查看更多>>摘要：Nonmetallic inclusions are well known to influence product quality and process stability in the production of steel. A process step that is very sensitive to the presence of nonmetallic inclusion (NMI) is continuous casting. Here, the so‐called clogging phenomenon can occur, resulting in a distinct disruption of the casting process and decreased steel quality. The presence of nonmetallic inclusions considerably contributes to the build‐up of deposits in the submerged entry nozzle provoking instabilities in the flow control system. Numerous research studies have been subject to different clogging mechanisms and related influencing parameters. Interfacial properties significantly influence the behavior of inclusions in the steel–refractory system. The present review demonstrates state of the art concerning the role of NMIs in the appearance of clogging. Particular focus is put on the wetting behavior between the different phases and their consequence for the deposition process. Industrial observations and laboratory methods are summarized and discussed; potential countermeasures are evaluated. A steel group that is especially prone to clogging are Ti‐ ultra low carbon (ULC) steels. An overview of the current understanding of their high clogging tendency and possible influences is presented, considering thermodynamic and interfacial aspects.
查看更多>>摘要：To explore the influence of nonuniform heat transfer on the grain structure and microsegregation of carbon in shells inside the mold, a multiscale model considering heat conduction and dendritic growth is constructed for the round billet continuous casting. Adopting measured heat flux as the boundary conditions, heat conduction in the mold is solved by the finite difference scheme, and dendritic growth is modeled by the cellular automaton model. The temperature distribution of the round billet under measured heat flux is calculated, and the grain structure and the microsegregation of carbon in four selected regions are simulated. Herein, it is shown in the results that the different local heat fluxes lead to dissimilar variations in the surface temperature and grain structure of the shell. A close relationship exists between the carbon microsegregation and local heat flux; the carbon microsegregation decreases with heat flux. The high heat flux accelerates columnar dendritic growth and fines the columnar dendritic array so that the secondary arms are less developed and the microsegregation is improved.
查看更多>>摘要：Herein, the effect of heat treatment with die quenching on Zn‐coated hot stamping steel is analyzed. Heating temperatures are 850, 880, 900, and 930?°C, and soaking times are 4 and 8?min. Then, microstructure, hardness, coating layer morphology, element diffusion and distribution, formation of microcrack and microvoid, and oxidation are analyzed. Results reveal that as heating temperature increases, the Vickers hardness of Zn‐coated hot stamping steel increases when soaking time is 4?min, while it decreases when soaking time is 8?min. The least average hardness value is still larger than 460, resulting from the formation of the martensitic phase. The diffusion tends to be significant as heating temperature and soaking time increase. Both the diffusion and the evaporation affect the thickness of the coating layer remarkably. The average layer thickness is at least 18.2?μm. Microcrack generates in the coating layer due to different thermal expansions between substrate and coating layer and the melting of Zn or Zn–Fe binary phase with high content of Zn. Microvoid forms in the coating layer, resulting from the Kirkendall effect and oxidation of the Zn element. Moreover, with the increase in heating temperature and soaking time, Fe2O3 is also generated on the coating surface along with ZnO.
查看更多>>摘要：In this article, thermomechanical controlled processing (TMCP) plus tempering (T) is adopted to acquire a novel 690?MPa‐grade high‐strength low‐carbon bainitic construction structural steel, which has an optimum balance of strength‐ductility and lower yield ratio (YR). The results show that the as‐rolled steel consists of bainitic ferrite, lath‐like bainite, and granular bainite. With an increase in the tempering temperature, a great deal of carbonitrides precipitates and maintains a small nano‐scaled size without coarsening. Their interaction with dislocations induces an increase in strength. When the tempering temperature further increases, some grain boundaries between adjacent bainitic laths gradually blur or even disappear, and the average width of the bainitic laths increases to ≈860?nm. The recovery of bainitic laths is the main reason for the decreased strength. Due to the synergistic effect of the small dot‐shaped martensite/austenite (M/A) constituents and grain boundaries misorientation distribution, maximum impact absorbed energy is achieved after tempered at 500?°C. Furthermore, the lower YR is achieved by appropriate control of strength difference between the soft bainitic ferrite and hard M/A constituents via tempering.
查看更多>>摘要：Herein, the 3D characterization of internal defects in medium carbon steel with different soft reduction (SR) parameters is investigated, as regards its spatial morphology and size distribution using X‐ray computed tomography. The size of defects and their shape complexity increase from the equiaxed toward the center of the ingot, and the total number of defects is larger at the equiaxed region, which exhibits the aggregation and growth of small spherical pores into the large defects from equiaxed toward the center region. The two types of shrinkage defects, including island and net shrinkage, are identified. With the minimum reduction amount of 2 and 4?mm, the number and size of defects along with the carbon macrosegregation in the equiaxed region and center of the ingot are less as compared to the high reduction amount of 6?mm and without SR technology. The size of gas pores with sphericity >0.6 is <70?um with different reduction amounts and exceeds up to 150 um without SR. Therefore, minimum reduction amounts can easily regulate the internal defects in medium carbon steel.
查看更多>>摘要：The monotonic tensile and tension–compression cyclic deformation behaviors of carbide‐free bainitic steel with two microstructures obtained by isothermal treatment (ISO) and air cooling followed by tempering (ACT) are investigated. Tensile results demonstrate that the ISO sample exhibits a lower yield strength but longer elongation due to more and bigger blocky retained austenite than that of the ACT sample, which can lead to a higher plastic deformation capacity for the former sample. Fatigue results indicate that the ACT sample shows a higher cyclic hardening capacity but lower cyclic softening capacity at lower strain amplitudes compared to the ISO sample, whereas an opposite phenomenon can be found at higher strain amplitudes. At given total strain amplitudes, the fatigue life of the ISO sample is shorter, which is mainly attributed to its lower yield strength and more brittle martensite. In comparison with the ACT sample, the ISO sample exhibits similar or slightly longer fatigue life at lower plastic strain amplitudes but shows shorter fatigue life at higher plastic strain amplitudes. Accordingly, a bilinear Coffin––Manson relationship is revealed for the ISO sample, which is closely associated with significantly more transformation at higher strain amplitudes compared to the lower strain amplitudes.
Stefan MonscheinKatharina S. RaggerDominik ZügnerJosef Fasching...
8页
查看更多>>摘要：To achieve higher strength and good hardenability and at the same time use the positive effects of thermomechanical controlled processing, the concept of Nb and Ti microalloyed steels is increasingly used for high‐strength low‐alloy (HSLA) steels with higher C contents. Herein, how the addition of Ti affects the grain growth and static recrystallization behavior of a Nb microalloyed HSLA steel with a C content of 0.23?wt% is investigated. For this reason, alloys with varying Ti and constant Nb content are produced and investigated by means of annealing and double‐hit deformation experiments. Atom probe tomography measurements reveal that the Nb concentration in the matrix decreases with increasing Ti content. Therefore, the static recrystallization behavior is steadily inhibited with decreasing Ti content, as more dissolved Nb is available for the formation of strain‐induced NbC precipitates. The annealing experiments show that the combined addition of Ti and Nb is most effective against grain coarsening, regardless of whether the Ti content is 90 or 180?ppm. To use the positive properties of Ti against grain coarsening and Nb to inhibit recrystallization, a middle content must be chosen when alloying Ti to HSLA steels with higher C content.
查看更多>>摘要：Laboratory experiments are performed to study the transient evolution of inclusions in Si–Mn‐killed stainless steels with additions of 40, 100, and 400?ppm cerium. With the increase of the cerium content in the molten steel, the evolution path of inclusions is Al2O3–SiO2–MnO–CaO?→?Ce2O3–Al2O3–SiO2–MnO–CaO?→?Ce2O3?→?Ce2O3–CeS. The addition of 40?ppm cerium gradually increases the Ce2O3 content in liquid oxide inclusions. After the addition of 100?ppm cerium, inclusions first evolve to Ce2O3–Al2O3–SiO2–CaO–CeS, then to Ce2O3. The CeS is generated as a transient product then disappears. After the addition of 400?ppm cerium, liquid Al2O3–SiO2–MnO–CaO inclusions are modified to solid Ce2O3–CeS ones. The addition of 40?ppm cerium into the steel lowers the size from 1.74 to 1.53?μm. After the addition of 100 and 400?ppm cerium into the steel, the size of inclusions immediately decreases due to the formation of small Ce2O3–CeS inclusions and then increases owing to the collision of solid inclusions. A higher cerium content in the steel promotes the collision of Ce‐rich inclusions.
查看更多>>摘要：High‐strength nonoriented silicon steel is widely used to make automobile engines. On the basis of ensuring certain magnetic properties, it also needs higher mechanical properties. The matching of magnetic and mechanical properties can be achieved by comprehensive control of normalized and final annealing. Different annealing temperatures and times are applied to clarify the change of texture, thus influencing magnetic induction, iron loss, and mechanical properties. Route B obtains the optimal normalization effect. The type and volume fraction of texture in the final annealing sheet differ a lot after incomplete and fully normalized annealing, depending on the degree of recrystallization. The final texture composition remains unchanged when normalized annealing is incomplete, while full normalized annealing leads to the disappearance of some textures. The mechanical and magnetic properties of the final annealing sheet show consistency when fully normalized. The sheet achieved by route B2 are Rp0.2 ≈513?MPa, Rm ≈646?MPa, elongation ≈17.2%, P10/400?≈?28.7?W?kg?1, and B50≈1.64?T, achieving the best mechanical and magnetic properties in combination.
查看更多>>摘要：Herein, a static mass and energy balance model of 430 stainless steel (SS) produced by the basic oxygen furnace (BOF)–argon oxygen decarburization furnace (AOD) process is established and verified by plant data. It is found that in the AOD, the energy input is efficiently utilized, the heat available for other uses is relatively low (4.0%), and the addition of SS scrap is limited. The high carbon content of dephosphorization hot metal (DPHM) and post‐combustion ratio (PCR) in AOD are conducive to promoting the recycling of SS scrap. In contrast, when the carbon content of DPHM and PCR is low, it is necessary to add an exothermic agent to the furnace. Due to the saving of nickel‐containing raw materials and China's high proportion of thermal power, the carbon emissions and energy consumption per ton 430 SS produced by the BOF–AOD process are 3131?kg‐CO2 and 24?161?MJ, which is much lower than per ton 304 SS produced by the electric arc furnace (EAF)–AOD process. Meaning the former is more conducive to the promotion of energy conservation and emission reduction.
NSTL
Wiley