Microstructural changes due to laser surface melting of an AISI 304 stainless steel

Abstract

Several techniques can be used to improve surface properties. These can involve changes on the surface chemical composition (such as alloying and surface welding processes) or on the surface microstructure, such as hardening and melting. In the present work surface melting with a 3kW CO2 cw laser was done to alter surface features of an AISI 304 stainless steel. Microstructure characterisation was done by optical and scanning electron microscopy. Vickers and Knoop microhardness tests evaluated mechanical features after surface melting. Phase transformation during rapid solidification is analysed and discussed

Microstructural analysis of AISI 304 bars welded with high speed pulsed discharges

“…A similar cooling rate is observed in the strip casting process [8]. On the other structures it must be pointed out that the columnar-cellular can be observed in the laser melting, requires a 10 5 K/s cooling rate [9]. The higher estimated cooling rate was 10 6 necessary K/s that explains the presence of ferrite.…”

Enhancement of corrosion resistance of nickel based superalloys by laser surface melting

“…These micrographs indicated that laser surface melting resulted in fine solidification structure of the alloys. This could be attributed to the faster cooling rates, developed as a consequence of the temperature gradients generated in the material 31,32 The solidification occurred epitaxially from the boundary between the treated region and the untreated matrix.…”

Fabrication of Mesh Patterns Using a Selective Laser-Melting Process

“…According to the optical microscope image obtained at 500× magnification, the microstructure consists of a γ-austenite matrix with δ-ferrite having a dendrite size of about 20 μm. During the solidification of austenitic stainless steel, such as AISI 304 stainless steel, the first phase to solidify as the temperature drops below the point of peritectic transformation is δ-ferrite [46]. Hence, δ-ferrite tends to transform into austenite (γ) during cooling.…”