## 4 Conclusions  
In the present research, the roles of laser surface-hardening treatment on the anti-wear performance of AGI and QTGI specimens were examined under equivalent macro-hardness. The microstructure, macro-harness, and micro-hardness values and wear tracks were evaluated to understand the phase transformations and possible wear mechanisms. Taken together, several conclusions can be drawn:  
* Four regions were found under the laser-hardened surface of LHAGI specimens. Zone 1 was the laser-hardened region containing the ledeburite and had a hardness of approximately 67 HRC. Zone 2 was an upper heat-affected zone containing martensite with a hardness of approximately 67 HRC. Zone 4 was the substrate containing the acicular ferrite and stable austenite with high carbon content and had a hardness of 41-27 HRC with austenite temperatures from 232 to 399 \({}^{\circ}\)C. Due to the tempering effect in Zone 3, the hardness decreased accordingly. The acicular ferrite became thick with the increasing austempering temperature. * Three regions were found under the laser-hardened surface of LHQTGI specimens. Zone 1 was the laser-hardened region containing the ledeburite and had a hardness of approximately 68 HRC. Zone 2 was the heat-affected zone containing the martensite and had a hardness of approximately 66 HRC. Zone 3 was the substrate containing the tempered martensite with a hardness ranging from 41 to 26 HRC with varying tempering temperatures from 316 to 482 \({}^{\circ}\)C.
* In reciprocating sliding wear tests, GI specimens without heat treatment had the lowest wear resistance due to the low surface hardness. The wear resistance was improved by applying the quench-tempering heat treatment and further improved by applying the austempering heat treatment. Both AGI and QTGI specimens had lower wear resistance when raising the austempering temperature or tempering temperature as a result of the reduction in hardness. After introducing the laser-hardening treatment, the wear performance of LHAGI and LHQTGI specimens was significantly enhanced because of the formation of high hardness ledeburitic and martensitic structures. The LHAGI specimens had higher wear resistance than the LHQTGI  
Figure 7: Worn Surfaces of LHAGI and LHQTGI Specimens: (**a**) 232 \({}^{\circ}\)C; (**b**) 316 \({}^{\circ}\)C.  
specimens. After analyzing the worn areas of the LHAGI and LHQTIGI specimens, it was found that cracks were the main wear mechanism. * Overall, the use of LHQTGI to replace AGI in some GI parts can be considered since LHQTGI had higher wear resistance than that of AGI. However, the substitution of AGI by LHQTGI needs to be further studied in regard to the other details in manufacturing and production processes and the specific mechanical properties. In addition, the wear loss of AGI could be reduced significantly after receiving laser surface-hardening treatment. The findings obtained in the present research provide value in the future designs of GI engineering components. Conceptualization, B.W. and G.C.B. ; methodology, B.W., Y.P. and R.W. ; validation, B.W., Y.P. and R.W. ; formal analysis, B.W. and Y.P. ; investigation, B.W. and Y.P. ; resources, G.C.B. ; data curation, B.W., Y.P. and R.W. ; writing--original draft preparation, B.W. and R.W. ; writing--review and editing, B.W. and G.C.B. ; supervision, G.C.B. ; project administration, G.C.B. ; funding acquisition, B.W. and G.C.B. All authors have read and agreed to the published version of the manuscript. This research was supported by the ACADEMIC AND RESEARCH DEVELOPMENT FUNDINGS at Zhejiang Sci-Tech University, grant number 11130131741904, grant number 11130231711923 and grant number 19022140-Y. This research was supported by the Tribology Laboratory, Department of Mechanical Engineering, Oakland University, Michigan, 48326, USA. The authors declare no conflict of interest. References  
* _[PERSON] et al. (2012)_ [PERSON]; [PERSON]; [PERSON] Laser modified thin layers in piston rings. _Mater. Sci. Forum._**2012**, _727-728_, 1931-1937.