Non-metallic Inclusions in Different Ferroalloys and Their Effect on the Steel Quality: A Review

Ferroalloys have become increasingly important due to their indispensable role in steelmaking. In addition, the demand for improved steel qualities has increased considerably, which in turn highlights the quality of ferroalloys. This is due to the fact that the impurities in ferroalloys directly and significantly influence the quality of steel products. To gain a better understanding of the main trace elements and inclusions in ferroalloys (such as FeSi, FeMn, SiMn, FeTi, FeCr, FeMo, FeNb, FeV, FeB, some complex ferroalloys) and their behaviours in steel melt after the additions of these ferroalloys, information from a large number of previous results on this topic was extensively reviewed in this work. The applications of different ferroalloys and their production trends were discussed. In addition, the effects of some trace element impurities from ferroalloys on the inclusion characteristics in steel were also discussed. The possible harmful inclusions in different ferroalloys were identified. Overall, the results showed that the inclusions present in ferroalloys had the following influence on the final steel cleanliness: (1) MnO, MnS and MnO–SiO2–MnS inclusions from FeMn and SiMn alloys have a temporary influence on the steel quality; (2) the effect of large size SiO2 inclusions (up to 200 μm) in FeSi and FeMo alloys on the steel cleanliness is not fully understood. The effect of Al, Ca contents should be considered before the addition of FeSi alloys. In addition, Al2O3 inclusions and relatively high Al content are commonly found in FeTi, FeNb and FeV alloys due to their production process. This information should be paid more attention to when these ferroalloys are added to steel; (3) except for the existing inclusions in these alloys, the Ti-rich, Nb-rich, V-rich carbides and nitrides, which have important effects on the steel properties also should be studied further; and (4) specific alloys containing REM oxides, Cr–C–N, Cr–Mn–O, Al2O3, Al–Ti–O, TiS and Ti(C, N) have not been studied enough to enable a judgement on their influence on the steel cleanliness. Finally, some suggestions were given for further studies for the development of ferroalloy productions.

Steel quality of rolling contact bearings produced by different manufacturers, used for mining equipment instrumentation

Severe operating conditions of mining equipment have a negative impact on the operating life of the rolling contact bearings used in such equipment. The main reasons for the premature failure of rolling contact bearings include, first of all, poor quality of the bearing steel as delivered and the defects of their subsequent heat treatment. The abovementioned reasons result in splitting of bearings, metal shelling and appearance of potholes on their tracks, as well as intense abrasive wear. Nevertheless, despite the importance of this issue, the quality of bearing steel, either as delivered or in finished bearings, is usually not under control.To solve this problem, the quality of bearing steel was studied, exemplified by the bearings of the Russian, Swedish (SKF) and Japanese (NSK) manufacturers, i.e., main suppliers of rolling contact bearings for mining equipment in Russia. The problem of bearing steel quality control was solved by developing a quality control methodology that took into account the state of the metal after metallurgical treatment and at the stage of bearing production. Based on this methodology, the main types of bearing steel defects affecting the mechanism of bearing failure are identified.It is found that the bearing steel quality of domestic manufacturers is highly competitive with foreign counterparts. A method of nondestructive control is also proposed for detecting possible microstructure defects in bearings, either as delivered or while in operation.