S. Gook

Hybrid laser arc welding of X80 and X120 steel grade

Abstract The aim of the present work was to investigate the possibilities of hybrid laser arc welding regarding reliable production of longitudinal welds of high strength pipe steels X80 and X120 and to evaluate achievable mechanical properties of laser hybrid welds. The study focused on weld toughness examination in low temperature range up to −60°C. Suitable filler materials were identified in the context of this task. It could be shown that metal cored electrodes guaranteed sufficient Charpy impact toughness at low temperature for both investigated materials. Modern arc welding technologies such as modified pulsed spray arc were used to promote deeper penetration of the filler material into the narrow laser welding gap. Edge preparation with a 14 mm deep root face was considered as optimum, because no penetration of the filler material could be detected beyond this depth limit, and therefore, any metallurgical influences on the weld metal properties through the welding wire could be excluded.

Hot cracking in high power laser beam welding of thick high strength structural steels under restraint conditions

High power laser beam welding represents a cost-effective alternative for fast joining of thick components. However, the reliability of the welded structures can be severely affected by solidification crack formation, caused by constructional restraints. Experimental investigations using 15 mm thick plates of the fine grained structural steel S690, welded with a 20 kW fiber laser under different restraint conditions revealed a relationship between hot cracking susceptibility and restraint intensity. Systematic laser welding experiments were conducted in the IRC (Instrumented Restraint Cracking)-test facility, under both free shrinkage as well as defined restraint intensities. In order to assess the stress-strain condition of the weld during solidification which is crucial in the hot crack formation process but also difficult, if not impossible to acquire experimentally, a two-dimensional thermo-mechanical finite element model of the IRC-Test was developed. The results constitute a good approach to explain and understand the detrimental effects of high restraints on hot cracking phenomena during laser beam welding.High power laser beam welding represents a cost-effective alternative for fast joining of thick components. However, the reliability of the welded structures can be severely affected by solidification crack formation, caused by constructional restraints. Experimental investigations using 15 mm thick plates of the fine grained structural steel S690, welded with a 20 kW fiber laser under different restraint conditions revealed a relationship between hot cracking susceptibility and restraint intensity. Systematic laser welding experiments were conducted in the IRC (Instrumented Restraint Cracking)-test facility, under both free shrinkage as well as defined restraint intensities. In order to assess the stress-strain condition of the weld during solidification which is crucial in the hot crack formation process but also difficult, if not impossible to acquire experimentally, a two-dimensional thermo-mechanical finite element model of the IRC-Test was developed. The results constitute a good approach to explain...

Weld seam formation and mechanical properties of girth welds performed with laser-GMA-hybrid process on pipes of grade X65

With the recent introduction of multi-kilowatt fiber lasers combining high beam quality with an impressive energy efficiency, it was possible to broaden the spectrum of laser beam and laser-hybrid welding applications widely. Application of these lasers for welding thick-walled structures in different branches of industry (e.g. power generation, shipbuilding, wind power, pipeline construction) is interesting, because the fiber lasers offer sufficient penetration depth to allow economically efficient welding of thick sheet metal, i.e. with a reduced number of welding passes and with a lower amount of filler material. A girth laser-hybrid process using a 20 kW fiber laser and a gas metal arc welding (GMAW) process was examined at BAM, Federal Institute for Materials Research and Testing, Berlin. The aim of this research was to obtain a stable and crack free girth process and to demonstrate the possibility of its application in pipeline construction. The experiments were carried out on 16 mm thick pipe rings with 914 mm pipe diameter of X65. As it could be shown in previous publications the rings can be welded using a girth hybrid process that is divided into two steps each in 5G position downhill. This paper will focus on imperfections of the weld seams in the different welding positions and on the methods for their avoiding. Influences of forming gas and scanner optic parameters on the appearance of the weld root were analyzed. A serie of welding experiments with preheating was performed. Mechanical properties and weld metal microstructure for the pipe segment welds were examined for different preheat temperatures.With the recent introduction of multi-kilowatt fiber lasers combining high beam quality with an impressive energy efficiency, it was possible to broaden the spectrum of laser beam and laser-hybrid welding applications widely. Application of these lasers for welding thick-walled structures in different branches of industry (e.g. power generation, shipbuilding, wind power, pipeline construction) is interesting, because the fiber lasers offer sufficient penetration depth to allow economically efficient welding of thick sheet metal, i.e. with a reduced number of welding passes and with a lower amount of filler material. A girth laser-hybrid process using a 20 kW fiber laser and a gas metal arc welding (GMAW) process was examined at BAM, Federal Institute for Materials Research and Testing, Berlin. The aim of this research was to obtain a stable and crack free girth process and to demonstrate the possibility of its application in pipeline construction. The experiments were carried out on 16 mm thick pipe rings...