In the metals industry, the difference between success and failure often hinges on microscopic details. Since component failure is often a direct result of microscopic defects, scanning electron microscopy (SEM) helps establish metrics for quality control to help manufacturers get to the root cause of their material concerns. But, if you’re conducting failure analysis on metals, how do you ensure you’re capturing every possible defect? Here, Dr. Franz Kamutzki, Sales Account Manager at industrial SEM specialist Thermo Fisher Scientific, offers his advice.
In recent years, the UK’s steel industry has faced a financially challenging climate, with fierce competition from abroad and high production costs. Amid these issues, crude steel production dropped from 7.2 million metric tonnes in 2021 to 5.96 million tonnes in 2022. However, according to Make UK data, UK demand for steel is set to grow by 2030, providing an excellent opportunity to reindustrialise and modernise production processes.
An effective and increasingly popular way to achieve this is by engineering materials at the nanoscale. Tailoring the structures of metal and steel at an extremely small scale helps to improve durability, reliability and cost. For example, when engineering metals for the aerospace sector, reducing weight and increasing stiffness can help to improve performance and extend the working life of the component parts.
Metals under the microscope
Even traditional processes are now augmented with microscopic inspection to determine the resulting material’s elemental and structural composition. Precise control of inclusions and precipitates is essential for effective metal production, but whether these additions strengthen the material or act as contaminants depends on their consistency and distribution.
Examples of these microscopic properties include nanoprecipitates, wherein small-scale precipitates are formed when the metal is rolled, annealed or hot pressed. Nanoprecipitation strengthened steels increasingly draw attention for their good weldability and high strength-to-weight ratio, facilitating the manufacturing process and making them ideal for use in applications such as aircraft structures.
However, the presence of inclusions and precipitates can also have detrimental effects on material quality. In the range of industries that use metal or steel, quality control measures are implemented to ensure material quality before it is used. For example, quality engineers must detect nanoscale morphological changes such as crack initiation sites, which can occur due to microstructural alternations during fatigue loading. Given that metals and steels used in demanding applications such as aircraft frames must withstand vibrations, pressure fluctuations and thermal stresses, accurately detecting crack initiation sites is an essential part of quality control.
Other nanoscale structural changes that require detection and control include grain boundaries, which are defects that can decrease the material’s electrical and thermal conductivity, as well as oxide inclusions that cause casting interruptions in steelmaking. Since steelmaking is a highly oxidising process, the quality is easily jeopardized by inclusions.
Fortunately, microscopy can detect any major faults in the final product and help maintain compliance with industry standards. For example, ASTM E45, which provides methods for microscopic examinations to evaluate non-metallic inclusions in steel, and E2283, which offers statistical methods for analysing the distribution of these inclusions
Simplifying microscopy with SEM
Scanning electron microscopy plays a vital role in characterising the composite materials employed in metal production. Take for instance, refractories, which are commonly used in steel production as protection in extreme environments such as heating furnaces and refining vessels. Due to high temperatures and corrosive conditions, the physical and chemical properties of the refractories are hugely important for stability and wear resistance. Typically fabricated by combining material types such as ceramic (oxide) powders, reactive metals or carbides, the refractories may be employed in pressed bricks, monolithic linings and carbon-bonded products used in continuous steel casting.
Conventional electron microscopy approaches provide a backscattered electron (BSE) image or secondary electron (SE) image of the distribution of different materials within the sample. However, these images would not disclose grain composition, with the information provided by the BSE image being insufficient to distinguish the different phases and possible contaminations within the refractory mixture.
However, elemental analysis based on instantaneously displayed information from the SEM image is much quicker and more informative. The unique automation capabilities of Thermo Fisher Scientific’s ChemiSEM technology enables high throughput chemical analysis with energy-dispersive X-ray spectroscopy (EDS) mapping. This means that a thorough overview of the elemental and structural composition of hundreds, if not thousands, of inclusions is possible in a manner of hours, as compared to the few dozen that would be found in a day of manual analysis.
Not only is statistical information on the bulk available, but individual precipitates can also be seen in the transmission electron microscope (TEM) with high detail, providing a multi-scale overview of the metal. Within steel and aluminium production where lightweighting is a priority, Thermo Fisher’s automated instruments can also carry out the critical task of nanoparticle counting.
Since metal components are frequently used in demanding environments, detecting and controlling microscopic material defects is crucial. While this requires extensive structural analysis, advanced approaches to SEM can simplify the process and save time, without compromising quality testing standards.
To learn more about how Thermo Fisher’s ChemiSEM technology can support your metal and steel quality control testing application, get in touch with our expert team.
