The microstructural features in the different regions of the weld bed are shown in Fig. 2. The weld metal has a structure of columnar grains that follow the thermal gradient imposed during the welding procedure. During cooling, the final transformation is the martensitc one, which could convey an autotempering process to some extent.
1143 Nilthon Zavaleta Gutiérrez et al. / Procedia Materials Science 8 ( 2015 ) 1140 – 1149
Autotempering would be unavoidable due to the low carbon content –and hence high Ms- of the steel (Aborn (1956)); the small, rod-like precipitates seen in the bulk of martensite laths would be M3C particles (M=Fe,Cr) formed during this process, Fig. 2(b). In the CGHAZ, austenite reaches high peak temperature values after full austenite transformation, these temperature values promoting an almost complete dissolution of the precipitates inherited from the as-received state and hence allowing for significant grain growth; the measured width of the CGHAZ was a 200 μm. The high temperature values are reached only in a narrow region away from the fusion line; this is probably due to a pronounced thermal gradient imposed from the weld metal to the base metal and coming from a reduced thermal conductivity of high-Cr steels as compared, for instance, with low carbon structural steels (Grong (1994)).