This paper presents a comparison between four TRIP steels, which belong to two groups with different chemical compositions. The first group is that of steels with a relatively low contents of Mn (1.5–2%), high Al (1–2%) and about 0.2% C, and the second includes steels with lower percentages of C (0.1%) and Al (max. 0.6%), but with high percentages of Mn (over 5%). The steels were heat treated by incomplete austenitization, isothermally cooled in salt baths at 400 °C, followed by air cooling. The heat-treated samples were subjected to the impact bending test. A comparative study was performed from the point of view of the intensity of the TRIP effect, the development of the retained austenite-to-martensite transformation under shock (studied by SEM), X-ray analysis and hardness measurements. It was found that appropriate and similar behaviors in terms of mechanical shock were shown by two steels belonging to different groups, with similar amounts of the retained austenite being turned into martensite fractions. The steel with the highest Mn percentage was distinguished by having the highest hardness (362 HV) and the highest retained austenite (obtained after heat treatment) and martensite fractions (caused by the TRIP effect) (10.63% and 2.17%, respectively).

Automotive industry is constantly interested in building cars made of light and high strength parts in order to reduce the emission levels, the fuel consumption and minimize the effects of a car crash. Some parts may be made of lighter materials, but the steel ones must compensate the strength needed for the car body. Research is made for finding new materials showing high strength combined with high ductility. Among them, transformation – induced – plasticity steels are of great interest, efforts being made to improve their characteristics. A new composition of such a steel is presented, its features being compared with those of three other steels of the same class and category. Optical microscopy at different magnifications is performed, together with Vickers hardness test. Structural particularities are found for each tested steel, justified by their own chemical compositions. The new steel reveals important characteristics: besides the mainly bainitic structure, it has both larger ferritic areas and amounts of retained austenite, making him proper for further study.

Andrei Constantin Berbecaru, George Coman, Catalin Stefan Gradinaru, Mirela Gabriela Sohaciu, Cristian Predescu, Ruxandra Elena Dumitrescu, Sorin Ciuca, Ioana Arina Gherghescu - Microstructural Characterization of Some Turbine Blade Martensitic Stainless Steels

The paper presents the impact of exceeding the railway rails lifespan which usually causes a railway structural failure, thus an accident. The research highlights the rails’s high degradation, especially on the running area, consisting in 60-70% weight loss by advanced wear of the rail, followed by fatigue fracture caused by alternating cyclic stresses that initiates the crack and also by tensile stresses resulting in the crack growth. The chemical composition, structural and mechanical properties were analyzed in order to establish the causes that led to the railway rails rupture.

The need to increase the reliability of the metal parts and the assessment of the cost-quality parameters of a matrix require big manufacturers to find new technological solutions focused on the following aspects: thin layer deposits, metallic coatings, use of bimetals, and multilayer materials. The coating of the copper-based quaternary alloys with carbon graphite impregnated polyester aims to improve the performance of the metal parts used in the aeronautics, automotive, and railway industries. The goal is to achieve the following objectives: to reduce the rate of premature failure, to reduce the maintenance and service costs, and to increase the service life (the competitiveness of the manufacturing companies is positively influenced by the latter). This paper studies the operating behavior of some copper-based quaternary alloys coated with carbon graphite-impregnated polyester. The influence of the carbon graphite coating is studied in terms of operating behavior, especially aiming to assess the intensity of the wear and the intensity of the accumulated wear. On the whole, proper wear behavior entails the possibility of obtaining an increase in the service life.