# Clinching of High-Strength Steel Sheets with Local Preheating
## 2 Materials and Methods  
### Experimental Materials  
The selection of the experimental material was targeted at two-phase hot-dip galvanized steels 1.5 mm thick and fine-grained micro-alloyed low-carbon hot-dip galvanized steels 1.5 mm thick. The material of the first experimental group belongs to progressive high-strength steels. Its designation, according to EN 10346/09 [45], was HCT 600 X+Z. The HCT 600 X+Z steel sheet had a surface galvanized on both sides, and the thickness of the sheet was 1.5 mm. In the second experimental group, the steel sheet HX420 LAD+Z was galvanized on both sides, and its thickness was 1.5 mm. The chemical composition of the steels was determined by optical emission spectroscopy (OES, Thermo ARL, Lausanne, Switzerland). The chemical elemental composition of the experimental materials was focused on the determination of the concentration of the main alloying elements (Tables 1 and 2). The mechanical properties of the experimental materials were determined by tensile testing at an ambient temperature according to ISO 6892-1:2019 [46] on flat samples 1.5 mm thick, with a measured length of L0 = 80 mm and a cross-member movement rate of 0.05 mm/min. For the ambient temperature tensile tests, a TiraTest 2300 universal testing machine (TIRA GmbH, Schalkau, Germany) with a force transducer up to 100 kN was used. The basic mechanical properties of the joined materials are shown in Table 3. \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline
**C** & **Mn** & **Si** & **P** & **S** & **Al** & **Cu** & **Ni** & **Cr** & **Ti** & **V** & **Nb** & **Mo** \\ \hline
0.075 & 1.880 & 0.016 & 0.015 & 0.005 & 0.055 & 0.022 & 0.009 & 0.208 & 0.001 & 0.003 & 0.003 & 0.170 \\ \hline \end{tabular}
\end{table} 
Table 1: Chemical elemental composition of HCT600X+Z steel, No. 1.0941 (wt.%). \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline
**C** & **Mn** & **Si** & **P** & **S** & **Al** & **Cu** & **Ni** & **Cr** & **Ti** & **V** & **Nb** & **Mo** \\ \hline
0.083 & 1.214 & 0.013 & 0.015 & 0.005 & 0.040 & 0.035 & 0.010 & 0.024 & 0.014 & 0.032 & 0.058 & 0.002 \\ \hline \end{tabular}
\end{table} 
Table 2: Chemical elemental composition of HX420 LAD+Z, No. 1.0935 (wt.%). HCT600X is a dual-phase (DP) steel with a multiphase structure consisting of hard martensite islands dispersed within a soft ferrite matrix. DP steel finds extensive application in the automotive sector. It is commonly employed in various structural components such as automobile chassis, beams, guide rails, and other parts. These parts experience intricate loads during practical usage, particularly in areas near geometric irregularities where stress tends to concentrate. Consequently, local plastic deformation may transpire when subjected to extreme loads [16; 18; 47]. HX420 LAD is a high-strength low-alloy (HSLA) steel, a subset of high-strength steels (HSSs). HSLA steels have gained significant popularity due to their improved weldability and cost-effectiveness. HSLA steel offers several advantages, such as high specific strength and good low-temperature toughness. Compared to traditional steel, it enables reduced material consumption, enhanced reliability, and decreased costs when manufacturing components with an equivalent load-bearing capacity [48]. The combination of micro-alloying and controlled rolling allows for the attainment of high strength, good toughness, and improved weldability in low-carbon plate steels. These improvements in the mechanical properties primarily stem from the refinement of the ferrite grain size and the controlled precipitation strengthening. Micro-alloying elements like titanium, niobium, and vanadium aid in grain refinement by precipitating in the austenite phase, and they contribute to dispersion hardening by precipitating in ferrite during the austenite-ferrite transformation [49; 50]. The effectiveness of titanium, niobium, and vanadium in these processes depends on the solubilities of their nitrides and carbides in austenite.