Effect of Austenite Conditioning on Martensitic Transformation in Commercial Grade Interstitial-Free Steel
- PDF / 7,588,420 Bytes
- 12 Pages / 593.972 x 792 pts Page_size
- 71 Downloads / 203 Views
TION
THE term interstitial-free (IF) steel refers to the fact that the steel contains interstitial elements carbon (C £ 30 ppm) and nitrogen (N £ 40 ppm) in a trace amount, resulting in high elongation, high plastic strain ratio (r-value) and good formability for deep drawing applications.[1,2] The steel has a wide range of applications in automotives, beverage cans, refrigerator enclosure, enamel wares, household appliances etc.[3–5] The liquid steel is processed to reduce C and N to a low level; later, the remainders are scavenged by Ti and Nb through the micro-alloy addition. Thus, the ability of the interstitial components to improve the strength of the steel is low. Authors from time to time have intended to address the issue via grain refining, bake hardening, solid solution strengthening, precipitation hardening, etc.[1] In spite of that, the strengthening remains a key issue in the current perspective. Knowing the fact that this steel is fully ferritic at room temperature,
M. SINHA, A. KARMAKAR, and S. GHOSH are with the Metallurgical and Materials Engineering, Indian Institute of Technology Roorkee, Roorkee, Uttarakhand 247 667, India. Contact e-mail: [email protected] B. SYED is with the R&D Division, TATA Steel, Jamshedpur, Jharkhand 831 001, India. Manuscript submitted 13 October 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS A
incorporating a harder phase-like martensite, a choice to translate this metal alloy into a structural steel. Hot deformation is a regular practice in steel industries. Without rolling and stamping in the hot stages, finishing the end products of steels is difficult. The process involves mechanical deformation and phase transformations simultaneously. Nikravesh et al.[6] have reported that the hot plastic deformation by 0.5 compressive strain hinders the martensitic transformation at lower cooling rates in 22MnB5 boron steel. In the comparison, Abbasi et al.[7] have obtained a fully martensitic structure by isothermal compression at the deformation temperature of 900 C with the strain of 0.5 in the same steel by water quenching. Wang et al.[8] have reported that martensitic transformation is difficult in the dynamically recrystallized austenite grains, as it accumulates a high density of crystal defects and grain refinement in the steel. The statically recrystallized grains exert resistance to the martensite formation, until they grow into large sizes. Further work suggests that hot deformed austenite promotes proeutectoid ferrite and pearlite in a Mn-Cr gear steel.[9] Increasing the amount of plastic deformation obstructs austenite to bainite transformation, thereby a gradual increase of the martensite/austenite constituent. Thus, various austenite states can produce a variety of microstructures. In the commercial IF steel, such effort is rare, until in the present work.
Martensitic transformation in deformed austenite includes mechanical deformation and cooling conditions. To invigorate them clearly, two sets of experiments are planned herewith. In the first of its kind, austenit
Data Loading...
