مدل سازي رفتار سيلان فولادهاي دوفازي با كسر حجمي متفاوت مارتنزيت توسط روش المان محدود

Modelling the flow behaviour of dual-phase steels with different martensite volume fractions by finite element method

فولادهاي دو فازي داراي ميكروساختاري متشكل از جزاير مارتنزيتي احاطه شده توسط فريت مي باشند. رفتار مكانيكي فولادهاي دو فازي شديدا وابسته به ميكروساختار مي باشد.لذا در نظر گرفتن پارامترهاي ميكروساختار جهت شبيه سازي رفتار سيلان بسيار مهم مي باشد. در اين پژوهش منحني سيلان فولادهاي دو فازي كم كربن با درصد حجمي مارتنزيت 27 و 52 درصد توسط روش المان محدود شبيه سازي مي شود. طبق مشاهدات ميكروسكوپي ميكروساختار جزاير مارتنزيتي در اين مدل سازي بصورت كروي در نظر گرفته شدند. منحني هاي سيلان حاصل از شبيه سازي داراي مطابقت خوبي با نتايج آزمايشگاه مي باشد. همچنين مشاهده شد كه نمونه حاوي درصد مارتنزيت بالا كه از مارتنزيت با كربن پايين برخوردار است داراي تغيير فرم پلاستيك در مارتنزيت مي باشد كه با نتايج حاصل از مشاهدات آزمايشگاه همخواني دارد.

Dual-phase (DP) steels have a composite-type microstructure consisting mainly of hard martensite islands embedded in a soft ferrite matrix. DP steels exhibit a characteristic combination of high strength, high work hardening rate and good ductility. Mechanical behaviour of DP steels is closely related to their microstructures. Hence, it is necessary to take into account their microstructural parameters in any attempt to estimate their flow behaviour. In this study, the flow curves of low carbon DP steels with 27 and 52% martensite produced by intercritical annealing processes at different temperatures were calculated using the finite element method (FEM). According to the results of microscopical observations of steel microstructures, martensite islands were assumed in the model to be spherical in shape. Moreover, in agreement with the experimental results in the literature clearly showing the possibility of martensite plastic deformation in similar steels during straining when its volume fraction is greater than about 30%, the plasticity of martensite islands in the steel microstructures was taken into account in the model by using their experimentally obtained stress-strain relations as a function of their estimated carbon contents. Having estimated the stress-strain behaviour of the ferrite phase in all steel samples using the microstructural parameters corresponding to the starting ferrite+pearlite steel, the flow curves of different DP steel samples with elastic martensite (in low martensite content steels) and elasto-plastic martensite (in high martensite content samples) were calculated. The calculated stress-strain curves exhibited reasonable agreements with the experimental stress-strain curves obtained from the tensile tests.