Laser Surface Treatment Of AISI 420 Tool Steel

Influence of pre-heating on the surface modification of powder-metallurgy processed cold-work tool steel during laser surface melting

“…5). The observed microstructures are typical for laser-melted tool steels [1,2,[4][5][6][7][8][9][10]13,15,18,21]. Usually, laser-melted tool steels contain martensite, retained austenite and carbides [5].…”

“…The results of the microhardness measurements for the different, distinct zones are presented in Table 3. The microhardness of the remelted layer is slightly lower when the specimens are pre-heated to 350 • C. When using a pre-heating, the highest microhardnesses were measured in the overlap zone (O), presumably due to the transformation of the destabilized retained austenite into martensite due to reheating by the subsequent laser treatment [5]. Relative to the substrate properties, the increase in hardness in the PFS zone and in the heat-affected zone (HAZ) may be attributed to the austenite formation, and the partial dissolution of carbides in this phase.…”

“…Important scientific contribution in this field and an insight into metallurgy, microstructure evolution, and mechanical properties of laser melted tool steels represent early works of Strutt et al [1,2], Mazumder [3] and Molian and Rajasekhara [4]. It was shown later by Vilar and Colaç o et al [5,6,[8][9][10], and Kusinski et al [7,11] that welldefined laser surface melting, controlled solidification as well as tempering are crucial for microstructure morphology and the proportions between martensite, retained austenite and carbides. Consequently, the mechanical properties of tool steels may be controlled.…”

“…4). The separate region designated as PFS (coloured white) at the bottom of the melt pool represents the plane front of the solidification [5,28].…”

“…In contrast to other techniques of joining (e.g., conduction welding) the laser surface melting (LSM) of tool steel enables the elimination of inclusions and carbide stringers and results in the formation of a very fine dendritic structure, usually containing a small proportion of carbides [5,9]. The principal aim of the application of the LSM technique in the surface processing of materials is to improve their properties through the formation of a hard, homogenous and ultrafine structure of the surface layer, without changing its chemical composition.…”