PetroMat

During carbonitriding of iron-manganese alloys employing liquid salt baths with high alkaline cyanate content, the presence of an unknown phase, identified as an iron-manganese carboxinitride of the (Fe, Mn) (C, N, O,) type, was observed on the sample surfaces. This phase forms easily and in considerable amounts on treating alloys containing more than 20 wt. % of manganese at temperatures of about 850 K and for times higher than 10 hours.

Samples of UNI 39 NiCrMo 3 and 38 CrAlMo 7 steels have been nitrocarburized with two different proprietary processes, namely the Degussa's Tenifer-TF1 and the Hydromecanique and Frottement's Sur Sulf salt bath treatments. With the former process two different melt compositions were adopted, keeping the CN** minus ions content either at the 0. 5 or at the 4 wt pct level (treatments Tenifer-TF1 A and B). The top surface layer constitution, as determined by X-ray diffraction analysis, is reported for the two steels heat-treated in the Tenifer-TF1 baths in figs.

In the present work the possibility to obtain large size castings of compacted graphite cast iron by inoculating ipereutectic pig iron melts with Fe-Si-Ca-Mg-Ti alloys with different calcium contents was first studied. Two alloys have been used: the first contained 4 divided by 5, 5 wt % Ca and the second less than 1 wt % of the element. The amount of inoculant alloy to be added to the melts was calculated so that the content of Mg in the casting agreed with the Sofroni equation. Casting temperatures were in the 1350-1400 degree C range.

To decrease the treatment time and to obtain better properties of the layers, the authors studied a cycle consisting in a pre-oxidation with sulfur dioxide, effected with the purpose of reducing the interconnected porosity, and a nitrocarburizing stage. Steel samples, containing little carbon (0. 01 wt pct) and copper (2 wt pct), with three different density ranges (6. 3 multiplied by (times) 10**3, 6. 7 multiplied by (times) 10**3 and 7. 2 multiplied by (times) 10**3 kg/m**3), were treated in a laboratory furnace with a small flow of SO//2 (1.

The chemical composition of sintered steels has been related to the physical and mechanical characteristics of the surface layers obtained by solid boronizing. Sintered samples of various composition and density were produced as bushings by mixing Hoganas powders and subsequent heating in industrial furnaces. Various conditions of temperature, time of treatment and chemical composition of the boriding agent were investigated. All the borided layers consisted of Fe//2B and FeB type borides.

Wear resistant hard surfaces and shock resistant cores enhance the life of mechanical components such as gears, shafts and cams. Low carbon steels can provide the core properties that such parts need while the surface characteristics can be created by the process of nitriding and nitrocarburizing. M. Rosso, G. Scavino and G. Ubertalli of the Department of Materials Science and Chemical Engineering, Polytechnic of Turin, Italy, use experimental results from research into nitrocarburizing to show the effect it has on sintered materials.

The corrosion resistance and electrochemical behavior of sintered AISI 304L and AISI 316L samples is evaluated in sulfate and chloride containing solutions. It is shown that the sintering atmosphere strongly influences the microstructure of austenitic stainless steels. Samples sintered in nitrogen-based atmosphere show better mechanical properties but lower corrosion resistance than samples sintered in vacuum because of the precipitation of chromium carbides.

Electrochemical investigations (polarization curves, polarization resistance measurements), together with weight loss measurements and quantitative chemical analysis of the solutions after immersion of samples were used to evaluate the corrosion behaviour of type 304L and 316L sintered austenitic stainless steels in sulphate and chloride containing solutions. The samples were sintered in nitrogen based atmosphere, at 1120 and 1190°C, and in vacuum at 1200°C and submitted to X-ray diffraction analysis and SEM observation together with EDS microanalysis before and after the corrosion tests.