November_December_2021_AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | N O V E M B E R / D E C E M B E R 2 0 2 1 3 0 S teel is vital for the durable infra- structure development needed for growing populations. It pro- vides affordable housing and mobility solutions and is indispensable for ener- gy generation and distribution. Due to its central role in making modern soci- ety sustainable, manufacturers are pre- paring the next generation of stronger, lighter, and more sustainable steel. This product development requires testing at micro- and nanoscale. In modern steel grades, the pres- ence of precipitates, such as titanium nitride and niobium carbide, is key. Their size, distribution, and density are of utmost importance. OCAS (OnderzoeksCentrum voor de Aanwending van Staal), a joint ven- ture between ArcelorMittal and the Flemish Region, is a research center active in metallurgy, coating, and steel application development. About 95% of OCAS’ work with transmission elec- tron microscope (TEM) instruments in- volves testing a high volume of steel precipitates. By analyzing the size, mor- phology, distribution, and elemental characteristics of precipitates at the nanometer scale, OCAS helps its cus- tomers develop steel with the specif- ic properties needed for high-strength structural applications. In the past, OCAS manually deter- mined the size distribution and chemi- cal composition of precipitates, a slow and cumbersome process. The work- flow involved capturing a TEM image of a sample, manually examining each precipitate with energy-dispersive x-ray spectroscopy (EDS) analysis, and then writing down the measurements. Data could only be gathered on 100-200 pre- cipitates per sample. Operators also lacked an overview image that en- abled them to see how both the small and large precipitates were distribut- ed across the sample and whether the distribution was homogeneous. Deter- mining the ratio between the small and large precipitates was not possible. Al- together, it typically took between one and three days to obtain the informa- tion required for a single sample, with 5-10 samples required for each project. To improve precipitate analyses, OCAS moved to Thermo Scientific’s au- tomated particle workflow (APW) in 2020, which made it possible to quan- tify nanosized precipitates more ac- curately in a shorter timeframe. This workflow increased efficiency and sta- tistical relevance of these analyses, enabling the research center to boost productivity and accuracy of results. PREPARING STEEL PRECIPITATE SAMPLES OCAS uses two methods of sample preparation to evaluate steel precipi- tates, depending on the request of the customer: replica and focused ion beam (FIB) lamella. In replica sample prepara- tion, the sample surface is polished and etched by acid; a thin, amorphous car- bon film of 20 nm is then deposited on the prepared sample surface. The car- bon film-coated sample surface is then etched again. With the dissolution of the ma- trix around the precipitates, the carbon film collects the precipitates that have been released from the sample surface and are floating in the acid. Those float- ing replica pieces are put on the copper mesh grid holder so the precipitates can be imaged and analyzed. Ultimately, the replica method can provide a large sample area. However, some precipi- tates might get lost during etching, and the precipitates may no longer retain their original spatial distribution. In FIB lamella sample prepara- tion, on the other hand, technicians use the Thermo Scientific SCIOS 2 Dual- Beam, an ultrahigh-resolution focused ion beam scanning electron micro- scope (FIB-SEM) system to prepare samples without changing the precip- itates’ spatial distribution. Using this method, they can quickly develop thin foil cross-sections that can be lifted out and attached to a TEM grid for analysis. This method retains particle orientation and size and lets technicians precisely hone in on specific areas they want to investigate. TEM SCREENING AND OVERVIEW MAP After replica sample preparation is complete, OCAS uses a Thermo Sci- entific Talos F200X G2 (scanning) trans- mission electron microscope ([S]TEM) STEEL PRODUCT DEVELOPMENT AIDED BY AUTOMATED PARTICLE WORKFLOW In steel production, an automated particle workflow can increase the efficiency and statistical relevance of nanosized precipitate analyses, resulting in increased productivity and accuracy. TECHNICAL SPOTLIGHT