@article { author = {Mostafapour, A. and Ebrahimpour, A.}, title = {The Effect of Two-stage Heat Treatment Temperatures on Initial and FSSWed Properties of TRIP Steels}, journal = {International Journal of Iron & Steel Society of Iran}, volume = {14}, number = {1}, pages = {1-9}, year = {2017}, publisher = {Iron & Steel Society of Iran}, issn = {2981-0388}, eissn = {2981-0396}, doi = {}, abstract = {In this paper, a 0.2 C–1.6 Mn–1.5 Si wt. % TRIP-aided cold-rolled steel sheet was fabricated and the optimal heat treatment conditions (Intercritical Annealing “IA” and Bainitic Isothermal Transformation “BIT”) were investigated to maximize the volume fraction and stability of the retained austenite. The effects of temperature on IA (770, 790 and 810 ºC) and BIT (330, 350 and 370 ºC) were studied via optical microscopy, SEM and XRD. Its tensile properties and formability were also evaluated. It is obtained that under conditions of 790 ºC /330 ºC and 770 ºC /350 ºC, the maximum and minimum amounts of the retained austenite resulted in a microstructure. Also,  for the case which heat treated under 790 ºC /330 ºC condition obtained the best formability by showing the highest elongation ( more than 40%) and the case that heat treated under 810 ºC /350 ºC condition  had the highest tensile strength (more than 800 MPa). The cases with the maximum (12.1 %) and minimum (8.1 %) volume fraction of the retained austenite were chosen to investigate the effect of initial microstructure on weldability of TRIP steels. Therefore these cases were joined by friction stir spot welding process under the same welding parameters. According to the microstructural observations, four different zones determined in the welding region: stir zone, thermomechanically affected zone and high and low temperature heat affected zones. It is obtained that the steel with higher amount of the retained austenite in initial microstructure shows better mechanical properties before and after FSSW process because of higher amount of the retained austenite which causes TRIP effect.  }, keywords = {TRIP steel,Friction stir spot welding,Heat treatment,Retained austenite,Microstructure}, title_fa = {The Effect of Two-stage Heat Treatment Temperatures on Initial and FSSWed Properties of TRIP Steels}, abstract_fa = {}, keywords_fa = {}, url = {https://journal.issiran.com/article_26179.html}, eprint = {https://journal.issiran.com/article_26179_8a6f3b00fcb61ff264033cf759a543b8.pdf} } @article { author = {Valaee, M. and Sheikhi, Mohsen and Mazaheri, Y. and Usefifar, G.R.}, title = {Resistance Spot Welding of Steels: Modeling and Simulation}, journal = {International Journal of Iron & Steel Society of Iran}, volume = {14}, number = {1}, pages = {10-16}, year = {2017}, publisher = {Iron & Steel Society of Iran}, issn = {2981-0388}, eissn = {2981-0396}, doi = {}, abstract = {Resistance spot welding (RSW) includes many variables that can influence the weld properties. The purpose of this study is to develop an analytical model for prediction of thermal history and weld microstructure in RSW and to find the most important process parameters that influence the weld microstructure. A one dimensional model is proposed for prediction about thermal history during cooling step of RSW process. The reliability of analytical model is evaluated by experiments and numerical simulations. The calculations reveal that the current analytical model is reliable particularly at the temperatures lower than Tm/2. Sheet surface temperature at electrode-sheet interface and sheet thickness are recognized as the most important factors affecting the cooling rate at T