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Nitriding is usually applied to alloyed steels with the scope of increasing their surface hardness and wear resistance. Warm working has been found to produce a fine-grained microstructure, which makes possible further treatment of low carbon steels. In combination with a low temperature thermochemical treatment, such as nitriding, warm working can be used to produce machine parts with a though core and with a hard, wear resistant surface layer. This paper presents a study of mechanical and structural properties of AISI 1015 carbon steel nitrided after warm rolling. The rolling was performed in the following conditions: temperature 670–550°C, rolling speed 1.39 s-1 and deformation ratio 36.4%. After rolling, the samples were reheated to 550°C for a duration varying from a few minutes to 10 hours. The microstructural changes were assessed by light microscopy and quantitative microscopy analysis. Warm rolled samples were ion nitrided at 510–520°C in dissociated ammonia. The microstructure was analyzed by scanning electron microscopy and the mechanical properties were evaluated by tensile testing, surface hardness and friction coefficient measurements. Prior application of warm rolling makes possible (in the sense that is a viable solution) the ion nitriding of low carbon steels in order to produce machine parts with improved mechanical properties in the core (due to warm rolling) and longer service life (due to ion nitriding).

Failure analysis investigates the causes of a product’s destruction. Its final objective is to suggest measures that can be taken in order to prevent or minimize the chance of failure in the most economical way. This paper studies the failure of a rotary cold working die. The tool was manufactured from AISI D2 tool steel and it was intended for cutting paper at room temperature. The tool failed during the setup process on the machine it was designed for, thus failing to commence the manufacturing process. The process was initiated by a crack that began at the point of a diameter change of the tool body in the attachment part, where the tool was fastened to the rest of the machine. This paper presents the first results of the die failure study. Historical data were collected: operating conditions, lifetime, restitution of sound operation, collection of recorded history, measurement of operating temperatures and hardness control. This was followed by optical inspection, selection and preparation of samples and macroscopic analysis of fracture surfaces. The paper presents conclusions on the fracture mechanism and form and suggests the first probable causes leading to die failure. The results could be useful for industry as regards the avoidance of such failures in the production process.