• <tr id="yyy80"></tr>
  • <sup id="yyy80"></sup>
  • <tfoot id="yyy80"><noscript id="yyy80"></noscript></tfoot>
  • 99热精品在线国产_美女午夜性视频免费_国产精品国产高清国产av_av欧美777_自拍偷自拍亚洲精品老妇_亚洲熟女精品中文字幕_www日本黄色视频网_国产精品野战在线观看 ?

    Optimisation of laser welding parameters for welding of P92 material using Taguchi based grey relational analysis

    2016-04-18 10:14:25ShnmugrjnRishhSHRIVASTAVASthiyBuvnshekrn
    Defence Technology 2016年4期

    Shnmugrjn B.*,Rishh SHRIVASTAVA,Sthiy P.,Buvnshekrn G.

    aWelding Research Institute,Bharat Heavy Electricals Ltd.,Tiruchirappalli 620014,Tamil Nadu,India

    bGE India Technology Centre,Bangalore,India

    cDepartment of Production Engineering,NIT,Tiruchirappalli,India

    Optimisation of laser welding parameters for welding of P92 material using Taguchi based grey relational analysis

    Shanmugarajan B.a,*,Rishabh SHRIVASTAVAb,Sathiya P.c,Buvanashekaran G.a

    aWelding Research Institute,Bharat Heavy Electricals Ltd.,Tiruchirappalli 620014,Tamil Nadu,India

    bGE India Technology Centre,Bangalore,India

    cDepartment of Production Engineering,NIT,Tiruchirappalli,India

    Creep strength enhanced ferritic (CSEF)steels are used in advanced power plant systems for high temperature applications.P92 (Cr-W-Mo-V)steel,classif i ed under CSEF steels,is a candidate material for piping,tubing,etc.,in ultra-super critical and advanced ultra-super critical boiler applications.In the present work,laser welding process has been optimised for P92 material by usingTaguchi based grey relational analysis (GRA). Bead on plate (BOP)trials were carried out using a 3.5 kW diffusion cooled slab CO2laser by varying laser power,welding speed and focal position.The optimum parameters have been derived by considering the responses such as depth of penetration,weld width and heat affected zone(HAZ)width.Analysis of variance (ANOVA)has been used to analyse the effect of different parameters on the responses.Based onANOVA,laser power of 3 kW,welding speed of 1 m/min and focal plane at-4 mm have evolved as optimised set of parameters.The responses of the optimised parameters obtained using the GRA have been verif i ed experimentally and found to closely correlate with the predicted value.

    Laser;Welding;Optimisation;Taguchi;P92

    1.Introduction

    The global initiative towards “Go Green”has urged all the manufacturing industries to improve the eff i ciency to reduce the greenhouse gases.In the power sector,it has led to the development of supercritical,ultra super critical and advanced ultrasuper critical boiler technologies,which operate at higher temperatures and pressures compared to conventional sub critical boilers.These developments increase the eff i ciency of operation thereby reducing the polluting emissions and demand the use of materials that can withstand such operating conditions [1].Stainless steels,Cr-Mo steels like P22,23,etc.,have been traditionally used for such applications in components like super heater tubes,panels,etc.To further increase the life of the components without hampering the heat transfer eff i ciency,9-12%Cr steels have been developed,which have better oxidation resistance,high temperature properties,etc. [2].The most commonly used material in this category is the 9Cr-1Mo(P91)steel due to its high thermal conductivity and low coeff i cient of thermal expansion compared to the closely competing austenitic stainless steels.P91 has been in use for applications experiencing temperatures of the order of 600 °C [3].However,the presence of Mo leads to the formation of deleterious phases,which will affect the high temperature performance of the components made of P91 material [4].To reduce the chance of formation of deleterious phases and to further enhance the high temperature performance,P92 steels have been developed by reducing the Mo content to 0.5%and adding 2%W to compensate for the loss in strength due to reduced Mo content.The material is being considered for applications like headers,panels,coils,etc.,in super critical and ultra super critical power plants.P92 materials have oxidation resistance similar to the P91 as the oxidation resistance is inf l uenced by the Cr content and both P91 and P92 materials have similar Cr content.The componentsfabricated with P92 willinvolveextensive welding.Hence,weldability of the material will be an essentialrequirement.P92 is also usually supplied in normalised and tempered conditions and will have fully martensitic microstructure at room temperature and hence,during welding should have issues similar to P91.The weldability issues in the material will include hard and brittle microstructure in weld and HAZ,susceptibility to hydrogen induced cracking (HIC),formation of soft intercritical zone,etc.[5,6].P91/92 material can be welded by almost all fusion welding processes.Laser welding with the capability of carrying out the welding in open atmosphere with just an inert gas shield is gaining attention for welding of such materials.The use of laser welding can offer benef i ts like easy shielding of molten pool to avoid hydrogen induced cracking,reduced chances of formation of soft intercritical zone because of high cooling rates associated with the process,reduced chances of formation of deleterious phase,etc.[7,8].However,there is limited information available in the open literature on laser welding of P92 material.Hence,in the present work,laser welding process has been attempted on P92 plates in bead on plate (BOP)mode.

    In any welding process,to achieve the desired properties,it is necessary to carry out the welding using optimised parameters.To obtain the optimised parameters,the scientif i c method is to use optimisation techniques.In the present work,Taguchi based grey relation analysis method has been used to optimise the parameters.Quite a good number of published literatures have proved the usability of optimisation techniques for both non-fusion and fusion welding including laser welding process of different materials.Ajith et al. [9]have used ANN to optimise friction welding of UNS S32205 duplex stainless steel and Magudeeswaran et al. [10]have optimised ATIG welding parameters using Taguchi followed by ANOVA and Pooled ANOVA to achieve the desired width to depth ratio to avoid hot cracking in the same material.Tamrin et al. [11]have optimised laser lap welding process using grey relational analysis for dissimilar welding of polymer to glass based ceramics to arrive at the optimum joint characteristics like joint strength,etc.and found that welding speed has the maximum inf l uence on the joint characteristics.Zhao et al.[12]optimised laser welding process for welding of thin gauge galvanised steel using response surface methodology (RSM)and they have found that welds made with optimised parameters had good bead geometry values.They could also f i nd out that with optimisation,the process eff i ciency could be enhanced and the average aspect ratio could be increased from 0.62 to 0.83.Reisgen et al.[13]have optimised CW CO2laser welding parameters like laser power,welding speed and focus position using RSM for welding of dissimilar thickness of Advanced High Strength Steels of DP 600 and TRIP steel to achieve good bead geometry parameters, mechanical properties and formability at a reduced cost of fabrication. Olabi et al.[14]have optimised laser welding parameters like laser power,welding speed and focal position using a combined approach withArtif i cial Neural Network (ANN)and Taguchi analysis to achieve optimal bead geometry values like the ratios of penetration to fusion zone width and penetration to HAZ width.They have arrived at an ANN model that will work for all the range of parameters experimented.Ruggiero et al. [15]have optimised CW CO2laser welding parameters using RSM for welding of dissimilar joint involving AISI 316 austenitic stainless steel and low carbon steel to arrive at optimum bead geometry values and welding cost.They have also found welding speed to be the most inf l uencing parameter and the welding cost was found to be greatly reduced based on their devised formula with the optimised parameters.E.M. Anawa and Olabi [16]have used Taguchi approach with ANOVA to arrive at the optimum set of laser welding parameters for achieving good mechanical properties tested by notched tensile specimen for a dissimilar combination of AISI 316 austenitic stainless steel to AISI 1008 low carbon steel. The mechanical properties of welded joints with optimum parameters were found to be better than the base material. They have found laser power to be the most inf l uencing factor in determining the strength of such dissimilar joints.The authors have also optimised the parameters for obtaining good fusion zone properties for the same combination of materials and they have found that with respect to the fusion zone properties,welding speed had the greatest inf l uence [17].The optimisation technique was found to be a very useful tool even for welding of nonmetals like plastics.Kumar et al. [18]have optimised the laser transmission welding parameters like current,standoff distance and clamping for welding of plastics.Pan et al. [19]used Taguchi method to optimise pulsed Nd:YAG laser welding parameters for welding of AZ31B Magnesium alloy to achieve the maximum tensile strength.The optimisation could yield a parametric combination that could increase the tensile strength by 2.5× compared to the original value as set for laser welding. Benyounis et al. [20]analysed the effect of laser power,welding speed and focal position of the laser beam with respect to the workpiece surface using RSM for CW CO2laser welding of medium carbon steel in butt joint conf i gurations. They have concluded that the proposed model could accurately predict the responses like depth of penetration,weld width and HAZ width within the parametric range that have been experimented.All the reported works not only prove the usefulness of the optimisation techniques for optimising the laser welding process for different materials but also prove to be a scientif i c way to reduce the number of experiments to arrive at a parameter to achieve the desired weld quality.

    In the present work,laser welding parameters were optimised usingTaguchi analysis with GRA for welding of P92 material using diffusion cooled slab CO2laser.The welding trials were carried out using Taguchi L9 orthogonal array in bead on plate (BOP)mode by varying laser power,welding speed and focal position.The trials were carried out twice in a random manner to avoid sequential error.The welds were cut in the transverse direction to study the macrostructure and bead geometry characteristics like depth of penetration,top weld width and HAZ width,which were taken as responses.The average of the responses was taken for the analysis.Subsequently,ANOVA was performed and the optimum parameters were derived.The optimum parameters obtained through the analysis were verif i ed experimentally and the results were presented and discussed.

    Table 1Chemistry of P92 base material in wt.%.

    2.Experimental procedure

    2.1.Laser welding experiments

    Laser welding experiments were performed in BOP mode by varying parameters like laser power,welding speed and focal plane position using an L9 orthogonal array on P92 plate material of dimensions 200 × 150 × 8 mm without any preheating. The chemistry of the material is given in Table 1 and the details of the parameters used for the trials are given in Table 2.The welding trials were performed twice in a random manner to avoid the sequential error.The welding trials were carried out using 3.5 kW slab CO2laser using Argon as shielding and plasma purge gas at 30 lpm in trailing mode using a 300 mm focal mirror,which gives a focal spot size of 180 μm in the Gaussian mode.The laser has a depth of focus of+/-3 mm with the present focal arrangement.The welding power was varied in the range of 2.5-3.5 kW,welding speed 1-5 m/min and focal plane position in the range of 0 to-4 mm (inside the material).All welds were cut in the transverse direction,polished and etched using Villella’s reagent to study the macrostructures.Macrostructures were taken using a Leica Stereo microscope.Subsequently,bead geometry measurements like depth of penetration,bead width and HAZ width were taken using the measurement software available in the microscope and the values were used as responses for optimisation.

    2.2.Optimisation of laser welding parameters

    Since multiple output parameters have to be dealt with,GRA basedTaguchi method was used for the analysis.To optimise the parametersusingGRA,theexperimentaldatawerenormalisedby assigningthevaluesbetween0and1.Subsequently,greyrelation coeff i cient was calculated,which shows the interconnection betweenthedesiredandobtainedexperimentaldata.Furthermore,the problem was converted to a single objective function by calculatingthegreyrelationalgrade,whichistheaverageofgrey relation coeff i cient.The combination of parameters with highest valueofgreyrelationalgradewillbetheoptimalsolution.Incase of laser welding,the prime objective will be to increase thepenetrationattheminimalweldandHAZwidth,asitconveysthat all the incident energy is effectively utilised to penetrate the material.Thiswillbeevenmorecriticalinaheatsensitivematerial like P92,where the interface between the HAZ and base metal(BM)will be the weakest zone.

    Table 2L9 Orthogonal array used for laser welding trials.

    Hence,in grey relational generation,the normalised top bead width and HAZ width correspond to the smaller-the-better(SB)criterion that can be expressed by Eq. (1)

    Penetration should follow the larger-the-better (LB)criterion,which can be expressed by Eq.(2)

    where xi(k)is the value after the grey relational generation,min yi(k)is the smallest value of yi(k)for the kth response,and max yi(k)is the largest value of yi(k)for the kth response.Grey relational coeff i cient can be calculated by using the formula given in Eq. (3)

    Suppose ideal sequence isxo( k )for a kth response,then its value will be the maximum value of that particular column which will always be 1 andΔoi=differenceof the absolute value xo(k)and xi(k),which means how much that particular value is deviating from ideal value,so the equation for calculating delta is given below

    ψ is a distinguishing coef fi cient 0 ≤ Ψ ≤1,here ψ =0.25 for all quality characteristics

    Δmin =the smallest value ofΔoi

    Δmax =the largest value ofΔoi

    After averaging the grey relational coeff i cients,the grey relational grade can be calculated as

    where n is the number of process responses.The higher value of grey relational grade corresponds to intense relational degreebetween the reference sequence xo(k)and the given sequence xi(k).

    Fig.1.Macrostructures of laser BOP welds.

    Finally,analysis of variance (ANOVA)was performed to fi nd out the effect of each parameter on the desired weld bead characteristics and to arrive at an optimal set of parameters.

    2.3.Con fi rmation experiments and weld characterisation

    Based on the ANOVA,the optimum welding parameters were found.Since the optimum parameters obtained were out of the set of trials performed,the con fi rmation experiments were carried out by conducting BOP trials on P92 plate using the optimum parameters obtained from the analysis.The welds were characterised for macrostructure and bead geometry values as described before.The welds were subjected to post weld heat treatment (PWHT)at a temperature of 760 °C for 3 hours.After PWHT,the hardness survey was conducted across the weld to check the presence of any soft intercritical zone in the HAZ/BM boundary.Microhardness measurements were taken using an automatic microhardness tester with a load of 200 g and inter indent spacing of 150 μm.Furthermore,microstructuresoftheweldsweretaken using optical microscope at a magnif i cation of 200× and 500× to study the phases and to check for the presence of any undesirable phases.

    3.Results and discussion

    Macrostructures of the weld for all the parameters experimented are given in Fig.1 and the bead geometry responses are given in Table 3.

    Table 3L9orthogonal array with values of responses.

    Table 4Grey relational generation of each performance characteristics.

    3.1.Optimisation of laser welding parameters

    3.1.1.Evaluation of optimal process condition

    In the evaluation process,initially,normalisation is used to convert the parameters with different units into a nondimensional value.This could be done using Eqs. (1)and (2). This has been performed considering “Larger the Better”for depth of penetration and “Smaller the Better”for both top weld width and HAZ width.Normalised values for top bead width,penetration and heat affected zone are given in Table 4.Table 5 shows the Δoivalues.

    The value of grey relational coeff i cient is given in Table 6,which will be used for calculating grey relational grade.In case of laser welding,the maximum depth of penetration achievable in single pass in the most desirable output and the width of the weld bead and HAZ should be kept as minimal as possible. Accordingly,the weightage used for top bead width is 0.2;and for depth of penetration,0.6;and HAZ,0.2.Weightage has been allotted considering the importance of these responses especially,whilst welding heat sensitive P92 materials.With the assigned weightage,the grey relational coeff i cient was calculated and the values are given in Table 6.Table 7 shows the value of grey relational grade which will be used for calculating S/N ratio.

    Table 8 shows the S/N ratio based on the larger the better criterion for overall grey relational grade and Fig.2 shows theS/N curve,which is the graphical representation to f i nd out the optimal sets of parameters.S/N ratio is the signal to noise ratio,so if the ratio is high,the desired effect is maximum with very minimal noise.From Fig.2,where A represents laser power,B represents welding speed and C represents focal plane position,it can be seen that the maximum value of S/N ratio is occurring at power 3 kW,speed 1 m/min and focal position of-4 mm.

    Table 5Evaluation of Δoifor each of the responses.

    Table 6Grey relational coeff i cient of each performance characteristics (βTBW=0.2,βpenetration=0.6,βHAZ=0.2).

    From the response table (Table 9),it can be seen that the range for welding speed is maximum followed by power and focal position,which means welding speed has highest impact on responses.This is in line with the f i ndings observed by other researchers elsewhere [8,12]on other materials during CO2laser welding.Based on the analysis,the optimal set ofparameter will be power 3 kW,speed 1 m/min and focal position of-4 mm.The optimal set of parameter obtained using grey relational grade is not in L9 orthogonal array used for carrying out the trials and hence,conf i rmation test has to be carried out by performing laser welding with the optimal parameters obtained from the analysis.

    Table 7Grey relational grade.

    Table 8 S/N ratio.

    Fig.2.S/N plot.

    3.2.Analysis of variance (ANOVA)

    ANOVA was performed to f i nd out the parameter that is most inf l uencing to the bead geometry values in the desirable manner.For analysing the effect of laser welding process parameters (power,welding speed,focal position)on total variation of response,the mean data of the overall grey relational grade were used.ANOVA results are shown in Table 10. As can be seen from the ANOVA table,all parameters have considerable F value,hence,all parameters are important. However,amongst the parameters,welding speed has the highest effect on the responses followed by laser power and then focal position.In any fusion welding process,the weld bead geometry values are highly dependent on the heat input and the heat input will be highly dependent on the welding speed rather than the power.Hence,in the present case also,the welding speed has the highest effect on the responses,which matches the f i ndings of other researchers for some other materials. However,the penetration capability of the laser will be directlyproportional to the power density,which depends on the given laser power and focal area.Since the laser is having near Gaussian beam quality with very high depth of focus,the focal spot size will not vary much with the focal plane variation.Hence,the variation in focal plane position has the least effect on the responses.Also,since focal spot size is almost constant,the power density is directly proportional to the laser power.Hence,laser power has turned out to be the second most inf l uencing parameter.

    Table 9Response table for grey relational grade.

    Table 10Analysis of variance.

    Fig.3.Macrostructure of the weld.

    3.3.Results of conf i rmation experiments

    Conf i rmation welding experiment was carried out in BOP mode using the optimal set of parameter,i.e.laser power-3 kW,welding speed-1 m/min and focal plane position of -4 mm.The macrostructure of the weld carried out using the optimal parameters is given in Fig.3.The bead geometry values obtained with the optimal parameters are given in Table 11. Macrostructure of the weld is uniform with no defects like cracks,porosities,etc.Grey relational grade is calculated for these sets of parameter and the value is 0.7688,which is the maximum amongst all the other 9 parameters experimented. This conf i rms that for the given set of conditions,the optimisation of parameters arrived at is correct.From the bead geometry analysis,the depth of penetration in this case is maximum.It can also be seen that from the microstructure(Fig.3)that the penetration in this case is maximum.

    The microstructures across different zones of the weld obtained with the optimised set of parameters across different zones are given in Fig.4.

    The microstructure contains tempered lath like martensite structure with carbides decorating the boundaries and also thegrains in all the three regions.The microstructure is found to be uniform with the average grain size in the range of 25 μm in base material,18 μm in the weld and around 15 μm in the HAZ. The microstructure is also found to be free from deleterious phases like δ-ferrite.Power beam welding processes,even though with very high cooling rates,do not form δ-ferrite if welding is carried out with optimum parameters.Since δ-ferrite is stable over a very narrow range of temperature during solidif i cation [21],in power beam welding process like laser welding,the region would have been crossed rapidly,and hence,there is no suff i cient time available for δ-ferrite to form or to grow even if it forms.Hence,this further conf i rms that the parameters are optimum.The microhardness variation across weld taken at top and bottom of the weld is given in Fig.5.

    Table 11Bead geometry values with optimised parameters.

    Fig.4.Microstructures across different zones of the weld.

    Microhardness values were in the range of 270-320 HV0.2in welds and 240-265 HV0.2in HAZ against 220-240 HV0.2in the base metal.Hardness survey has indicated that weld and HAZ are stronger than the base material and have not shown any signif i cant softening in the HAZ-BM boundary,which indicates that with optimum parameters,in laser welding,formation of soft intercritical zone can be avoided.Laser welding due to its cooling rate could suppress the formation of this soft undesirable zone.It could be observed from Fig.5 that the hardness values in the welds are more in the bottom side compared to the top side even after 3 h of soaking at 7600C during post weld heat treatment.Usually,the bottom of the welds will be even narrow and hence,the cooling rates will be much higher in the bottom region compared to the top.This higher cooling rate results in elevated hardness in the bottom portion.This conf i rms two things.First,laser welding with narrow weld and HAZ will be a potential candidate for welding such materials and with optimisation of laser welding parameters,good mechanical and microstructural properties could be obtained. Second,the use of ″Smaller the Better″rule for both weld and HAZ width in such heat sensitive materials is proved to be right.

    Fig.5.Microhardness variation across weld.

    4.Conclusions

    From the study and analyses,the following conclusions could be made:

    1)Taguchi based optimisation of laser welding parameters for autogenous laser welding of P92 material has shown that for the given conditions,3 kW of laser power,1 m/ min welding speed and positioning the focal plane of the laser at 4 mm from the surface of the base material have evolved as the optimal parameters.

    2)From ANOVA,amongst the parameters experimented,welding speed has the most signif i cant contribution with 74.39%followed by laser power with 14.63%and focal length with 10.97%

    3)Microhardness survey across welds with optimised parameter did not indicate any softening in the HAZ/BM boundary and microstructural analysis did not reveal any deleterious phases,which conf i rms that the parameters obtained through optimisation are valid.

    Acknowledgment

    We sincerely thank the management of Bharat Heavy Electricals Ltd.,for funding this research programme.We extend our gratitude to Mr.R.Easwaran,General Manager,WRI&Labs,for guiding us throughout the research work.

    [1]Viswanathan R,Purgert R,Goodstine S,Tanzosh J,Stanko G,Shingledecker JP,et al.U.S.program on materials technology for ultrasupercritical coal-f i red boilers.Advances in materials technology for fossil power plants.In:Proceedings of the 5th international conference. 2008;05226G:1-16.

    [2]Viswanathan R,Purgert R,Rao U.Materials for ultra-supercritical coal-f i red power plant boilers.In:Proceedings of 2nd regional conference on energy technology towards a clean environment;2003.p.1-14.

    [3]Hamada K,Tokuno K,Takeda T.Dispersion hardening effects of Nb-V precipitates in Mod.9Cr-1Mo steels.Nucl Eng Des 1993;139:277-81.

    [4]Naoi H,Ohgami M,Hasegawa Y,Mimura H,F(xiàn)ujita T.Advanced heat resistant steel for power generation.London:The Institute of Materials;1999.p.259-69.

    [5]Onoro J.Martensitic microstructure of 9-12%Cr steel weld metals.J Mat Proc Technol 2006;180:137-42.

    [6]Francis JA,Mazur W,Bhadeshia HKDH.Type IV cracking in ferritic power plant steels.Mat Sci Technol 2006;22:1387-95.

    [7]Lee WH,Shiue RK,Chen C.Mechanical properties of modif i ed 9Cr-1Mo steel welds with notches.Mat Sci Eng A 2003;A356:153-61.

    [8]Shanmugarajan B,Padmanabham G,Kumar H,Albert SK,Bhaduri AK. Autogenous laser welding investigations on modif i ed 9Cr-1Mo (P91)steel.Sci Technol Weld Joining 2011;16:528-34.

    [9]Ajith PM,Barik BK,Sathiya P,Aravindan S.Multiobjective optimization of friction welding of UNSS32205 duplex stainless steel.Def Technol 2015;11:157-65.

    [10]Magudeeswaran G,Nair SR,Sundar L,Harikannan N.Optimisation of process parameters of the activated tungsten inert gas welding for aspect ratio of UNS S32205 duplex stainless steel welds.Def Technol 2014;10: 251.

    [11]Tamrin KF,Nukuman Y,Sheikh NA,Harizam MZ.Determination of optimum parameters using grey relational analysis for multi-performance characteristics in CO2laser joining of dissimilar materials.Opt Lasers Eng 2014;57:40-7.

    [12]Zhao Y,Zhang Y,Hu W,Lai X.Optimization of laser welding thin-gage galvanized steel via response surface methodology.Opt Lasers Eng 2012;50:1267-73.

    [13]Reisgen U,Schleser M,Markov O,Ahmed E.Optimization of laser welding of DP/TRIP steel sheets using statistical approach.Opt Laser Technol 2012;44:255-62.

    [14]Olabi AG,Casalino G,Benyounis KY,Hashmi MSJ.An ANN and Taguchi algorithms integrated approach to the optimization of CO2laser welding.Adv Eng Softw 2006;37:643-8.

    [15]RuggieroA,Tricarico L,Olabi AG,Benyounis KY.Weld-bead prof i le and costs optimization of the CO2dissimilar laser welding process of low carbon steel and austenitic steel AISI316.Opt Laser Technol 2011;43: 82-90.

    [16]Anawa EM,Olabi AG.Optimization of tensile strength of ferritic/ austenitic laser-welded components.Opt Lasers Eng 2008;46:571-7.

    [17]Anawa EM,Olabi AG.UsingTaguchi method to optimize welding pool of dissimilar laser-welded components.Opt Laser Technol 2008;40:379-88.

    [18]Kumar N,Ramesh R,Pal PK.Multi-objective optimization in through laser transmission welding of thermoplastics using grey-based Taguchi method.Proc Mat Sci 2014;5:2178-87.

    [19]Pan LK,Wang CC,Hsiao YC,Ho KC.Optimization of Nd:YAG laser welding onto magnesium alloy via Taguchi analysis.Opt Laser Technol 2004;37:33-42.

    [20]Benyounis KY,Olabi AG,Hashmi MSJ.Effect of laser welding parameters on the heat input and weld-bead prof i le.J Mat Proc Technol 2005;164-165:978-85.

    [21]Jeyaganesh B,Raju S,Rai AK,Mohandas E,Vijayalakshmi M,Rao BS,et al.Differential scanning calorimetry of diffusional and martensitic phase transformations in some 9 wt-%Cr low carbon ferritic steels.Mat Sci Technol 2011;27:500-12.

    Received 3 March 2016;revised 10 April 2016;accepted 11 April 2016 Available online 22 April 2016

    Peer review under responsibility of China Ordnance Society.

    *Corresponding author.Tel.:+91-94890 56100.

    E-mail address:bsrajan@bheltry.co.in (Shanmugarajan B.).

    http://dx.doi.org/10.1016/j.dt.2016.04.001

    2214-9147/? 2016 China Ordnance Society.Production and hosting by Elsevier B.V.All rights reserved.

    ? 2016 China Ordnance Society.Production and hosting by Elsevier B.V.All rights reserved.

    视频区图区小说| 一区二区日韩欧美中文字幕| 久久久久久久久免费视频了| 别揉我奶头~嗯~啊~动态视频 | 天堂中文最新版在线下载| 午夜日本视频在线| 一二三四在线观看免费中文在| 久久久久网色| 青草久久国产| 亚洲精品一区蜜桃| 在线观看www视频免费| 国产片特级美女逼逼视频| 欧美国产精品va在线观看不卡| 国产免费一区二区三区四区乱码| 免费少妇av软件| 老司机在亚洲福利影院| 欧美少妇被猛烈插入视频| 午夜影院在线不卡| 久久午夜综合久久蜜桃| 女人久久www免费人成看片| 亚洲欧美清纯卡通| 亚洲 欧美一区二区三区| 交换朋友夫妻互换小说| 黄色一级大片看看| 色播在线永久视频| 中文字幕人妻丝袜制服| 水蜜桃什么品种好| 国产亚洲精品第一综合不卡| 国产高清国产精品国产三级| 一级毛片 在线播放| 丰满乱子伦码专区| 国产欧美亚洲国产| 久热这里只有精品99| 丝袜喷水一区| 国产精品人妻久久久影院| 别揉我奶头~嗯~啊~动态视频 | avwww免费| 亚洲图色成人| av在线播放精品| 久久 成人 亚洲| 新久久久久国产一级毛片| 亚洲精品成人av观看孕妇| 巨乳人妻的诱惑在线观看| 如何舔出高潮| 亚洲av在线观看美女高潮| 悠悠久久av| 亚洲精品第二区| 国产精品99久久99久久久不卡 | 欧美精品一区二区大全| 免费不卡黄色视频| 亚洲色图 男人天堂 中文字幕| 久久ye,这里只有精品| 成人漫画全彩无遮挡| 日本vs欧美在线观看视频| 99国产综合亚洲精品| 久久精品国产亚洲av涩爱| 一边摸一边做爽爽视频免费| 亚洲欧美成人综合另类久久久| 中文天堂在线官网| 国产成人精品福利久久| 美女视频免费永久观看网站| 国产亚洲一区二区精品| 在线免费观看不下载黄p国产| 亚洲精品中文字幕在线视频| 一边摸一边做爽爽视频免费| 亚洲精品在线美女| 高清不卡的av网站| 日本91视频免费播放| 国产亚洲精品第一综合不卡| 午夜福利视频在线观看免费| 成人免费观看视频高清| 美女午夜性视频免费| 国产xxxxx性猛交| bbb黄色大片| 免费不卡黄色视频| 天堂8中文在线网| 国产精品 欧美亚洲| 青春草亚洲视频在线观看| 中文乱码字字幕精品一区二区三区| 黄色 视频免费看| 中国三级夫妇交换| 99香蕉大伊视频| 亚洲人成电影观看| 七月丁香在线播放| 国产国语露脸激情在线看| 久久久久久久久久久免费av| 亚洲成av片中文字幕在线观看| 久久毛片免费看一区二区三区| 免费高清在线观看日韩| 国产不卡av网站在线观看| 国产成人一区二区在线| 亚洲成人av在线免费| 波野结衣二区三区在线| 日本色播在线视频| 亚洲色图 男人天堂 中文字幕| 少妇人妻 视频| 欧美中文综合在线视频| 国产精品女同一区二区软件| 亚洲精品第二区| 国产乱人偷精品视频| 久久亚洲国产成人精品v| 韩国av在线不卡| 不卡av一区二区三区| 激情视频va一区二区三区| 亚洲成人一二三区av| 精品免费久久久久久久清纯 | av女优亚洲男人天堂| 女人被躁到高潮嗷嗷叫费观| 一级毛片黄色毛片免费观看视频| 韩国av在线不卡| 美女午夜性视频免费| a级毛片在线看网站| 自线自在国产av| 国产精品av久久久久免费| 国产精品久久久久久精品古装| h视频一区二区三区| 亚洲激情五月婷婷啪啪| 日日啪夜夜爽| 一级片免费观看大全| 欧美精品av麻豆av| 如何舔出高潮| 少妇人妻 视频| 人人妻人人添人人爽欧美一区卜| tube8黄色片| 亚洲欧洲日产国产| 天堂俺去俺来也www色官网| av有码第一页| 欧美激情极品国产一区二区三区| 在线看a的网站| 婷婷色麻豆天堂久久| 捣出白浆h1v1| 国产成人91sexporn| 欧美乱码精品一区二区三区| 亚洲欧美清纯卡通| 9热在线视频观看99| 美女视频免费永久观看网站| 国产日韩欧美亚洲二区| 午夜免费男女啪啪视频观看| svipshipincom国产片| 亚洲国产欧美网| 免费在线观看视频国产中文字幕亚洲 | 中文字幕另类日韩欧美亚洲嫩草| 男女免费视频国产| 久久国产精品男人的天堂亚洲| 亚洲一区中文字幕在线| 老司机深夜福利视频在线观看 | 久久久久久久大尺度免费视频| 尾随美女入室| 成人毛片60女人毛片免费| 麻豆精品久久久久久蜜桃| 亚洲天堂av无毛| 精品视频人人做人人爽| 大片免费播放器 马上看| 麻豆乱淫一区二区| 亚洲精品自拍成人| 男女免费视频国产| 一边亲一边摸免费视频| 亚洲色图综合在线观看| av视频免费观看在线观看| 在线看a的网站| 成人免费观看视频高清| svipshipincom国产片| 午夜福利免费观看在线| 啦啦啦啦在线视频资源| 日韩av免费高清视频| 不卡视频在线观看欧美| 男女国产视频网站| 19禁男女啪啪无遮挡网站| 美女国产高潮福利片在线看| 国产麻豆69| 中文字幕人妻丝袜一区二区 | 黄片播放在线免费| 国产精品久久久久久人妻精品电影 | 永久免费av网站大全| 免费黄网站久久成人精品| 亚洲人成77777在线视频| av网站在线播放免费| 久久人妻熟女aⅴ| 国产精品免费大片| 国产av码专区亚洲av| 久久久国产一区二区| 丝袜脚勾引网站| 97人妻天天添夜夜摸| 亚洲成人国产一区在线观看 | 美女主播在线视频| 久久久久国产精品人妻一区二区| 日韩熟女老妇一区二区性免费视频| www.精华液| 99re6热这里在线精品视频| 日韩大片免费观看网站| 久久久久久久精品精品| 中文字幕亚洲精品专区| 国产熟女午夜一区二区三区| e午夜精品久久久久久久| 国产黄色视频一区二区在线观看| 欧美老熟妇乱子伦牲交| 国产黄频视频在线观看| 日韩精品免费视频一区二区三区| 久久毛片免费看一区二区三区| 日本vs欧美在线观看视频| 亚洲国产精品国产精品| 欧美人与善性xxx| 免费日韩欧美在线观看| 人成视频在线观看免费观看| 一区福利在线观看| 免费观看a级毛片全部| 国产免费又黄又爽又色| 日本wwww免费看| 午夜影院在线不卡| 国产熟女欧美一区二区| 高清欧美精品videossex| 亚洲精华国产精华液的使用体验| 亚洲一卡2卡3卡4卡5卡精品中文| 欧美成人午夜精品| 日韩精品有码人妻一区| 成年人午夜在线观看视频| 啦啦啦 在线观看视频| 黑人欧美特级aaaaaa片| 欧美激情 高清一区二区三区| 老司机在亚洲福利影院| 亚洲欧洲日产国产| 亚洲人成电影观看| 两个人免费观看高清视频| 免费日韩欧美在线观看| 国产精品人妻久久久影院| 九草在线视频观看| 韩国av在线不卡| 啦啦啦 在线观看视频| 久久久精品区二区三区| 综合色丁香网| 精品久久久久久电影网| 看免费成人av毛片| 少妇 在线观看| av网站在线播放免费| 亚洲成人av在线免费| 男人舔女人的私密视频| av国产久精品久网站免费入址| 一级爰片在线观看| 性少妇av在线| 18禁观看日本| 国产精品一国产av| 97精品久久久久久久久久精品| 黑丝袜美女国产一区| 欧美日韩av久久| 在线观看免费日韩欧美大片| 不卡av一区二区三区| 亚洲少妇的诱惑av| 免费观看人在逋| 欧美日韩视频高清一区二区三区二| 肉色欧美久久久久久久蜜桃| 亚洲欧洲日产国产| 亚洲国产精品成人久久小说| 大话2 男鬼变身卡| 国产免费视频播放在线视频| 欧美日韩福利视频一区二区| 国产 精品1| 美女扒开内裤让男人捅视频| 51午夜福利影视在线观看| 在线观看一区二区三区激情| 精品免费久久久久久久清纯 | 中国三级夫妇交换| 久久精品人人爽人人爽视色| 亚洲国产精品国产精品| 人人妻人人澡人人看| 在线观看免费高清a一片| 成人午夜精彩视频在线观看| 国产日韩一区二区三区精品不卡| 久久久久久人妻| 十八禁网站网址无遮挡| 欧美日韩亚洲国产一区二区在线观看 | 亚洲成人国产一区在线观看 | 日韩 亚洲 欧美在线| 岛国毛片在线播放| 久久久精品94久久精品| 国产在线免费精品| 国产亚洲午夜精品一区二区久久| 女人高潮潮喷娇喘18禁视频| 这个男人来自地球电影免费观看 | 黄片无遮挡物在线观看| 亚洲情色 制服丝袜| 九草在线视频观看| 国产亚洲欧美精品永久| 欧美亚洲日本最大视频资源| 国产男女超爽视频在线观看| 女人精品久久久久毛片| av有码第一页| 可以免费在线观看a视频的电影网站 | 久久97久久精品| av线在线观看网站| 国产一区二区激情短视频 | 国产精品国产av在线观看| 亚洲第一青青草原| 菩萨蛮人人尽说江南好唐韦庄| 超碰97精品在线观看| 国产精品 国内视频| 啦啦啦在线观看免费高清www| 久久人人97超碰香蕉20202| 精品国产乱码久久久久久男人| www.熟女人妻精品国产| 精品国产一区二区久久| 一级黄片播放器| 国产精品久久久人人做人人爽| 一级,二级,三级黄色视频| 午夜日韩欧美国产| 久久久久久久久久久免费av| 国产av一区二区精品久久| 免费观看a级毛片全部| av电影中文网址| av国产久精品久网站免费入址| 美女视频免费永久观看网站| 一级黄片播放器| 最近中文字幕2019免费版| 久久久久视频综合| 国产成人av激情在线播放| 久久久精品免费免费高清| 观看av在线不卡| 观看美女的网站| 麻豆精品久久久久久蜜桃| 男人操女人黄网站| 夫妻午夜视频| 婷婷色av中文字幕| 性高湖久久久久久久久免费观看| 最近最新中文字幕免费大全7| 一级黄片播放器| 天天添夜夜摸| 欧美精品亚洲一区二区| 黄色一级大片看看| 高清不卡的av网站| 亚洲国产日韩一区二区| 欧美久久黑人一区二区| 婷婷色麻豆天堂久久| av女优亚洲男人天堂| 欧美日韩一区二区视频在线观看视频在线| 大片免费播放器 马上看| 黄片小视频在线播放| netflix在线观看网站| 免费在线观看完整版高清| 久久99精品国语久久久| 国产1区2区3区精品| 一区二区日韩欧美中文字幕| 操出白浆在线播放| 黑人巨大精品欧美一区二区蜜桃| 亚洲七黄色美女视频| 精品久久久精品久久久| 欧美 亚洲 国产 日韩一| 国产男女超爽视频在线观看| 91精品国产国语对白视频| 人人妻人人澡人人爽人人夜夜| 天堂8中文在线网| 亚洲,欧美精品.| 久久久久人妻精品一区果冻| 80岁老熟妇乱子伦牲交| 成人影院久久| 九九爱精品视频在线观看| 亚洲av国产av综合av卡| 美国免费a级毛片| 亚洲国产日韩一区二区| 久久免费观看电影| 免费看不卡的av| 99国产精品免费福利视频| 日韩免费高清中文字幕av| 久久天堂一区二区三区四区| 美女主播在线视频| 久久精品亚洲熟妇少妇任你| 免费看不卡的av| av片东京热男人的天堂| 少妇人妻精品综合一区二区| 国产精品.久久久| 亚洲精品国产色婷婷电影| www.自偷自拍.com| 久久免费观看电影| 精品少妇内射三级| 国产乱人偷精品视频| 国产探花极品一区二区| 大话2 男鬼变身卡| 亚洲成国产人片在线观看| 日日撸夜夜添| 国产1区2区3区精品| 妹子高潮喷水视频| 在线观看免费视频网站a站| 精品免费久久久久久久清纯 | 一级毛片 在线播放| 成人国产麻豆网| netflix在线观看网站| 赤兔流量卡办理| 亚洲熟女精品中文字幕| 一级毛片我不卡| 久久精品国产亚洲av涩爱| 国产精品人妻久久久影院| 午夜精品国产一区二区电影| 欧美在线一区亚洲| 久久 成人 亚洲| av视频免费观看在线观看| 少妇人妻久久综合中文| 国产亚洲av高清不卡| 精品免费久久久久久久清纯 | 久久性视频一级片| 日韩欧美精品免费久久| 一本一本久久a久久精品综合妖精| 少妇的丰满在线观看| 啦啦啦中文免费视频观看日本| 国产精品久久久久久人妻精品电影 | 中国三级夫妇交换| 亚洲欧美激情在线| 中文欧美无线码| 老司机影院成人| 亚洲av日韩在线播放| 国产精品一区二区在线不卡| 大话2 男鬼变身卡| 久久影院123| 欧美精品高潮呻吟av久久| 777米奇影视久久| 亚洲av在线观看美女高潮| 国产极品天堂在线| 日本av手机在线免费观看| 久久毛片免费看一区二区三区| 亚洲av男天堂| 欧美国产精品va在线观看不卡| 免费在线观看完整版高清| 国产激情久久老熟女| 久久国产精品男人的天堂亚洲| 中文欧美无线码| 少妇人妻精品综合一区二区| 亚洲人成网站在线观看播放| 男人操女人黄网站| 侵犯人妻中文字幕一二三四区| 免费观看av网站的网址| 丝袜人妻中文字幕| 亚洲欧美清纯卡通| 欧美日韩亚洲综合一区二区三区_| 少妇的丰满在线观看| 成人亚洲精品一区在线观看| 青草久久国产| 亚洲自偷自拍图片 自拍| 捣出白浆h1v1| av一本久久久久| 美女脱内裤让男人舔精品视频| 久久人人爽av亚洲精品天堂| 亚洲一码二码三码区别大吗| 精品一区二区三区av网在线观看 | 久久免费观看电影| 中文字幕高清在线视频| 亚洲欧美成人精品一区二区| 亚洲四区av| 国产毛片在线视频| 亚洲欧洲日产国产| 亚洲国产日韩一区二区| 大片电影免费在线观看免费| 夫妻性生交免费视频一级片| 成人漫画全彩无遮挡| 国产午夜精品一二区理论片| 91精品国产国语对白视频| 秋霞伦理黄片| 黄色毛片三级朝国网站| h视频一区二区三区| 18禁裸乳无遮挡动漫免费视频| 五月天丁香电影| 精品酒店卫生间| 夜夜骑夜夜射夜夜干| 精品少妇黑人巨大在线播放| 高清欧美精品videossex| 久久av网站| 在线观看免费高清a一片| 国产免费又黄又爽又色| av在线app专区| 精品亚洲成国产av| 国产欧美日韩综合在线一区二区| 国产日韩欧美视频二区| 国产精品久久久久久人妻精品电影 | 亚洲一区中文字幕在线| 夫妻性生交免费视频一级片| 国产亚洲av高清不卡| 丝袜美腿诱惑在线| 亚洲精品av麻豆狂野| 高清视频免费观看一区二区| 久久久久精品国产欧美久久久 | 国产精品嫩草影院av在线观看| 亚洲欧美成人精品一区二区| 国产亚洲av高清不卡| 最近中文字幕2019免费版| 999精品在线视频| 最近中文字幕2019免费版| 一二三四在线观看免费中文在| 天堂中文最新版在线下载| 国产精品麻豆人妻色哟哟久久| 欧美精品一区二区免费开放| 成人午夜精彩视频在线观看| 99香蕉大伊视频| 国产精品久久久久久精品古装| 久久久国产一区二区| 国产乱人偷精品视频| 久久久久精品久久久久真实原创| 日韩 欧美 亚洲 中文字幕| 爱豆传媒免费全集在线观看| 免费观看人在逋| 亚洲 欧美一区二区三区| 国产探花极品一区二区| 9191精品国产免费久久| 人妻一区二区av| 丰满迷人的少妇在线观看| 久久精品国产亚洲av高清一级| 久久精品久久精品一区二区三区| 国产精品一国产av| 最近手机中文字幕大全| 国产成人91sexporn| 日韩 亚洲 欧美在线| 亚洲国产欧美一区二区综合| 中文字幕高清在线视频| 国产午夜精品一二区理论片| 久久久久久久精品精品| 亚洲精品一区蜜桃| 国产成人免费观看mmmm| av线在线观看网站| svipshipincom国产片| 精品国产露脸久久av麻豆| 欧美久久黑人一区二区| 精品福利永久在线观看| 少妇猛男粗大的猛烈进出视频| 哪个播放器可以免费观看大片| 9热在线视频观看99| 亚洲成国产人片在线观看| 中文字幕制服av| 午夜免费鲁丝| 久热这里只有精品99| av不卡在线播放| 国产男女超爽视频在线观看| 男人舔女人的私密视频| 91aial.com中文字幕在线观看| 亚洲第一青青草原| 大片电影免费在线观看免费| 免费观看av网站的网址| 亚洲,一卡二卡三卡| 纵有疾风起免费观看全集完整版| av国产久精品久网站免费入址| 人人妻人人澡人人看| 亚洲成人一二三区av| 亚洲天堂av无毛| 18禁动态无遮挡网站| 亚洲欧洲国产日韩| 国产精品久久久久久久久免| 亚洲 欧美一区二区三区| 亚洲精品久久成人aⅴ小说| 免费在线观看视频国产中文字幕亚洲 | 精品国产国语对白av| 国产高清不卡午夜福利| 如何舔出高潮| 中文字幕人妻熟女乱码| 亚洲美女搞黄在线观看| 日本爱情动作片www.在线观看| 男人添女人高潮全过程视频| 精品少妇一区二区三区视频日本电影 | 日韩精品有码人妻一区| 国产精品av久久久久免费| 综合色丁香网| 大香蕉久久成人网| 国产黄色视频一区二区在线观看| 自拍欧美九色日韩亚洲蝌蚪91| 国产精品久久久av美女十八| 欧美人与性动交α欧美软件| 久久精品国产亚洲av涩爱| 狂野欧美激情性bbbbbb| av网站免费在线观看视频| 国产色婷婷99| 一本色道久久久久久精品综合| 欧美激情高清一区二区三区 | 制服丝袜香蕉在线| 亚洲一区中文字幕在线| 色精品久久人妻99蜜桃| 欧美成人午夜精品| 日韩一卡2卡3卡4卡2021年| 国产乱人偷精品视频| 亚洲情色 制服丝袜| 亚洲在久久综合| 妹子高潮喷水视频| 欧美日韩一级在线毛片| 精品国产一区二区三区久久久樱花| 99久久综合免费| 极品人妻少妇av视频| 中文字幕制服av| 亚洲欧美一区二区三区久久| 成人免费观看视频高清| 十八禁高潮呻吟视频| 美女主播在线视频| 黄色一级大片看看| 午夜免费鲁丝| 女性生殖器流出的白浆| 午夜91福利影院| 国产免费福利视频在线观看| 成年人午夜在线观看视频| 久久免费观看电影| 少妇精品久久久久久久| 18禁裸乳无遮挡动漫免费视频| 人人妻人人澡人人爽人人夜夜| 人妻人人澡人人爽人人| 国产免费福利视频在线观看| 亚洲国产看品久久| 亚洲免费av在线视频| 天天影视国产精品| 欧美中文综合在线视频| 日韩av不卡免费在线播放| 老司机影院成人| 又大又爽又粗| 国产精品久久久久久精品古装| 亚洲欧洲日产国产| 美女中出高潮动态图| av天堂久久9| 在线天堂中文资源库| 一区二区三区四区激情视频| 国产成人精品在线电影| 久久精品久久久久久久性| 99香蕉大伊视频| 亚洲精华国产精华液的使用体验| 欧美另类一区| 成年人免费黄色播放视频| 男人爽女人下面视频在线观看|