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Comparison between the Methods of Determining the Critical Stress for Initiation of Dynamic Recrystallization in 316 Stainless Steel

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Journal of Materials Science & Technology 2008年第6期24卷 840-844页

作者： M.Jafari a.najafizadeh Department of Materials Engineering Isfahan University of TechnologyIsfahanIran

Several methods have been proposed to calculate the critical stress for initiation of dynamic recrystallization （σc） on the basis of mathematical methods. One＇ of them is proposed by Stewart et al. in which this critical point appears as a distinct minimum in the （-dθ/dσ vs σ） through differentiating from θ vs σ. Another one is presented by najafizadeh and Jonas by modifying the Poliak and Jonas method. According to this method, the strain hardening rate was plotted against flow stress, and the value of σc was attained numerically from the coefficients of the third-order equation that was the best fit from the experimental θ-σ data. Hot compression tests were used in the range of 1000 to 1100℃ with strain rates of 0.01^-1 s^-1 and strain of I on 316 stainless steel. The result shows that najafizadeh and Jonas method is simpler than the previous one, and has a good agreement with microstructures. Furthermore, the value of normalized critical stress for this steel was obtained uc=σc/σp=0.92.

关键词： Dynamic recrystallization Critical stress Strain hardening rate

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Investigation of Hot Deformation Effect on Martensite and Bainite Transformation in Two Super High Strength Steels

Investigation of Hot Deformation Effect on Martensite and Ba...

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第五届国际材料与热加工物理模拟及数值模拟学术会议

作者： R.Taherian A. Bapari a.najafizadeh R. Shateri Ph.D Student in "Shiraz University" Material Engineering Faculty Shiraz Iran M.Sc in "Isfahan University of Technology" Material Engineering Faculty Isfahan Iran Full Professor in "Isfahan University of Technology" Material Engineering Faculty Isfahan Iran

In this article two CCCT （ Compression Continuous Cooling Transformation） diagrams of steel NiCrMoV and one CCCT diagram of steel CrMoV, dynamic and static hot deformation tests were drawn by using respectively. In comparison to the CCCT and CCT （Continuous Cooling Transformation） diagrams in two steels, it can be deduced Md, Bd have been increased. It seems that temperature of deformation is the most effective parameter affects on Md and Bd. If deformation temperature is selected so that SRX （Static Recrystallization） or DRX （Dynamic Recryastallization） is onset, the Md and Bd increase. Also the kind of deformation affects on more austenite grain size than shifting Md and Bd. In addition, in all CCCT diagrams, bainite areas have been developed. It means Bd dominates Md. It seems, that is because of grain refinement of austenite grains that causes promoting BN （Bainite Nucleation） in comparison to MN （Martensite Nucleation）. It was observed by deformation, the lamellar martensite and bainite lathes have gotten thinner and finer and their parcels got smaller. In addition, it is predicted existing many types of carbide, and nitrides by stabilizer elements as Cr, Mo, V and Si cause increasing strength and hardenability of these steels and Ni and Mn are two only elements that inhibit forming ferrite and pearlite.

关键词： CCCT SRX DRX Hot Deformation.

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Development of a New Ultrafine/Nano Ferrite-Carbide Microstructure by Thermomechanical Processing

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Acta Metallurgica Sinica(English Letters) 2015年第2期28卷 249-253页

作者： Yousef Mazaheri Ahmad Kermanpur Abbas najafizadeh Navid Saeidi Department of Materials Engineering Isfahan University of Technology

The steel with the new microstructure, bimodal submicrometer equiaxed ferrite grains with uniformly dis- tributed nanosized cementite particles, was manufactured by a new approach utilizing simple cold-rolling and subsequent annealing of a dual phase ferrite-martensite starting structure. The mean ferrite grain size and carbide size range of the specimen after 80% cold-rolling and subsequent annealing at 600 ℃ for 20 min were 0.35 μm and 70-140 nm, respec- tively. A combination of bimodal ultrafine ferrite and nanoscale carbides used as a more effective method for achieving an excellent balance in strength-ductility. The strength of the steel with the new microstructure increased to about 880 MPa （nearly 60% higher than that of the as-received state, e.g., 540 MPa）, without significant loss of ductility.

关键词： Low-carbon steel Dilatometry Thermomechanical processing Grain refinement Mechanical properties

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Buckling of 2D-FG Cylindrical Shells under Combined External Pressure and Axial Compression

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Advances in Applied Mathematics and Mechanics 2013年第3期5卷 391-406页

作者： R.Mohammadzadeh M.M.najafizadeh M.Nejati Department of Mechanical Engineering Islamic Azad UniversityArak BranchArakIran Young Researchers Club Islamic Azad UniversityArak BranchArakIran

This paper presents the stability of two-dimensional functionally graded(2D-FG)cylindrical shells subjected to combined external pressure and axial compression loads,based on classical shell *** material properties of functionally graded cylindrical shell are graded in two directional(radial and axial)and determined by the rule of *** Euler’s equation is employed to derive the stability equations,which are solved by GDQ method to obtain the critical mechanical buckling loads of the 2D-FG cylindrical *** effects of shell geometry,the mechanical properties distribution in radial and axial direction on the critical buckling load are studied and compared with a cylindrical shell made of *** numerical results reveal that the 2D-FGM has a significant effect on the critical buckling load.

关键词： Mechanical buckling 2D-FG cylindrical shell combined load classical shell theory GDQ method

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H pylori seroprevalence in patients with lung cancer

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World Journal of Gastroenterology 2007年第16期13卷 2349-2351页

作者： Katayoon najafizadeh Sayeed Falah Tafti Masoud Shiehmorteza Masoud Saloor Masoud Jamali Department of Respiratory Medicine National Research Institute of Tuberculosis and Lung Diseases Tehran 19556 Iran

AIM: To assess H pylori seroprevalence in lung cancer and determine whether there is a potential association between lung cancer and H pylori infection. METHODS: The study was conducted on forty consecutive patients with lung cancer, confirmed by pathology (32 men, 8 women; mean age 55.50 ± 11.91 years, range 16-77 years). Forty healthy subjects (25 men, 15 women; mean age 43.08 ± 12.60 years, range 20-79 years) from the patients’ family members were matched to each case subject on the basis of age and socioeconomic status. H pylori infection was detected with a commercially available immunoglobulin G (IgG) enzyme-linked immunosorbent assay (Trinity kit, Biotech co., USA), previously validated in adults (86% sensitivity, 96% specificity) against a gold standard of culture and histology. RESULTS: H pylori seropositivity was present in 52.5% of patients with lung cancer in comparison to 45.0% of healthy control subjects. Although H pylori seropositivity was more frequent in lung cancer patients than in controls, the difference did not reach statistical significance (OR = 1.35, 95% CI = 0.56-3.25; P = 0.65). In addition, there was no significant difference between cases and controls in terms of gastrointestinal symptoms. CONCLUSION: The earlier described association between H pylori infection and lung cancer was not supported in this study. Further studies with larger sample sizes should be undertaken to assess the frequency of H pylori infection in patients with lung cancer and their potential association.

关键词： Lung neoplasm H pylori Helicobacter infections/complications Carcinoma/Non-small cell Carcinoma/Squamous cell Case-control studies

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Grain Size Effect on the Martensite Formation in a High-Manganese TWIP Steel by the Rietveld Method

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Journal of Materials Science & Technology 2010年第2期26卷 181-186页

作者： G. Dini A. najafizadeh S.M. Monir-Vaghefi R. Ueji Department of Materials Engineering Isfahan University of Technology Department of Advanced Materials Science Faculty of EngineeringKagawa University

The aim of the present work was to study the effect of austenite grain size （AGS） on the martensite formation in a high-manganese twinning-induced plasticity （TWIP） steel. The results of a quantitative microstructural characterization of the steel by the whole X-ray pattern fitting Rietveld software, materials analysis using diffraction （MAUD）, indicated that the volume fraction of αbcc-martensite increases with increasing AGS. However, the value of the stacking fault probability （Psf） does not show a large variation for samples with different values of AGS under water-quenching conditions.

关键词： Austenite grain size Martensite formation TWIP steel Stacking fault probability

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Experimental investigation of process parameters during graphitization of catalytic coke

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International Journal of Coal Science & Technology 2019年第4期6卷 611-620页

作者： Kobra Pourabdollah Masoud Samadian Zakaria Seyed Mohammad Mir najafizadeh Fatemeh Motaghedi Chemistry and Chemical Engineering Research Center of Iran TehranIran Department of Research and Technology Tehran Province Gas CompanyTehranIran

The aim of this project is studying the effect of thermal operation parameters on the graphitization of self-diffused ethane-based catalytic *** novelty of this study refers to self-diffused metals that had given unique properties to the catalytic coke and had improved the graphitization degree at low *** main feature of this research is presenting a remarkable energy saving approach that uses low-cost installations for production of graphitized *** experiments were performed in two steps including preparation of self-diffused ethane-based catalytic coke and then low-temperature graphitization of coke samples below 1500 ℃.Characteristic tests were performed by determination of electrical resistivity and XRD pattern of graphitized samples including graphitization degree,aromaticity,coke rank,number of carbon rings,graphene thickness and *** results revealed that the blanket atmosphere,final temperature and exposure time had the greatest impact on the aforementioned criteria,while the role of thermal ramp and sulfur content of catalytic coke was *** electrical resistivity tests on the graphitized sample showed how the electrical resistivity of graphitized samples is a function of graphitization degree.

关键词： Graphite Catalytic coke Self-diffusion Desulfurization

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Effect of Thermo-Mechanical Treatment on Mechanical Properties and Microstructure of Fe-31Mn-4Si-2Al-Nb-Ti TWIP Steel

Effect of Thermo-Mechanical Treatment on Mechanical Properti...

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2011 International Conference on Advanced Materials Engineering(ICAME 2011)

作者： Davood Zamani Abbas najafizadeh Hossein monajati Gholam Reza Razavi Department of Materials Science and Engineering Najafabad Branch Islamic Azad University Isfahan Iran Department of Materials Engineering Isfahan University of Technology Isfahan Iran

The effect of addition of Nb and Ti also thermomechanical treatment on mechanical properties and microstructure of a twinning induced plasticity（TWIP） steel have been *** results indicated that addition of Nb and Ti enhances strength also increasing cold rolling reduction has been increased *** ductility increased with increasing annealing temperature however strength *** centric limit of partial recrystallization regime,maximum increasing in work hardening capacity and also almost high yield strength has been ***,utilization of large cold rolling reduction and subsequently annealing treatment in the centric limit of partial recrystallization region was suggested as an effective method to obtain TWIP steel with an excellent combination of strength and ductility.

关键词： TWIP Steel Ti partial recrystallization cold Rolling annealing

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17—4PH不锈钢组织变化研究有进展 008

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中国冶金报

作者： Hamed Mirzadeh Abbas najafizadeh 陈宁

本报讯近日，德黑兰大学的学者研究了17-4PH不锈钢的热变形和动态再结晶行为。该研究主要得出以下结果：一是17-4PH不锈钢的大多数流变曲线，在热压缩试验中表现出典型的动态再结晶(DRX)行为——达到单峰应力值后，应力便逐渐下降，...

本报讯近日，德黑兰大学的学者研究了17-4PH不锈钢的热变形和动态再结晶行为。该研究主要得出以下结果：一是17-4PH不锈钢的大多数流变曲线，在热压缩试验中表现出典型的动态再结晶(DRX)行为——达到单峰应力值后，应力便逐渐下降，趋向一个稳定的应力状态。单峰和多峰?

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