Microstructural Modification and Tensile Behavior of IF Steel Processed through Surface Mechanical Attrition Treatment
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https://doi.org/10.1007/s11837-020-04400-4 2020 The Minerals, Metals & Materials Society
ADVANCES IN SURFACE ENGINEERING
Microstructural Modification and Tensile Behavior of IF Steel Processed through Surface Mechanical Attrition Treatment YAGNESH SHADANGI and VAKIL SINGH1
,1,2,3 KAUSIK CHATTOPADHYAY,1
1.—Department of Metallurgical Engineering, Indian Institute of Technology (BHU), Varanasi, Varanasi, Uttar Pradesh 221005, India. 2.—e-mail: [email protected]. 3.—e-mail: [email protected]
The present investigation deals with the impact of surface mechanical attrition treatment (SMAT) on the surface roughness, microstructure, phase stability, hardness, and tensile properties of interstitial-free (IF) steel. SMATed IF steel was characterized by visible-light microscopy, x-ray diffraction analysis, scanning electron microscopy and transmission electron microscopy, and microindentation and tensile testing. The grain refinement and strengthening of the IF steel were found to be dependent on the duration of SMAT. The optimal combination of strength and elongation was observed in the IF steel SMATed for 200 s, showing a microhardness gradient up to a depth of 900 lm and peak surface hardness of 2.6 GPa. The 0.2% yield strength of the IF steel was increased by 125% with an appreciable elongation ( 44%) almost comparable to that of the untreated material. Furthermore, IF steel SMATed for 200 s followed by stress relief at 300C and 500C was found to exhibit thermally stable gradient microstructures with good strength and ductility.
INTRODUCTION Interstitial-free (IF) steel has found broad applications in the automotive sector for fabricating body panels. The high formability and nonaging behavior make it advantageous due to its easy drawability into complex shapes.1 To reduce the carbon footprint of vehicles, a material with high strength-toweight ratio for better fuel efficiency and to fulfil safety norms is desired. Many of the commercially available grades of steel [i.e., dual phase and highstrength low-allow (HSLA)] used in the automotive sector show high strength but lack formability. The strength of IF steel may be enhanced by either alloying or mechanical working. Precipitation hardening with Cu,2–4 nitriding with potassium nitrate salt,5 and strengthening with P6,7 and B8 are efficient methods for enhancing the strength of IF steel. Apart from precipitation strengthening of IF steels, attempts have been made to strengthen this steel by cold working and applying various severe
(Received June 15, 2020; accepted September 22, 2020)
plastic deformation (SPD) techniques such as accumulative roll bonding (ARB), equal-channel angular pressing (ECAP), surface mechanical grinding treatment (SMGT), high-pressure torsion (HPT), laser shock peening (LSP), surface mechanical attrition treatment (SMAT), etc.8–26 IF steel cold rolled to 90%, 95%, 98%, and 98.5% reduction in thickness showed peak hardness of 1.46 GPa, 1.62 GPa, 1.85 GPa, and 3.13 GPa, respectively.8 Several investigations have been
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