The mechanics behind formation of secondary ledeburite during tool steel welding

In this article we describe the microstructural changes in the heat affected zone (HAZ) of the tool steel W. Nr. 1.2379, which was surfaced or welded by the submerged arc welding technique (SAW) with different welding parameters. Microstructure of the welds and of the surfacing welds was analysed by optical and scanning electron microscope. In this research, we particularly studied microstructural changes in the area of primary chromium carbides in the HAZ and their effect on the weld crystalization. We came to the conclusion that the temperature in the HAZ is high enough during the welding process that it caused primary carbides to dissolve and concentration of the carbide-forming elements and carbon increased in the surrounding austenite matrix area to eutectic composition, which remelts and solidified as secondary eutectic (ledeburite).Original Abstract: U ovom prilogu opisujemo mikrostruktume promjene u zoni toplinskog utjecaja (ZTU) alatnog celika W. Nr. 1.2379, koji je bio navaren ili zavaren po postupku zavarivanja pod praskom s razlicitim parametrima zavarivanja. Mikrostrukturu zavara i navara analizirali smo pomocu opticnog i rasterskog (skenirajuceg) elektronskog mikroskopa. U analiziranju smo posebno utvrdivali mikrostruktume promjene u okolini primarnih kromovih karbida u zoni toplinskog utjecaja i njihov utjecaj na kristalizaciju zavara. Utvrdili smo, da su temperature u zoni toplinskog utjecaja za vrijeme zavarivanja dovoljno visoke da se za vrijeme rastapanja primarnih karbida u okolnoj matici do te mjere povecala koncentracija karbidotvomih elemenata i ugljika, daje nastala tz. talina eutekticnog sastava, koja se stvrdnula u sekundarni eutektik (ledeburit), na kojemu se na granici ZTU/zavara pokrene kristalizacija zavara.