Original Article

Pilot production and evaluation of mechanical, corrosion, and metallurgical properties of stainless steel-clad rebars

¹ Computational and Experimental Materials Innovation Group (CEMIG), Department of Metallurgical Engineering, NED University of Engineering and Technology, Karachi, Pakistan
² Amreli Steels Limited, Karachi, Pakistan

^* e-mail: m.siddiqui@cloud.neduet.edu.pk

Received: 9 October 2024
Accepted: 3 March 2025

Abstract

This study thoroughly assesses the mechanical, corrosion, and metallurgical properties of stainless steel-clad rebars for their potential in enhancing construction materials. Using the solid-liquid casting technique, Amreli Steels Limited in Pakistan pilot-produced Austenitic Stainless Steel (ASS)/Carbon Steel (CS) clad rebars. Molten Grade 60 carbon steel (ASTM 615) was cast into red-hot austenitic stainless steel pipes (AISI 316L) both vertically and horizontally. Horizontally cast samples showed significantly improved bonding between stainless steel cladding and carbon steel core after hot-rolling at 1120 °C. While tensile properties generally met ASTM 615M yield strength criteria, they slightly deviated in ultimate tensile strength and percent elongation. Microstructural analysis revealed an austenite phase on the surface side and pearlite/ferrite in the core, yet inherent defects like microcracks and pinholes compromised mechanical performance. Surface hardness measured commendably at 24.6 HRC, declining notably deeper into the rebar. The core region had a hardness of 11.5 HRC, while the interface between stainless steel (SS) layer and core recorded 7.2 HRC. Electrochemical analysis indicated a lower corrosion rate of 0.8 mm/year in SS-clad rebar compared to Grade 60 steel’s 1.20 mm/year, highlighting enhanced corrosion resistance in 3.5% NaCl solution. Additionally, SS-clad rebars exhibited a two-time constant feature [R(Q(R(QR)))] similar to AISI 316L SS, contrasting with Grade 60 steel’s single time constant [R(QR)], suggesting a bi-layer characteristic (inner barrier oxide layer and outer hydroxide layer) in SS-clad Grade 60. Polarization resistance of the barrier layer and capacitance measured 35.07 Ω cm² and 18.9 mF cm⁻², respectively, underscoring favorable passive film properties. This investigation provides crucial insights for optimizing construction materials and addressing corrosion-induced deterioration.