SEARCH RESULT

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

Finer martensitic and ferritic microstructures are demanded to obtain high strength and toughness for dual phase steels. In this study, reducing of prior austenite grain size selected as an effective method to reduce the size of dual phase microstructure. The effect of prior austenite grain size on microstructure of medium carbon dual phase steel produced by intercritical annealing were investigated for different austenitizing conditions. Annealing experiments were performed to fully austenitizate the steel at different austenitizing temperatures (900, 950, 1000ᵒC) and times (5, 10, 15 min) and followed by quenching. Finally, as-quenched martensitic microstructures were intercritical annealed at 760ᵒC for 15 min to attain martensitic and ferritic dual phase steel. The microstructures were analyzed using light microscopy and image analysis methods. It is concluded that grain size of dual phase steel is reducing by decreasing of the austenitizing temperature and the holding time.

International Iron & Steel Symposium
UDCS

Ersoy Erişir Özge Ararat Oğuz Gürkan Bilir