Interactions of the process parameters and mechanical properties of laser butt welds in thin high strength low alloy steel plates

Abstract

High strength low alloy steels subjected to the thermomechanical control process present excellent strength–toughness combination, high strength/weight ratio, and weldability. Therefore, they are widely used in structural components, such as pressure vessels, oil/gas transportation pipes, lifting equipment, vehicles, shipbuilding and offshore industries, and in the automotive industry where low thickness (0.8–3 mm thickness) is of great importance. Usually, these steels are welded by conventional gas metal arc welding, which creates wide heat-affected zones, large residual stresses, and distortion in the welded parts. Laser welding is nowadays an alternative process to weld high strength low alloy steel parts due to its advantages. The aim of this work is to understand the effect of process parameters on defects, weld bead geometry, microstructure, and mechanical properties, namely hardness and tensile strength. We identify the main laser welding parameters and their influence on the weld bead geometry and defects, for a 3 mm thick high strength low alloy steel welded under a maximum power of 2 kW. A cross section of the weld seam was optimized achieving a good geometry without porosity. The threshold value of the heat input to achieve complete penetration was determined for different focus diameters. The microstructure, size, and hardness of the heat-affected zone and of the fusion zone are strongly influenced by the heat input. The values of the tensile strength achieved in butt welds were close to the base metal by an appropriate selection of the laser welding parameters and the heat input.

Influence of Local Properties on Fatigue Crack Growth of Laser Butt Welds in Thin Plates of High-Strength Low-Alloy Steel

“…Figure 2 presents a representative example of metallographic analysis where Figure 2b corresponds to underfill defect, Figure 2c shows the toe of the weld root and Figure 2d illustrates an undercut defect. For the heat input range used in the present work, Figure 2b showed that the HAZ was divided into two important zones: softened ferritic-bainitic with fine grain (FG) and bainitic-martensitic with coarse grain (CG) as was found in [29]. Figure 2b also shows the macrostructure of the FZ and the BM.…”

“…This steel is composed of a fine-grain ferritic-bainitic microstructure. The chemical composition can be consulted in Table 1 and this material showed a yield strength of 808 MPa, a tensile strength of 838 MPa and 15% of elongation at failure [29]. Five series were welded using the parameters presented in Table 2.…”

“…It is important to mention that in the S5 series the welding speed on the top side was different for each sample (1.75, 1.80, 1.90, 1.95 and 2.00 m/min) while the weld pass on the bottom side was constant for all samples (2.50 m/min). The heat inputs used in welding were chosen to achieve different hardnesses in the welded series, but at the same time were maintained at a low heat input to obtain small HAZs, low softening and similar tensile mechanical properties to the BM as shown in [29].…”

Laser welding of austenitic ferrofluid container for the KRAKsat satellite

“…One of the heat sources is laser, which is now widely used for welding and material processing [11][12][13][14] and can potentially be used to weld a container. Steels with BCC [15][16][17] and FCC [18][19][20] crystallographic space groups, aluminum alloys [21], titanium alloys [22], nickel alloys [23], plastics [24], and composites [25] can be laser beam welded. These joints are characterized by a narrow weld and a heat-affected zone with mechanical properties similar to those of joints made with conventional electric arc processes [26] and often exceeding them.…”

Microstructure and tensile properties of the different thickness ASSAPH440 high strength steel/DC52D+ZF45 galvanized cold rolled sheet dissimilar metal welding joint by CO2 laser welding for automobile manufacturing

“…In recent years, there are many researchers investigating the high-strength dissimilar metal laser welded joints with a different thicknesses. Gustavo [30] has studied the relationship between the process parameters and the geometry size of laser welded joint of high strength low alloy steel (HSLA). They found that as the laser power increases or welding speed decreases, the width and the penetration of the welded joints increases, which is consistent with our experiment results (show in figures 5-7).…”