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DISCREpANCIES IN THE REGRESSION MODEllING OF RECRYSTAllIZATION RATE AS USING THE DATA FROM pHYSICAl SIMUlATION TESTS

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Acta Metallurgica Sinica(English letters) 2004年第3期17卷 221-228页

作者： l.p.karjalainen M.C.Somani S.F.Medina Department of Mechanical Engineering University of OuluFIN-90014 OuluFinlandDepartment of Mechanical EngineeringUniversity of OuluFIN-90014 OuluFinlandCentro Nacional de Investigaciones Metallurgicas(CENIM-CSIC) ES-28040 Madrid Spain

The analysis of numerous experimental equations published in the literature reveals awide scatter in the predictions for the static recrystallization kinetics of steels. Thepowers of the deformation variables, strain and strain rate, similarly as the powerof the grain size vary in these equations. These differences are highlighted and thetypical values are compared between torsion and compression tests. potential errorsin physical simulation testing are discussed.

关键词： physical simulation static recrystallization regression modeling hot working steel

Effects of plastic Deformation and Stresses on Dilatation duringthe Martensitic Transformation in a B-bearing Steel

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Journal of Materials Science & Technology 2001年第2期17卷 203-206页

作者： M. C.Somani and l.p.karjalainen Dept. of Mechanical Engineering, University of Oulu, Oulu, Finland M. Oldenburg and M.Eriksson Dept. of Mechanical Engineering, lulea University of Technology, lulea, Sweden Dept. of Mech. Eng. Univ. of Oulu Oulu Finland

To provide data for improved modelling of the behaviour of steel components in a simultaneous forming and quenching process, the effects of plastic deformation and stresses on dilatation during the martensitic transformation in a B-bearing steel were investigated. It was found that plastic deformation of austenite at high temperatures enhances ferrite formation significantly, and consequently, the dilatation decreases markedly even at a cooling rate of 280'C/s. The created ferritic-martensitic microstructure possesses clearly lower hardness and strength than the martensitic structure. Elastic stresses cause the preferred orientation in martensite to be formed so that diametric dilatation can increase by nearly 200% under axial compression.

关键词： Effects of plastic Deformation and Stresses on Dilatation duringthe Martensitic Transformation in a B-bearing Steel

Observations on the Formation of Ultrafine Ferrite Grain Size in Steels by physical Simulation Routes

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Observations on the Formation of Ultrafine Ferrite Grain Siz...

Improving the Mechanical properties of Copper Alloys by Thermo-Mechanical processing

The Fourth International Conference on physical and Numerical Simulation of Materials processing (ICpNS’2004)

作者： l.p.karjalainen M.C.Somani University of Oulu Department of Mechanical Engineering p.O.Box 4200 FIN-90014 Oulu FINlAND University of Oulu Department of Mechanical Engineering p.O.Box 4200 FIN-90014 Oulu FINlAND

Some observations are reported on the simulation of two thermo-mechanical routes to produce ultra-fine ferrite grain size in steels. One C-Mn grade and Nb, Nb-Ti and Nb-high Ti bearing steels were used in the tests performed on a Gleeble simulator and a laboratory rolling mill. The routes included severe hot deformation of prior grain-refined austenite at the temperatures close to Ar3 (DIF) and static recrystallization of fine-grained cold-rolled martensite (SRM). It was observed that the hot deformation induces the formation of ferrite above the Ar3 temperature of the steel, but severe reductions are required for the complete transformation. Strain of 1.2 can result in about 70% of ferrite with the grain size of about 1.4 - 2 urn in all the studied steels. Similarly, in short annealing of cold-worked martensite, the static recrystallization can also lead to a grain size of about 1.5 μm. The distribution of carbon varies in the microstructures. carbon being in the second phase in the DIF route and in carbide particles in the SRM route, which may have a significant influence on the mechanical properties and the thermal stability of ultrafine grain structure.

关键词： Ultrafine grain size Steels physical simulation Strain-induced ferrite Cold rolling and annealing

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Improving the Mechanical Properties of Copper Alloys by Ther...

Observations on the Formation of Ultrafine Ferrite Grain Size in Steels by physical Simulation Routes

The Fourth International Conference on physical and Numerical Simulation of Materials processing (ICpNS’2004)

作者： M.C.Somani l.p.karjalainen University of Oulu Department of Mechanical Engineering 4KOMT p.O. Box 4200 90014 Oulu FINlAND University of Oulu Department of Mechanical Engineering 4KOMT p.O. Box 4200 90014 Oulu FINlAND

Systematic physical simulation of thermo-mechanical processing routes has been applied on a Gleeble 1500 simulator to four copper alloys (wt-%) Cu-0.57Co-0.32Si, Cu-0.55Cr-0.065p/Cu-0.22Zr-0.035Si and Cu-l.01Ni-0.43Si aimed at clarifying the influences of processing conditions on their final properties, strength and electrical conductivity. Flow curves were determined over wide temperature and strain rate ranges. Hardness was used as a measure of the strength level achieved. High hardness was obtained as using equal amounts (strains 0.5) of cold deformation before and after the precipitation annealing stage. The maximum values achieved for the Cu-Co-Si, Cu-Cr-p, Cu-Zr-Si and Cu-Ni-Si alloys were 190, 165, 178 and 193 HV5, respectively. A thermo-mechanical schedule involving the hot deformation-ageing-cold deformation stages showed even better results for the Cu-Zr-Si alloy. Consequently, the processing routes were designed based on simulation test results and wires of 5 and 2 mm in diameters, have been successfully processed in the industrial scale.

关键词： Copper alloys Thermo-mechanical processing Ageing Strength Flow stress Hardness

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Journal of Materials Science & Technology 2003年第z1期19卷 112-114页

作者： l.X. pan l.p. karjalainen M. C. Somani University of Oulu Department of Mechanical Engineering P.O. Box 4200 FIN-90014 Oulu Finland University of Oulu Department of Mechanical Engineering P.O. Box 4200 FIN-90014 Oulu Finland University of Oulu Department of Mechanical Engineering P.O. Box 4200 FIN-90014 Oulu Finland

Some observations are reported on the simulation of two thermomechanical routes to produce ultrafine ferrite grainsize in steels. One C-Mn grade and Nb, Nb-Ti and Nb-high Ti bearing steels were used in the tests performed ona Gleeble simulator and a laboratory rolling mill. The routes included severe hot deformation of prior grain-refinedaustenite at the temperature close to Ar3 (DIF) and static recrystallization of fine-grained cold-rolled martensite(SRM). It was observed that the hot deformation induces the formation of ferrite above the Ar3 temperature of thesteel, but severe reductions are required for the complete transformation. Strain of 1.2 can result in about 70% offerrite with the grain size of about 1.4～2μm in all the studied steels. Similarly, in short annealing of cold-workedmartensite, the static recrystallization can also lead to a grain size of about 1.5 μm. The distribution of carbonvaries in the microstructures, carbon being in the second phase in the DIF route and in carbide particles in the SRMroute, which may have a significant influence on the mechanical properties and the thermal stability of ultrafine grainstructure.

关键词： Ultrafine grain size, Steels, physical simulation, Strain-induced ferrite, Cold rolling and annealing

Crystallographic Analysis of Martensite in 0.2C-2.0Mn-1.5Si-0.6Cr Steel using EBSD

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Journal of Materials Science & Technology 2011年第10期27卷 920-930页

作者： pasi p.Suikkanen Cyril Cayron Anthony J.DeArdo l.pentti karjalainen Department of Mechanical Engineering University of OuluBox 420090014 University of Oulu CEA LITEN17 rues des Martys38054GrenobleFrance Department of Mechanical Engineering and Materials Science University of Pittsburgh

The crystallography of martensite formed in 0.2C-2.0Mn-1,5Si-0.6Cr steel was studied using the electron backscattered diffraction （EBSD） technique. The results showed that the observed orientation relationship （OR） was closer to that of Nishiyama-Wassermann （N-W） than Kurdjumov-Sachs. The martensite consisted of parallel laths forming morphological packets. Typically, there were three different lath orientations in a morphological packet consisting of three specific N-W OR variants sharing the same {111} austenite plane. A packet of martensite laths with a common {111} austenite plane was termed a crystallographic packet. Generally, the crystallographic packet size corresponded to the morphological packet size, but occasionally the morphological packet was found to consist of two or more crystallographic packets. Therefore, the crystallographic packet size appeared to be finer than the morphological packet size. The relative orientation between the variants in crystallographic packets was found to be near 60°〈110〉, which explains the strong peak observed near 60° in the grain boundary misorientation distribution. Martensite also contained a high fraction of boundaries with a misorientation in the range 2.5-8°. Typically these boundaries were found to be located inside the martensite laths forming sub-laths.

关键词： Martensite Austenite Nishiyama-Wassermann orientation relationship EBSD Crystallography packet

Crystallographic Analysis of Isothermally Transformed Bainite in 0.2C-2.0Mn-1.5Si-0.6Cr Steel Using EBSD

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Journal of Materials Science & Technology 2013年第4期29卷 359-366页

作者： pasi p.Suikkanen Cyril Cayron Anthony J.DeArdo l.pentti karjalainen Ruukki Metals Oy Rautaruukintie 155P.O.Box 93FI-92101 RaaheFinland Department of Mechanical Engineering University of OuluP.O.Box 420090014 University of OuluFinland Ruukki Metals Oy Rautaruukintie 155P.O.Box 93FI-92101 RaaheFinland. CEA LITEN17 rues des Martys38054 GrenobleFrance Department of Mechanical Engineering and Materials Science University of Pittsburgh848 Benedum HallPittsburghPA 15261-2285USA

The crystallography of bainite, transformed isothermally at 450 ℃ in 0.2C-2.0Mn-1.5Si-0.6Cr steel, was investigated by electron backscatter diffraction （EBSD） analysis. The orientation relationship （OR） was found to be closer to Nishiyama-Wassermann （N-W） than Kurdjumov-Sachs orientation relationship. Bainite microstructure consisted of parallel laths forming a morphological packet structure. Typically, there were three different lath orientations in a morphological packet. These orientations were dictated by a three specific N-W OR variants sharing the same {111} austenite plane. A packet of bainite laths with common {111} austenite plane was termed as crystallographic packet. Generally, the crystallographic packet size corresponded to the morphological packet size. locally, crystallographic packets with only two dominant orientations were observed. This indicates strong local variant selection during isothermal bainite transformation. The relative orientation between the variants in crystallographic packets was found to be near 60°/〈110〉. This appears to explain the strong peak observed in the grain boundary misorientation distribution near 60°. Bainite also contained pronounced fraction of boundaries with their misorientation in the range of 2.5°-8° with quite widely dispersed rotation angles. Spatially these boundaries were found to locate inside the bainite laths, forming lath-like sub-grains.

关键词： Bainite Austenite Nishiyama-Wassermann orientation relationship Electron backscatter diffraction OEBSD) Crystallography packet

ApplICATIONS OF pHYSICAl SIMUlATION IN THE DEVElOpMENT OF HOT WORKING pROCESSES

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Acta Metallurgica Sinica(English letters) 2000年第1期13卷 291-300页

作者： l. p. karjalainen (Department of Mechanical Engineering, University of Oulu, Oulu, Finland)

Modelling has become a more and more valuable tool in the design, control and development of steel processing. Empirical regression equations, physically based approachs, artificial neural networks and hybrid models are being theied in computer modelling. In all cases, relevant data are necessary, which can be most economically obtained by physical simulation. physical simulation with a Gleeble simulator has been used in a large number of tasks at the University of Oulu for ten years in cooperotion with the Finnish metals industry. Some examples of these will be described and discussed below, such as the optimization of the recrystallization controlled rolling process, the improvement of the hot strength model for the control of coiling tension and the optimization of continuous strip annealing ***,brief remarks will be then on a couple of projects now under way.

关键词： physical simulation,hot working,recrystallization,phase transformation continuous annealing

A NEURAl NETWORK-BASED MODEl FOR pREDICTION OF HOT-ROllED AUSTENITE GRAIN SIZE AND FlOW STRESS IN MICROAllOY STEEl

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Acta Metallurgica Sinica(English letters) 2000年第2期13卷 521-530页

作者： J. T.Niu,l.J.Sun and p.karjalainen 1) Harbin Institute of Technology, Harbin 150001, China 2) University of Oulu, FIN-90571, Oulu, Finland

For the great significance of the prediction of control parameters selected for hot-rolling and the evaluation of hot-rolling quality for the analysis of prod uction problems and production management, the selection of hot-rolling control parameters was studied for microalloy steel by following the neural network principle. An experimental scheme was first worked out for acquisition of sample data, in which a gleeble-1500 thermal simolator was used to obtain rolling temperature, strain, stain rate, and stress-strain curves. And consequently the aust enite grain sizes was obtained through microscopic observation. The experimental data was then processed through regression. By using the training network of Bp algorithm, the mapping relationship between the hotrooling control parameters (rolling temperature, stain, and strain rate) and the microstructural paramete rs (austenite grain in size and flow stress) of microalloy steel was function appro ached for the establishment of a neural network-based model of the austeuite grain size and flow stress of microalloy steel. From the results of estimation made with the neural network based model, the hot-rolling control parameters can be effectively predicted.

关键词： microalloy steel controlled rolling austenite grain size flow stress neural network Bp algorithm