Generally, tool steels for cold work are obtained by rolling and forging processes. They are treated to have a structure conferring to the material a high toughness limit in terms of wear resistance and endurance. The objective of this study is the thermochemical heat treatment of industrial steel blades made of AISI 02 types, intended for polymer crushing. The effects of nitrocarburizing (Tenifer) and gaseous carbonitriding processes on surface characteristics are considered. These surface treatments increase the usefulness of properties, that is, fatigue strength, wear and corrosion resistance of this microalloyed steel. The influence of treatment duration and the thickness of the layers on surface properties are investigated. The analysis and characterization are carried out using physical analysis [optical microscopy, scanning electron microscopy, X-ray diffraction and glow discharge optical emission spectroscopy (GDOES) techniques] and mechanical measurements (microhardness, weight loss and residual stresses) of treated material. The results are intended to contribute in defining and optimizing the adequate choice of treatments for this type of steel in industrial conditions.

The effect of post-oxidizing treatment on the characteristics of modified surface layers produced by salt bath nitrocarburizing on the industrial American Iron and Steel Institute (AISI) 02 tool steel types is investigated. Nitrocarburizing treatment is performed for 6 h and 8 h at 570• C and post-oxidizing treatment for 30, 60 and 90 min at 520 • C, using argon-steam mixture. Formed layers are characterized by their basic properties such as thickness layer, depth, surface hardness and wear resistance. Detailed estimation of the modified metal surface quality, in terms of chemical composition, formed phases, microstructures and diffusion mechanisms are performed by metallographic techniques, EDX, X-ray diffraction, scanning electron microscopy (SEM) and glow discharge optical electron spectroscopy (GDOES). The corrosion resistance was investigated in 0.4 M H 2 SO 4 solutions, using steady-state electrochemical polarization methods. The obtained results revealed the existence of a superficial oxide layer which consists of magnetite (Fe 3 O 4 ) and hematite (Fe 2 O 3 ) and the presence of an ε-phase associated with a small amount of γ -phase. Important improvements in wear, microhardness and corrosion resistance occur after these treatments and it is specifically concluded that the sole application of a nitrocarburizing treatment does not significantly ameliorate the corrosion resistance of the as-received steel. In fact, post-oxidation treatment contributes to increase corrosion resistance by forming a dense magnetite layer and at the same time, it partially covers the compound layer pores.

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Gaseous carbonitriding effects on improvement of surface characteristics of new hot working tool steel close to as either chromium AISI H11 or AISI H13 are investigated. Experimental results are related to three aspects: formed layers, microstructure and obtained precipitates. The formed layers are characterised by their basic properties, which are thickness, depth, formed phases, hardness and wear resistance. Microstructure and the diffusion mechanism suggested that high temperature gas carbonitriding process has the potential of improving the mechanical properties with shorter processing time. The arrangement of carbonitrides, nitrides, chromium oxides and retained austenite and Fe 3 C carbides allowed obtaining tool performance from the moderate low mass. Microstructural characterisations were performed by metallographic techniques, electron dispersive energy, X-ray diffraction techniques, optical and scanning electron microscopy and glow discharge optical electron spectroscopy. The mechanical properties were assessed mainly by standard hardness and wear tests.

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