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Refinement mechanism of cerium addition on solidification structure and sigma phase of super austenitic stainless steel S32654

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Journal of Materials Science & Technology 2022年第7期102卷 105-114页

作者： Shucai Zhang Jiangtao Yu Huabing Li Zhouhua Jiang Yifeng Geng Hao Feng Binbin Zhang Hongchun Zhu School of Metallurgy Northeastern UniversityShenyang 110819China School of Materials and Metallurgy University of Science and Technology LiaoningAnshan 114051China

The influence of Ce addition on the solidification structure and σphase of super austenitic stainless steel S32654 was systematically investigated via microstructural characterization and thermodynamic calcula- tion. The results indicate that a small addition of Ce could modify MgO and MnS into Ce-bearing inclu- sions Ce_(2)O_(3)and Ce_(2)O_(2)S. Ce addition led to noticeable refinement of both the dendrite structure and σphase. The refinement mechanism could be attributed to the combined actions of effective Ce-bearing inclusions and solute Ce. Effective Ce-bearing inclusions could serve as heterogeneous nucleation cores of austenite as well as σphase, which provided a favorable prerequisite for their refinement. Solute Ce significantly enhanced the undercooling degree of the system, further promoting dendrite structure re- finement. Meanwhile, solute Ce improved the eutectic precipitation conditions of σphase and further promoted its nucleation, while the dendrite refinement limited its growth space. Finally, more fine and dispersed σphase particles formed in S32654 with Ce addition. The refinement of dendrite structure and σ phase will reduce the temperature and time required for high-temperature homogenization, which is beneficial to the hot working of this steel.

关键词： Super austenitic stainless steel Cerium Solidification structure sigma phase Refinement

Non-isothermal Dissolution Modelling of sigma phase in Duplex Stainless Steels

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Acta Metallurgica Sinica(English Letters) 2016年第9期29卷 859-868页

作者： Paolo Ferro Alberto Fabrizi Franco Bonollo Department of Management and Engineering University of PadovaStradella San Nicola 336100 VicenzaItaly

In this work, the non-isothermal dissolution kinetics of the sigma phase in duplex stainless steels has been studied and modelled. A semi-empirical model is proposed to describe the kinetics of sigma phase precipitation/dissolution during continuous heating starting from the isothermal transformation kinetics. The proposed model, which presumes validity of the additivity rule, is validated by means of experimental investigations. A good agreement is found between experimental and analytical results.

关键词： Kinetics Non-isothermal dissolution Modelling Semi-empirical models sigma phase Duplex stainless steels

Effect of solution treatment on microstructures and mechanical properties of AISI 321 service

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Acta Metallurgica Sinica(English Letters) 2011年第3期24卷 243-248页

作者： Yanhui ZHAO Haitao MA Lai WANG Changhai SUN Chao GUO School of Materials Science and Engineering Dalian University of Technology Dalian 116024 China West Pacific Petrochemical Company Ltd. Dalian 116600 China

A detailed knowledge of changes in microstructures and mechanical properties that occur in AISI 321 stainless steels service before and after solution treatment is of great interest, since the ductility and toughness of AISI 321 stainless steels may change drastically after service for a long time. After solution treatment at 1050 ℃, the microstructures of AISI 321 stMnless steels service for 80 000 h at 700 ℃ indicate that the content of sigma phase significantly decreased, the grains of austenite grew and the amount of twins together with the size increased with solution treatment time. The results of mechanical properties tests show that the impact toughness at room temperature was superior at solution treatment, and there was no obvious change in the impact toughness between different times of solution treatment at room temperature.

关键词： Austenitic stainless steels Microstructure Mechanical properties Solution treatment sigma phase

Microstructure Evolution of a Cold-rolled 25Cr-7Ni-3Mo-0.2N Duplex Stainless Steel during Two-step Aging Treatments

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Acta Metallurgica Sinica(English Letters) 2013年第5期26卷 517-522页

作者： Tian LIANG Xiaoqiang HU Xiuhong KANG Dianzhong LI Shenyang National Laboratory for Materials Science Institute of Metal ResearchChinese Academy of Sciences

A cold-rolled 25Cr-7Ni-3Mo-0.2N duplex stainless steel（DSS） has been aged in two steps. Firstly, the aging treatment at interval of 50℃ in a temperature range from 900 to 1050℃ was carried out in order to obtain fine grains. Secondly, another aging treatment at 850℃ was performed to reveal the σ-phase precipitation behavior. A detailed microstructure evolution during those two aging steps was observed by the optical microscope（OM）, the scanning electron microscope（SEM）, the electron backscatter difraction（EBSD） and the transmission electron microscope（TEM）. The results revealed that the micro-duplex structure with grain size of lower than 10 μm appeared after the first aging step. However, their grain size was rapidly increased with increasing aging temperature. Meanwhile, the δ → γ and/or δ → γ ＋ σ transformations took place in association with the occurrence of the extensive recovery or a little recrystallization in δ-grains. During the second aging treatment, σ-phase mainly nucleated at δ/γ interfaces and further grew along those interfaces into various morphologies（e.g., butterfly and granule）. A novel precipitation behavior was found in this study that the γ-grain boundaries bulged not only into the δ-grains as usual, but abnormally into the σ-phase precipitates without the prior precipitation of the isolated secondary austenite γ2or another phases.

关键词： Duplex stainless steel Microstructure evolution sigma phase Aging treatment Micro-duplex structure

Effect of Aging Time and Temperature on Mechanical Properties and Microstructural Evolution of 2205 Ferritic-Austenitic Stainless Steel

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Journal of Materials Science & Technology 2009年第5期25卷 597-602页

作者： H.Keshmiri A.Momeni K.Dehghani G.R.Ebrahimi G.Heidari Esfarayen Steel Complex Department of Mining and Metallurgy Amir Kabir University of Technology Tarbiat Moalem University of Sabzevar

Duplex stainless steels （DSS） with ferritic-austenitic microstructures offer good combination of resistance to pitting corrosion and high strength that are not concomitantly attainable using conventional single phase austenitic or ferritic stainless steels, The DSS used in this investigation was 2205 alloy having a stable microstructure consisting of about 45% ferrite and 55% austenite at ambient temperature. In order to investigate aging behavior of this steel and the influences on mechanical properties, different aging treatments were conducted at temperatures of 350-950℃ for various aging time of 15, 30, 60 and 180 min. The aged specimens were subjected to impact testing and hardness measurements. Finally, the changes in microstructure due to aging were studied by optical and scanning electron microscopy. The results showed that aging at temperatures lower than 550℃ for different time had negligible effects on mechanical properties. Besides, no considerable changes in term of precipitation of harmful intermetallic particles were observed in microstructure below this temperature. However, a critical temperature range, 550-650 ℃, was introduced here. Aging in this range led to a significant decrease in toughness and notable increase in hardness. The formation of intermetallic phases such as CT was recognized as the major reason for the observed changes.

关键词： Duplex stainless steel Aging Toughness sigma phase

A New Economical sigma-Free Duplex Stainless Steel 19Cr-6Mn-1.0Mo-0.5Ni-0.5W-0.5Cu-0.2N

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Journal of Iron and Steel Research(International) 2011年第4期18卷 52-57页

作者： CHEN Hong DING Tie-suo LI Jun XIAO Xue-shan ZHAO Jun-liang JIANG Lai-zhu Institute of Materials Shanghai University Shanghai 200072 China Baoshan Iron and Steel Co Ltd Shanghai 200431 China

A new resource-saving duplex stainless steel with composition of 19Cr-6Mn-1.0Mo-0.5Ni-0.5W-0.5Cu-0.2N has been developed,and the microstructure,mechanical properties and corrosion properties have been investigated.The results show that the alloy has a balanced ferrite-austenite relation,and the ferrite content rises with the solution treatment temperature.The designed alloy is free of precipitation of sigma phase when aged at 650,750 and 850 ℃ for 3 h,respectively,whereas a few Cr23C6 precipitates are found after being aged at 750 ℃ for 8 h.Charpy impact tests indicate that the impact energy of the alloy is 68,200 and 220 J at-40,0 and 25 ℃,respectively.The designed alloy solution treated at 1050 ℃ for 30 min has a much higher yield strength and similar corrosion resistance compared with those of AISI 304 austenitic stainless steel.Moreover,the production cost of the alloy is about $ 1000 per ton which is lower than that of AISI 304.

关键词： duplex stainless steel sigma phase mechanical property pitting corrosion

sigmaPLUG—A NEW TEMPERATURE INDICATOR FOR REMAINING LIFE ASSESSMENT OF HIGH TEMPERATURE COMPONENTS

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Acta Metallurgica Sinica(English Letters) 1999年第1期12卷 104-107页

作者： J.K.L. Lai, C.H. Shek and K.W. Wong Department of Physics and Materials Science, City University of Hong Kong, 27887808, China

Improved life assessment techniques will enable engineering components to be replaced before failure, thereby reducing the risk of industrial accidents as well as minimizing financial loss due to unscheduled outages. For components operating at high temperatures, temperature measurement is very important. In many situations, the environmental conditions are too hostile for conventional techniques to be used. Researchers over the world have been looking for new techniques for temperature measurement and one such device, called Feroplug, has been developed previously by the and coworkers. The Feroplug has been patented in USA, UK and Europe by the British Technology Group. The underlying principle of the Feroplug is based on the transformation of ferrite in some specially designed duplex stainless steels. This paper describes a new invention called sigmaplug which is a new development of the Feroplug but using an entirely different physical principle. It was discovered that the sigma phase in Fe

关键词： ferrite sigma phase duplex stainless steel temperature indicator remaining life assessment roplug materials undergoes a ferromagnetic transition at low temperatures and this property can be used to indicate temperature. The new sigmaplug can great

Thermal aging effect on 2205 duplex stainless steel

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Baosteel Technical Research 2017年第3期11卷 24-29页

作者： WANG Zhiyu CHEN Xu Research Institute Baoshan Iron & Steel Co. Ltd. Shanghai 201900 China

The effect of isothermal aging treatment on the mechanical and corrosion properties of 2205 duplex stainless steel was investigated by means of impact toughness test and micro-hardness measurement in combination with the critical pitting temperature （CPT） technique. The corresponding fractography of the steel was then observed after the impact toughness test. The results demonstrated that, at the critical temperature for precipitation of the sigma （σ） phase, e. g., 850 ℃, the impact toughness decreased rapidly and the micro-hardness increased gradually with increasing aging time. The CPT decreased from 61 to 15 ℃ as the aging time increased from 4 rain to 8 h. In addition, optical microscopy, transmission electron microscope （TEM） and X-ray diffraction studies showed that the ferrite in the steel transformed into secondary austenite and σ phase.

关键词： duplex stainless steel thermal aging sigma phase impact toughness corrosion resistance

Microstructure and corrosion behaviour aging at 750℃in 25%Cr duplex stainless steel

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Microstructure and corrosion behaviour aging at 750℃in 25%C...