## 8 Conclusions  
Wear maps for three different highly alloyed steel grades (two cold working steels and a hot working one) under a certain set of operating conditions were constructed by applying ANN modelling on an extended and reliable database of tribological experimental results.  
Experimental results were obtained by performing plane-contact sliding tests under non-lubrication conditions on a pin-on-disk tribometer. The specimens were tested both in an untreated state, with different hardening levels, and after surface treatment of nitrocarburizing (Tuffrriding technique).  
From the numerous ANN models tested, the 8-8-1 BPNN model was selected as the optimum ANN for the prediction of the wear of the three tool steels; the transfer functions are the log-sigmoid transfer function for the hidden layer and the hyperbolic tangent sigmoid transfer function for the output layer.  
From the application of the optimum ANN, the main results can be summarized as follows:  
* Wear-related information can be easily presented in a comprehensive manner by the design of wear maps, as derived through the ANN modelling. Wear maps are user-friendly and allow the determination of areas under steady-state wear, which are recommended for use.
* When the operational parameters are evaluated as severe, it is recommended to select different steel grades.
* Higher values of bulk hardness correspond to a more extended steady-state wear region.
* Surface treatment by nitrocarburizing of the hardened steel has a beneficial effect, as it limits the region of non-recommended use.
* For a certain steel grade, the increase of the sliding speed decreases the region of recommended use.
* Nitrocarburizing seems to be more effective in the case of hot working steel grade than in the cases of cold working grades.  
In addition, the proposed optimum ANN model seems to offer a simple design/educational tool, which can assist both for educational purposes, as well as the interpretation of the surface treatment effects on the tribological performance of tool steels.  
The following are available online at [[http://www.mdpi.com/2076-3417/9/14/2788/s1](http://www.mdpi.com/2076-3417/9/14/2788/s1)]([http://www.mdpi.com/2076-3417/9/14/2788/s1](http://www.mdpi.com/2076-3417/9/14/2788/s1)), Database.  
L.C., P.G.A., P.P.P., and N.M.V. conceived and designed the research; [PERSON] and A.D.S. performed the computational implementation of the mathematical models; and all the authors reviewed and revised the manuscript.  
This research received no external funding.  
**Acknowledgments:** The authors would like to thank [PERSON], Prof. at University of Transport Technology, Hanoi, Vietnam, and [PERSON], PostDoc Researcher at the Centre of Tropical Geoengeneering (GEOTROPIK), School of Civil Engineering, Faculty of Engineering, Universiti Teknologi Malaysia, for their valuable comments and discussions. The authors would also like to express his acknowledgement to Ph.D. student [PERSON] and to undergraduate students [PERSON] and [PERSON] for their assistance in the interpretation of the experimental results. Authors would also like to acknowledge financial support for the publication of this work from the Special Account for Research of ASPETE through the funding program \"Strengthening ASPETE's research\".  
**Conflicts of Interest:** The authors confirm that this article content has no conflict of interest.