Effect of alumina and titanium nitrides inclusions on mechanical properties in high alloyed steels

peer reviewedevery commercial steel product in varying amounts. Since inclusions significantly influence properties and behaviour of materials and at the same time give indications on the quality of the steel, it is quite interesting to precise their nature and their origin. In this paper concerning a project involved in the COST 517 framework, studied alloys are high alloy steels. The raw materials were obtained from the conventionally electrical cast ingot and the Electro Slag Refining processes. The purpose is to compare various inclusions produced by these different processes and their effect on the mechanical properties. The raw material because of the melting processes themselves, leads to a product with a good to a great cleanliness, and tiny inclusions, which are haphazardly distributed. The actual ASTM E45 chart seems to be inappropriate, as the inclusions founded are too small in size. Therefore, we manage to develop a specific procedure for the study of such inclusions. The different types of inclusions encountered are oxides, titanium nitrides, and manganese sulphides. Studying the effect on mechanical properties, oxides often seem to initiate fatigue fracture

Physical metallurgy of a HSS material for hot rolling mill rolls

peer reviewedHigh Speed Steel (HSS) cast rolls are used in front finishing stands of hot strip mills. Good wear resistance and hardness at high temperatures, are defining features of HSS. Many types of carbides are present in these alloys, each having different effect upon their final properties. As a result, nature, morphology and amount of these carbides are factors of important concern. Identification and characterisation of carbides were realised. MC, M2C, M7C3 carbides were found. Some relationships with mechanical properties were obtained especially in the field of the solidification sequence that affects grain size and carbides dispersion

Image analysis of carbides in high speed steel rolls and their relationship with the mechanical properties

Image analysis is used to describe quantitatively various different natures of carbides in high speed steel rolls. After an etching judiciously selected, the identification and the extraction of the carbide types are based on spectral differences. For every carbide type, three parameters are measure : the size, the spatial distribution and the volume fraction. The size of martensite grain is also measured

Quantitative description of MC, M2C, M6C and M7C3 carbides in high speed steel rolls

peer reviewedOne goal of the COST 517 project entitled “Effects of inclusions and carbides on the mechanical properties of alloyed steels” is to establish quantitative and statistical relations between the microstructure and the mechanical properties of rolls materials. This paper presents the different steps necessary to characterise the microstructure and the carbides presents in high-speed steel rolls. First, carbides were examined by SEM and EDX microscopy. Then, images of samples were acquired by optical microscopy and analysed to finally measure quantitative parameters describing the grains and the carbides

Assessment of corrosion resistance, material properties, and weldability of alloyed steel for ballast tanks

Ballast tanks are of great importance in the lifetime of modern merchant ships. Making a ballast tank less susceptible to corrosion can, therefore, prolong the useful life of a ship and, thereby, lower its operational cost. An option to reinforce a ballast tank is to construct it out of a corrosion-resistant steel type. Such steel was recently produced by POSCO Ltd., South Korea. After 6 months of permanent immersion, the average corrosion rate of A and AH steel (31 samples) was 535 g m−2 year−1, while the Korean CRS was corroding with 378 g m−2 year−1. This entails a gain of 29 %. Follow-up measurements after 10, 20, and 24 months confirmed this. The results after 6 months exposure to alternating wet/dry conditions are even more explicit. Furthermore, the physical and metallurgical properties of this steel show a density of 7.646 t/m3, the elasticity modulus 209.3 GPa, the tensile strength 572 MPa, and the hardness 169HV10. Microscopically, the metal consists of equiaxed and recrystallized grains (ferrite and pearlite), with an average size of between 20 and 30 µm (ASTM E 112—12 grain size number between 7 and 8) with a few elongated pearlitic grains. The structure is banded ferrite/pearlite. On the basis of a series of energy dispersive X-ray spectrometer measurements the lower corrosion rate of the steel can be attributed to the interplay of Al, Cr, their oxides, and the corroding steel. In addition, the role of each element in the formation of oxide layers and the mechanisms contributing to the corrosion resistance are discussed