Laser welding of the new grade of advanced high-strength steel Domex 960

Abstract

The article presents the results of investigations on autogenous laser welding of the new-generation advanced high-strength steels (AHSS) Domex 960, classified as thermomechanically rolled steel by the manufacturer. There is little information about welding this steel grade, relating only to arc-welding methods. Therefore, a modern disk laser was used for the butt-joint welding of 5.0 mm steel sheets. The results of a microstructure study, tensile tests, technological bending tests, impact-toughness tests and also microhardness measurements showed that a low heat input during the laser welding of the new Domex 960 grade steel is advantageous. A low heat input and thus a high cooling rate of the weld metal and the heat-affected zone (HAZ) led to the formation of a favourable fine-grained microstructure, providing also high mechanical properties of butt joints, comparable to the properties of the base metal. Despite the high cooling rates, there was no significant increase in the microhardness measured across the butt joints. Moreover, a slight decrease in the microhardness was observed in the HAZ. Keywords: laserlaser welding, disk laser, thermomechanically rolled steel, advanced high-strength steel, fine-grained steel, properties of welded jointŝ lanek predstavlja rezultate preiskav avtogenega laserskega varjenja nove generacije naprednih visokotrdnostnih jekel (AHSS), jekla Domex 960, ki so ga proizvajalci opredeljujejo kot termomehansko valjano jeklo. Malo je informacij o varjenju te vrste jekla, nekaj le za metode oblo~nega varjenja. Za sole`no varjenje 5 mm debelih plo~evin je bil uporabljen modern diskasti laser. Rezultati {tudija mikrostrukture, nateznih preizkusov, tehnolo{kih upogibnih preizkusov, preizkusov udarne`ilavosti in tudi meritev mikrotrdote, so pokazali, da je ugoden majhen vnos toplote med laserskim varjenjem nove vrste jekla Domex 960. Majhen vnos toplote in zato velika hitrost ohlajanja kovine v zvaru in v toplotno vplivani coni (HAZ), povzro~i nastanek`eljene drobno zrnate mikrostrukture in tudi zagotavlja visoke mehanske lastnosti sole`nega zvara, v primerjavi z lastnostmi osnovne kovine. Kljub velikim hitrostim ohlajanja, ni bilo ob~utnega pove~anja mikrotrdote, izmerjene preko sole`nega zvara. Poleg tega je bilo v HAZ opa`eno rahlo zmanj{anje mikrotrdote. Klju~ne besede: lasersko varjenje, diskasti laser, termomehansko valjano jeklo, napredna visokotrdnostna jekla, drobno zrnato jeklo, lastnosti zvarjenih spojev

Hybrid Laser Deposition of Fe-Based Metallic Powder under Cryogenic Conditions

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Assessment of Steel Subjected to the Thermomechanical Control Process with Respect to Weldability

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Effect of cooling rates on the weld heat affected zone coarse grain microstructure

“…During welding, the temperature in the weld coarse grained heat affected zone (CG HAZ) can reach above 1100 °C 6. Heat input and consequential CG zone decrease the weld toughness [7]. Due to high temperature, the initial tempered martensite microstructure of the as delivered steel undergoes austenite transformation into a CG HAZ.…”