The concepts of oxide metallurgy and inclusion engineering can be utilized to improve the properties of low-alloy steels. These concepts aim at controlling the formation of intragranular ferrite (IGF), often a desirable microstructure providing good mechanical properties without the need for expensive alloying elements. IGF formation is stimulated to occur at non-metallic inclusions and form an arrangement of fine, interlocking ferrite grains. A method that has contributed significantly to investigations in this field lately is high-temperature confocal laser scanning microscopy (HT-CLSM). HT-CLSM is suited for in situ studies of inclusion behavior in liquid steel and phase transformations in solid-state steel, where in particular, displacive phase transformations can be studied, since they provide sufficient topographic contrast. The purpose of the present report is to provide a brief review of the state of the art of HT-CLSM and its application for in situ observations of ferrite formation in inclusion-engineered steels. The scientific literature in this field is surveyed and supplemented by new work to reveal the capability of HT-CLSM as well as to discuss the effect of factors such as cooling rate and parent grain size on IGF formation and growth kinetics. The report concludes with an outlook on the opportunities and challenges of HT-CLSM for applications in oxide metallurgy.

The effects of Co, Ni together with W addition on the precipitation sequence, amount, and composition of carbides and FCC matrix in Fe–C–V–Cr–Mo based alloys are investigated with the help of Partial Equilibrium (PE) approximation and thermodynamic calculations as well as differential scanning calorimetry (DSC) and electron backscatter diffraction (EBSD) - energy dispersive spectrometer (EDS) analyses. Results show that, individually, Co and Ni elements strengthen the matrix by their great solubility in FCC matrix; W element enlarges the hardness of the alloy through benefiting the formation of M6C carbide. Mutually, the addition of Co and Ni together with W increases the precipitation temperature of the eutectic carbides, although the addition of Co and Ni itself exerts little influence on the nature (type, amount, and composition) of the carbides. These predictions combined with the experimental verifications provide potentials for the alloy design and the property control in high speed steels.

Intragranular ferrite (IGF), which nucleates from specific inclusion surfaces in low alloy steels, is the desired microstructure to improve mechanical properties of steel such as the toughness. This microstructure is especially important in the coarse grain heat affected zone (CGHAZ) of weldments. The latest review paper focusing on the role of non-metallic inclusions in the IGF formation in steels has been reported by Sarma et al. in 2009 (ISIJ int., 49(2009), 1063-1074). In recent years, large amount of papers have been presented to investigate different issues of this topic. This paper mainly highlights the frontiers of experimental and theoretical investigations on the effects of inclusion characteristics, such as the composition, size distribution and number density, on the IGF formation in low carbon low-alloyed steels, undertaken by the group of Applied Process Metallurgy, KTH Royal Institute of Technology. Related results reported in previous studies are also introduced. Also, plausible future work regarding various items of IGF formation is mentioned in each section. This work aims to give a better control of improving the steel quality during casting and in the heat affected zone (HAZ) of weldment, according to the concept of oxide metallurgy.

The effect of the Ti, Al contents on the metamorphic evolution of inclusions of Ti–Al complex oxides including TiN and MnS are investigated in common carbon steels with TiO2 and TiN particle additions. The study is carried out based on both SEM-EDS analyses and Thermo-Calc equilibrium calculations. Moreover, the particle size distributions are investigated by using the electrolytic extraction method. Based on the results of this study, the following is suggested: (i) the steel composition is controlled to contain small amount of the Al content (<0.005 mass%) and large amount of the Ti content (>0.035 mass%) in order to obtain a high number of fine particles containing a Ti-rich oxide phase when adding TiO2 and TiN particles; (ii) this consideration is reasonable from the view point of the agglomeration degree of different inclusion materials, which are estimated from the attractive force (van der Waals force and liquid-capillary force) and the contact angle.