The application of electromagnetic measurements for the assessment of skin passed steel samples

This paper begins by exploring the relationship between magnetic properties such as coercive field, RMS Magnetic Barkhausen Noise (MBN), initial and differential permeability and percentage elongation of skin passed samples for three different steels; interstitial free, micro alloyed and dual phase. A closed magnetic loop system is used to measure the fundamental magnetisation properties and a system based on an impedance analyser and a cylindrical coil is used to determine low field differential permeability. The results show that coercive field increases consistently with increasing percentage elongation for all three steels, as increasing material hardness causes an increase in magnetic hardness and a corresponding increase in coercive field. This effect levels off at higher values as dislocation density saturates. As would be expected, the inverse trend is observed for differential permeability. Similar results are also reported for MBN and initial and low field differential permeability measurements for the interstitial free and dual phase steel, but the behaviour for the micro alloyed samples appears to be more complex. Finally, the paper considers the response of two on-line measurement systems that exploit these magnetic relations. The first system applies pulse excitation and measures the resulting remnant magnetisation and the second analyses the harmonic response from AC excitation. Both systems can detect microstructural changes associated with varying magnetic properties during strip production

Ultrasonic Assessment of Metal Microstructures, Modelling and Validation

The uniformity of strip rolled steel and its mechanical properties are intrinsically linked to the complex microstructure along the strip length. Ultrasonic methods are sensitive to differences in grain size, grain distribution and texture. This with the intention to provide suitable tools to inline monitors the properties of hot rolled steel.In this paper, we present a comparison of results from numerical and analytical simulations of the elastic wave propagation in deterministic and stochastic models of the microstructures. Modelled microstructures are used to provide the flexibility of assessing single microstructural parameters of different steel grades and rolling conditions. The individual simulations are validated against laser ultrasonic measurements on metal sheets in thickness range of 2mm-5mm, which were independently characterized metallurgically.The correlation to parameters as texture, grain size and dual phase composition was addressed. The simulation facilitates the development of methodologies to identify quantitative values that will enable to non-destructively assess the quality of a component. Different methods are developed based on changes in attenuation and velocity. These were tested against the simulated as well as the experimental data

Validation of models for Laser Ultrasonic spectra as a function of the grain size in steel

To reduce costs of production and increase economic sustainability it is necessary to introduce quality assessment in an early stage in the manufacturing process. In an ongoing European project (Product Uniformity Control – PUC), the intention is to use ultrasonic information to assess microstructure parameters that are related to macroscale qualities such as mechanical properties. Laser induced ultrasonic technique (LUS) requires no media and can generate and detect ultrasonic information at some distance from the component. This technique is therefore addressed within this project as a solution to measure ultrasonic properties in an industrial environment.Mathematical modelling of the ultrasonic wave propagation problem has been used in order to get a deeper understanding of the physics and to identify ultrasonic properties that can be used as an indirect measurement of grain size. The use of both analytical and numerical models enabled extensive parametric studies together with investigation of ultrasonic interactions with well-defined individual microstructures.The LUS technique has previously been applied to e.g. monitor grain growth during thermomechanical processing of metals. These applications identified and used a correlation with the frequency content of the attenuation. This have been investigated as a possible indirect measurement of grain size, also in this project. The models have been used to verify the correlations and to evaluate different procedures that could be applied as an industrial solution. The suggested procedure is based on deconvolving two successive echoes and has been experimentally validated by two different LUS systems. The reference samples used in the validation were produced by changing the annealing temperature and time to obtain a variation in grain sizes. These grain sizes were then identified by EBSD and the samples were examined in terms of grain size influence on spectral attenuatio

Results of the European collaborative project “Product Uniformity Control“ to improve the inline sensing of mechanical properties and microstructure of automotive steels

A European consortium consisting of four major steel manufacturers and ten academic technology institutes has conducted a research and development project, called “Product Uniformity Control“ (PUC) in the period 2013 to 2017. This project aimed to develop and improve non-destructive (inline) measurement techniques to characterise the (uniformity of the) microstructure of steel strip products.In this project, a multitude of strip steel samples from various stages of production have been collected from the four participating steel manufacturers. The samples have been characterised in various ways, namely on their (1) non-destructive measurement parameters using different techniques suited for inline evaluation, (2) fundamental ultrasonic and electromagnetic properties (wave speed, ultrasonic attenuation, magnetisation loops, coercive field), (3) tensile properties (stress-strain curves) and (4) microstructure (by optical micrographs and EBSD images). The correlations between these different characterisations will be addressed.Besides the experimental characterisation, a strong accent has been on modelling activities: during the project, fundamental models have been developed to describe, starting from 2D and 3D microstructures, the ultrasonic and magnetic properties, which are next used as input to sensor models that predict the output of the inline measurement systems.This contribution will present the recent results of both the experimental and the modelling work, and underline their mutual importance in the interpretation of the measured data for the benefit of inline characterisation of the mechanical properties complementary to traditional destructive tensile testing

Product uniformity control - A research collaboration of european steel industries to non-destructive evaluation of microstructure and mechanical properties

In steel manufacturing, the conventional method to determine the mechanical properties and microstructure is by offline, destructive (lab-)characterisation of sample material that is typically taken from the head or the tail of the coil. Since coils can be up to 7 km long, the samples are not always representative for the main coil body. Also, the time delay (typically a few days) between the actual production and the availability of the characterisation results implies that these results cannot be exploited for real-time adaptation of the process settings. Information about the microstructure and material properties can also be obtained from electromagnetic (EM) and ultrasonic (US) parameters, which can be measured in real-time, non-destructively, and over the full length of the steel strip product. With the aim to improve the consistency in product quality by use of inline EM and US measurements, a European project called "Product Uniformity Control" (PUC) has been set up as a broad collaboration between 4 major European Steel Manufacturers and 10 Universities / Research institutes. Using both numerical simulations and experimental characterisations, we study the inline measured EM and US parameters in regard of the microstructural and mechanical properties. In this way, we aim to establish an improved understanding of their mutual relationships, and to apply this knowledge in existing and new nondestructive evaluation techniques. In this paper, the concerted approach of modelling and experimental validation will be addressed, and results of this work will be shown in combination with inline measured data.com</p