2 results listed
Advanced High Strength Steels (AHSS) grades are currently the fastest growing materials in the
automotive industry. AHSS offer a great potential for the development of automobile bodies with their
mechanical properties of high formability and strength. Dual phase (DP) steels are increasingly
popular AHSS grade in the automotive industry due to the excellent combination of high strength
and good formability. The intercritical annealing of DP steel is generally two-stage heat treatment.
DP steel sheet is annealed in the intercritical temperature range to produce ferrite and
austenite and followed by accelerated cooling to transform the austenite phase to martensite. This
study aims to examine effect of a cyclic intercritical annealing below and above A1 temperature on
DP steel microstructure with comparison to the conventional intercritical annealing. The
specimens were conventional intercritically annealed at different temperatures between 720 °C and
760°C. In cyclic intercritical annealing experiments, the temperature is cycled between 630 °C and an
intercritical annealing temperature without any isothermal holding. After the conventional and
cyclic intercritical annealing, the samples were investigated using light microscope and scanning
electron microscope. Experimental results showed that a refinement of martensite and ferrite dual phase
microstructure compare to conventional intercritical annealing.
International Iron & Steel Symposium
UDCS
Ayşe Kavruk
Oğuz Gürkan Bilir
Özge Ararat
Ahmet Efe Gezmişoğlu
Influence of different austenitization conditions on retained austenite quantity and composition investigated
on SAE 52100 steel. SAE 52100 steels are being widely used as bearing component regarding to their
hardness and wear resistance. Traditional production cycle includes hot rolling, spheroidization, cold rolling,
quenching from two phase region and tempering steps. This cycle results with martensitic matrix and
undissolved course carbides. Course carbides maintain adequate wear performance but due to course
carbides providing appropriate nucleation sites for crack propagation and growth this structure shows poor
fatigue behavior. Previous studies showed better carbide size and distribution with experimental two step
hardening cycle. This cycle results with considerable increase at retained austenite fraction. It’s well known
that mechanically unstable retained austenite improves fatigue resistance in this type of steel.
Transformation retained austenite to martensite caused by deformation eliminates local stresses and retards
crack propagation and growth. XRD studies are carried on to determining retained austenite quantity with
various austenitizing conditions. Computational simulations with Thermo-Calc and Dictra are used for
predicting carbon concentration gradient of austenite during austenitization which determines retained
austenite fraction at the end. A good correlation between XRD data and simulation results was obtained.
International Iron & Steel Symposium
UDCS
Ersoy Erişir
Oğuz Gürkan Bilir
Ahmet Efe Gezmişoğlu