1. Introduction
2. Experimental Procedures
Table 1
SM45C | Chemical composition (wt.%) | ||||||||||
C | Mn | Si | Cr | Ni | Mo | V | W | P | S | Fe | |
0.41 | 0.70 | 0.25 | 0.02 | 0.03 | - | - | - | 0.03 | 0.05 | Bal. |
3. Result and Discussion
3.1 Hardness Distribution and Micro Structure of Surface Melted Hardened Zone
3.2 Hardness and .micro structure between melted zone and base material
Table 2
Area | BM | H1 | H2 | H3 | H4 | H5 | M1 | M2 | W.Q |
---|---|---|---|---|---|---|---|---|---|
Hv | 180~200 | 280~300 | 350~400 | 450~510 | 570~590 | 590~600 | 590~600 | 650~660 | 580 |
3.3 Phase transformation of surface melted hardened zone
4. Conclusion
1) The depth of surface melting hardening layer was minimum 0.8mm, maximum 1.0mm.
2) The hardness of surface melted zone inside was 650-660 Hv without reference to the location, and it is about 60 Hv higher than HAZ maximum hardness (590-600 Hv). Based on the comparison of micro structure between melted zone and HAZ by EBSD, the hardness of melted zone is higher because the microstructure is minute.
3) The cooling speed of laser surface melting hardening treatment is 605 °C/s (calculated with t85 formula) and it is faster than water cooling, so the melted zone transformed as complete martensite, and the microstructure is very minute.
4) The macrostructure inside surface melted zone has dendrite form; also there are Mn, Si element segregate at the dendrite boundary, MnS at dendrite boundary, and Al based oxide in transgranular. However, there are no such inclusions in HAZ. Based on the interpretation of phase transformation with binary system constitutional diagram, Mns was crystallized in liquid state, and Al affiliation oxide was seems to be formed with oxygen in the air. Segregated Mn and Si, and concentrated sphere shaped Al, S, and O is existed at the band zone in the microstructure.