ENHANCING MECHANICAL PROPERTIES OF INTERSTITIAL FREE STEEL BY VARIOUS HEAT TREATMENT PROCESSES

ENHANCING MECHANICAL PROPERTIES OF INTERSTITIAL FREE STEEL BY VARIOUS HEAT TREATMENT PROCESSES

MRINMOY SINHA14921006Ph.D RESEARCH SCHOLARDEPT. OF METTALURGICAL AND MATERIALS ENGG.

SUPERVISOR: Dr. SADHAN GHOSH

BRIEF OUTLINEOBJECTIVE: To increase the mechanical properties i.e. Strength, Toughness and Hardness with less changes in Ductility/Formability by various heat treatment processes on IF Steel.

LITERATURE SURVEY

EXPERIMENTAL: High temperature simulation.Thermo-Calc simulation.RESULTS: Experimental AnalysisMicroscopic observation.Grain size calculation. MOTIVATION OF THE WORKKEY FEATURES: INTERSTITIAL FREE (IF) STEELSContains less amount of interstitial elements (C30 ppm & N40 ppm)No yield point phenomenon.Ductile & soft.Excellent deep drawability.APPLICATIONS:Automobile car body due to superior formability.White goods industry (TV, Fridge etc).BASIC REQUIREMENTS:To enhance mechanical properties i.e. Strength and Hardness.Grain refinement by heat treatment.Microstructural analysis of grains and phases.

PROCESSING OF STEELS

*For IF Steels:Typically TS360 Mpa & YS200 MPa.

* HSLA and Ultra low carbon steels, Panya Buahombura, School of Metallurgical Engg., Suranaree University of TechnologyOVERVIEW OF IF STEEL

* Materials Science and Metallurgy, 4th ed,. Pollack, Prentice-Hall, 1998.Ultra low carbon content.C0.005%Low Hardness and Tensile Strength.Superior formability and high deep drawability.Dominance of Ferrite grains in microstructural content.

Relationship between carbon content, microstructure and mechanical properties of plain carbon steels in normalized condition. Typical uses of these steels are also included.LITERATURE REPORT TO INCREASE STRENGTHGRAIN REFINEMENT: Strength can be increased but temporal.

After recrystallization annealing post deformation, strength starts falling due to very high cold stored energy in the steel matrix. * Fukuda et al., Japan society of tech., vol.13 (1972) 841.LITERATURE REPORT TO INCREASE STRENGTHSOLID SOLUTION STRENGTHENING: Not much effective by Mn, Si additions as it deteriorates galvanizing properties and painting.* Tither et al., Iron and Steel Institute of Japan, Tokyo, 1994, pp. 293-324.

P - Plastic strain ratio and yield stress increases but it causes cold work embrittlement

Si - Forms SiO2 on the surface that have a detrimental effect on coating adhesion

Mn - Reduces both plastic strain ratio and elongation.

LITERATURE REPORT TO INCREASE STRENGTHPRECIPITATION STRENGTHENING: Cu, Ti & Nb addition and subsequent ageing treatment.Gladman et al., Proc. Conf. Microalloying75, Ed. Korchynsky, M., Union Carbide, New York, 1977.R.Rana et.al., Age hardening analysis of a hot rolled copper-alloyed interstitial free steel, Materials Letters, in press online 2007.

Process is not commercially viable as addition of Cu (low melting point) in molten steel causes evaporation.Maintaining coherent size precipitate is difficult during ageing treatment of industrial processing.

LITERATURE REPORT TO INCREASE STRENGTHTRANSFORMATION STRENGTHENING: Formation of fine equiaxed grains by transformation mechanism associated with austenite Ferrite transformation. As-cast sampleIsothermal holding at 900C for 3 min(1) Annealing(2) Normalizing(3) Water quenching(3)(2)(1)

Length (15 mm) x dia (10 mm) Heat Treatment in Gleeble 3800 Different heat treatment methods lead to formation of various microstructures like ferrite, bainite and martensite which have unique mechanical properties.Grain size can also be affected by changing the soaking time at high temperatures.

THERMO-CALC SIMULATION

at 900 0C:Volume fraction of: - 0.09% - 0.91%

Evaluating the heat treatment parameters using Thermo-Calc SGTE database results helps in approximating the test conditions.Optimum condition: Fine austenite grain size around 900C with reducing isothermal holding time seems to enhance the mechanical properties.THERMAL ANALYSIS DSC

Thermo-Calc data is validated with DSC plot.OPTICAL MICROSCOPY ANALYSISAS-RECEIVED SAMPLE MICROSTRUCTURE ANALYSIS: Grain size: 115.86 m (Calculated by linear intercept method).High ductility due to larger ferrite grainHardness: 89.38 VHN (HV10)

Optical microstructure of as-received sample, reportedly ferrite grain at room temperature. HARDNESS VARIATION AFTER HEAT TREATMENTHardness is double in water quenched samples. HV10 (VHN)SUMMARYIn literature it shows that strength increases, but at the cost of ductility.Heat treatment is done to increase the strength and hardness, and to reduce the cost.Grain refinement and microstructural evolution found during heat treatment.Hardness value was doubled in water quenched sample.

FUTURE SCOPE OF WORKUnderstanding this work at higher temperature (930C), whether ferrite completely transforms into austenite.Transmission electron microscopy (TEM) to distinguish passible bainite or martensite phases.Stress vs strain plot before and after transformation.Fracture analysis.

REFERENCESS.J Shankar, Materials for automobiles (2011).R Rana, W Bleck, S. B. Singh, O. N. Mohanty, Mater. Lett. 61 (2007) 2919. G Tither , C.I. Garcia, M Hua, A.J. DeArdo, in Proceedine of the International Forum for Phvsical Metallurw of IF Steels, Iron and Steel Institute of Japan, Tokyo, Japan, 1994, pp. 293-324. J. W. Lee, H. M. Baek, S. K. Hwang, Materials & Design 55 (2014) P. 898-904.Cao et. al, J. Mater. Sci. 46 (2011) 6203.K Banerjee, Physical Metallurgy and Drawability of Extra Deep Drawing and Interstitial Free Steels, Recrystallization, (2012), Prof. Krzysztof Sztwiertnia (Ed.), ISBN: 978-953-51-0122-2, InTech.W.F Hosford & W.A Backholen (1964). Fundamentals of deformation processing, Syracuse, Press, New York. P. 259.W.T Lankford, S.C Snyder & J.A Bauscher (1950). Trans.AS1/I, Vol. 42, P.1197-1232.

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