1. Material Analysis of Thermo-Mechanically Treated Steel and Re-bar
Shree Bubesh Kumaar Sridhar and Dr. Lesley Frame
University of Bridgeport, Bridgeport, CT.
Introduction:
This is an industrial driven pilot research project composing an experiment conducting material analysis on steel re-bars. It is focused mainly on the material composition of the steel for various grades available in the market provided by our suppliers. Material analysis is carried out on the samples by standard metallurgical methods of investigation to find the variability in the composition of the material due to the presence of residual elements such as Ti, Nb, V, Cr, B, Sn, Cu, Ni, Al, N introduced unintentionally by the recycled content of steel scrap, thereby bringing out the significant of this project that how material composition affects the manufacturing processes and functionality of the product in the future.
Background Study:
Steel is one of the most widely used metal in the world for various constructional and manufacturing purposes. It is widely recognized and accepted due to its enormous strength and durability. Steel is manufactured by traditional blast furnace, basic oxygen furnace or by an electric arc furnace. It is an alloy of iron and carbon. Steel can be recycled numerous times as we can reduce waste generation and additional mining. During manufacturing processes of the steel, elements such as copper, tin, lead, zinc, bismuth, antimony, arsenic, nickel, chromium and molybdenum are added unintentionally due to the presence of the steel scrap, which changes the chemical composition of the material and accounts for changes in the properties, characteristics and performance of the produced product.
Thermo-mechanically treated bars known as the TMT bars or rebars, are being used for building and bridge constructional purposes along with concrete. They are manufactured from different forms of steel as raw material through a series of heat treatment, casting and rolling processes. After the series of quenching, tempering, and air cooling processes, the steel bars get the hard-outer surface and soft inner area enabling high strength. high ductility, and regain toughness characteristics. These bars are known for their corrosion, and earthquake resistance. They are manufactured to requirements that vary in length, diameter, grades of strength, mechanical and chemical properties. Ref. [1-5].
Hot Rolled Steel Re-Bar
Ref. [2]
Material Analysis:
Sectioned specimens from the sample steel rebars obtained from our Supplier 1 and 2, is cold mounted with epoxy resin, grinded to obtain flat surface, polished with diamond abrasives to 1 micron finish, and etched with 4% Nital for twenty seconds to reveal microstructural features and observed the samples at high magnifications through microscope. Grain sizes were measured using ASTM E112 Line Intercept Method and Hardness of the sample specimen were measured with Wilson Rockwell Hardness Tester on C scale. Ref. [6,7]. Our samples 1006B, 10B21 were hot rolled and their general compositional steel chemistry are as follows. Ref [8].
Manufacturing of Thermo-Mechanically Treated Steel Products
Preliminary Conclusions:
From the initial result values obtained, it is observed that there is a difference of 1.25 in the grain size and 4.5 in the hardness number for the same grades of steel from different suppliers. This difference will play a key role in affecting the manufacturing processes of the steel during scrap recycling and will eventually affect the performance of the steel or the product in the near future which is caused by the steel chemistry. Future work includes chemical analysis of steel, examination of additional samples, comparison of processing methods and higher magnification analysis of the microstructure.
Results:
After several polishing and etching, material analysis was conducted using standard metallographic investigation method, the grain sizes were measured using the ASTM E112 Line Intercept Method by using the photoshop tool. Intial results that were obtained are as follows. b a
Micrographs of etched versions of samples 0001 (a), 0002 (b), 0003 (c) and 0004 (d) can be found. c d
Acknowledgements:
Thank you to Supplier 1 & Supplier 2 for providing samples, CBRC Laboratory – University of Bridgeport for research facilities.
Author Contact:
References:
[1] GPH ispat ltd. (2017). PRODUCTION PROCESS. Retrieved October 10, 2017 from
[2] Khatu TMT. (2015). Home. [Image file]. Retrieved Nov 17, 2017 from
[3] KAMDHENU GROUP. (2017). TMT BARS. Retrieved October 10, 2017 from
[4] Isteel Forever. (2015, September 26). Isteel TMT Making process Video [Video file]. Retrieved October 10, 2017 from
[5] SHREE SIDHBALI INDUSTRIES LIMITED. (2014). TMT MANUFACTURING PROCESS. Retrieved October 10, 2017 from
[6] Kay Geels, Daniel B. Flower, Wolf Ulrich Kopp, and Michael Ruckert. (2013). Metallographic and Materialographic Specimen Preparation, Light Microscopy, Image Analysis and Hardness Testing. (
[7] George F. Vander Voort. (2007). Metallography: Principles and Practice. (
[8] Material composition. Retrieved April 2, 2018 from