A Novel Method to Measure Cleanliness in Steel Using Ultrasonic C-Scan Image Analysis

Abstract

The traditional method of measuring the cleanliness level of steel is to measure its total oxygen (TO), which does not provide information about the size, location, and distribution of more harmful macroinclusions. The present article highlights a novel method for cleanliness assessment in steel samples using ultrasonic C-scan image analysis. The method provides quick and large volume inspection and ability to catch macroinclusions that possess difficulty during further processing of the thin gage steel products, particularly for auto grades such as interstitial-free (IF) steel. This method deals with a multiscan, immersion ultrasonic system using high-frequency focused beam and image analysis software. A good correlation was found between ultrasonic parameter counts and TO in steel samples taken from tundish during the continuous casting of slab. The ultrasonic counts were also found to be correlated with some steelmaking parameters.

Inclusion characterisation – tool for measurement of steel cleanliness and process control: Part 1

“…Some common methods to estimate steel cleanliness are indirect methods that include total oxygen O T analysis, changes in slag composition or elemental fades/gains, clogging in submerged entry nozzles, and use of slag tracers. 1 Direct methods to evaluate steel cleanliness through inclusion characterisation in steel samples are techniques such as metallographic examination by scanning electron microscope (SEM) equipped with or without field emission gun, [2][3][4] laser techniques, 5,6 remelt button analysis technique, [7][8][9] optical emission spectrometry with pulse discrimination analysis (OES-PDA), [10][11][12] ultrasonic testing, [13][14][15] liquid metal cleanliness analyser, 16 electrolytic extraction, 17 confocal laser scanning microscope, 18,19 cathode luminescence microscope (CLM) 20 etc. Detailed reviews of steel cleanliness measurement techniques were presented by Zhang and Cai, 21 Zhang and Thomas, 22 Burty et al, 23 Jacobi and Wunnenberg 24 and Louis et al, 25 among others.…”

Discriminating pores from inclusions in rolled steel by ultrasonic echo analysis

“…Before Fourier transformation, the echo signal was four times zero padded and windowed from the zero-crossing points of the derivative of the echo envelope (calculated using the Hilbert transform) to minimize the effect of the grain structure-induced scattering. The analyzed frequency range was windowed to the ultrasonic transducer's −20 dB bandwidth (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20).…”

“…Ultrasonic non-destructive testing (NDT) employing an immersion pulse-echo setup is a potential method for flaw detection in steel [3,4]. The method provides an inclusion and pore count based on larger sampled volumes than the abovementioned common methods, thus potentially improving the quality control.…”

The Ultrasonic Detection of Macro-Inclusions in Steel

“…Metallographic examination can only observe the two-dimensional section of the inclusions [2]; electrolytic extraction could get the inclusions, but during this process, many inclusions are destroyed and lost [3]. MIDAS method often was used to analysis macro-inclusions in large volumes of steel; it was a good method to evaluate cleanliness levels of the steel [4,5].…”