**5. Conclusions**

In this review, some aspects regarding the critical hardness ratio used to define the mild–severe wear transition in abrasion were presented. Based on the approaches described during the article, the following conclusions can be forward:


#### **Acknowledgements**

The author acknowledges CNPq for his scholarship funding through process 310523/2020-6.

#### **Nomenclature**


*Tribology of Machine Elements - Fundamentals and Applications*
