Control of MnS and Fe3P precipitate are of vital importance for the quality of the bearing steels. The precipitation behavior is not only related to shortening the bearing steel's fatigue life, but also to another serious engineering problem i.e. changing the billet final solidification position. In order to distinguish the different precipitate behavior on the influencing of the final solidification position, a slice moving method combined with Kobayashi approximation and the MnS and Fe3P precipitation is developed. The continuous casting billet of seve-component bearing steel, i.e. Fe-C-Cr-Mn-Si-P-S system, is considered as the raw material. Upon the present chemical composition of 0.004 to 0.007 mass% S and 0.011 to 0.012 mass%P in 100Cr6 (DIN -Norm) and RAD1 (GB-Norm) alloy, the MnS but not Fe3P precipitate covers the billet cross section. The onset of Fe3P precipitation is at 0.019 mass% P in 100Cr6 alloy and 0.021 mass% P in RAD1 alloy. The distribution of the maximum amount of MnS and Fe3P precipitate is similar, i.e. concentrating at the billet center. The increase of P composition, besides accelerating the precipitation of MnS and Fe3P, elongates the liquid core length. In contrast, the increase of S composition and the precipitation of MnS greatly shortens the liquid core length. Thus it is vital to control composition of S, P solute to a low level in bearing steels in order to stabilize the final solidification position.

A microscopic cellular automaton combined with macroscopic heat and solute transport was developed to simulate the mutual growth and evolution of austenite and M7C3 carbide grains during Fe-C-Cr ternary alloy solidification process. The diffusion of solute C and Cr are contributed together to the constitutional undercooling, together with curvature undercooling, for obtaining the grain growth rate of austenite and M7C3 carbide. Results show that, the absorption of solute C and Cr by M7C3 grain and rejection by austenite grain promote the two grains' cooperative growth. Once they approach to each other, the austenite grain quickly overgrows towards the M7C3 grain till finally envelops it. The simulated solidification morphology of the Fe-4wt%C-17wt%Cr alloy, predicted averaged grain size of M7C3 carbides and C and Cr concentration in austenite grains agree with the experimental measurements and solidification path prediction. The predicted average liquid concentration curve fits with the LR, GS and PE prediction at the initial M7C3 precipitation regime and after austenite grains fully enveloping towards the M7C3 grains, returns to overlap the LR, GS and PE prediction curves.

This work reported the wetting and spreading behavior of pure iron droplet on single crystal TiO2 substrate. During the heating process, a "FeO center dot TiOx separated liquid phase" appeared at the temperature below the melting point of the pure iron, and completely covered the lower half of the iron droplet. The observed high-wetting behavior of the droplet is due to the spreading of the "separated liquid phase" rather than the iron droplet flow. According to both thermodynamic considerations and experimental measurements, the "separated liquid phase" is formed through the chemical interactions among the iron specimen, oxygen gas in the Ar atmosphere and TiO2 substrate.

This article seeks to demonstrate a direct and simplified correlation between the measurement of the wettability and the agglomeration potency of the inclusion particles in liquid ferrous alloy. The established methodology has been validated by the agreement between the calculated coagulation coefficient of Al2O3 particles and the experimental data in the open literature. Subsequently, the coagulation coefficient of Al2O3, MgO, and Ti2O3 particles in ferrous alloy melts was evaluated quantitatively by the proposed method using the actual experimental data of contact angle and surface tension. Meanwhile, the effect of the matrix composition has been investigated by comparing the Hamaker constant and coagulation coefficient between Ti2O3/pure iron and Ti2O3/low-carbon steel systems. It is noted that the change of coagulation coefficient associated with the contact angle is caused by the formation of a new phase at the oxide/metal interface at the high temperature. The present work aims to provide a deep understanding of the connection between inclusion motion behavior in the liquid alloy and the high temperature interfacial phenomenon.

The carbide precipitation nature of an automobile gear material, i.e. Fe-C-Mn-Si-Cr-Mo alloy, during carburization and element addition process are investigated through PE+PA+LR prediction. Results show that, carburization process greatly increases the amount of cementite as well as the hardness index at the surface part. Besides, the addition of Ti and V helps to formation of TiC and (V, Mo)C carbides but suppress the precipitation of cementite, which contributes equivalent hardness at surface and lighter weight to the alloy.

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 comprehensive study of inclusion and microstructure characteristics in steel with TiO2 addition has been presented in this work, including wetting behavior between TiO2 and pure Fe, evaluation of inclusion agglomeration tendency, effective nuclei inclusion identification and in-situ observation of intragranular ferrite (IGF) formation. The obtained results show that TiO2 is an effective additive because it is strong wetting with liquid iron and has obvious dispersion potency. Thereafter, the effective nuclei inclusion to induce IGF formation in steel with TiO2 addition is characterized as Ti3O5 phase. The kinetic study of IGF formation using high temperature confocal laser scanning microscope shows that the fraction of IGF increases as the cooling rate increases from 3.6 to 70 °C/min and with increasing prior austenite grain size. Furthermore, it is noted that IGF morphology is refined and the onset temperatures of IGF and GBF decrease with increasing cooling rate. Finally, the onset temperature of GBF formation is higher for the steel containing a smaller grain size, however, the onset temperature of IGF formation is independent of the grain size. This work aims to give a better control of the inclusion modification as well as improving the steel quality in secondary refining and casting process, according to the concept of inclusion engineering.