*Advanced Applications of Hydrogen and Engineering Systems in the Automotive Industry*

treatment. Increasing the freezing time has no significant effect on controlling the residual stresses, as may be seen from **Figure 15**, around 30% reduction in residual stresses is observed after stable freezing despite prolonged exposure to freezing. Reduction in residual stresses reaches 45% after cyclic freezing. However, for most of the current study, stable freezing rather than cyclic freezing was used, where the samples were exposed to 30°C for 24 hours, for reasons of cost efficiency and easy handling associated with the process. This method may be considered as a "shallow" cryogenic treatment, as the freezing was extended to only 30°C (compared to temperatures of – 100°C used in industrial cryogenic treatments) (**Figure 16**).
