Otomotiv endüstrisinde iç ve dış panellerin üretiminde kullanılan arayer atomsuz (Interstitial–FreeSteel) çelikler, çok az miktarlarda karbon ve azot içermeleri nedeniyle pres altında şekillendirmeyeuygun çeliklerdir. Arayer atomsuz çeliklerde, şekillendirilebilme özelliğini olumsuz yönde etkileyenarayer atomlarının (C ve N), çelik üretim prosesi esnasında bileşimden kontrollü bir biçimde uzak- laştırılması Titanyum (Ti) ve/veya Niobyum (Nb) atomlarının C ve N atomları ile reaksiyona gire rek çökelti fazları oluşturması ile olmaktadır. Sıcak haddeleme prosesinde slab fırınında belli sıcak lığa kadar ısıtılarak çökeltilerin çözeltiye alınması sağlanır. Bu işlem nihai sıcak band dokusunu vetane büyüklüğünü belirleyici ilk prosestir. İkmal ve sarılma sıcaklıkları da arayer atomsuz çeliküretiminde önemli olan proses parametrelerdir. Her iki proses parametresi de çökelti ve tane bü yüklüğünü önemli ölçüde etkileyerek çeliğin nihai mekanik özellikleri üzerinde büyük oranda etkiliolmaktadır. Şekillendirilebilme özelliğinin önemli bir göstergesi olan r değerinin arttırılmasında enönemli parametre soğuk ezme oranıdır. Artan tavlama sıcaklığı tane büyüklüğünün artmasında etki li olmaktadır. Çelikhane prosesinden itibaren sıcak haddeleme ve soğuk haddeleme prosesleriarayer atomsuz çeliğin mekanik özellikleri üzerinde etkili olmaktadır. Endüstriyel ölçekte gerçekleş tirilen bu çalışmada, çelik kimyasal bileşiminde bulunan Ti ve Nb elementleri ile soğuk haddelemeve sürekli tavlama parametrelerinin optimizasyonu sonucunda mekanik özelliklerde oluşan değişim- ler irdelenmiştir. Yapılan çalışmaların sonucunda Ti+Nb elementleri içeren kompozisyonlarda,yüksek ezme oranları (%80) ve tavlama sıcaklıklarında (870°C) yüksek r değerleri elde edilmiştir.Otomotiv sektörünün önemli oranda kullandığı arayer atomsuz çeliklerin mekanik özelliklerindeiyileştirmeler sağlanarak endüstrinin kullanımına sunulmuştur.

Interstitial free steels (if steels) are very suitable ma terial for automotive industry and they are used forinner and outer body panel applications due to theirhigh formability properties. They have extremelyhigh formability characteristics under formingpresses. Interstitials damages formability character istics of steel. Elimination of interstitials (C and N)is achieved through careful control of the steelmak ing process by the addition of titanium and/or nio bium to react with carbon and nitrogen to form pre cipitates. In the hot rolling process, firstly, slabs areheated upto some temperature and those precipitatesare taken into solid solution. This process affectsgrain size and texture of hot rolled product. Theother important process parameters in hot rollingare; finishing temperature and coiling temperature.Both parameters mainly affect grain size and size ofthe precipitates in hot rolled coil.and thus mechani cal properties are affected. The most important pa rameter for formability is r value. And it is mainlyaffected by cold deformation.ratio. Also increasingannealing temperature increases grain size and re sults in higher formability. All the process parame ters through steelmaking to the cold rolling processaffects mechanical properties of interstitial freesteels and thus affects r value of interstitial freesteel. In this study, mechanical properties relatedwith steel chemical composition by optimizing Tita nium (Ti) and Niobium (Nb) contents and continuouscold rolling and annealing parameters were investi gated in industrial scale. As a result, the highest rvalues were obtained at 80 % cold deformation ratioand annealing at 870 C for steel with Ti+Nb alloy ing addition.In this study, experiments were done in industrialscale. Firstly, interstitial free steels containing tita nium and titanium+niobium were produced at steelshop. And then slabs produced at continuous castingmachines were hot rolled After hot rolling process,those coils were sent to cold mill for cold rolling andannealing process. Also some coils were sent to gal vanising line after cold deformation. Each processare controlled by high level process computers inErdemir plants. Therefore process parameters fortrial coils are taken from this computer results.Chemical analysis of heats were done at steel shopchemical laboratories and they were produced ac cording to instructions given by metallurgical de partment. Mechanical test samples were taken aftercontinuous annealing line and continuous galvanis ing line processes. Mechanical properties includingyield strength, tensile strength, and elongation atfracture strain hardening exponent and anisotropycoefficient were determined by mechanical tensiletests. Tensile specimens were cut along rolling di rection, transverse direction and 45° to the rollingdirection. Samples were taken from the middlesection of each coil. Tests were done on Zwick Z-100testing machine. All tests were made at a strain ratioof 2 % Lo/min. The tensile test samples were proc essed according to DIN EN 10002-1 type 2 stan dards.The effect of process parameters on mechani cal properties were investigated according to theseresults. Optical microscopy was used for the micro structural examinations and grain size measure ments of the samples. Microstructural examinationswere conducted on the cross sections perpendicularto the rolling direction. Microstructures of materialsincluding ferrite grain size, carbide type and distri butions were investigated with a leco 500 opticalmicroscope. Also scanning electron microscopy wasused for the determination of the microstructure andcarbide distribution of the samples. The scanningelectron microscope was a jeol 5600 jsm type ma chine. As a result of microstructure analysis effect ofprocess parameters on microstructures analysed. Inthis study, texture analysis was conducted with arigaku d-max ultima x-ray diffractometer with a polefigure attachment. Test samples were prepared fromannealed samples, punched to a 4mm diameter andthen metallographically prepared.The next step was data collection from an x-ray dif fractometer. The xrd measurements of samples werecarried out in the range of 20-90 2teta degrees with0.02 steps. Then pole figure measurements weredone with different alfa and beta angles in 110, 111and 200 diffraction lines. As a result of that study,the best composition of interstitial free steel contain ing titanium and niobium were determined by opti mization of titanium and niobium content. Also thebest process parameters at the cold mill determinedthrough analysis of results taken from mechancaltests and microstructure analysis in which the high est r value obtained. And interstitial free steel pro duced after that study put into use for the automotivemarket as a new quality of steel.