Utilization of Waste Materials for the Manufacturing of Better-Quality Wear and Corrosion-Resistant Steels

Utilization of Waste Materials for the Manufacturing of Better-Quality Wear and Corrosion-Resistant Steels WEN HAO KAN, SIYU HUANG, ZIYAN MAN, WILSON HANDOKO, LI CHANG, FARSHID PAHLEVANI, KIM RASMUSSEN, and VEENA SAHAJWALLA Decarburization of steels during heat treatment is a major problem for wear applications and for thin structural components as it often results in poorer surface hardness, strength, and fatigue performance. Additionally, corrosion is a major problem in many engineering applications. To address these issues, this study introduces a novel low-cost surface treatment that utilizes raw materials obtained from automotive waste. This technique was applied on a high-carbon low-alloy martensitic steel that is commonly used in industrial applications for its hardness, strength, and low production cost. The reduction in decarburization led to improved abrasion performance, while the steel’s corrosion resistance was significantly improved through the formation of a thin ceramic layer across the steel’s surface. This treatment, therefore, not only offers a cost-effective solution to decarburization and corrosion, but it also promotes a more sustainable future. https://doi.org/10.1007/s11661-020-05686-4 Ó The Minerals, Metals & Materials Society and ASM International 2020 I. INTRODUCTION MARTENSITIC steels are very commonly used in structural applications due to their high strength, which include examples such as the automotive industry where martensitic advanced high-strength steels are used for lightweight design without sacrificing strength,[1] the oil and gas industry where martensitic stainless steels are favored for both strength and corrosion resistance,[2] and also in many high-wear applications due to their superior hardness such as for bearings[3] and tools.[4] Many of these alloys achieve their remarkable mechanical properties, and in the case of martensitic stainless WEN HAO KAN is with the Australian Centre for Microscopy & Microanalysis, The University of Sydney, Sydney, NSW 2006, Australia and also with the School of Aerospace, Mechanical and Mechatronic Engineering, The University of Sydney, Sydney, NSW 2006, Australia. Contact e-mail: SIYU HUANG, ZIYAN MAN and LI CHANG are with the School of Aerospace, Mechanical and Mechatronic Engineering, The University of Sydney. WILSON HANDOKO, FARSHID PAHLEVANI and VEENA SAHAJWALLA are with the Centre for Sustainable Materials Research and Technology (SMaRT Centre), School of Materials Science and Engineering, University of New South Wales, Sydney, NSW 2052, Australia. KIM RASMUSSEN is with the School of Civil Engineering, The University of Sydney, Sydney, NSW 2006, Australia. Wen Hao Kan and Siyu Huang have contributed equally to this work. Manuscript submitted July 10, 2019. METALLURGICAL AND MATERIALS TRANSACTIONS A steels, corrosion resistance, through high alloying contents, but this, however, drives up the cost of production. Another problem often encountered in the manufacturing of martensitic steel components is decarburization during the austenizing heat treatment process since carbon from the steel’s surface readily reacts with ambient oxygen at this temperature range.[5,6] Due to the adverse effect that this has on a number of mechanical properties such as hardness, wear resistance, fatigue performance, and strength,[5,7,8] there are specifications that dictate the allowable limits of decarburization. In an industrial context, accurate measurements of decarburization depth[5,7,8] and methods employed to control decarburization, such as the use of a protective gas (though this only reduces but cannot eliminate it entirely[9]), often increase the cost of production. A recent technology developed by Pahlevani et al.[10,11] not only offers a possible cost-effective approach to the manufacturing of higher-quality steel by solving the decarburization problem, but it also attempts to provide a solution to global waste management by utilizing resources from waste materials to do so. Automotive waste, for instance, is a good source of useful alloying elements such as N, C, Al, Ti, and Si. Thus, by heat treating steel with automotive waste, Pahlevani et al. demonstrated that it is possible for a steel to be fabricated with a thin ceramic surface layer instead of a decarburized layer.[11] Furthermore, it is well known that ceramic coatings on a steel substrate can improve corrosion resistance,[12,13] and therefore, this approach also has the potential to offer adequate corrosion protection to the steel without the need for high alloying contents.[14] Handoko et al. has also shown that by thermally treating a steel with automotive waste and slag (both being waste products that typically end up in landfills), decomposed C in the automotive waste reacts with the O in the oxide phases in the slag to form CO and CO2, thus allowing other elements to form various ceramic phases on the steel’s surface.[14,15] Therefore, this study explores the possibility of using this novel automotive waste- and slag waste-treatment process to minimize the decarburization of carbon steels and also to form a thin ceramic layer to improve both surface abrasion resistance and surface corrosion resistance. II. MATERIALS AND METHODS A high-carbon low-alloy steel with a nominal composition shown in Table I was used as the substrate for this study to highlight the potential of the proposed novel treatment process on low-cost steels. Prior to any treatment process, the steel was first cut into multiple samples with the geometry and dimensions specifically designed for the abrasion testing rig as shown in Figure 1. The waste raw materials used for the treatment process are mixtures of steel-making slag and automotive shredder residue (ASR). The composition of the slag measured using X-ray fluorescence spectroscopy (XRF) is shown in Table II. Two different ratios of slag to ASR were explored, one with a ratio of 1:1 and another with a ratio of 1:3. As for the as-received ASR, ferrous and non-ferrous metals were first removed using magnetic and eddy current separation which resulted in the remaining ASR being composed mostly of plastics. The details of the as-received ASR, alongside its thermal degradation kinetics, can be found here[16] and the composition of the ASR is also shown here in Table III. As shown in the table, in addition to plastics such as polypropylene and polyethylene, the ASR also contains some amount of free carbon. Prior to the thermal treatment process, the waste mixtures were ground into powder using a cryogenic mill. The thermal treatment process involved submerging the steel samples into the waste mixtures, heat treating at a temperature of 1000 °C for up to 4 hours with a constant flow of argon to minimize decarburization, and finally with a water quench. There is also a filtration system in place for harmful gases that escape the ASR from this process. For simplicity, we will herein refer to the steel that is treated wit (...truncated)