Theme 5: New Processes for New Products

Smart Sensors for Real-Time Measurement

Product Development, Late Stage Definition and Integration

This theme looks at the potential of using novel chemistries, processes and measurements to produce new products or improve the efficiency and consistency of existing high value steels.

One area of focus is microstructural monitoring during processing, whilst the other looks at the development of ultra-high-performance steel for improved processing efficiency, reduced process energy requirements, ultra high strength for equivalent lighter weight products and novel processes which enable late differentiation of the steel into a range of diverse products.

Task 8: Smart Sensors For Real-Time Measurement

Project Leaders: Professor Claire Davis
Researchers: Dr Lei (Frank) Zhou
Project Partners: WMG University of Warwick, University of Manchester, Primetals Technology Limited, British Steel, Liberty Steel

Introduction

Improved monitoring of processes is key to sustainability, growth and modernisation for the steel industry. Electromagnetic (EM) sensor signals are sensitive to the relative magnetic permeability of steel, which varies with changes in microstructural features. Therefore, the EM method can be used as a process control tool to provide feedback on microstructural development during processing or as a characterisation tool to complement or replace the current destructive examination methods.

Project Aims

To design, build and install an EM sensor array into a furnace-run-out table, and carry out modelling and experimental studies to link sensor signal to magnetic properties and microstructures for specific complex geometry steel products (wire/rod - image below, and narrow strip). To  develop an improved fundamental understanding of the link between magnetic signals and microstructure, including changes in magnetic signal with temperature.

Planned impact

EM sensor arrays for real-time in-situ monitoring, characterisation and control of steel microstructures during steel processing for a range of grades and applications

Progress to date

• A four-EM sensor heads array system has been designed, built and installed in the lab furnace-roller table.

• The sensor array FE model has been developed and validated for samples with known magnetic properties.

• Further funding has been secured for sensor array systems to be installed in industrial steel mills.

• In-situ monitoring of recovery and recrystallisation for IF steel has been demonstrated

• In-situ magnetic domain observation using Lorentz microscopy in the TEM with a high-temperature sample holder has been completed showing domain movement under changing magnetic fields and temperature.

• High temperatures magnetic properties measurements for use in models for sensor-microstructure transformation monitoring and to examine effects of microstructural parameters.

Impact and future plans

EM systems are used in the steel industry for wide strip steels to monitor phase transformation following hot rolling and to predict mechanical properties in the final product.  A new sensor array system has been developed for use with complex geometries, such as narrow strip and rod. The next stage is lab tests for high-temperature phase transformation monitoring of high carbon steels before installation in industrial steel mills, which will require analysis of the complex signals generated.  Further funding has been secured for this work via the High Value Manufacturing Catapult at WMG.

The sensor array and other commercial sensors operate at room temperature, even when monitoring hot steel. Another area for future impact is the development of high-temperature in-situ sensors for monitoring thermal-induced microstructural changes.  Funding has been secured for this work via an EPSRC project (EP/W024713/1).

Researcher’s career development

During the project period, the T8 researcher Dr Frank Zhou also worked on an industrial contract with Primetals Technology Limited (PTL) for modelling the commercial EMspec sensor system and signal interpretation. He successfully obtained a SUSTAIN ECR grant in Feb 2021 and a TFI ECR grant in June 2022. He has also submitted a fellowship application to EPSRC.

Key Publications

• L. Zhou, P. Kok and C. L. Davis, “Effect of ferrite grain size on initial relative permeability in low carbon steels” Journal of Magnetism and Magnetic Materials, Vol 519, Feb 2021, 167439

• L. Zhou, F. Wu, R. Hall, and C. Davis, “Electromagnetic sensors for in-situ dynamic microstructure monitoring of recovery and recrystallisation in interstitial free steels”, JMMM, vol 551, June 2022, 169187

• J.W. Wilson, F. Zhou, C.L. Davis, A.J. Peyton, “High Temperature Magnetic Characterisation of Structural Steels Using Epstein Frame” Measurement Science and Technology 32 (2021) 125601

• S. Kahrobaee, I.A. Akhlaghi, F. Zhou and C. Davis, “Detection of decarburising depth in Hadfield steels using a multi-magnetic NDE method” Non-destructive Testing and Evaluation

• F. Wu, L. Zhou, J. Soulard, B. Silvester, C. Davis, “Quantitative characterisation and modelling of effect of cut edge damage on the magnetic properties in NGO electrical steel”, J. Magn. Magn. Mater. 551 (2022)

Task 9: Late Stage Product Definition and Integration

Project Leaders: Professor Mark Rainforth, Professor Eric Palmiere, Dr Martin Strangwood
Researchers: Dr Peng Gong
Project Partners: University of Sheffield, WMG University of Warwick, British Steel, Liberty Steel, Tata Steel UK

Introduction & Aims

1. Efficiency in steel production requires minimal changes  in the upstream procedures with product differentiation occurring during the latter stages of processing

2. Tight product specifications are difficult to meet with complex steel microstructures that are formed through multiple process steps

3. Understanding is required about fundamental metallurgical issues:

   • Effect of austenite structure on transformation product, particularly martensite (Ms, lath hierarchical structure)

   • Retained and reverted austenite

   • Competition between carbide formation and formation of reverted austenite

   • Alloy partitioning between phases

   • Effect of segregation on the above

Planned impact

The research will lead to adjustments in the hot rolling and heat treatment schedules to improve properties and deliver a more consistent product

Industry Context

Efficiency in steel production requires minimal changes in the upstream procedures (i.e. steelmaking) with product differentiation occurring during the latter stages of processing. Efficiency in product use requires design of high-quality steels with appropriate mechanical properties and life-time durability. This activity considers both of these aspects, focusing on different steel grades and product portfolios but utilising the strength of UK metallurgical research to provide new products and processes to position the industry at the forefront of development. This project has generic applicability across all the steel manufacturers in SUSTAIN.

Progress to date

In the area of late-stage product definition & integration, a Super 13% Cr steel was taken as a model steel for looking at the manipulation of phase content to alter mechanical properties through late-stage processing. Detailed analysis of commercial Super 13% Cr steels with tensile properties that are in, and out, of specification has been undertaken. These steels contain a significant variation in reverted austenite content. Detailed microstructural analysis showed that micro segregation is not responsible for the variations in the yield strength. The only likely explanation is small changes in tempering temperature which gives large differences in retained austenite content.

In order to develop a steel that is more controllable, the role of the Ni and Mn content on austenite quantity and stability has been investigated. Systematic changes in Ni and Mn composition have been achieved through trial casts, but with compositions that remain within the specification range. Changes in Ni and Mn content have major effects on the reverted austenite content, not just the peak quantity, but also the shape of the peak. This is not explained by changes in the transformation temperatures. Ni strongly partitions to the austenite, while Mn weakly partitions. The amount and stability of the austenite relates directly to the amount of Ni and Mn within it. Therefore, there is scope to control the amount, and stability, of the austenite by changes in the Ni and Mn compositions.

Key findings

• The amount and composition of reverted austenite formed during the heat treatment of a Super 13Cr steel is a strong function of time and temperature, with even small (~5ᵒC) changes in temperature resulting in large changes in austenite content

• The carbon content in reverted austenite is a linear function of the tempering temperature for the first temper but does not change on the second temper

• The nickel content decreases in the austenite with tempering temperature on the first temper but increases slightly on the second temper. The chromium and molybdenum do not partition strongly during tempering

• The second temper results in austenite that is much more resistant to strain induced transformation, as a result of solute redistribution

• Variations in reverted austenite content result in significant variations in the yield strength, making the difference as to whether they are in or out of specification

• Large variations in reverted austenite content in the commercial product are not a result of compositional variations in the product; no local segregation can explain the differences

• Accordingly, the variations in reverted austenite have to be a result of small differences in heat treatment temperature

Key Publications

• Kwok, T. W. J., Gong, P., Xu, X., Nutter, J., Rainforth, W. M., & Dye, D. (2022). Microstructure Evolution and Tensile Behaviour of a Cold Rolled 8 Wt Pct Mn Medium Manganese Steel. Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science, 53(2), 597–609

• Jones, B. L., Jolfaei, M. A., Hobson, S., Rainforth, W. M., & Davis, C. L. (2022). Magnetic characterisation of strain ageing in near eutectoid drawn pearlitic wire using an electromagnetic (EM) sensor. Engineering Failure Analysis, 131

• Gong, P., Turk, A., Nutter, J., Yu, F., Wynne, B., Rivera-Diaz-del-Castillo, P., & Mark Rainforth, W. (2022). Hydrogen embrittlement mechanisms in advanced high strength steel. Acta Materialia, 223

• Gao, J., Jiang, S., Zhang, H., Huang, Y., Guan, D., Xu, Y., Guan, S., Bendersky, L. A., Davydov, A. v., Wu, Y., Zhu, H., Wang, Y., Lu, Z., & Rainforth, W. M. (2021). Facile route to bulk ultrafine-grain steels for high strength and ductility. Nature, 590(7845), 262–267

• Gong, P., Wynne, B. P., Knowles, A. J., Turk, A., Ma, L., Galindo-Nava, E. I., & Rainforth, W. M. (2020). Effect of ageing on the microstructural evolution in a new design of maraging steels with carbon. Acta Materialia

• Guo, Q., Li, X., Gong, P., Nutter, J., Rainforth, W. M., & Luo, H. (2021). Why Does Nitriding of Grain-Oriented Silicon Steel Become Slower at Higher Temperature? Steel Research International, 92(4)