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Effect of thermal cycles on microstructure of reduced activation steel fabricated using laser melting deposition

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Journal of Iron and Steel Research International 2021年第3期28卷 316-326页

作者： Qian An zhi-xin Xia Chi Zhang zhi-gang yang Hao Chen School of Material Science and Engineering Tsinghua UniversityBeijing100084China Shagang School of Iron and Steel Soochow UniversitySuzhou215021JiangsuChina

Reduced activation steel was successfully fabricated by laser melting deposition employing a Gaussian and a ring-shaped *** microstructure evolution of the reduced activation steel was investigated using the scanning electron microscope,transmission electron microscope and electron backscatter *** experimental results showed that the grains close to the substrate were smaller than the grains in the upper *** to those deposited using a Gaussian laser,the samples deposited using a ring-shaped laser showed a more homogeneous ***,a finite element analysis(FEA)model was applied to reveal the thermal history during laser melting *** simulation results were well validated with the experimental *** results indicate that the peak temperature increases and the cooling rate decreases,as the layer gets further from the ***,the temperature and the cooling rate resulting from the Gaussian laser model were higher at the midline of the samples and lower around the edges,whereas those of the ring-shaped laser model were consistent with both at the center and around the edges.

关键词： Laser melting deposition Reduced activation steel Microstructure evolution Thermal cycle Finite element analysis

Effects of Ni on austenite stability and fracture toughness in high Co-Ni secondary hardening steel

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Journal of Iron and Steel Research International 2017年第2期24卷 177-183页

作者： Chen-chong Wang Chi Zhang zhi-gang yang Key Laboratory of Advanced Materials of Ministry of Education School of Materials Science and Engineering Tsinghua UniversityBeijing 100084 China

Three kinds of high Co Ni secondary hardening steels with different Ni contents were studied. The nanoscale austenite layers formed at the interface of matensite laths were observed. Both observation and diffusion kinetic simulation results showed that both Ni and Co did not obtain enough time to get the equilibrium content in this system. The Ni content in austenite layers decreased significantly, and Co content increased slightly with the decrease of Ni content in overall composition. The austenite stability was estimated by Olson-Cohen model, in which both chemical and mechanical driving force could be calculated by equilibrium thermodynamic and Mohr＇s circle methods, respectively. Simulation and mechanical test results showed that The decrease of Ni content in austenite layers would cause the change of austenite stability and decrease the fracture toughness of the steels. When the Ni content in the overall composition was lower than 7 wt. %, the Ni content in y phase would be lower than 20 wt.%. And the simulation value of M; （stress induced critical martensite transformation temperature） would be up to 80 ℃, which was about 60℃ higher than room temperature. Based on the analysis, the Ni content in the overall composition of high Co Ni secondary hardening steels should be higher than 8 wt. % in order to obtain a good fracture toughness.

关键词： Austenite stability Transformation-induced plasticity Fracture toughness Diffusion kinetic Element distribution

Hot roll bonding between commercially pure titanium and high-strength low-alloy steel using Fe interlayer

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Journal of Iron and Steel Research International 2019年第10期26卷 1126-1136页

作者： Xi-yang Chai gang Chen Feng Chai Tao Pan zhi-gang yang Cai-fu yang Department of Structural Steel Central Iron and Steel Research InstituteBeijing 100081China School of Materials Science and Engineering Tsinghua UniversityBeijing 100084China

Hot roll bonding was carried out between commercially pure titanium TA2 and high-strength low-alloy steel Q390 using no interlayer and Fe interlayer at temperatures of 850,900,950 and 1000℃with a total reduction ratio of 86.7%.Interfacial microstructure and bonding property of clad plates were investigated by electron microscopy and shear *** results showed that with the increase in heating temperature,the shear strength of titanium clad steel plates decreases *** with that of titanium clad steel plates with no interlayer,inserting Fe interlayer between titanium and steel can improve the shear strength at 850 and 900℃but deteriorate the shear strength at 950 and 1000℃.The reason for this consequence was that Fe interlayer prevented the reaction diffusion of C in titanium to form a thinner TiC layer at 850 and 900℃,while Fe interlayer promoted the reaction diffusion of Fe in titanium to generate thicker Fe2Ti and FeTi intermetallic compound layers at 950 and 1000℃.

关键词： Titanium clad steel plate Fe interlayer TiC Intermetallic compound Hot roll bonding

Carbide precipitation and element distribution in high Co-Ni secondary hardening steel

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Journal of Iron and Steel Research International 2018年第3期25卷 340-346页

作者： Chen-chongWang Chi Zhang zhi-gang yang Jie Su State Key Laboratory of Rolling and Automation Northeastern University Shenyang 110819 Liaoning China Key Laboratory of Advanced Materials of Ministry of Education School of Materials Science and EngineeringTsinghua University Beijing 100084 China Institute for Structural Materials Central Iron and Steel Research Institute Beijing 100081 China

As the increasing need of the steels with both high strength and hydrogen embrittlement resistance ability, carbide precipitation and element distribution in high Co-Ni secondary hardening steel were concerned. Carbide precipitation and element distribution in M54 were observed using carbon replicas method. Both simulation and observation results showed that MC and M2C formed in the steel. MC was round particle, which would act as grain refiners. And MzC was needle-like phase, which would be remarkable strengthening phases. Nb and V were main metallic elements in MC phase. Mo and Cr were main metallic elements in MzC phase. W, Co, and Ni were probably mainly dissolved in the matrix. As the carbide precipitation in AerMetl00 was M2C, which had similar size and shape with M2C in M54, the tensile strength and yield strength of AerMetl00 and M54 were similar. Compared with traditional high Co-Ni secondary hardening steel, M54 had higher hydrogen embrittlement resistance ability, probably because of element W in the matrix.

关键词： Carbide precipitation Element distribution Carbon replicas method Secondary hardening steel Thermodynamic simulation

Diffusion mechanism in molten salt baths during the production of carbide coatings via thermal reactive diffusion

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International Journal of Minerals,Metallurgy and Materials 2017年第12期24卷 1448-1458页

作者： Aliakbar Ghadi Hassan Saghafian Mansour Soltanieh zhi-gang yang Center of Excellence for High Strength Alloys Technology School of Metallurgy and Materials EngineeringIran University of Science and Technology Key Laboratory of Advanced Materials of Ministry of Education School of Materials Science and EngineeringTsinghua University

The diffusion mechanism of carbide-forming elements from a molten salt bath to a substrate surface was studied in this research, with particular focus on the processes occurring in the molten bath at the time of coating. Metal, oxide, and metal-oxide baths were investigated, and the coating process was performed on H13 steel substrates. Scanning electron microscopy and electron-probe microanalysis were used to study the coated samples and the quenched salt bath. The thickness of the carbide coating layer was 6.5 ± 0.5, 5.2 ± 0.5, or 5.7 ± 0.5 μm depending on whether it was deposited in a metal, oxide, or metal-oxide bath, respectively. The phase distribution of vanadium-rich regions was 63%, 57%, and 74% of the total coating deposited in metal, oxide, and metal-oxide baths, respectively. The results obtained using the metal bath indicated that undissolved suspended metal particles deposited onto the substrate surface. Then, carbon subsequently diffused to the substrate surface and reacted with the metal particles to form the carbides. In the oxide bath, oxide powders dissolved in the bath with or without binding to the oxidative structure(Na_2O) of borax; they were then reduced by aluminum and converted into metal particles. We concluded that, in the metal and oxide baths, the deposition of metal particles onto the sample surface is an important step in the formation of the coating.

关键词： thermal reactive diffusion diffusion mechanism carbide coating films metal particles borax bath

The effect of single-horn glaze ice on the vortex structures in the wake of a horizontal axis wind turbine

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Acta Mechanica Sinica 2015年第1期31卷 62-72页

作者： Zhe-Yan Jin Qiao-Tian Dong zhi-gang yang School of Aerospace Engineering and Applied Mechanics Tongji University School of Automotive Studies Tongji University Shanghai Automotive Wind Tunnel Center

The present study experimentally investigated the effect of a simulated single-horn glaze ice accreted on ro- tor blades on the vortex structures in the wake of a hori- zontal axis wind turbine by using the stereoscopic particle image velocimetry （Stereo-PIV） technique. During the ex- periments, four horizontal axis wind turbine models were tested, and both ＂free-run＂ and ＂phase-locked＂ Stereo-PIV measurements were carried out. Based on the ＂free-run＂ measurements, it was found that because of the simulated single-horn glaze ice, the shape, vorticity, and trajectory of tip vortices were changed significantly, and less kinetic en- ergy of the airflow could be harvested by the wind turbine. In addition, the ＂phase-locked＂ results indicated that the pres- ence of simulated single-horn glaze ice resulted in a dramatic reduction of the vorticity peak of the tip vortices. Moreover, as the length of the glaze ice increased, both root and tip vortex gaps were found to increase accordingly.

关键词： Stereo-PIV Single-horn glaze ice. Tip vorticesRoot vortices Wind turbine icing

Experimental and theoretical analysis of equilibrium segregation and radiation-induced segregation of Cr at grain boundariesin a reduced activation ferritic/martensitic(RAFM)steel

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Journal of Iron and Steel Research International 2021年第4期28卷 445-452页

作者： Li-dong Xia Hao Chen zhi-gang yang Chi Zhang Key Laboratory of Advanced Materials of Ministry of Education School of Materials Science and EngineeringTsinghua UniversityBeijing 100084China

Helium ion irradiation at 350℃was performed to study equilibrium segregation and radiation-induced segregation(RIS)of Cr at grain boundaries in reduced activation ferritic/martensitic *** concentration at grain boundary was measured by scanning transmission electron microscopy with an energy-dispersive *** measured Cr concentration at grain boundaries in heat treated zone was 11.7 and 12.8 wt.%in irradiated zone,respectively,which matched well to the calculated results from Mclean and modified Perk *** segregation and RIS of Cr mechanisms were theoretically *** analysis indicates that as temperature rises,equilibrium Cr segregation decreases monotoni-cally,while RIS of Cr has a bell-shape profile,which increases first and then *** is also shown that at low and high temperatures,equilibrium segregation of Cr is higher than that of RIS;at intermediate temperatures,equilibrium Cr segregation is lower than RIS.

关键词： Reduced activation ferritic/martensitic steel Equilibrium Cr segregation Radiation-induced segregation Grain boundary Rate theory Mclean equation

Precipitate Behavior in Fe–20Cr–30Ni–2Nb Austenitic Heat-Resistant Steel

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Acta Metallurgica Sinica(English Letters) 2015年第4期28卷 424-429页

作者： Hiroki Ishikawa Chi Zhang Sheng-Wei Chen zhi-gang yang School of Materials Science and Engineering Tsinghua University Department of Chemistry and Materials Science Tokyo Institute of Technology

In this study, the precipitation behavior of a new austenitic heat-resistant steel （Fe-20Cr-30Ni-2Nb, in at%） was investigated. The effects of alloying addition of boron （B） and lanthanum （La） on the microstructure of the austenitic steel were scrutinized using SEM, EPMA, TEM, and XRD. The results showed that the addition of B enhanced the precipitation of bar-type Laves phase. A small precipitate with high La concentration was observed at the grain boundary in the alloy without aging; similar precipitates without La also presented in region adjacent to the La single phase. This result indicates that La can exist independently and does not contribute to the formation of new compounds. However, in both B- and La-modified alloy, B appeared in the precipitate free zone. In the alloy containing both B and La, only Fe2Nb Laves- phase precipitates, as indicated by the XRD result.

关键词： Precipitation free zone Grain boundary Phase transformation Microstructure Fe-20Cr-30Ni-2Nb austenitic heat-resistant steel

Variation in retained austenite content and mechanical properties of 0.2C–7Mn steel after intercritical annealing

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International Journal of Minerals,Metallurgy and Materials 2016年第2期23卷 161-167页

作者： Chuan Zhao Chi Zhang Wen-quan Cao zhi-gang yang School of Materials Science and Engineering Tsinghua University Institute for Structural Materials Central Iron and Steel Research Institute

The effects of annealing time and temperature on the retained austenite content and mechanical properties of 0.2C-7Mn steel were *** retained austenite content of 0.2C-7Mn steel was compared with that of 0.2C-5Mn *** is found that 0.2C-7Mn steel exhibits a similar variation trend of retained austenite content as 0.2C-5Mn ***,in detail,these trends are different.0.2C-7Mn steel contains approximately 7.5vol%retained austenite after austenitization and *** stability of the reversed austenite in 0.2C-7Mn steel is lower than that in 0.2C-5Mn steel;in contrast,the equilibrium reversed austenite fraction of 0.2C-7Mn steel is substantially greater than that of 0.2C-5Mn ***,the retained austenite content in 0.2C-7Mn steel reaches 53.1vol%.The tensile results show that long annealing time and high annealing temperature may not favor the enhancement of mechanical properties of 0.2C-7Mn *** effect of retained austenite on the tensile strength of the steel depends on the content of retained austenite;in contrast,the 0.2%yield strength linearly decreases with increasing retained austenite content.

关键词： manganese steel annealing austenite mechanical properties