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In this study, the influence of the welding speed, the arc power and the laser focal position on the solidification crack formation for partial penetration laser hybrid welded thick-walled plates were investigated. Experimentally, a direct correlation between the welding speed and the crack number was observed. That is by reducing the welding velocity the crack number was decreased. The focal position shows also a significant influence on the crack number. Since by focusing the laser on the specimen surface, the crack number has been significantly diminished.
The wire feed speed showed a very slight influence on the crack formation. That is due to the large distance between the critical region for cracking and the arc region.
The numerical model shows a high-stress concentration in the weld root for both components (vertical and transversal).
Numerically, the reduced welding speed showed a strong impact on stress, as the model demonstrated a lower stress amount by decreasing the welding speed. The solidification cracking in the weld root is a result of interaction between metallurgical and geometrical and thermomechanical factors.
In this study, the influence of the welding speed and the arc power on the solidification crack formation for partial penetration laser hybrid welded Thick-Walled plates were investigated. Experimentally, a linear correlation between the welding velocity and the crack number was observed. That is by reducing the welding velocity the crack number was reduced.
The reduced welding velocity showed a strong impact on stress, as the model demonstrated a very lower stress amount in comparison to the reference case. The reduction of the welding speed could be a helpful technique to reduce the hot cracking. The wire feed speed showed a very slight influence on the crack formation. That can be returned to the large distance between the critical region for cracking and the arc region.
In this study, the influence of the welding speed and the arc power on the solidification crack formation for partial penetration laser hybrid welded Thick-Walled plates were investigated. Experimentally, a linear correlation between the welding velocity and the crack number was observed. That is by reducing the welding velocity the crack number was reduced.
The reduced welding velocity showed a strong impact on stress, as the model demonstrated a very lower stress amount in comparison to the reference case. The reduction of the welding speed could be a helpful technique to reduce the hot cracking. The wire feed speed showed a very slight influence on the crack formation. That can be returned to the large distance between the critical region for cracking and the arc region.
Solidification cracking of metals is a well-researched topic in the field of welding science. A material’s susceptibility to solidification cracking can be tested using numerous different specialized test procedures, one of which is the Modified Varestraint-/Transvarestraint test (MVT). It was developed at BAM in 1982 and is internationally standardised. Over the decades, this test has been extensively used to characterise the solidification cracking resistance of many different materials.
The present study was conducted to further investigate the influences of the standardised MVT testing parameters, as well as the characteristics of evaluation methods on the results. Several different high alloyed martensitic LTT (low transformation temperature) filler materials, CrNi and CrMn type, were used. In previous pilot studies, these alloys have shown a rather distinctive solidification cracking behaviour. During testing, energy input per unit length and bending speed were varied (especially the latter is usually kept at standard values), in addition to the most commonly altered factor - total deformation.
First, the effects of different process parameter sets on the solidification cracking response were measured using the standard approach - microscopic analysis of the specimen surface. It was found that not all parameter changes had the expected outcome. For the Cr8Ni6 and Cr11Mn5 filler materials, influences of energy input per unit length and welding speed were in direct opposition.
In order to investigate those apparent contradictions, μCT scans of MVT specimens were made. The results consistently show sub surface cracking, to significant, yet varying extents. Different primary solidification types were found using WDX-analysis, an aspect that is believed to be the main difference between the CrNi- and CrMn-type materials and their cracking characteristics.
Results show that when it comes to testing of modern high-performance alloys, one set of standard MVT testing parameters might not be equally suitable for all materials. Also, to properly accommodate different solidification types, sub-surface cracking has to be taken into account.
The shape of the weld pool in laser beam welding plays a major role to understand the dynamics of the melt and its solidification behavior. The aim of the present work was its experimental and numerical investigation. To visualize the geometry of the melt pool in the longitudinal section a butt joint configuration of 15 mm thick structural steel and transparent quartz glass was used. The weld pool shape was recorded by means of a high-speed video camera and two thermal imaging MWIR and VIS cameras. The observations show that the dimensions of the weld pool vary depending on the depth. The regions close to the surface form a teardrop shaped weld pool. A bulge-region and its temporal evolution were observed approximately in the middle of the depth of the weld pool. Additionally, a transient numerical simulation was performed until reaching a steady state to obtain the weld pool shape and to understand the formation mechanism of the observed bulging phenomena. A fixed keyhole with an experimentally obtained shape was used to represent the full-penetration laser beam welding process. The model considers the local temperature field, the effects of phase transition, thermo-capillary convection, natural convection and temperature-dependent material properties up to evaporation temperature. It was found that the Marangoni convection and the movement of the laser heat source are the dominant factors for the formation of the bulging-region. Good correlation between the numerically calculated and the experimentally observed weld bead shapes and the time-temperature curves on the upper and bottom surface were found.