Classification of Hot-Rolled Plates Using the Mahalanobis Distance of NMIs in Ti-Stabilized Austenitic Stainless-Steel Produced by Secondary Metallurgy.

Franci Vode,Gorazd Kosec,Franc Tehovnik,Darja Steiner Petrovič

doi:10.3390/ma15020684

Franci Vode, Gorazd Kosec + Show 2 more

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https://doi.org/10.3390/ma15020684

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Abstract

Three charges of scrap-based, Ti-stabilized, Cr-Ni-Mo austenitic stainless steel in the form of hot-rolled steel plates were characterized. Based on automated metallographic analyses of representative microstructures, a quality characterization in terms of cleanliness of the hot-rolled steel plates was performed. Elevated contents of impurities, especially Pb, Bi, and oxygen, which affect the hot workability of stainless steels, were detected. The recycled FeTi-cored wire was the main source of the elevated levels of impurities detected in the hot-rolled, Ti-stabilized, stainless-steel plates. Related to this, elevated levels of nonmetallic inclusions (NMIs) and segregations were formed. The three charges were classified based on calculations of the Mahalanobis distance (MD) between the inclusions. The charge with the smallest number of nonmetallic inclusions was set as the reference class. The selection of outlier inclusions based on their MDs and their back-representation into ternary diagrams gave relevant metallurgical information about the abnormalities. The advantage of this technique is that the calculations of the MD and the threshold can be fully automated.

Highlights

The energy-intensive steel industry is responsible for approximately 25% of the global direct greenhouse-gas emissions [1,2]
The selection of outlier inclusions based on their Mahalanobis distance (MD) and their back-representation into ternary diagrams gave relevant metallurgical information about the abnormalities
The advantage of this technique is that the calculations of the MD and the threshold can be fully automated

Summary

Introduction

The energy-intensive steel industry is responsible for approximately 25% of the global direct greenhouse-gas emissions [1,2]. CE as a concept of sustainable competitiveness involves the valorization of steelmaking leftovers for internal reuse (i.e., dusts, slags, sludge), enhanced steel scrap recycling, the use of secondary carbon carriers from nonsteel sectors as a reducing agent, and energy sources in the steelmaking process chain, as well as various business models with comprehensive supply chain analyses [3]. As foreseen in the steel industry, electric arc furnace (EAF) steelmaking, either scrap-based or based on hydrogen-directreduced iron, will contribute substantially to the reduction of CO2 emissions [4]. There will still be a need to introduce carbon into the EAF process, either to carburize the steel or to create foaming slag to improve the energy efficiency of the steelmaking process. To develop a fully green steel using EAF, it will be necessary to use alternative carbon sources that are either renewable or circular (e.g., biomass, plastic, rubber wastes, etc.) [4]

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