**4. Conclusions**

The influence of crack size on stress evaluation of low alloy steel with MMM technology was discussed in this study. It can be concluded that:

**Author Contributions:** Conceptualization and methodology, B.L.; formal analysis, P.F.; validation, R.L.; writing—review and editing, P.H.; supervision, S.D.

**Funding:** This research was funded by the National Natural Science Foundation of China, grant number 51775254.

**Conflicts of Interest:** The authors declare no conflict of interest.