ارزيابي ريز ساختار خواص فولاد ساده كربني رويه سختي شده با پوشش غني از بر

چكيده انگليسي :

Characterization and Microstructural Evaluation of Boride Rich Hardfaced Carbon Steel Mohammad Hassan Amushahi Forushani hassan1362@ma iut ac ir 13 April 2009 Department of Materials Engineering Isfahan University of Technology Isfahan 8415683111 IranDegree M Sc Language Farsi Supervisors F Ashrafizadeh M Shamanian ashrafif@cc iut ac ir shamanian@cc iut ac irAbstractIn recent years applying boride rich cored wires is growing in industry This is because of special propertiesproduced by coating these materials in surfacing The cored wires are applicable in different industriesespecially where corrosion and wear are important Hardfacing of low carbon steel using a boron rich coredwire alloy has been investigated Arc spraying and gas metal arc welding GMAW methods were used in orderto form a series of boride rich layers on the surface of low carbon steel Experimental samples were preparedand coating was carried out under various conditions Optical and electron microscopy hardness andmicrohardness testing XRD and pin on disk wear test were used to evaluate the microscopic structure surfaceroughness mechanical properties type of boride layers resistance and friction coefficient of boride layers respectively The results showed that the layer produced by arc spraying has a laminar type microstructureincluding iron borides Fe2B and probably FeB Fe oxide and voids The results of XRD showed that thereare sharp peaks for Fe Fe2B and FeB phases in the coating but by accurate comparison of the patterns it canbe seen that the more strong peaks belong to Fe2B Considering the diffraction patterns it can be said that thestructure consists of hard Fe2B layers low Fe eutectic content plus Fe2B and undesirable FeB phase Thebonding of coating layer to the substrate is mechanical Structure of the GMAW layer consists mainly Fe2Bprimary borides and probably FeB among a eutectic of borides and Fe XRD pattern Showed that boridephases content will increase from the interface to the substrate surface The bonding between coating layer andthe substrate is of metallurgical type Boride composition in arc sprayed layers caused an increase inmicrohardness up to of 2300 Vickers and values of 1500 Vickers in GMAW deposits Considering the wearpath wear particles and surface of the pins by electron microscopy and EDS it was observed that the mainwear type was sliding wear Oxidation plastic deformation and lamination mechanisms took place in weartesting Boride layers formation caused a considerable increase in wear resistance and a decrease in frictioncoefficient Cooperation of the results indicated that the wear resistance in arc sprayed layers was higher thanGMAW layers This difference in the wear rates is explained in terms of the much higher hardness of the boridesand the different wear mechanisms In particular the transition from mild to sever wears mechanism occurringin steel suppressed in the case of the borided coatings due to their higher load bearing capacity In the case ofthe plain steel used as a substrate the dominating mechanism is plastic deformation ploughing associated tocracking and delamination at the highest load while in the case of the boride coating delamination mainly of theeutectic takes place throughout the entire load range Apart from a global lowering of the wear rate to the effectof increased hardness the rich boride coating modifies profoundly the wear mild to sever wear occurring in thebare steel This is achieved because the hard and strong borides support efficiently the applied load withoutbreaking Using the arc spayed layer at moderate temperature showed that this layer is stable to 550 C andmaintains its mechanical properties Key Words Alpha 1800 Arc spray GMAW Microhardness XRD Wear

عموشاهي فروشاني، محمد حسن

ارزيابي ريز ساختار خواص فولاد ساده كربني رويه سختي شده با پوشش غني از بر

پاشش قوسي , جوشكاري قوسي فلز-گاز , XRD , سايش