Journal of Iron and Steel Research International最新文献

A novel Al-alloyed press-hardening steel (PHS) was developed, which exhibits excellent tensile, bending and antioxidation properties. Al is a ferrite-forming element that can hinder the formation of cementite and enhance the stability of austenite. The incorporation of Al not only induces the formation of ferrite within martensitic matrix but also enhances the stability of retained austenite (RA). The microstructure of novel steel consists of martensite, ferrite, and RA after press hardening. Investigations into the role of Al in RA development were supported by thermo-kinetic calculations. The simultaneous introduction of ferrite and RA into the martensitic matrix via tailored chemical compositions significantly enhances the elongation and bending toughness of the novel PHS. Additionally, Al can form a dense Al oxide at the bottom of oxide layer, resulting in the improved antioxidant properties. Compared to 22MnB5 steel, it is an exciting discovery as there is a significant improvement in total elongation and bending toughness of novel PHS without compromising strength. The novel PHS, with its exceptional balance of strength and ductility, will play a crucial role in reducing weight when it replaces the existing class 22MnB5 PHS in different structural components of vehicle bodies.

Combined with the hydrogen pre-charging and tensile testing methods, the effect of charged hydrogen content on the microstructure and mechanical behavior of an as-forged Ti–6Al–4V alloy was investigated. After performing hydrogen charging for 2, 4, 6, 8 and 10 h at a constant cathodic current density value of 75 mA/cm² in a corrosion medium of 3.5 wt.% NaCl solution, the hydrogen contents in the charged samples increased gradually from 73 × 10⁻⁴ to 230 × 10⁻⁴ wt.%. When the hydrogen content was less than 190 × 10⁻⁴ wt.%, the charged hydrogen atoms were present as the solute atoms in the matrix, resulting in the enhanced tensile strength due to the solid solution strengthening of hydrogen atoms. Moreover, the reduced axial ratio c/a for α-Ti matrix due to the hydrogen dissolution was beneficial to improving the ductility of the hydrogenated samples. The critical hydrogen content for simultaneously improving the ductility and strength is determined to be 99 × 10⁻⁴ wt.%. When the hydrogen content was 230 × 10⁻⁴ wt.%, a small number of δ-TiH_x hydrides and micro cracks formed in the localized areas of α-Ti matrix, resulting in the simultaneous decrease of ductility and strength.

To reveal the intricate mechanisms underlying the melting and dissolution processes of scraps in the iron ladle, the melting characteristics of three carbon steels with different C concentrations at the bath temperatures of 1623 and 1723 K were studied. Upon immersing scraps into the molten metal, the liquid metal immediately froze around the submerged parts of scrap cylinders. Whereafter, the solid shell completely melted at both bath temperatures after the immersion time of 5 s. The maximum thickness of solidified steel shells significantly decreased with increasing the bath temperature. The findings also suggested that the melting rate of scrap cylinder exhibited a positive correlation with the C concentration in the scrap and the bath temperature. Quantitatively, the mass transfer coefficients of C for the low carbon (0.18 wt.%), medium carbon (0.32 wt.%), and high carbon (0.61 wt.%) concentrations in the scrap cylinders at 1723 K were determined by a kinetic model, which were 8.78 × 10⁻⁵, 9.57 × 10⁻⁵ and 10.00 × 10⁻⁵ m s⁻¹, respectively, and those corresponding values decreased to 3.87 × 10⁻⁵, 4.49 × 10⁻⁵ and 3.54 × 10⁻⁵ m s⁻¹ at 1623 K. However, there was little difference observed among the heat transfer coefficients of hot metal for the three carbon steels, which were estimated to have an average value of 16.36 and 18.82 kW m⁻² K⁻¹ at the experimental temperatures of 1623 and 1723 K, respectively. The results from the experiments and mathematical models showed good consistency at both bath temperatures, providing feasible guidance for efficient melting of steel scraps in the iron ladle.

The municipal solid waste incineration fly ash (MSWI-FA) contains a large amount of heavy metals, and the process of iron ore sintering and treating fly ash needs to pay attention to the migration characteristics of heavy metals. The impact of the application of MSWI-FA in the sintering process on the emission law of heavy metals in the collaborative treatment process was studied, and corresponding control technologies were proposed. The results showed that the direct addition of water washing fly ash (WM-FA) powder resulted in varying degrees of increase in heavy metal elements in the sinter. As the amount of WM-FA added increases, the content of heavy metal elements correspondingly increases, and an appropriate amount of WM-FA added is 0.5%–1.0%. The migration mechanism of heavy metals during the sintering treatment of WM-FA was clarified. Heavy metals are mainly removed through direct and indirect chlorination reactions, and Cu and Cr can react with SiO₂ and Fe₂O₃ in the sintered material to solidify in the sinter. Corresponding control techniques have been proposed to reduce the heavy metal elements in WM-FA through the pre-treatment of WM-FA. When the WM-FA was fed in the middle and lower layers of the sintered material, the high temperature of the lower layer was utilized to promote the removal of heavy metals. The Ni element content has decreased from 130 to 90 mg kg⁻¹, and the Cd removal rate has increased by 23%. The removal rates of Cd and Cr elements increase by 2.4 and 5.5 times, respectively. There is no significant change in sintering indexes.

The La_1.7Pr_0.3Mg₁₆Ni hydrogen storage alloy was prepared by medium-frequency induction melting, and then the composite hydrogen storage alloy powder of La_1.7Pr_0.3Mg₁₆Ni + x wt.% (x = 0, 2, 4, and 6) graphene was prepared by ball milling for 10 h. The effect of the addition of graphene on the activation and hydrogen de/absorption properties of La_1.7Pr_0.3Mg₁₆Ni alloy was studied. The result demonstrated that these composite alloys were composed of La₂Mg₁₇, La₂Ni₃, and Mg₂Ni phases. After saturated hydrogen absorption, it was composed of LaH₃, Mg₂NiH₄, and MgH₂ phases, while during the dehydrogenation process, it was composed of LaH₃, Mg, and Mg₂Ni phases. The addition of graphene can help get a more homogeneous granule after ball milling and accelerate the first activation of dehydrogenation/hydrogen absorption. The hydrogen release activation energy of the alloys first decreases and then increases as the graphene content increases from x = 0 wt.% to x = 6 wt.%. The minimum activation energy of the composite hydrogen storage alloy is 51.22 kJ mol⁻¹ when x = 4 wt.%.

Pinless friction stir spot welding (P-FSSW) was performed to manufacture Mg/steel lap joints. Orthogonal tests for P-FSSW of Mg/steel were investigated, and the main factors affecting the properties of Mg/steel lap joints were derived. The shear force of the Mg/steel lap joints gradually increased and then decreased as the welding time increased. Maximum shear force was 5.3 kN. Fe–Al intermetallic compound (IMC) was formed at the Mg/steel interface near the steel side, and Mg–Al IMCs were formed at the Mg/steel interface near the Mg alloy side. Mg/steel lap joint was transformed from an initial solid-state welding to fusion-brazing welding as the welding time increased. No hole defects were formed in Mg/steel solid-state welding joints, whereas hole defects appeared in Mg/steel fusion-brazing welding joints. The temperature field of Mg/steel lap joints was simulated to analyze hole defects generated during the welding process. Hole defects can be eliminated by changing the spindle deflection angle, and the shear force decreased. Excessive spindle deflection can also lead to failure to form a stable joint. Hole defects were removed because the spindle deflection angle reduced the interfacial reaction temperature, and a solid-state welding joint was formed, which resulted in an absence of fusion-brazing welding hole formation.

Ti₃SiC₂ ceramic and SUS430 ferritic stainless steel were welded by the transient liquid phase (TLP) diffusion bonding method using an Al interlayer at 850–1050 °C in vacuum. The evolution of phase and morphology at the interface and bonding strength were systematically investigated. The results show that Ti₃SiC₂ and SUS430 were well bonded at 900–950 °C. Three reaction zones were observed at the interface. At the joint interface area adjacent to alloy, the alloy completely reacted with liquid Al to form Al₈₆Fe₁₄. At Ti₃SiC₂/Al interface, Ti and Si diffused outward from Ti₃SiC₂ into the molten Al to form Fe₃Al + Al₅FeSi + TiAl₃ zone. Adjacent to Ti₃SiC₂ matrix, Ti₃Si(Al)C₂ + TiC_x zone was formed by the loss of Si. The evolution mechanism of TLP-bonded joints was discussed based on the interface microstructure and product phases. In addition, the tensile strength of the joint increased with increasing bonding temperature. The corresponding maximum value of 59.7 MPa was obtained from SUS430/Al (10 μm)/Ti₃SiC₂ joint prepared at 950 °C.

Lightweight refractories for the working lining of high-temperature furnaces play an important role in the smelting of advanced steels and superalloys. To prepare lightweight refractories for the working lining of high-temperature furnaces, the synthesis of lightweight aggregates is the basis. Recently, the research on the synthesis of lightweight aggregates with high service temperature, low thermal conductivity, high strength, and good slag resistance has received widespread attention. The available literature on the synthesis of lightweight aggregates was summarized, including corundum, mullite, mullite–corundum, spinel, corundum–spinel, cordierite, cordierite–mullite, calcium hexaluminate, corundum–calcium hexaluminate, bauxite, magnesia, magnesia-based, and forsterite-based aggregates. Finally, the future development trend of lightweight aggregates was proposed.

We proposed a new technique route of directional solidification for the manufacture of super slab. A 7-t laboratory-scale thick slab was casted and characterised for trial. To further understand the process, the evolution of the multiple physical fields during the directional solidification was simulated and verified. Similar to the convectional ingot casting, a negative segregated cone of equiaxed grains was formed at the bottom, and a seriously positive segregated region was formed beneath the top surface of the slab. Specific measures on the lateral walls, base plate, and free surface were strongly recommended to ensure that the slab is relatively directionally casted. A water-cooling copper base plate accelerates the solidification rate and the columnar growth along the vertical direction. It inhibits the sedimentation of equiaxed grains and enlarges the columnar zone. Based on the simulation analysis, it can be concluded that the directional solidification technique route is promising to manufacture super slab with lower segregation level, and less porosities and inclusions.

The phase volume fraction has an important role in the match of the strength and plasticity of dual phase steel. The different bainite contents (18–53 vol.%) in polygonal ferrite and bainite (PF + B) dual phase steel were obtained by controlling the relaxation finish temperature during the rolling process. The effect of bainite volume fraction on the tensile deformability was systematically investigated via experiments and crystal plasticity finite element model (CPFEM) simulation. The experimental results showed that the steel showed optimal strain hardenability and strength–plasticity matching when the bainite reached 35%. The 3D-CPFEM models with the same grain size and texture characters were established to clarify the influence of stress/strain distribution on PF + B dual phase steel with different bainite contents. The simulation results indicated that an appropriate increase in the bainite content (18%–35%) did not affect the interphase strain difference, but increased the stress distribution in both phases, as a result of enhancing the coordinated deformability of two phases and improving the strength–plasticity matching. When the bainite content increased to 53%, the stress/strain difference between the two phases was greatly increased, and plastic damage between the two phases was caused by the reduction of the coordinated deformability.