Microstructural Design of the Cast Iron via Laser Hardening with Defocused Beam of the Continuous Wave CO2 Laser

Abstract

The cast iron is widely used in mechanical parts due to its good properties, as damping, good fluidity, resistance to deformation, excellent machinability and low cost. However, the number of its applications are reduced because its low corrosion, wear and friction resistance. The microstructure of the metallic materials has high influence on these properties. Laser hardening can improve these properties via designing of the microstructure. The evaluation of the laser parameter influence on the microstructural features is vital for a correct design of the microstructure and therefore, good improvement of the metallic material properties. Although the various laser parameter influence has been analysed on sundry papers, the influence of the distance from focal point and scan speed in the laser hardening microstructures has been rarely evaluated in the literature. Thus, the influence of this parameter on the microstructures generated through laser hardening is the subject matter of this work. The experiments were carried out with continuous wave carbon dioxide laser on samples of ground cast iron. The atmosphere was air flow at 0.7MPa, the laser operated at 100W and the scan rates were 1mm/s and 5mm/s. The distances to focal point of the laser beams ranged from 0.0mm to 5.6mm. The microstructures of the samples were revealed via nital and evaluated with optical microscopy. This work shown that the microstructure of gray iron cast can be designed by mean of laser hardening. In addition, laser hardened zones had various microstructures (e.g. austenitic, martensitic, pearlite and dendritic). The type of the microstructures in laser treated zones was determined by distance from focal point and scan speed. Moreover, the width and the depth of the laser hardened zones were generally enlarged with the increasing of the distance from focal point. Furthermore, the laser irradiation at slow rates, i.e. 1mm/s, produced laser hardened zones larger than laser scan at 5mm/s. In future works, the hardness, wear and friction resistance of the laser hardened samples will be evaluated because the literature review indicates that austenitic and martensitic microstructures show high values of these properties.

Improving Commercial Motor Bike Rim Disc Hardness Using a Continuous-Wave Infrared Fibre Laser

“…However, at higher SS, the area was smaller with larger Dz. The spatial energy distribution of the laser beam adheres to a Gaussian pattern, with W m determined by Equation ( 6) [35].…”

“…When D Z and SS are high, only the central portion of the laser beam can initiate material melting, causing W to decrease with increasing D Z at high SR. Regarding SS, the molten width exhibits an exponential inverse relationship with this parameter, as indicated in Equation ( 6) [35].…”

“…In this context, A represents the laser radiation absorption of the metal alloy (0.65 [39]), δ signifies the thermal conductivity [35], and l Ther represents the thermal laser energy penetration. The latter parameter, l Ther , will be elaborated upon subsequently, as its definition is contingent upon the laser parameters.…”

“…where ε is a geometrical factor and σ is the thermal diffusivity [35]. D z can also define the types of microstructures by means of the cooling time (t c ), as seen in Equation ( 9) [3,5].…”

Improving the Properties of Gray Cast Iron by Laser Surface Modification

“…The study showed that the wear mechanism of curved 40CrNiMo steel consists mainly of abrasive wear, and its hardness also increased significantly after laser quenching. Similarly, Sharp et al [ 31 ], in their study of the microstructure of gray cast iron after laser quenching, demonstrated that gray cast iron produces martensite, austenite, dendritic crystals, and pearlite after laser quenching, thereby improving its mechanical properties. In the studies of the properties of ductile iron after laser quenching, Eduardo et al [ 32 ] treated the surface of ductile iron by laser quenching, and it was found that the hardness of the heat-treated specimens could reach up to 1145 HV, indicating that laser quenching can improve the hardness and wear resistance of ductile iron.…”