Laser transformation hardening of carbon steel: microhardness analysis on microstructural phases

Abstract

This study investigates the microhardness and microstructure of different steels hardened by a fibre laser. Rolled steel, quenched and tempered steel, annealed alloyed steel and conventionally through hardened steel were tested. Microhardness (HV0?01) was measured in martensite, pearlite, ferrite and cementite structures at different depths below the laser irradiated surface. The microhardness results were compared with the conventional macrohardness (HV5) results. The grain size of rolled ferritic-pearlitic steels had distinct effect on microhardness. The macrohardness of quenched and tempered steel might be markedly influenced by the homogeneity of alloy contents. In high carbon steel, cementite is y150 HV harder than pearlite. Annealed alloyed steels achieved high surface hardness but poor hardened depth. Dispersed granular pearlite did not affect the microhardness of soft annealed steel. The macrohardness of the base material was close to the microhardness of the softer phase structure. The measured microhardness was about 100-250 HV higher than the macrohardness.

Analysis of Steel Structures 5140 after Laser Treatment

“…It means, that after the metal sample have wells material within the groove should have the same hardness. [3] For the proof of this supposition microhardness was measured in the direction from the laser impact zone to non-exposed zone. Figure 3 illustrates that the microhardness of the material does not vary in the area of laser impact.…”

Influence of Laser-Assisted Fusing on Microstructural Evolution and Tribological Properties of NiWCrSiB Coating

“…The process improves the wear and corrosion resistance of the molds that must be capable of long-term service in severe service environments. Especially, a diode laser has higher beam absorptivity for the metallic materials as compared with that of CO 2 [14], Nd: YAG [15] and fiber [16] lasers and a large area of sample can be treated by the rectangular beam shape with a flat top energy distribution. Thus, the heat treatment using a diode laser (i.e., laser-assisted fusing) could be regarded as a strong candidate for fusing a thermal-sprayed layer to develop the high-durability continuous-casting molds.…”

Microstructural Characterization of Surface Softening Behavior for Cu-Bearing Martensitic Steels after Laser Surface Heat Treatment

“…Selective control of surface material properties is also possible through laser processing. A high-power diode laser is often used in this type of surface modification process [18][19][20][21][22][23][24] because of its high metal absorptivity and typically rectangular beam shape (similar to a top hat in both directions), which allows for a larger treatment area than CO 2 [25], Nd:YAG [26], disks [27], and fiber lasers [28,29]. Therefore, the diode laser process is a strong candidate for the surface modification treatment of mold material used in the plastic injection process owing to its superior work efficiency compared to gas nitriding, plasma nitriding, plasma carburizing, chemical vapor deposition, ion beam treatment, and electron beam processes.…”