear, 1” x 3” x 5/16″ samples were prepared according to ASTM G-65 standard. For adhesive wear, specimens wit ring-shaped: φ ext. = 40 mm, φ int = 20 mm and 10 mm thick, according to ASTM G -77. The CN treatment was carried out, at high temperatures: 800 – 850 – 900 – 950 °C, immersing the samples in a salt bath: 6% NaCN + 80% BaCl2 + 14% NaCl before entering the muffle furnace, with soaking time of 3 hr. Hardness tests were performed on a Rockwell Durometer taking measurements on the HRC scale. The adhesive wear tests were carried out on a parallel lathe coupling the Amsler device, following the ASTM G-77 standard. The abrasive wear tests were performed according to the ASTM G65 standard. Microscopy was done at the optical level. A maximum hardness of 63.5 HRC was found in all samples, representing an increase of 11.3% with respect to the state of supply (T&R). In abrasive wear, its value increased to 66%, compared to supply samples. The most suitable microstructure is presented by cyanide samples at 850ºC, with a layer of compounds (hard layer) formed by: massive cementite; tempered martensite and carbide. It is concluded that when applying cyanide to ASTM A-517 steel, the hardness and wear properties are increased to optimal values, if the cyanide treatment (CN) is carried out at 850 °C.