A simple route for preparation of TRIP-assisted Si-Mn steel with excellent performance using direct strip casting

The complex producing procedures and high energy-consuming limit the large-scale production and application of advanced high-strength steels(AHSSs).In this study,the direct strip casting(DSC)technology with unique sub-rapid solidification characteristics and cost advantages was applied to the production of low-alloy Si-Mn steel with the help of quenching&partitioning(Q&P)concept to address these issues.Compared this method with the conventional compact strip production(CSP)process,the initial microstructure formed under different solidification conditions and the influence of heat treatment processes on the final mechanical properties were in-vestigated.The results show that the initial structure of the DSC sample is a dual-phase structure composed of fine lath martensite and bainite,while the initial structure of the CSP sample consists of pearlite and ferrite.The volume fraction and carbon content of retained austenite(RA)in DSC samples are usually higher than those in CSP samples after the same Q&P treatment.DSC samples typically demonstrate better comprehensive mechanical properties than the CSP sample.The DSC sample partitioned at 300℃ for 300 s(DSC-Pt300)achieves the best comprehensive mechanical properties,with yield strength(YS)of 1282 MPa,ultimate tensile strength(UTS)of 1501 MPa,total elongation(TE)of 21.5%,and product of strength and elongation(PSE)as high as 32.3 GPa·%.These results indicate that the excellent mechanical properties in low-alloy Si-Mn steel can be obtained through a simple process(DSC-Q&P),which also demonstrates the superiority of DSC technology in manufacturing AHSSs.

Effect of phosphorus content on interfacial heat transfer and film deposition behavior during the high-temperature simulation of strip casting

The interfacial wettability and heat transfer behavior are crucial in the strip casting of high phosphorus-containing steel.A hightemperature simulation of strip casting was conducted using the droplet solidification technique with the aims to reveal the effects of phosphorus content on interfacial wettability,deposited film,and interfacial heat transfer behavior.Results showed that when the phosphorus content increased from 0.014wt%to 0.406wt%,the mushy zone enlarged,the complete solidification temperature delayed from1518.3 to 1459.4℃,the final contact angle decreased from 118.4°to 102.8°,indicating improved interfacial contact,and the maximum heat flux increased from 6.9 to 9.2 MW/m2.Increasing the phosphorus content from 0.081wt%to 0.406wt%also accelerated the film deposition rate from 1.57 to 1.73μm per test,resulting in a thickened naturally deposited film with increased thermal resistance that advanced the transition point of heat transfer from the fifth experiment to the third experiment.

Kinetics of austenite growth and bainite transformation during reheating and cooling treatments of high strength microalloyed steel produced by sub-rapid solidification

First,strip cast samples of high strength microalloyed steel with sub-rapid solidification characteristics were prepared by simulated strip casting technique.Next,the isothermal growth of austenite grain during the reheating treatment of strip casts was observed in situ through confocal laser scanning microscope(CLSM).The results indicated that the time exponent of grains growth suddenly rise when the isothermal temperature higher than 1000℃.And the activation energy for austenite grain growth were calculated to be 538.0 kJ/mol in the high temperature region(above 1000℃)and 693.2 kJ/mol in the low temperature region(below 1000℃),respectively.Then,the kinetics model of austenite isothermal growth was established,which can predict the austenite grain size during isothermal hold very well.Besides,high density of second phase particles with small size was found during the isothermal hold at the low temperature region,leading to the refinement of austenite grain.After isothermal hold at different temperature for 1800 s,the bainite transformation in microalloyed steel strip was also observed in situ during the continuous cooling process.And growth rates of bainite plates with different nucleation positions and different prior austenite grain size(PAGS)were calculated.It was indicated that the growth rate of the bainite plate is not only related to the nucleation position but also to the PAGS.

Dissolution of TiO_(2) and TiN inclusions in CaO–SiO_(2)–B_(2)O_(3)-based fluorine-free mold flux

Mold flux serves the crucial metallurgical function of absorbing inclusions, directly impacting the smoothness of the casting process as well as the cast slab quality. In this study, the dissolution behavior and mechanism of Ti O_(2)and Ti N inclusions in molten Ca O–Si O_(2)–B_(2)O_(3)-based fluorine-free mold flux were explored by in situ single hot thermocouple technology combined with X-ray photoelectron spectroscopy.The results showed that Ti O_(2) inclusions are effectively dissolved by the molten slag within 76 s, during which the original octahedral [Ti O_(6)]^(8-)structures are destroyed and convert to the networker tetrahedral [Ti O_(4)]^(4-)structures. However, the dissolution rate is much lower for Ti N inclusions than for Ti O_(2)inclusions. This can be attributed to the fact that the Ti N particles need to be oxidized and then dissolved in the molten slag to form tetrahedral [Ti O4]4-and octahedral [Ti O_(6)]^(8-)structures during the Ti N inclusion dissolution process, which is accompanied by the generation of a large amount of N_(2)gas. Moreover, Ca Ti O_(3)crystals tend to nucleate and grow on bubble surfaces with sufficient octahedral [Ti O_(6)]^(8-)structures and Ca^(2+)ions, eventually resulting in the molten slag being in a solid–liquid mixed state.

Wetting behavior of CaO-Al_(2)O_(3)-based mold flux with various BaO and MgO contents on the steel substrate

The Interfacial phenomena in mold have a great impact on the smooth operation of continuous casting process and the quality of the casting product.In this paper,the wetting behavior of CaO-Al_(2)O_(3)-based mold flux with different BaO and MgO contents was studied.The results showed that the contact angle between molten flux and interstitial free(IF)steel substrate increased from 62.4°to 74.5°with the increase of BaO content from 3 wt%to 7 wt%,while it decreased from 62.4°to 51.3°with the increase of MgO content from 3 wt%to 7 wt%.The interfacial tension also increased from 1630.3 to 1740.8 mN/m when the BaO content increased,but it reduced from 1630.3 to 1539.7 mN/m with the addition of MgO.The changes of contact angle and interfacial tension were mainly due to the fact that the bridging oxygen(O^(0)) at the interface was broken into non-bridging oxygen(O^(-)) and free oxygen(O_(2-)) by MgO.However,more O^(-) and O_(2-) connected into O^(0) when BaO was added,since the charge compensation effect of BaO was so stronger that it offset the effect of providing O_(2-).

High Temperature-preventing Cultivation Technology of Single-season Middle Rice for High Yield and High Quality in Jianghuai Area

In recent years,with the global climate change,the frequency and duration of high temperature in summer and autumn have increased,causing high temperature heat damage to summer crops such as rice and maize.From the end of July to early August is the main period of high temperature occurrence,during which the daily average temperature above 30℃is a high probability event,and even the highest temperature is above 38℃,while this period coincides with the booting-blooming-filling stage of the single-season middle rice in Jianghuai,especially the middle-season indica rice,so it often leads to the degradation of rice spikelets,pollen abortion,difficulty in pollen dispersion,and even difficulty in heading,resulting in a serious decline in the seed setting rate and poor filling of grains,which finally affect the yield and quality.Based on the goal of high-yielding high-quality rice cultivation,this paper proposed targeted technical measures for single-season middle rice from the aspects of planting time sequence optimization,selection of high-temperature-resistant varieties,population construction,fertilizer and water management technology,and how to compensate for the occurrence of unexpected disasters to promote plant growth.This study provides technical support for high-yielding high-quality stress-resistant and disaster-reducing rice cultivation technology.

Recent research progresses in ether-and ester-based electrolytes for sodium-ion batteries

Owing to the natural abundance and low cost of sodium resources,sodium-ion batteries(SIBs)have drawn considerable attention for state-of-the-art power storage devices over the last few years.To enable advanced SIBs with a brighter future,great effort has been made,not only through optimizing the electrode materials,but also with rationally designing various electrolyte systems.Among the available electrolyte systems,organic electrolytes,especially those based on esters as well as ethers,are the most promising ones for practical application in the foreseeable future,due to their numerous inherent advantages.This review is concerned with the recent research progresses on organic electrolytes for SIBs,focusing on etherbased and ester-based ones.

Designing high-strength titanium alloy using pseudo-spinodal mechanism through diffusion multiple experiment and CALPHAD calculation

This study used the pseudo-spinodal mechanism to obtain the ultrafineαphase for designing highstrength titanium alloy.Diffusion multiple experiments were designed to find the composition range of TM-x Mo-y V alloy(TM:Ti-4.5 Al-2 Cr-2.5 Nb-2 Zr-1 Sn)for obtaining ultrafineαphase.CALPHAD results confirm that when the alloy composition is located near the intersection of theαandβphase free energy curves,the alloy will undergo pseudo-spinodal transformation and obtain the ultrafineαphase.The designed TM-6 Mo-3 V alloy has a yield strength of 1411 MPa and an elongation of 6.5%.The strength of the alloy depends on the thickness,fraction of theαphase and the solid solution strengthening effect of the alloying elements.The deformation mechanism of the alloy is the dislocation slip of theαandβphases and the twin deformation of theαphase.The large number ofα/βinterfaces produced by the fineαphase is the main reason for limiting the ductility of the alloy.The use of the pseudo-spinodal mechanism combined with diffusion multiple experiments and CALPHAD is an effective method for designing high-strength titanium alloys.

Five-channel frequency-division multiplexing using low-loss epsilon-near-zero metamaterial waveguide

The rapidly growing global data usage has demanded more efficient ways to utilize the scarce electromagnetic spectrum resource. Recent research has focused on the development of efficient multiplexing techniques in the millimeter-wave band(1-10 mm, or 30-300 GHz) due to the promise of large available bandwidth for future wireless networks. Frequency-division multiplexing is still one of the most commonly-used techniques to maximize the transmission capacity of a wireless network.Based on the frequency-selective tunnelling effect of the low-loss epsilon-near-zero metamaterial waveguide, we numerically and experimentally demonstrate five-channel frequency-division multiplexing and demultiplexing in the millimeter-wave range.We show that this device architecture offers great flexibility to manipulate the filter Q-factors and the transmission spectra of different channels, by changing of the epsilon-near-zero metamaterial waveguide topology and by adding a standard waveguide between two epsilon-near-zero channels. This strategy of frequency-division multiplexing may pave a way for efficiently allocating the spectrum for future communication networks.