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The influence of cerium treatment on the inclusion evolution and as-cast microstructure of high-strength low-alloy steel was investigated. Properties including the inclusions characteristics, element distribution, and the in situ solidification were analyzed by scanning electron microscopy, energy-dispersive spectroscopy, and high-temperature confocal laser scanning microscopy, respectively. The results indicated that, after the addition of Ce, the Al 2 O 3 inclusions evolved to form Ce 2 O 2 S and CeAlO 3 inclusions, which exhibited a decrease in size alongside corresponding increase in their number density. The equiaxed grain ratio exhibited by the as-cast microstructure increased significantly upon the addition of Ce, while a reduction in the segregation and a corresponding increase in the homogeneity of the carbon distribution within the as-cast microstructure were also achieved. The results of the in situ observation of the solidification suggested that the addition of Ce significantly reduced the solidification temperature range, thus reducing the carbon segregation. The nucleation effect imparted by Al 2 O 3 , Ce 2 O 2 S, and CeAlO 3 on the δ-Fe formation was discussed in the context of the disregistry theory, which revealed that the formation of a large number of fine Ce 2 O 2 S inclusions promoted δ-Fe formation via heterogeneous nucleation.

In accordance with the minimum degree of disregistry mechanism in oxide metallurgy, the intragranular acicular ferrite (IAF) generated by microalloying elements in austenite was studied. Herein, the effect of Mg treatment on the microstructure and toughness of the heat-affected zone (HAZ) in shipbuilding steel was investigated. Mg treatment produced inclusions that influenced the formation of acicular ferrite in the microstructure. This refined the HAZ microstructure and improved its toughness. Electron backscatter diffraction was used to determine the oxides of titanium and the MgO·Al 2 O 3 or MgAl 2 O 4 complex inclusions that induced the formation of IAF. MnS precipitated on MgAl 2 O 4 on a specific habit plane and in a specific direction. MnS had a specific orientation relationship with MgAl 2 O 4 , i.e., { 100 } MgAl 2 O 4 //{100} MnS . The 35-mm-thick plate obtained in the industrial test after welding at a welding heat input of 120 kJ/cm had an average impact absorbed energy of 282.7 J at − 40 °C and 2 mm from the weld joint in the HAZ. The two-dimensional disregistry index between inclusions can be used as the basis for controlling their distribution and adsorption force. Microalloy addition in the order of Al–Mg–Ti is key to obtaining abundant dispersion and fine nucleation in austenite.

Ti(C,N) concentration was found to be lower on the hearth sidewall of a blast furnace and increased gradually toward the bottom of the blast furnace. The Ti(C,N) protective layer in a blast furnace is thin. Therefore, the formation of a Ti(C,N) protective layer was promoted by studying the heterogeneous nucleation principle of titanium compounds on different substances and regulation measures for the deposition process of titanium compounds on refractories or impurities. The lattice disregistry between the titanium compounds and the main components in the refractory or the main impurities in the protective layer was calculated using a two-dimensional disregistry equation to study the heterogeneous nucleation principle of titanium compounds. The results revealed that in refractory materials, the heterogeneous nucleation of carbonitride is weak when C, SiO 2 , and Al 2 O 3 are used as heterogeneous nucleation substrates, and the heterogeneous nucleation of carbonitride is strong when TiO 2 and SiC are used as heterogeneous nucleation substrates. As nucleation phases, TiC, TiN, Ti(C 0.3 ,N 0.7 ), and Ti(C 0.5 ,N 0.5 ) have similar heterogeneous nucleation ability in single component refractory, and the type of carbonitride has little effect on the lattice disregistry. The impurities in the protective layer as the substrate phases are not conducive to the heterogeneous nucleation of carbonitride. When CaS was used as the substrate phase, the heterogeneous nucleation ability of carbonitride was the worst. Both carbon and alumina were not conducive to the heterogeneous nucleation of carbonitride, but carbon was more unfavourable than alumina.

A room-temperature electrodeposition method with an organic electrolyte was developed to fabricate a HNO 3 -pretreated graphene paper Cu (GP′–Cu) composite. To improve the interfacial bonding of GP′–Cu composite, magnetron sputtering technology was used to create a “sandwich” structural gradient GP′–Cu composite. The selection of the intermediate transition layer metal was based on two-dimensional disregistry. Scanning electron microscopy, X-ray photoelectron spectroscopy, and other analytical methods confirmed that the addition of an intermediate transition metal (Cr, Ni) layer reduced the gap distance and enhanced the interfacial bonding of the GP′ and Cu deposited layers. The GP′–Ni–Cu composite exhibited the largest increase in tensile strength and conductivity. In addition, it had the highest thermal diffusivity and elongation at break among the GP′–Cu, GP′–Cr–Cu and GP′–Ni–Cu composites.

The ridging defect on the surface of stainless steel products is related to the solidification structure of ferritic stainless steel. Refining the solidification structure and increasing the proportion of equiaxed grains are necessary to lessen the ridging defect. Therefore, a new idea of using a heterogeneous nucleating agent which was composed of the composite core containing Ti was proposed, that is, a large amount of dispersed fine particles were initially formed on the solidification front, and a great amount of δ iron was then nucleated using these fine particles as the heterogeneous cores. Through analyzing the crystallographic relationship between different crystals and inducing the calculation formulas of disregistry, the disregistry between the different oxides and TiN and δ iron was explored and the type of nucleation core was determined. The key parameters of forming the composite core containing Ti were obtained through a thermodynamic calculation. The experimental results further confirm the correctness of the theoretical analysis.

According to the selection principle of grain refiners and calculation of planar disregistries, CeO2 and TiB2 particles were selected as the grain refiners of pure nickel. The change of grain size and refining effects of different refiners under the same melting conditions were investigated. The results show that the grain size of pure nickel gradually reduces with increasing the amount of grain refiners. And with increasing the amount of CeO2 up to 0.7 wt%, the grain size of pure nickel decreases from 323.0 to 53.5 lm. In addition, when the amount of TiB2is0.7 wt%, the grain size is reduced to 41.3 lm.

The formation and growth behavior of inclusions in the liquid steel were studied based on 45 steel by virtue of high temperature confocal laser scanning microscope. The structures of all kinds of complex inclusions formed in the process of cooling and solidification of liquid steel were analyzed, and disregistries between various inclusions were calculated. The results showed that inclusions with high melting point precipitated firstly, and inclusions with low disregistries precipitated later. The latter precipitated and grew up on the surface of the former, and finally clear layered complex inclusions formed. The low disregistry mechanism could not fully explain the forming reasons of all complex inclusions, but no matter which kind of mechanism leading to the formation of complex inclusions, its basic principle is that the first precipitated phase provides a low nuclear power interface for the latter, which can reduce the nucleation interface and strain energy barrier of the latter.

The effects of Mg addition on the formation of nonmetallic inclusions and solidification structure of Ti-sta- bilized ultra-pure ferritie stainless steels were investigated by experimentally casting ingots with different composi tions. Thermodynamic analyses on the formation of complex inclusions after adding Mg into steels were carried out combined with the scanning electron microscopy energy dispersive spectrometry （SEM EDS） analysis. And the EDS analysis showed that in steel samples with Mg addition, a new spinel crystal phase combined with AI2O3- TiOx formed. It was also found that after Mg addition, the proportions of equiaxed grain zone of 409L, 4003, 439 and 443NT steels increased from 10.2%, 21.8%, 13.4% and 18.6% to 84.3%, 92.3%, 91.1% and 100.0%, respec tively. Since the planar disregistry between spinel and TiN is 5. 1%0, spinel could promote the precipitation of TiN and increase the number density of TiN inclusions in steel melts. The mechanism of solidification structure refinement after adding Mg into steels supposed that the complex inclusions of spinel and TiN in high number density enhanced columnar-to-equiaxed transition, since the planer disregistry between δ phase and spinel is 1.4 %.

The effects of chemical compositions and austenitizing temperature on the formation of intragranular acicular ferrite (IAF) of 16Mn steel, a grade of low alloying steel with carbon content of 0.13∼0.19% and manganese content of 1.20∼1.60%, were systematically investigated. The in situ observation of the evolution of IAF at Mg-containing inclusions was carried out using a high-temperature laser scanning confocal microscopy (LSCM). The nucleation and growth of ferrites, the formation of IAF induced by inclusions, and the size of austenite grain at 1200 °C was directly observed using the LSCM. The results show that the inclusions can be transformed into MgAl 2 O 4 , Mg 2 SiO 4 and MgO after treated by Mg. Trace amount of Mg can induce the IAF nucleation. With the increasing of Mg addition, the percentage of IAF in steel greatly increases, while the optimum content of Mg is around 0.0022 wt%. The appropriate austenitizing temperature is around 1200 °C and the optimal prior austenite grain size is about 130 µm. The temperature range for IAF transformation is around between 571 °C and 627 °C, and the time for which is about 12 s. The disregistries between MgAl 2 O 4 , MgO and α-Fe are as small as 0.6% and 4.03%, they are so small that may act as highly effective nuclei of IAF during γ [arrow right] α transformation.