ساخت و مشخصه يابي فولاد زنگ نزن آستنيتي پرنيتروژن Fe-Cr-Mn-Mo به روش آلياژ سازي مكانيكي و بررسي شرايط بهبود فاكتور PREN

چكيده انگليسي :

Production and Characterization of High Nitrogen Stainless Steel Fe Cr Mn Mo by Mechanical Alloying and Investigation of Conditions for Improving PREN Value Fariba Tehrani f tehrani@ma iut ac ir March 8 2010 Department of Materials Engineering Isfahan University of Technology Isfahan 84156 83111 IranDegree M Sc Language FarsiDr Mohammad Hasan Abbasi Prof Supervisor E mail Abbasi32@cc iut ac ir Dr Mohammad Ali Golozar Prof Supervisor E mail golozar@cc iut ac irAbstractNi free high nitrogen stainless steels have many applications especially in biomaterials due to properties suchas good mechanical properties excellent corrosion resistance particularly resistance to pitting corrosion crevice corrosion and intergranular corrosion and no allergical effects Pitting corrosion resistance isestimated by PREN value PREN wt Cr 3 3 wt Mo 16 wt N 1 wt Mn So that by increasingthe PREN value pitting corrosion resistance is enhanced For this reason the purpose of this research is toproduce nanostructured high nitrogen austenitic stainless steel Fe Cr Mn Mo by mechanical alloying MA and investigate the influential factors on improvement of PREN value For this purpose firstly the effect ofMo on to transformation was investigated Then the influence of particle size of iron powder on the rateof to transformation was evaluated Finally chemical composition was changed for increasing the PRENvalue For this purpose the amount of Mn was reduced and Mo content was increased MA was performed innitrogen atmosphere using a high energy planetary ball mill Microstructural and phase analysis of the milledpowders were carried out employing scanning electron microscopy SEM and X Ray diffraction XRD respectively The absorbed nitrogen contents were determined using nitrogen analyser equipment In order to investigate the effect of Mo Fe 18Cr 11Mn 4Mo and Fe 18Cr 11Mn 6Mo powder mixturesprepared from iron powder with mean particle size 47 34 m were milled under nitrogen atmosphere for100 hr It was observed that by increasing Mo content from 4 to 6 wt the d value was enhanced leadingto an enhancement of the phase transformation rate However increasing the Mo content led to the reductionof chemical potential for austenite stability Consequently completion of phase transformation required moreenergy and longer milling times In addition by decreasing particle size of initial iron powder increasinginitial surface area of iron powder particles not only absorbed nitrogen content increased more effectiveelement for improving the PREN value but also the rate of phase transformation significantly enhanced Asa result the necessary milling time for completion of to phase transformation was decreased from 100 to8 hr On the other hand increasing the rate of phase transformation prepared the possibility of reduction inMn content from 11 to 8 wt and also increase in Mo content from 4 to 8 wt The results obtained showedthat the PREN value could be increased from 35 36 to 55 6 due to the possibility of change in chemicalcomposition Finally the results of the heat treatment of the produced high nitrogen steel powder at 1100 Cafter 1 hr indicated that it has a high thermal stability because of the existence of nitrogen in grainboundaries So the variations of grain size were slight after annealing from 8 to 30 nm As a result grain structureremained nanometric Furthermore investigation of the amount of nitrogen showed that the amount ofnitrogen before and after annealing was nearly constant Keywords High nitrogen stainless steel Mechanical alloying PREN value Phase transformation Nanostructure

طهراني، فريبا السادات

ساخت و مشخصه يابي فولاد زنگ نزن آستنيتي پرنيتروژن Fe-Cr-Mn-Mo به روش آلياژ سازي مكانيكي و بررسي شرايط بهبود فاكتور PREN

استحاله فازي , نانو ساختار