# Virtual Sensor for Estimating the Strain-Hardening Rate of
## 2 Materials and Methods  
### Materials  
Several ASS grades were selected to cover a broad range of chemical compositions. Samples were obtained from industrial sheets with a thickness between 3.0 and 5.0 mm, following hot-rolling and intermediate annealing stages, corresponding to 1D mill finishing as per European Standard EN-10088-2 [34]. The number of collected samples was between one and five, depending on the industrial availability of each selected ASS. The average chemical compositions of the analysed steel grades are summarised in Table 1.  
This selection covers a range of austenitic grades, starting from high-alloyed AISI 310S/EN 1.4845, AISI 309S/EN 1.4833, and AISI 904L/EN 1.4539, which have a high content of Cr, Ni, Mo, and/or Cu. These grades are designed to increase mechanical behaviour, corrosion resistance, and oxidation at high temperatures for applications such as furnaces, electrical resistances, high temperatures, refractories and tubes. On the other end of the spectrum are low Ni-austenities such as AISI 201/EN 1.4372 and ACX 041. These grades contain higher Mn levels to substitute Ni, ensuring the stability of austenite during cold forming. Their mechanical properties and corrosion resistance are lower, but enough for their use in decoration and households. Additionally, the study includes the standard AISI 304/EN 1.4301 grade, with a medium content of Ni and Cr being extensively used in the food industry, tableware, household items and drawing applications. Other grades considered are the medium-alloyed austenitic AISI 301/EN 1.4310 steel, with higher C to increase the strength for applications like architectural and automotive elements, and the AISI 316L/EN 1.4404 type with higher Ni and Mo content to improve corrosion resistance, making it suitable for the chemical industry.  
Initially, longitudinal strips are cut from each industrial sheet and cold-rolled in a Norton duo mill at a laboratory scale, applying thickness reductions ranging from 10% to 70%. Subsequently, the cold-rolled strips undergo machining and tensile testing according to ASTM E8/E8M standards. The engineering stress-strain flow curves for each steel grade are obtained, as illustrated in Figure 1a for the sample A2, and mechanical parameters, maximum tensile strength (\(Rm\)), yield strength at 0.2% strain (\(Rp_{0.2}\)), and elongation (\(A_{50}\)), are calculated.  
\begin{table}
\begin{tabular}{l c c c c c c c c c c c c} \hline
**ID.** & **AISI [36]** & **EN [34]** & **C** & **Si** & **Mn** & **Cr** & **Ni** & **Cu** & **Mo** & **N** & **Nb** & **Ti** & **S** \\ \hline A1 & 301 & 1.4310 & 0.105 & 0.86 & 1.24 & 16.78 & 6.71 & 0.20 & 0.34 & 0.069 & 0.013 & 0.008 & 0.0010 \\ \hline A2 & 304 & 1.4301 & 0.029 & 0.38 & 1.75 & 17.89 & 8.06 & 0.42 & 0.25 & 0.074 & 0.011 & 0.010 & 0.0010 \\ \hline A3 & 316L & 1.4404 & 0.022 & 0.35 & 1.38 & 16.70 & 10.28 & 0.32 & 2.26 & 0.053 & 0.021 & 0.009 & 0.0020 \\ \hline A4 & (ACX 041) & - & 0.083 & 0.43 & 9.62 & 15.95 & 1.46 & 0.19 & 0.03 & 0.160 & 0.005 & 0.019 & 0.0020 \\ \hline A5 & 310S & 1.4845 & 0.045 & 0.55 & 1.36 & 24.60 & 19.15 & 0.18 & 0.01 & 0.025 & 0.011 & 0.003 & 0.0010 \\ \hline A6 & 201 & 1.4372 & 0.076 & 0.50 & 7.06 & 16.12 & 4.32 & 0.58 & 0.18 & 0.083 & 0.008 & 0.004 & 0.0010 \\ \hline A7 & 904L & 1.4539 & 0.019 & 0.42 & 1.50 & 19.58 & 24.52 & 1.40 & 4.25 & 0.015 & 0.022 & 0.006 & 0.0010 \\ \hline A8 & 309S & 1.4833 & 0.044 & 0.49 & 1.63 & 22.37 & 13.94 & 0.28 & 0.49 & 0.058 & 0.007 & 0.013 & 0.0010 \\ \hline \end{tabular}
\end{table}
Table 1: Identification and chemical composition, by weight percentage (wt %), of the selected industrial hot-rolled and annealed sheets. Grades without a standard designation are referred to by their internal Acernox ID (in brackets) [35].