Thoughts on the Implementation Path to a Carbon Peak and Carbon Neutrality in China’s Steel Industry

1.The CO_(2) emission status of the steel industry in China As an important basic sector of the national economy,China’s steel industry is a major energy consumer and a major emitter of carbon dioxide(CO_(2)).Based on previous studies[1-3],Fig.1 shows a preliminary estimation of the CO_(2) emissions of the steel industry in China from 1991 to 2019.

Carbide precipitation and microstructure refinement of Cr-Co-Mo-Ni bearing steel during hot deformation

The dynamic recrystallization and carbides precipitation of the Cr-Co-Mo-Ni bearing steel were investigated by hot compression tests performed at temperatures ranging from 850 °C to 1080 °C with strain rate of 1-20 s-1. The activation energy(Q) for the tested steel is calculated to be around 682.99 k J/mol at a deformation strain of 0.6. Microstructural analysis by SEM shows that the dynamic recrystallization(DRX) behavior is dependent sensitively on the deformation strain, temperature and strain rate, while an exponential relationship between DRX grain size and Z parameter is obtained from the computational formula. Moreover, the M6C-type carbides(<1 μm) act as the main prohibitor of grain coarsening, and the polynomial regression relationship between them is worked out. With electron backscatter diffraction(EBSD) observation, DRX is the main nucleation mechanism responsible for the formation of new grains during hot compression. In conclusion, the interaction between DRX affected by hot deformation parameters and carbides precipitation determines the ultimate grain size refinement.

Characterization of the microstructure and hardness of the HAZ in a 800MPa grade RPC steel

The microstructure and hardness of the HAZ in a 800MPa grade ultra-low-carbon microalloyed steel were studied. The results indicate that the heat affected zone(HAZ) of the RPC (Relaxation- Precipitation- Controlling) steel possesses a continuous gradient structure, and can be classified into three zones, i.e. CGHAZ(coarse-grain HAZ), FGHAZ(fine-grain HAZ) and ICHAZ(intercritical temperature HAZ). The microstructures in the HAZ are all composed of bainite-like structure. The microstructure in the CGHAZ mainly consists of lath-like bainite and granular bainite . The influences of heat input and t_ 8/5 on the hardness in the HAZ of RPC steel are notable. With the increase of heat input and t_ 8/5 , the softening tendency of HAZ becomes obvious. The hardening phenomenon that normally occurs in the CGHAZ does not take place with this steel in the range of experimental conditions. The softening in the ICHAZ is bound to occur. Hence appropriate welding technologies need to be selected.

Microstructure and mechanical properties of a cast heat-resistant rare-earth magnesium alloy

Microstructure,mechanical properties and phase transformation of a heat-resistant rare-earth(RE)Mg-16.1Gd-3.5Nd-0.38Zn-0.26Zr-0.15Y(wt.%)alloy were investigated.The as-cast alloy is composed of equiaxedα-Mg matrix,net-shaped Mg5RE and Zr-rich phases.According to aging hardening curves and tensile properties variation,the optimized condition of solution treatment at 520℃for 8 h and subsequent aging at 204℃for 12 h was selected.The continuous secondary Mg5RE phase predominantly formed at grain boundaries during solidification transforms to residual discontinuousβ-Mg5RE phase and fine cuboid REH2particles after heat treatment.The annealed alloy exhibits good comprehensive tensile property at 350℃,with ultimate tensile strength of 153 MPa and elongation to fracture of 6.9%.Segregation of RE elements and eventually RE-rich precipitation at grain boundaries are responsible for the high strength at elevated temperature.

Effect of heat treatment on microstructural evolution,mechanical properties and tribological properties of H13 steel prepared using selective laser melting

H13 tool steel was successfully prepared by selective laser melting(SLM)technology.The effects of heat treatment on the microstructure,mechanical properties,and tribological properties of SLMed H13 steel were investigated.The heat treatment process involved a solution treatment and a double aging treatment of the deposited H13 tool steel prepared by SLM.The aim is to optimize the microstructure and mechanical properties of SLMed H13 steel.Due to the rapid heating and cooling effects of SLM,carbide precipitation in the deposited H13 steel was not uniform and residual stresses were present.The purpose of the solution treatment is to dissolve the solution at a high temperature to eliminate the residual stresses and defects introduced by the SLM-forming structure.The solution treatment and first aging treatment produced the precipitation of small carbides at the grain boundaries and inside the crystals,which increased the hardness of SLMed H13 steel.The hardness increased from 538±4.0 HV of the as-deposited sample to 548±5.8 HV of samples after the first aging treatment.Accordingly,the ultimate tensile strength and the elongation at break decreased from 1882 MPa and 11.5%in the as-deposited sample to 1697 MPa and 7.9%in those after the first aging treatment,respectively.Furthermore,the friction coefficient and wear rate in the as-deposited sample decreased from 0.5160 and 2.36×10^(–6)mm^(−3)N^(−1)m^(−1)to 0.4244 and 1.04×10^(–6)mm^(−3)N^(−1)m^(−1),respectively.However,the distribution of carbides inside the crystals was not uniform.The second aging treatment adjusted the morphology of carbide precipitation and made it more uniform,but the precipitation of carbides grew and settled at the bottom of the grain boundaries.The hardness decreased to 533±6.7 HV compared with that with the first aging treatment,but the ultimate tensile strength and plasticity reached a balance(1807 MPa,14.05%).Accordingly,the friction coefficient and wear rate also showed a stable and decreasing trend(0.4407,0.98×10^(–6)mm^(−3)N^(−1)m^(−1)).

中国新材料科学技术的创新发展研究

New materials,which are also known internationally as"advanced materials,"refer to newly emerging materials with excellent performance and special functions or traditional materials with significantly improved performance or new functions after improvement and modification.At present,the multidisciplinary cooperation of information technology,biotechnology,new energy technology,and new materials technology is triggering a new round of scientific and technologicalrevolution and industrial transformation[1].

Fundamentals of fast reduction of ultrafine iron ore at low temperature

Fundamentals on the fast reduction of ultrafine iron ore at low temperature, including characterization of ultrafine ore, deoxidation thermodynamics of stored-energy ultra.fine ore, kinetics of iron ore deoxidation, and deoxidation mechanism, etc., and a new ironmaking process are presented in this article. Ultrafine ore concentrate with a high amount of stored energy can be produced by mechanical milling, and can be deoxidated fast below 700℃ by either the coal-based or gas-based process. This novel process has some advantages over others： high productivity, low energy consumntion, and environmental friendliness.

Microstructure and mechanical properties of a low activation cast WTaHfTiZr refractory high-entropy alloy

In the face of the requirement that nuclear fusion reactor materials exhibit more excellent thermal,mechanical and physical properties,a novel refractory highentropy alloy,WTaHfTiZr was proposed.The constituent elements were selected in consideration of low activation,high melting point and high thermostability.The alloys were prepared by arc melting.The as-cast alloy shows a dendrite microstructure with two disordered BCC phases,which caused by the preferential nucleation of W and Ta with much higher melting points during solidification.It exhibits a high compressive yield strength of 1,900 MPa and fracture strain of 8.1% at room temperature,and its yield strengths are up to 612 MPa at 700 ℃ and 203 MPa at 1,000 ℃,respectively.The high strengths are attributed mainly to solid solution strengthening and second phase strengthening.This alloy shows great promise as one of the next-generation nuclear fusion reactor materials.

Preparation and properties of dental zirconia ceramics

Y2O3-stabilized tetragonal zirconia polycrystalline （Y-TZP） ceramics with high-performance were prepared for dental ap- plication by use of the micro-emulsion and two-step sintering method. The crystal phase, morphology, and microstructure of the reaction products were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, and transmission electron mi- croscopy （TEM）. XRD results show that the ceramics mainly consist of tetragonal zirconia. Physical and mechanical properties test results show that the bending strength, fracture toughness, and the density of full sintered Y-TZP ceramics are 1150 MPa, 5.53 MPa.m1/2, and 6.08 g/cm3, respectively, which suggest that the material is relatively suitable for dental restoration. The dental base crown machined with this material by CAD/CAM system exhibits a verisimilitude configuration and the material＇s expansion coefficient well matches that of the glaze. These results further indicate that the product can be used as a promising new ceramic material to fabricate dental base crowns and bridges.

Domain Structure and Magnetization Process in Short Glass-Coated Amorphous Microwires with Positive Magnetostriction

The domain structure and magnetisation process in short glass-coated amorphous Fe45Co20Ni10Si9B16 microwires are investigated by analyzing the hysteresis loops measured by a vibrating sample magnetometer.Methods of calculating the thickness of the outer shell and the critical length to observe magnetic bistability have been established.The thickness of the outer shell is 2.3μm and the critical length is 8.11 mm for a microwire with a metallic core diameter of 31.1μm and a glass coat thickness of 10.6μm.The experimental results demonstrate the reliability of this method to calculate the critical length.

Noncollinear Magnetism Calculation of Iron Clusters with Spin-Orbit Coupling

We study iron clusters containing 2~13 atoms by ab initio calculations with both collinear and noncollinear magnetic methods.Spin-orbit coupling is only available in the noncollinear method.After full structural relaxations,it is found that atom positions derived from the noncollinear method have better stability in all clusters,including those having coparallel spin arrangements.Binding energies of clusters calculated by the noncollinear method are also 17.3~19.8 meV/atom lower,which are too large to ignore.By comparing the magnetic properties and electronic structures from the two methods,we believe that the difference has resulted from spin-orbit coupling.We recommend reconsidering the importance of the noncollinear magnetic method with spin-orbit coupling in magnetic systems.Especially in transition metal clusters when atom positions and energy values are important for determining the crucial properties.

The Nanoscale Density Gradient as a Structural Stabilizer for Glass Formation

The rapid cooling of a metallic liquid(ML)results in short-range order(SRO)among the atomic arrangements and a disordered structure in the resulting metallic glass(MG).These phenomena cause various possible features in the microscopic structure of the MG,presenting a puzzle about the nature of the MGs’microscopic structure beyond SRO.In this study,the nanoscale density gradient(NDG)originating from a sequential arrangement of clusters with different atomic packing densities(APDs),representing the medium-range structural heterogeneity in Zr_(60)Cu_(30)Al_(10)MG,was characterized using electron tomography(ET)combined with image simulations based on structure modeling.The coarse polyhedrons with distinct facets identified in the three-dimensional images coincide with icosahedron-like clusters and represent the spatial positions of clusters with high APDs.Rearrangements of the different clusters according to descending APD order in the glass-forming process are responsible for the NDG that stabilizes both the supercooled ML and the amorphous states and acts as a hidden rule in the transition from ML to MG.

Multi-performance evaluation of high-throughput accelerated corrosion test for high-strength low-alloy 921A steel

The corrosion behavior of high-strength low-alloy 921A steel in a simulated marine atmospheric environment was studied using a high-throughput experimental method.The corrosion behavior,corrosion morphology,and corrosion products of 921A steels were analyzed using various techniques,including corrosion mass loss method,polarization curve,white-light interferometry,scanning electron microscopy,energy-dispersive spectrometry,microbeam X-ray fluorescence spectrometry,X-ray diffraction technique,and X-ray photoelectron spectroscopy.The test results indicated that 921A steel exhibits better corrosion resistance than Q450NQR1 steel in simulated harsh atmospheric environments,as evidenced by a lower corrosion mass loss rate throughout the corrosion tests.The corrosion products of both steels consisted ofα-FeOOH,Fe_(3)O_(4),andγ-FeOOH,withα-FeOOH being more prevalent in the rust layer of 921A steel than in Q450NQR1 steel.The inner rust layer of 921A steel also exhibited an appositional enrichment region of Cr,Ni,Mo,and V,leading to its superior corrosion resistance compared to that of Q450NQR1 steel.The efficacy of high-throughput accelerated corrosion experimental methods was highlighted for evaluating the corrosion resistance of steel materials in harsh environmental conditions.The findings suggest that 921A steel exhibits better corrosion resistance compared to Q450NQR1 steel and has the potential to be more suitable in harsh marine atmospheric environments.The characterization of the rust layer structures and composition reveals the parallel enrichment of certain elements in the inner rust layer of 921A steel,which enhances its corrosion resistance.

Solidification behaviour and hot cracking susceptibility of a novel Ni-based superalloy

A novel Ni-based superalloy GH4151,with a γ′ volume fraction of about 55%and a service temperature capability up to 8oo oC,was investigated.Due to the different cooling conditions of various regions during the solidification of ingots,significant cooling rate variations may lead to the occurrence of hot cracking.Conventional scanning laser microscope was utilised to investigate the solidification process and phase precipitation behaviour of the GH4151 under wide range cooling rates.The characteristics of L→γ transformation were analysed,and the growth rates of at each stage were calculated.The segregation behaviour was predicted using the Scheil equation,and the predicted results match well with the experimental results.The sensitivity coefficient for hot cracking was modified,and cracking sensitivity coefficient values for the alloy under different cooling rates were computed,revealing that the alloy is most susceptible to hot cracking at 10℃/min cooling rate.Therefore,controlling the cooling rate can reduce the possibility of hot cracking in ingot.

Microstructure and Precipitation Behavior in HAZ of V and Ti Microalloyed Steel

Three steels containing 0.05%C-0.1%V-0.01%N （steel V-LN）,0.05%C-0.1%V-0.02%N （steel V-HN）,and 0.05%C-0.1%V-0.02%N-0.01%Ti （steel V-HN-Ti）,which were all essentially vanadium microalloyed steels,were subjected to simulating the microstructure of a coarse grained heat affected zone （CGHAZ）. The process involved reheating to 1 350 ℃,rapid cooling to room temperature,and varying the welding heat input from 15 kJ/cm to 54 kJ/cm,including four cooling rates of t8/5 equal to 7.5 s,20 s,40 s,100 s,and the relationship of heat input to t8/5 was calculated by Quiksim software. The microstructure and precipitation of vanadium and titanium carbon nitrides are studied. The results indicate that the microstructure consists of granular bainite and some side plate ferrite in the grain boundary when the steels are produced with the highest heat input. As the heat input decreased,numerous polygonal ferrites and grain boundary ferrites appeared,and the size apparently increased. When the steel contained high nitrogen,it was considerably easier to form martensite-austenite island,which was even worse for the toughness and other properties of the steel. For the limitation of cooling time,vanadium carbon nitrides could not precipitate sufficiently,but as titanium was added,the unmelted or precipitated TiN on cooling absorbed some fraction of nitrogen in the matrix and made more precipitate positions for the round V（C,N）,and thus several useful round particles could be seen in titanium-contained steel,and most of them were around TiN. By this experiment,we can conclude that with the help of titanium,nitrogen-enhanced steel had a better prior austenite grain size,was considerably easier to precipitate,reduced free nitrogen in the matrix effectively,and provided a very effective mechanism for restriction grain growth in the HAZ.

Thermodynamic Calculation and MnS Solubility of Mn-Ti Oxide Formation in Si-Mn-Ti Deoxidized Steel

Mn-Ti oxides in Si-Mn-Ti deoxidized steels after cooling in the furnace were investigated. The composition and morphology of inclusions were analyzed by using FE-SEM with EDS. Mn-Ti oxides were found to be effective sites to induce intragranular ferrite formation. The thermodynamic calculation was employed to interpret the critical condition for Mn-Ti oxide formation. Mn-Ti oxide formation was controlled not only by Mn and Ti content, but also by total oxygen content in steel. When the Mn and Ti contents were around 1.5% and 0. 005% --0.01%, respectively, Mn-Ti oxide could form as the total oxygen content was 0. 001%- 0. 002 %. The experimental results were in good agreement with thermodynamic calculation results. Also, MnS solubilit：（ was examined in Mn-Ti oxide inclusion system. With an increase of MnO content in Mn-Ti oxide, MnS solubility in the oxides increased. MnS precipitation benefited from high MnO content in Mn-Ti oxide.

Editorial for Special Issue on Materials Genome Engineering

With the rapid advancement of computing and information technology at the turn of the 21st century,the power of data collection and processing has multiplied tremendously.Based on this a game-changing advancement,science is at the advent of the “fourth paradigm”of massive data plus artificial intelligence,in which the efficiency of scientific research is continuously improved,research time is shortened,and research cost is reduced[1].

Influence of Ti on Weld Microstructure and Mechanical Properties in Large Heat Input Welding of High Strength Low Alloy Steels

The influence of Ti on weld microstructure and mechanical properties in large heat input welding of high strength low alloy steels is investigated. The results indicate that a moderate amount of Ti is still effective for grain refinement even under larger heat input and a large amount of acicular ferrite （AF） is formed in the weld metal when Ti content is within 0. 028%--0. 038%. With increasing Ti content, proeutectoid ferrite in the weld metal decreases, whereas bainite and M-A constituent increase. The type of inclusion in the welds varies from Mn-Si-AI-O to Ti-Mn- A1-O and finally to Ti-A1-O as Ti content increases from 0 up to 0. 064%. As for adding 0. 028%--0. 038% Ti, high weld toughness could be attained since most inclusions less than 2 tim which contain Ti20s provide the effective nu- clei for aeicular ferrite formation. However, the toughness of the weld metals severely reduces when Ti content is over the optimum ranRe of 0. 028%--0. 038%.

Microstructures and Properties of X60 Grade Pipeline Strip Steel in CSP Plant

The microstructures and properties of X60 grade pipeline strip steel were researched.With Nb microalloying and TMCP,the X60 grade pipeline strip steel was developed in the Baotou CSP Plant.The mechanical properties meet the demands on machining and using of pipeline manufacture.The X60 strip steels had been used extensively,which had fine and uniform structures,good performance and excellent toughness.

Microstructure Evolution and Mechanical Properties of HR3C Steel during Long-term Aging at High Temperature

Microstructure evolution and the changes in mechanical properties of HR3 Csteel during long-term aging at650,700 and 750℃ were investigated.The precipitated phases of the aging steel included M23C6 carbides,Z-phase and a trace amount of Nb（C,N）.The M23C6 carbides were distributed mainly at the grain boundary,while Z-phase was mainly inside the grains.Amounts of both M23C6 carbides and Z-phase during the aging process increased with increasing aging period and temperature.Coarsening of M23C6 carbides was influenced significantly by aging time and temperature,while the size of the Z-phase was relatively less affected by the aging time and temperature,which had a steady strengthening effect.Coarsening of the M23C6 carbides was the main reason for the decline in high temperature yield strength during long-term aging at 750℃.The M23C6 carbides were linked into a continuous chain along the grain boundary which accounted for the decrease of toughness during aging.