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Journal of Iron and Steel Research(International) 2022年第4期29卷 665-676页

作者： Jian Han Lian-meng Liu Xin-ya Chen Min-fang Chen Lei Cui Yang-chuan Cai Yin-bao Tian School of Materials Science and Engineering Tianjin University of TechnologyTianjin 300384China School of Materials Science and Engineering Tianjin UniversityTianjin 300072China

An innovative grade of ferritic stainless steel,ultra-pure 18Cr–2Mo thick plate,was designed and produced for special industrial application.In order to maintain its mechanical properties after joining,three advanced joining methods,hybrid laser arc welding,activated flux tungsten inert gas welding and friction stir welding,were selected and conducted to connect the thick plates.The feasibility of three joining methods,the microstructure and mechanical properties were compared,and the results have demonstrated that the sound joint was successfully produced using the selected parameters through friction stir welding.The obtained hardness and impact toughness of the weld zone were satisfying.In terms of activated flux tungsten inert gas welding,the crack will be created due to microstructural brittleness.And as for hybrid laser arc welding,the weld zone is narrow,and the addition of wire during welding for the top weld metal area leads to higher formation ratio of low-angle grain boundaries,which is beneficial to performance of the joint.However,there is still a weak area in the fusion line of the welded joint.The result has illustrated that the welding of innovative ultra-pure ferritic stainless steel thick plate by friction stir welding is feasible.

关键词： Ultra-pure ferritic stainless steel Hybrid welding Activated flux tungsten inert gas Friction stir welding Microstructural evolution Mechanical property

Effect of boron on dissolution and repairing behavior of passive film on S31254 super-austenitic stainless steel immersed in H_(2)SO_(4) solution

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Journal of Iron and Steel Research(International) 2022年第6期29卷 1012-1025页

作者： Tong-hao Wang Jian Wang Jin-gang Bai Shu-jing Wang Chao Chen Pei-de Han School of Materials Science and Engineering Taiyuan University of TechnologyTaiyuan 030024ShanxiChina Technology Center Shanxi Taigang Stainless Steel Co.Ltd.Taiyuan 030003ShanxiChina

The impact of boron on the dissolution and repairing behavior of passive films formed on S31254 super-austenitic stainless steel(SASS)was investigated.SASS was immersed in 0.5 mol/L of H_(2)SO_(4) for 0,2,6,10,and 14 days to explore the evolution of the passive film.The electrochemical impedance spectroscope(EIS),the Mott–Schottky analysis,and X-ray photoelectron spectroscope were utilized to analyze the semiconductor properties and compositions of the passive films.EIS showed a decrease and consequent increase over 14 days;the same pattern was observed for Cr_(2)O_(3) and Cr/Fe.However,the defect density of the passive film exhibited a reverse trend.The variation in film thicknesses indicated that the passive films possessed dissolution and repairing behavior.SASS passive film had a double-layer structure;the outer layer was found to be rich in Fe3+and Cr(OH)3,but low on Mo6+,while the inner layer was rich in Cr_(2)O_(3) and low in Mo4+.The addition of boron increased the corrosion resistance and could promote the efficiency of the passive film repair,likely by promoting the migration of Mox+,which promoted the repairing of the passive film.

关键词： Passive film S31254 super-austenitic stainless steel Boron Dissolution Repairing

Effect of strain rate on fracture behaviour of Cr18Ni11Ti stainless steel at high temperatures

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Journal of Iron and Steel Research(International) 2022年第6期29卷 1004-1011页

作者： Xin-li Song Chang-hu Huang Juan Jia Jing Liu The State Key Laboratory of Refractories and Metallurgy Wuhan University of Science and TechnologyWuhan 430081HubeiChina Hubei Engineering Technology Research Center of Marine Materials and Service Safety Wuhan 430081HubeiChina

The effect of strain rate on the fracture behaviour of Cr18Ni11Ti stainless steel at high temperatures was analysed.The steel was subjected to solid solution treatment at 1050°C and ageing at 650°C for 24 h.The high-temperature tensile properties of Cr18Ni11Ti stainless steel were subsequently investigated via high-temperature tensile testing at 650°C and different strain rates(1.43×10^(–1),1.43×10^(–2),1.43×10^(–3),1.43×10^(–4),and 1.43×10^(–5) s^(–1)).The microstructure,precipitated phase,tensile fracture surface,and dislocation of the experimental steel were analysed by scanning electron microscopy,transmission electron microscopy and energy spectrometry.The results show that Cr18Ni11Ti stainless steel is mainly austenite,with a large number of twin crystals,chromium-rich precipitated phase and composite precipitated phases of TiC and AlMgCaO.With decreases in strain rate,the yield strength,ultimate tensile strength,and reduction in area also decrease.When the strain rate is high,obvious necking and ductile fracture occur in the experimental steel.However,when the strain rate is reduced to 1.43×10^(–5) s^(–1),the necking phenomenon is not obvious and intergranular brittle fracture appears.Greater segregation of P and S contents at grain boundaries,or dislocation motion creep and grain-boundary sliding creep,leads to brittle fracture of the steel at lower strain rates of 1.43×10^(–4) to 1.43×10^(–5) s^(–1).

关键词： stainless steel Strain rate High-temperature mechanical property Grain boundary segregation Dislocation

Morphologies of secondary austenite in 2507 duplex stainless steel after heat treatment

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Journal of Iron and Steel Research(International) 2022年第6期29卷 994-1003页

作者： Xiao-han Wu Zhi-gang Song Bao-shun Wang Ming-hua Wu Qi-liang Nai Liang Yao Han Feng Wen-jie Zheng School of Material Science and Engineering University of Science and Technology BeijingBeijing 100083China Special Steel Institute Central Iron&Steel Research InstituteBeijing 100081China Engineering Research Center of High-Performance Nuclear Power Pipe Forming of Zhejiang Province Huzhou 313028ZhejiangChina Yongxing Special stainless-Steel Co. Ltd.Huzhou 313005ZhejiangChina Zhejiang Jiuli Hi-Tech Metals Co. Ltd.Huzhou 313028ZhejiangChina

The microstructure evolution of secondary austenite in 2507 duplex stainless steel was investigated by means of optical metallography,scanning electron microscopy and confocal scanning laser microscopy.Four types of secondary austenite(γ2)morphologies including partially transformed austenite,grain boundary austenite,Widmannstätten austenite(WA)and intragranular austenite could be formed during cooling after solution treatment.It was concluded that secondary austenite morphology was mainly dependent on cooling rates.Two mechanisms of WA formation were proposed.WA nucleated at grain boundary of ferrite or at the formed phase boundary.Transmission electron microscopy(TEM)analysis displayed that WA grew in parallel to the ferrite.The effects of Cr_(2)N on secondary austenite precipitation were discussed in detail.Once Cr_(2)N was involved,a mechanism was proposed that secondary austenite formed by element diffusion,leading to the migration of the austenite–ferrite interface.Cr_(2)N acted as the nucleation sites forγ2 and provided the nitrogen for the transformation;meanwhile,the precipitation of Cr_(2)N during the rapid cooling was captured by TEM.A process of nucleation followed by diffusion was concluded to be the formation of secondary austenite with no Cr_(2)N precipitated.The decomposition of secondary austenite was also studied,which was found to be a diffusion mechanism followed by displacement in connection with the element distribution.

关键词： Secondary austenite Duplex stainless steel Heat treatment Cooling rate Element diffusion

Water quality induced corrosion of stainless steel valves during long-term service in a reverse osmosis system

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Journal of Environmental Sciences 2020年第3期32卷 218-226页

作者： Xiyan Xu Shuming Liu Ying Liu Kate Smith Xiaoting Wang Junyu Li Ziqing Ma Zhangqing Wang Yong Cui School of Environment Tsinghua University100084BeijingChina Beijing Yizhuang Water Co. Ltd.100176BeijingChina

The current study analyzes the contribution of 10 water quality parameters(including pH,turbidity,conductivity,total dissolved solids(TDS),hardness,total organic carbon(TOC),alkalinity,calcium ions,chlorides and sulfates) to corrosion extent of stainless steel valves taken from different locations in a reverse osmosis system of a reclaimed water plant.The valves were in service for 5 years.Raman spectroscopy and X-ray photoelectron spectroscopy analyses are conducted to quantify corrosion products on different valves under various water quality conditions.On that basis,bivariate and multivariate regression analyses between the 10 water quality parameters and the corrosion extent of valve specimens(represented by metal loss percentage(MLP) values) are carried out to check the contribution of those water quality parameters to MLP.The results indicate that the proportions of metal oxides as corrosion products vary according to the corrosion extent of the valves.Although no linear correlation is founds all 10 water quality parameters except for pH show a significant positive correlation with the MLP values of the valve specimens.Moreover,results of multivariate regression suggest that the variation of MLP can be explained by turbidity,TDS,TOC and sulfates.A positive contribution of turbidity,TDS and TOC to MLP is observed,whereas the contribution of sulfates is negative.The results from the current work help to identify the reasons for water quality-induced failure of stainless steel equipment in RO systems.

关键词： Reverse osmosis system Water quality stainless steel Corrosion Correlation

Optimization of resistance spot brazing process parameters in AHSS and AISI 304 stainless steel joint using filler metal

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Defence Technology（防务技术） 2019年第3期15卷 450-456页

作者： Niwat Mookam Department of Industrial Engineering Technology Rajamangala University of Technology Rattanakosin Wang Klai Kangwon CampusHuahin

The aim of this research study was to determine optimal resistance spot brazing parameters for joining between AHSS and AISI 304 stainless steel by using filler metal. The key parameters investigated in this study consist of the brazing current, electrode pressure and brazing time. The Taguchi method was applied to the design of experiments. Signal-to-Noise ratio was introduced in the study to identify optimal levels from the process where input parameters yield increased shear strength. Brazing was thus implemented with 5,000A brazing current, 0.70 MPa electrode pressure, and 1.50s brazing time. The maximum shear strength obtained was 54.31 N·mm^-2 in accordance with input parameter settings. In addition, Cu-rich phase and Ag0.4Fe0.6 intermetallic phases were found at the interface zone.

关键词： Resistance spot brazing Filler metal AHSS stainless steel Intermetallic phases

On microstructure characterization of Fe-Cr-Ni-Mo-N super-austenitic stainless steel during hot deformation

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Journal of Iron and Steel Research(International) 2019年第10期26卷 1080-1087页

作者： Yan-sen Hao Jian Li Wan-chun Liu Wei-na Zhang Zhen-yu Liu State Key Lab for Rolling Technologies and Automation Northeastern UniversityShenyang 110819LiaoningChina

Hot compression tests of Fe-Cr-Ni-Mo-N super-austenitic stainless steel were carried out in the temperature range of 950-1150℃with a strain rate of 0.01-10 s-1,in which dynamic recrystallization(DRX)mechanisms and coincident site lattice(CSL)boundary evolution in consideration of adiabatic heating were investigated.The results show that discontinuous DRX was the main DRX mechanism.Due to the high stacking fault energy(162-173 mJ/m2),subgrain evolution occurring in dynamic recovery process was stimulated at high temperatures and high strain rates.DRX behavior was accelerated by higher strain rate and adiabatic heating.Also,amounts of fine annealing twin boundaries were observed in the specimens deformed at higher strain rates and higher temperatures.By analyzing the length fractions of∑3 boundary in overall boundaries and in CSL boundaries,the results indicate that∑3 regeneration mechanism and new twinning mechanism take effect concurrently for twin-related grain boundary when the specimens were deformed at 950℃with a strain rate of 0.01-10 s-1.With increasing strain rate or deformation temperature,the propagation of∑3 boundaries was mainly dominated by new twinning mechanism.

关键词： Super-austenitic stainless steel Dynamic recrystallization Adiabatic heating Coincident site lattice boundary Hot deformation

Effect of Short-Time Aging on the Pitting Corrosion Behavior of a Novel Lean Duplex stainless Steel 2002

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Acta Metallurgica Sinica(English Letters) 2019年第6期32卷 755-763页

作者： Tian-Yi Sun Yan-Jun Guo Yi-Ming Jiang Jin Li Department of Materials Science Fudan University

The effect of short-time aging in the temperature range between 400 and 1000°C on the pitting corrosion behavior and mechanical property of a novel lean duplex stainless steel(LDSS)2002 was investigated through the potentiostatic critical pitting temperature(CPT)tests and the Charpy impact tests.Both the pitting corrosion resistance and the toughness of aged specimens degraded due to the precipitation of detrimental secondary phases and the most significant reduction of CPT and impact energy emerged at 650°C concurrently.The CPT of LDSS 2002 specimen aged at 650°C decreased by 28°C,and the impact energy dropped from 69 to 29 J/cm2 compared with the solution-annealed sample.Transmission electron microscopy characterization showed that the main precipitates in LDSS 2002 were Cr2N and M23C6 along the ferrite–austenite grain boundaries.

关键词： Lean duplex stainless steel Aging Pitting corrosion Impact energy Precipitates

Intergranular corrosion behavior and mechanism of the stabilized ultra-pure 430LX ferritic stainless steel

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Journal of Materials Science & Technology 2019年第8期35卷 1787-1796页

作者： Peize Cheng Ning Zhong Nianwei Dai Xuan Wu Jin Li Yiming Jiang Department of Materials Science Fudan University Shanghai 200433 China Institute of Marine Materials Science and Engineering Shanghai Maritime University Shanghai 201306 China

Intergranular corrosion(IGC) behavior of the stabilized ultra-pure 430 LX ferritic stainless steel(FSS) was investigated by using double loop electrochemical potentiokinetic reactivation(DL-EPR) and oxalic acid etch tests to measure the susceptibility of specimens given a two-step heat treatment. The results reveal that IGC occurs in the specimens aged at the temperature range of 600–750℃ for a short time. The aging time that is required to cause IGC decreases with the increase of aging temperature. A longer aging treatment can reduce the susceptibility to IGC. The microstructural observation shows that M(23)C6 precipitates form along the grain boundaries, leading to the formation of Cr-depleted zones. The presence of Cr-depleted zones results in the susceptibility to IGC. However, the atoms of stabilizing elements replace chromium atoms to form MC precipitates after long-time aging treatment, resulting in the chromium replenishment of Cr-depleted zones and the reduction of the susceptibility to IGC.

关键词： Intergranular corrosion Ferritic stainless steel Double loop electrochemical potentiokinetic reactivation (DL-EPR) TEM Cr-depleted zone

Microstructural evolution and mechanical properties of friction stir-welded C71000 copper–nickel alloy and 304 austenitic stainless steel

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International Journal of Minerals,Metallurgy and Materials 2018年第11期25卷 1294-1303页

作者： Hamed Jamshidi Aval Department of Materials and Industrial Engineering Babol Noshirvani University of Technology

Dissimilar joints comprised of copper–nickel and steel alloys are a challenge for manufacturers in modern industries, as these metals are not thermomechanically or chemically well matched. The present study investigated the effects of tool rotational speed and linear speed on the microstructure and mechanical properties of friction stir-welded C71000 copper–nickel and 340 stainless steel alloys using a tungsten carbide tool with a cylindrical pin. The results indicated that a rotational-to-linear speed ratio of 12.5 r/mm did not cause any macro defects, whereas some tunneling defects and longitudinal cracks were found at other ratios that were lower and higher. Furthermore, chromium carbide was formed on the grain boundaries of the 304 stainless steel near the shoulder zone and inside the joint zone, directing carbon and chromium penetration toward the grain boundaries. Tensile strength and elongation percentages were 84% and 65% of the corresponding values in the copper–nickel base metal, respectively.

关键词： dissimilar friction stir welding copper–nickel alloy austenitic stainless steel microstructure mechanical properties