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Zn-Al-Mg alloy coating, the most promising protective steel coating of the 21st century, is widely employed in construction, automotive, and other fields, due to its high surface and edge corrosion. In recent years, with the increasing demand for Zn-Al-Mg coating, a series of basic studies on Zn-Al-Mg coating materials has been carried out by foreign scholars, making significant progress and achievements. Simultaneously, the gap in the galvanizing industry between domestic and international has been expanding year by year. In order to gradually reduce gradually this gap with foreign countries, it is necessary to summarize and review the research achievements of foreign researchers. In this paper, the research progress into high corrosion resistant Zn-Al-Mg hot dip coatings was reviewed from the perspective of interfacial reactions in pots, coating structures, corrosion mechanisms of surface and cut edges, as well as corrosion product types of Zn-Al-Mg coatings. According to the range of Al content, laboratory and commercial Zn-Al-Mg coatings are divided into three types: "low-aluminum, " "medium-aluminum, " and "high-aluminum" coatings. There are differences in these coatings, including growth kinetics in the intermetallic compound layers of the different types of coating. In order to control the thickness of the coating, reasonable immersion time and temperature should be controlled. There are also differences in the solidification structures of the three types. Primary Al or Zn crystal, Zn/MgZn2 binary eutectics, and Zn/MgZn2/Al ternary eutectics would form in "low-aluminum" and "medium-aluminum, " while Al-rich dendrites, an intergranular Zn-rich phase, a Mg2Si phase, and a MgZn2 phase would occur with "high-aluminum" coatings. During surface corrosion in "low-aluminum" or "medium-aluminum, " the MgZn2 phase is ionized first, giving rise to a dense corrosion product to inhibit corrosion, such as basic zinc salt (BZS) or layered double hydroxide (LDH). Meanwhile, in the cut edge, a self-healing phenomenon occurs; the proposed explanation in this paper for this is Mg-containing corrosion product flowing or pH changing. However, there are some disputed aspects that need further study. In the hot dipping process, the intermetallic compound thickness should be controlled by the interfacial reaction at the steel/liquid melts through changing the molten bath temperature and holding time. The influence of Mg2Zn11 phase and MgZn2 on the corrosion resistance of Zn-Al-Mg coating is also controversial, so that the microstructure of Zn-Al-Mg coating needs further investigation for corrosion. Furthermore, a kinetic model of the corrosion process should be established to discover the controlling factors in the corrosion reaction, so that the life of the coating can be extended.

A developed and verified thermodynamic model based on the atom and molecule coexistence theory (AMCT) is employed to predict activities relative to pure liquids in standard state in Mg-Al, Mg-Zn, Al-Zn and Mg-Al-Zn melts through the calculated mass action concentrations of structural units, i.e., Ni. According to AMCT, Ni can be extrapolated and calculated by the chemical equilibrium constant of a structural molecule, i.e., Ki, in the Mg-Al-Zn ternary system and binary subsystems. In this paper, the standard Gibbs free energy function, for reported activities and mixing thermodynamic properties in Mg-Al, Mg-Zn and Al-Zn melts, was regressed and optimized. The results showed that Ki and Ni were deduced by Gibbs free energy function at the studied temperature. The results of calculating thermodynamic properties in the full composition range for liquid Mg-Al-Zn from 880 to 1100 K, as well as Mg-Al from 923 to 1073 K, Mg-Zn from 880 to 973 K and Al-Zn from 1000 to 1073 K, are presented in the paper by coupling with Ni and AMCT. An excellent agreement is noticed between the calculated values of this study and measured thermodynamic data from the references, suggesting that the AMCT can be well applied to describe and predict the activities of the Mg-Al-Zn system and its subsystems.

Inconel 718, a precipitation strengthening nickel-based superalloy, is widely used in aerospace and other high-temperature process industries because of its adequate strength, ductility, and good workability.The increasing demand for alloys with remarkable comprehensive performance necessitates the development of alloys with highly uniform microstructures and highly homogeneous composition;therefore, electroslag remelting (ESR) has attracted much attention in metallurgical circles.However, strong chemical reactions, such as (Al2O3) +[Ti]= (Ti O2) +[Al], usually occur at the electrode-slag interface (ESI) or the droplet-slag interface (DSI) and the metal pool-slag interface (MSI) ;therefore, the concentrations of Al and Ti cannot be maintained within specifications, or the elements cannot be uniformly distributed along the height of the ingots during the ESR process.Consequently, mechanical property deteriorates and the production cost of nickel-based alloy increases.To overcome these issues, in this study, a thermodynamic model for calculating equilibrium content of Al and Ti in a nickel-based alloy during ESR was developed based on the ion and molecule coexistence theory (IMCT) .The chemical composition of slags plays a key role in the physicochemical properties of slags and controls the loss of alloying element during ESR process.Therefore, the respective relations between the activity and activity ratio of individual slag components with chemical composition of Ca O-Si O2-MgO-Fe O-Al2O3-Ti O2-Ca F2slag were studied.Furthermore, effect of the slag composition on the equilibrium content of Al and Ti in Inconel 718 superalloy under various metallurgical temperatures during ESR was investigated.The results indicate that the equilibrium content of Al increases with increasing temperature, however, the equilibrium content of Ti decreases.MgO and Ca F2have little influence on the control of the loss of active alloy elements.

This paper reviewed the recent development of primary carbides in H13 steel from the aspects of solidification segregation theory, solidification method, production process, and alloy design. The relationship between the production process of H13 steel and the characteristics of primary carbides was clarified. During the solidification of H13 steel, primary carbides can be easily generated by dendritic segregation. The primary carbides in H13 steel can be divided into polygonal, stripy, blocky, and eutectic structures according to the different shapes and can be divided into MC, M2C, M7C3, and M23C6 according to the different structures. The primary carbides can also be classified as Mo-rich, V-rich, and Ti/Nb-rich carbides according to the different compositions. Primary carbides are detrimental to the performance of H13 steel because cracks can easily form around primary carbides during service of the materials. The widely used methods of controlling the primary carbides in H13 steel under industrial production conditions, including solidification control, modification treatment, high-temperature diffusion of the ingot, and alloy composition optimization, were introduced. Modification treatment and solidification control are able to control the size and quantity of primary carbides but are unable to avoid the precipitation of primary carbides entirely. The stability of primary carbides can be relieved by composition optimization. High-temperature homogenization treatment of ingot is the most important means of controlling primary carbides in H13 steel. However, the heating temperature and holding time need further investigation.

A thermodynamic model for gas-solid reduction reactions of iron oxides was established based on the minimized Gibbs free energy principle. On the basis of the model calculation results, the equilibrium diagram for the gas-solid reduction reactions of iron oxides was graphed; the equilibrium results are in good agreement with the reported experimental data. Comparison with the data from common metallurgical books and thermodynamic databases indicates big differences in thermodynamic data from different references. Thermodynamic equilibrium was investigated for the stepwise reduction sequence of iron oxides. The thermodynamic equilibrium was calculated for iron oxide reduction using CO-H2 mixtures as a reducing agent. According to the calculation results, the formula for the gas utilization ratio η总 in the equilibrium state was deduced, and the three-dimensional equilibrium diagram of iron oxide reduction using CO-H2 mixtures was graphed. As compared with the reported experimental data indicates the correctness of calculation results.

In-situ research was conducted to illuminate the high-temperature behavior of primary carbide in H13 steel that had been cast in different ways. Experimental observations indicate the obvious segregation of Cr, Mo, V, and C in the interdendrite zone of continuously cast and electroslag remelting (ESR) samples. In the interdendrite zone, primary carbide is composed of Cr, Mo, V, and Ti. A liquid phase was observed to occur around the primary carbide of two as-cast samples cast by continuous casting and ESR processes when heated to 1200℃ and 1250℃, respectively. The temperature at which the liquid phase appears agrees well with theoretical calculations. The liquid-phase region expands as the heating temperature increases and the continuous casting sample shows a larger liquid zone. The emergence of a partial liquid phase accelerates the diffusion of the segregated elements and is an important factor in the high-temperature behavior of primary carbide.

Optical microscopy (OM), scanning electron microscopy (SEM), and electron microprobe analysis (EMPA) were used to determine the nature of carbonitrides decomposition in H13 hot work die steel under high temperature, including its morphology, size and composition. Most of the original carbonitrides are long strip (Vx,Mo1-x)(Cy,N1-y) ranging between 10~30 μm with a few square (Tix,V1-x)(Cy,N1-y). The result shows that the edge of the carbonitrides becomes saw-toothed after holding at 1200℃ for 2.5 h, and fine decomposed particles are formed. The average length of carbonitrides, mainly (Tix,V1-x)(Cy,N1-y), is reduced to 12.9 μm as increasing the holding time for 10 h. When the steel is held at 1250℃ for 5 h, about 87% of the carbonitrides disintegrate, especially (Vx,Mo1-x)(Cy,N1-y) dissolving and disappearing, and the carbonitrides size is less than 20 μm. When holding at 1250℃ for 10 h, all the carbonitrides remained are (Tix,V1-x)(Cy,N1-y), of which 70% are square and 93% decompose to fine particles, and can be controlled to size below 10 μm. It is deduced that (Tix,V1-x)(Cy,N1-y) decomposition is related to Fe diffusion by EMPA analysis and that the Fe content in (Tix,V1-x)(Cy,N1-y) gradually enhances while Ti and V contents decline. The carbonitrides reliably decompose at the position of small curvature radius and defect position, forming fine particles of 0.1~1 μm. The original carbonitrides disappear by zone dissolution from outer to inner. The equilibrium temperature of carbonitrides dissolution has a relationship with its constituents based on the two-sublattice model, and dissolution temperature for most (Tix,V1-x)(Cy,N1-y) in sample is between 1200℃ and 1246℃, which fits well with the experimental results.

To investigate the laws relating to the mole fraction of a component in a binary solution and its vapor pressure, the entropies of dissolution from the solid phase to the liquid phase of 48 typical compounds were assessed and the compounds were confirmed to not decompose during the phase transition processes. Under the condition where a compound also exists in a binary liquid melt, both of the components in the whole concentration range obey Raoult's law. Specifically, there is no such thing as an"activity"as defined by Lewis. The so-called "activity" is actually the balance mole fraction in the case where all components in the system are considered by comparing with the measured activity data for Mg-Si, Sb-In, and Fe-Mn binary systems. It is verified that the calculated equilibrated mole fraction represents the activity, thereby the binary metallic melts involve no activity. In addition, a general formula is deduced for the equilibrium mole fraction in the binary system in the case where the melt contains one intermetallic compound. In particular, the cases corresponding to A2B-type or AB-type intermetallic compounds were discussed. Finally, a broad sense Raoult's law was proposed that it is applicable in all three regions in binary solution divided by different temperatures:(I) the region corresponding to temperatures above the melting point of the component,(Ⅱ) the region corresponding to temperatures lower than the melting point of the pure component but greater than the liquidus temperature, and (Ⅲ) the region corresponding to temperatures lower than the liquidus temperature.

Three kinds of primary carbonitrides were classified in H13 hot work die steel through experiment,including (Vx,Mo1-x)(Cy,N1-y) rich in V and C,(Tix,V1-x)(Cy,N1-y) rich in Ti and N,and (Tix,V1-x)(Cy,N1-y) rich in V and C,some having a core in the center.The element variation and Gibbs energy of the carbonitrides during H13 solidification were analyzed based on the solidification segregation model and the two-sublattice model,taking the interaction between components into account as well as the alloying element content and C/N ratio of the three types of primary carbonitrides.It is found that Tiand N-rich (Tix,V1-x)(Cy,N1-y) forms when the solid fraction reaches 0.9,while the other Vand C-rich (Tix,V1-x)(Cy,N1-y) generates when the solid fraction is greater than 0.96 during solidification.The critical solid fraction for the formation of these two (Tix,V1-x)(Cy,N1-y) decreases with increasing Ti and N contents soluted in the carbonitrides.The formation of (Vx,Mo1-x)(Cy,N1-y) during solidification can be affected by the x value.The critical solid fraction decreases as less vanadium is soluted in (Vx,Mo1-x)(Cy,N1-y),leading to larger size carbonitrides demonstrated by the models,which fit well with experimental data.The influence of oxides and carbonitrides on heterogeneous nucleation for the carbonitrides was also researched through lattice misfitting analysis.

Plate products of DH36 high-strength ship plate steel,roll formed by a steelworks in China,were investigated. Analyzing by mathematical simulation method,a mathematical model was built for the connection between main chemical components and basic mechanical properties of DH36 high-strength ship plate steel. Based on the model,the impact of composition fluctuation of manganese on various mechanical properties was emphatically analyzed. The results show that the influence of manganese on impact energy mainly appears as the negative linear relationship. The impact of manganese on the yield strength,tensile strength and reduction of area also appears as the linear relationship,and the slope is impacted by other elements and needs further investigation.

A thermodynamic model is proposed for calculating the mass action concentration of structural units in the Al-Ti binary melt system based on the atom-molecule coexistence theory. The standard equilibrium constants of reactions for forming three associated molecules as Al3Ti,Al Ti,and Al11Ti5 in the Al-Ti binary melt system at the temperature of 2073 to 2273 K are calculated based on the activity reported in the literature,and the expressions of the standard molar Gibbs free energy change of reactions are obtained.Meanwhile,the calculated mass action concentrations NAl and NTi of Al and Ti are compared with the reported activities of both Al and Ti in the full composition range of the Al-Ti binary melt system at different temperatures from the literature. The results show that the calculated mass action concentrations NAl and NTi are in agreement with the activities aAl and aTi in the reported literature. The relationship between the calculated mass action concentration Ni and the calculated equilibrium amount of substance ni of Al3Ti and Al11Ti5 in the Al-Ti binary melt system is rod-type. However,the relationship between the calculated mass action concertation NAlTi and the calculated equilibrium amount of substance nAlTi in this binary melt system is spindle-type.