Volume 56, Issue 8

To reveal the prior austenite grain (PAG) boundaries in Ferritic Martensitic steels with reduced activation by a peculiar etchant mixture of hydrochloric acid, nitric acid, and water has been developed. Etching with this system successfully delineates both, inside the grain and grain boundaries in RAFM steels at annealing temperatures 950–1250 °C and observed the abnormal grain growth at 1250 °C. Other two etchants Vilella's and Waterless Kalling's agents are uneffective at 1250 °C and do not reveal the abnormal grain growth. The specimens were austenitized at temperatures in the range 950–1250 °C. The suitable etching agent is successful to observe the micro structural features of RAFM steels.

A mixture consisting of TiO 2 nanoparticles and pure iron powder was directly added into molten steel, and its effects on inclusion and microstructure have been studied. Through a scanning electron microscope (SEM) and an Energy Dispersive Spectrometer (EDS), Ti-containing inclusions, in which the elements of Si, Mn and Al co-existed, were observed. Moreover, compared with the non-treated sample, statistical results indicated that the inclusion in the treated sample was refined and its number per unit area increased by 50 %. These phenomena meant the adding validity of TiO 2 nanoparticle, and may be due to the decomposition reaction of TiO 2 and the higher Gibbs free energy of the nanoparticles. After etching, it was found that the Ti-bearing inclusions can induce intragranular acicular ferrite nucleation. This appearance was consistent with the Ti-containing inclusion introduced through the internal precipitation method.

Polymer bonded Nd-Fe-B magnets belong to the group of composite materials which consist mainly of two components: A polymer binder (PPS, PA) and magnetic particles of Nd-Fe-B alloy. The introduction of 3D printing using the method of Fused Deposition Modelling (FDM) as an alternative technology for the production of polymer bonded magnets is aimed at lowering costs of small-scale production while preserving good magnetic and mechanical properties, such as those obtainable by injection moulding. The purpose of the research work was to identify: (i) The optimal composition and properties of compounds (filament) used for 3D printing of polymer bonded magnets and (ii) Finally, the optimal processing parameters of 3D printing, which would give printed polymer bonded magnets characteristics similar to those produced by injection moulding.

Advanced High-Strength Steels (AHSS) are of interest as, owing to their increased strength, they are able to absorb more energy than conventional steels in a car crash. Thus, thinner metal sheets can be used for car design so that vehicle weight and fuel consumption are reduced. The elements Si, Mn, Al, and B are added in order to achieve the desired AHSS alloy properties. Corrosion protection for the automotive sheet metal is mainly ensured by hot-dip galvanizing. The sheets are further processed by hot forming. Hot-dip galvanized steel sheets made of 20MnB8 were examined after high temperature tensile tests. Metallographic examinations were performed on tensile test specimens which were tested at temperatures between 400 and 800 °C and strain rates between 0.05 and 5 s −1 . Liquid metal embrittlement was observed at temperatures above 700 °C. Lower strain rates resulted in a smaller degree of liquid metal embrittlement. In order to avoid the occurrence of liquid metal embrittlement during hot forming of galvanized AHSS sheets, the relevant process parameters need to be further optimized.