Effect of flash processing on recrystallization behavior and mechanical performance of cold-rolled IF steel

Flash processing(FP)has attracted considerable attention due to its high efficiency,economic advantages,and the extraordinary opportunity if offers to improve the mechanical properties of steel.In this study,we investigated the influences of FP on the recrystallization(REX)behavior and mechanical performance of cold-rolled IF steel.Using a thermomechanical simulator,we performed both single-stage FPs,at heating rates of 200℃/s and 500℃/s,and two-stage FP,with an initial preheating to 400℃ at a rate of 5℃/s and then to peak temperatures at a rate of 200℃/s.In comparison to continuous annealing(CA),single-stage FP can effectively refine the recrystallized grain sizes and produce a similar or even sharperγ(ND(normal direction)//{111})texture component.In particular,the heating rate of 500℃/s led to an increase in the yield strength of about 23.2%and a similar ductility.In contrast,the two-stage FP resulted in a higher REX temperature as well as a certain grain refinement due to the stored strain energy,i.e.,the driving force of REX,which was largely consumed during preheating.Furthermore,both stronger{110}<110>and weakerγtexture components appeared in the two-stage FP and were believed to be responsible for the early necking and deterioration in ductility.

Effect of La on the Corrosion Behavior and Mechanism of 3Ni Weathering Steel in a Simulated Marine Atmospheric Environment

The corrosion behavior and mechanism of 3Ni weathering steel in a simulated oceanic atmospheric environment are investigated in order to comprehend the impacts of La,as determined through electrochemical analysis and rust layer characterization.The results of this study demonstrate that the addition of La enhances the corrosion resistance of 3Ni weathering steel in the marine atmospheric environment,thereby reducing the corrosion rate and improving the protection of the rust layer.The influence of La on corrosion resistance can be attributed to two primary factors.Firstly,La functions as a grain refiner,minimizing the potential difference of the micro-regions on the substrate surface,thereby significantly reducing the corrosion of bare steel in the marine environment.Secondly,La inhibits the process of Fe_(3)O_(4) oxidation back toγ-FeOOH during corrosion at the local site,thus decreasing the formation ofγ-FeOOH and enhancing the charge transfer resistance.This research work may serve as a reference for expanding the application of rare earth elements in the field of weathering steel.

Local chemical ordering coordinated thermal stability of nanograined high-entropy alloys

Nanograined(NG)materials often suffer from low thermal stability owing to the high volume fraction of grain boundaries(GBs).Herein,we investigate the possibility of utilizing local chemical ordering(LCO)for improving the thermal stability of NG FeCoNiCrMn highentropy alloys(HE As).NG HE As with two different grain sizes were considered.Tensile tests and creep test simulations were then performed to reveal the influence of LCO on the mechanical properties and thermal stability of NG HE As.After performing hybrid molecular dynamics and Monte Carlo simulations,Cr atoms were found to accumulate at GBs.By analyzing the atomic structure evolution during the deformation process,we found that the formation of LCO effectively stabilized the GBs and inhibited GB movement.In addition,dislocation nucleation from GBs and dislocation movement was also hindered.The inhibiting effect of LCO on GB movement and dislocation activity is more prominent than in the NG model with smaller grain sizes.The current simulation results suggest a possible strategy for enhancing the thermal stability of NG HEAs for service in a high-temperature environment.

High cycle fatigue behavior of titanium microalloyed high-strength beam steels

The realization of an ideal combination of mechanical and fatigue properties is prerequisites for practical application of titanium(Ti)microalloyed steel in automotive field.The fatigue behavior of four Ti microalloyed high-strength beam steels with different Ti contents was systematically studied.The results show that the content of microalloying element Ti has a significant effect on the fatigue properties,especially in the steel with a high Ti content.For the experimental Ti microalloyed steel,inclusion-induced crack initiation is the main fatigue failure mode.Different from general fatigue fracture mechanism in Ti-contained steel,no TiN,which is the most detrimental to fatigue behavior,was found in fatigue crack initiation area.However,the large-sized TiN and oxide complex inclusion with a core-shell structure is the dominant cause of fatigue fracture.Because of the intense-localized deformation at the interface between complex inclusion and matrix,the angular TiN in the outer shell has a serious deteriorating effect on the fatigue properties,which is consistent with the result of the Kernel average misorientation map.Besides,the modification effect of a small amount of MnS on large-sized inclusion is not obvious and has little effect on the fatigue behavior.For more practical guidance,the critical inclusion sizes of the experimental steels were also investigated by experimental extrapolation method.With the increasing tensile strength,the inclusion sensitivity of the experimental steels increases,leading to the small critical inclusion size.

Metallurgical Interpretation on Grain Refinement and Synergistic Effect of Mn and Ti in Ti-microalloyed Strip Produced by TSCR

The grain refinement mechanism and synergistic effect of Mn and Ti involved in the Ti-microalloying technology of thin slab casting and direct rolling （TSCR） were elucidated. Because the inevitable precipitation of TiN in high Ti-containing liquid steel decreases the volume fraction of TiN precipitated from austenite and the rapid coarse- ning rate leads to a large size of TiN particles, a relatively weak inhibition effect on the recrystallized grain growth was obtained compared with that in the low Ti-containing steel. However, the ferrite grain size in high Ti-containing steel can be refined by the so-called non-recrystallization rolling. The complex addition of Mn and Ti can improve the strength and toughness of strip remarkably, and the mechanisms are that Mn decreases the transformation tempera- ture, refines the ferrite grains, and enhances the formation of bainite and TiC precipitation in ferrite.

Influence of coiling temperature on microstructure and mechanical properties of a hot-rolled high-strength steel microalloyed with Ti,Mo and V

Influence of coiling temperature(CT)on the microstructure and mechanical properties of a hot-rolled high-strength steel microalloyed with Ti,Mo and V was elucidated.The precipitation behavior of nano-sized particles was investigated by theoretical calculation and quantitative analysis.And the results revealed that V-enriched(Ti,Mo,V)C precipitated in the ferrite matrix.As the CT decreased,the site fractions of Ti in(Ti,Mo,V)C changed little,the site fractions of Mo increased,and the site fractions of V decreased accordingly.Moreover,the low CT could refine the microstructure and precipitated particles but suppress the precipitation of(Ti,Mo,V)C particles simultaneously,leading to the volume fraction of(Ti,Mo,V)C significantly decreasing,consequently causing an increment of grain refinement strengthening and a reduction in precipitation hardening.When the CT was 600℃,the steel characterized by fine polygonal ferrite,a small amount of bainite and nano-sized(Ti,Mo,V)C precipitates exhibited the optimum mechanical properties with the ultimate tensile strength of 870 MPa,yield strength of 807 MPa and elongation to fracture of 17%.

Application of phase-field modeling in solid-state phase transformation of steels

Solid-state phase transformation is usually associated with excellent mechanical properties in steel materials.A deep understanding of the formation and evolution of phase structure is essential to tailor their service performance.As a powerful tool for capturing the evolution of complex microstructures,phase-field simulation quantitatively calculates the phase structures evolution without explicit assumptions about transient microstructures.With the development of advanced numerical technology and computing ability,phase-field methods have been successfully applied to solid-state phase transformation in steels and greatly support the research and development of advanced steel materials.The phase-field simulations of solid-phase transformation in steels were summarized,and the future development was proposed.

Research status and prospect of direct strip casting manufactured lowcarbon microalloyed steel

Direct strip casting(DSC)is one of the cutting-edge technologies for the steel industry in the twenty-first century.Under the background of carbon peak and carbon neutrality,DSC technology has a bright future of applications as it requires less production time and space with reduced energy consumption.Owing to its sub-rapid cooling rate during solidification and low reduction during hot rolling,DSC process exhibits a series of unique physical metallurgy characteristics.The process characteristics of DSC process and the microstructural evolution during the thermomechanical processing of low-carbon microalloyed steel are reviewed.The effects of hot rolling,cooling,coiling temperatures and microalloying elements on the microstructure and mechanical properties are then discussed.Finally,the future development orientations of DSC technology are suggested to fully utilize its unique features for the enhancement of its competitiveness and for the promotion of carbon neutrality of the steel industry.

Effects of strain rate on austenite stability and mechanical properties in a 5Mn steel

The austenite stability and the mechanical properties in a typical medium Mn grade steel,i.e.,5Mn steel,were investigated under a wide range of strain rates through the combination of experimental and theoretical methodologies.The obtained results indicate that austenite is more stable at a high strain rate,which is due to the suppression of the austenite to martensite transformation.This suppression is attributed to the increased stacking fault energy and the high deformation energy barrier.Moreover,the suppression of martensitic transformation also leads to the decrease in the ultimate tensile strength and the uniform elongation.Owing to the increase in an adiabatic heating temperature,an increase in the uniform elongation is acquired at a high strain rate.The obtained fundamental study results shed light on a wide application of the medium Mn steel under different strain rate conditions.