Microstructure and property of 1.6% C ultrahigh carbon steel after laser surface treating

In order to study the surface microstructure and property variation of ultrahigh carbon steel after laser treating, ultrahigh carbon steel(mass fraction of C is 0. 016) was treated with 2kW continuous wave CO_2 laser. Then its microstructure was observed with a scanning electron microscope and its hardness was measured with a microhardness tester. Through theoretical analysis and experiments verification, the microstructure and microhardness curve along the depth direction were obtained. The results show that the laser treated layer includes surface melted layer, overheating layer and transformation hardening layer. The melted layer is composed of cystiform-dendritic and divorced eutectic. The grain size in transformation hardening layer is finer than that in other layers, its microhardness is higher and its hardness can reach 750HV～905HV, which indicates a typical laser quenching microstructure. With the increase of laser power (1000W～1200W), the volume fraction of cystiform-dendritic and divorced eutectic in melted layer increased, however the quantities of martensite decreased, each layer's width and depth were reduced, and microhardness decreased. It is helpful to refine microstructure of ultrahigh carbon steel and improve its property.