# Investigation of Impact Behavior of STS304L Steel Plate Under Cryogenic Temperature
## 3 Results and Discussion
### Impact Energy Absorption Mechanism  
The Charpy V-notch test has long been widely used to determine the ductile-to-brittle transition temperature (DBTT) as a criterion for evaluating the temperature sensitivity of energy absorption capacity. Previous studies revealed that austenitic stainless steel exhibited a 47.2% decrease in energy absorption capacity at \(-\)196 \({}^{\circ}\)C compared with that at 20 \({}^{\circ}\)C [24]. However, this result did not define a specific DBTT point. In contrast, this study found that the energy absorption capacity at \(-\)193 \({}^{\circ}\)C increased by 68.80% compared with that at 20 \({}^{\circ}\)C, primarily due to the specimen geometry, particularly thickness and notch effects, which influence stress states and energy absorption mechanisms. Moreover, defining a specific DBTT point in austenitic stainless steel is challenging because of its unique mechanical properties at cryogenic temperatures. These results indicate that austenitic stainless steels exhibit an excellent impact resistance in cryogenic environments.  
\begin{table}
\begin{tabular}{c c c c} \hline
**Test Temperature** & **Crack Initiation** & **Peak Force** & **Stiffness** \\
[\({}^{\circ}\)**C**] & **Energy [J]** & **[N]** & **[N/mm]** \\ \hline
20 & 110 & 19,137 & 2064.8 \\ \(-\)100 & 175 & 27,561 & 2673.8 \\ \(-\)193 & 185 & 32,607 & 3018.2 \\ \hline \end{tabular}
\end{table}
Table 3: Summary of drop-weight impact test results at crack initiation.  
Figure 7: (**a**) Schematic of force–displacement history at crack initiation and (**b**) force–displacement history and cracked specimen at different temperatures.  
Total energy can be classified as elastic deformation energy and permanent deformation energy. Permanent deformation energy can be further subdivided into plastic deformation energy, martensitic transformation energy, and heat dissipation energy. Therefore, the total impact energy absorption of the specimen can be represented as follows:  
\[E_{total}=E_{el}+E_{pe}=E_{el}+\left(E_{pl}+E_{T}+E_{H}\right) \tag{2}\]  
where \(E_{el}\) is the elastic deformation energy of the specimen, \(E_{pe}\) is the permanent deformation energy of the specimen, \(E_{pl}\) is the plastic deformation energy of the specimen, \(E_{T}\) is martensitic transformation energy of the specimen, and \(E_{H}\) is the energy dissipated as heat.  
According to previous studies, elastic deformation energy and heat dissipation are negligible compared with other energy absorption factors [25]. Additionally, strain-induced martensitic transformation consumes part of the plastic deformation energy [26], making plastic deformation energy the dominant contributor to the total impact energy absorption. The shape of the impactor also plays a key role in plastic deformation and energy absorption capacity in drop-weight impact tests.  
The hemispherical impactor used in this study accelerates circumferential necking due to friction between the specimen and impactor surface [27]. The maximum friction effect occurs immediately before crack initiation, influencing the energy absorption mechanism. Therefore, further evaluation of plastic deformation in drop-weight impact tests is required to better understand its dominant role in total impact energy absorption and its dependence on the impactor shape and deformation mechanisms.