Abstract It was verified that SAE 4130 steel plates crack when laser beam welded at room temperature (RT). To overcome this problem, this work proposes a high temperature (HT) laser welding in order to reduce the residual stresses and create a bainitic structure instead of a martensitic one. A conventional post-welding heat treatment (PWHT) had been used as a comparison for HT. The centerline crack disappeared after a heat treatment of both in-situ (HT) or after inserting in a furnace (PWHT) at 500 °C for 10 minutes. The finite element analyses indicated a residual stress reduction from 163.70 to 3.72 MPa in the fusion zone (FZ) of the welds from RT to HT. The hardness obtained in FZ depends on the thermal cycle induced microstructure of the welds as 400 HV, 340 HV and 250 HV, for martensite (RT), tempered martensite (PWHT) and bainite (HT) micro-constituents. The proposed in-situ high-temperature laser beam welding method proved its usefulness to solve the center crack issue in SAE 4130 joints.

ABSTRACT Stainless steel and copper alloys joints are often applied in aerospace, marine and power industries where both high thermal and electrical conductivity (Cu) and corrosion resistance (steel) are required. In the aerospace industry, in particular for the combustion chamber of rocket engines, copper and steel combinations offer perfect materials selection due to their combined high thermal conductivity and good stiffness. In this work, laser welds were produced with intensity between 3.8 × 104 and 5.7 × 104 W/mm2 and a heat input between 72 and 108 J/mm, giving an aspect ratio of 1.8. The microstructure of the weld beads was marked by chemical heterogeneities due to the phase separation between Cu and Fe in the liquid state. The phase separation gave rise to globular precipitates which further transform due to a secondary precipitation at temperatures below 1000 °C. The steel side part of the weld presents around 20% Cu, leading to a liquation of the grain boundaries and cracking at high heat inputs. The hardness values situated between both base materials and the tensile shear behavior, when the weld is sufficiently tough, present strength up to 350 MPa and elongation up to 10%.

ABSTRACT The heat input is the amount of energy supplied per unit length of the welded workpiece. In this study, the effect of two different heat inputs in laser beam welding of a high strength aluminum alloy AA6013-T4 was evaluated from macrostructural and microstructural points of view. The experiments were performed using a continuous wave 2 kW Yb-fiber laser with 100 µm spot size on the upper surface of the workpiece. Keeping the heat input at a given level, 13 or 30 J/mm, the laser power was changed from 650 W to 2 kW and the welding speed from 33 to 150 mm/s. In the condition of higher heat input 30 J/mm it was possible to obtain both cutting and welding processes. For 13 J/mm, welding processes were obtained in conduction and keyhole modes. The equiaxed grain fraction changed with changing speed for the same heat input. The laser processing induced a decrease in the hardness of the weld bead of about 25% due to the solubilization of the precipitates. The estimated absorptivities of the laser beam in the liquid aluminum changed largely with experimental conditions, from 4.6% to 10.5%, being the most significant source of error in measuring the real amount of energy absorbed in the process. For the same heat input the macrostructure of the welded surfaces, i.e., humps and dropouts, changed as well. All these facts indicate that the heat input is not a convenient method to parameterize the laser beam welding parameters aiming the same weld features.

Duplex stainless steels have been extensively used in parts that are subject to corrosive environments and that have high mechanical strength requirements. Welding usually distorts the well-balanced austenite-ferrite ratio, and can produce brittle intermetallic phases; therefore, post-welding heat treatments are usually required. For applications where post-welding treatments are not possible, low heat input methods, such as micro-tungsten inert gas welding (TIG) and laser beam welding (LBW), can be used. The present investigation analyzed the microstructure, mechanical, and corrosion properties of 2507-classduplex steel tubes after welding. The microstructures of the heat-affected zones and the fusion zones contained variable amounts of ferrite and austenite. In the heat-affected and fusion zones in the TIG samples, the microstructures were primarily composed of ferrite grains with allotriomorphic austenite at the grain boundaries, intragranular Widmanstätten needles and plate-like precipitates. The LBW samples showed much finer microstructures, which contained austenite in the grain boundaries and fine austenite precipitates in the ferrite grains. Deleterious intermetallic phases, such as σ-phases, were not observed using X-ray diffraction. The tensile strength properties were very similar for the TIG and LBWsamples, reaching tensile strengths of approximately 840 MPa and total elongations between 61 and 87%. The heat-affected zone of the TIG welds were particularly susceptible to corrosion (0.05 mm/year) compared to the base metal (0.007 mm/year) and the laser welds (0.01 mm/year). Therefore, laser welding is a promising technique for the welding of 2507-class duplex tubes.

AISI 300M ultrahigh strength steel has been used in a number of high demanding applications, such as the VLS Brazilian rocket project. This work intends to propose laser beam welding, with subsequent tempering, as a possible route for the fabrication of engineering pieces of this steel. A 2 kW fiber laser was used to produce welded coupons for metallographic, hardness and tensile strength tests. It has been shown that convenient laser parameters for a 3 mm thick plate are 50 mm/s welding speed and 1200 W laser power. However, both welded materials and heat-affected zones presented high hardness and negligible plastic deformation. In order to produce useful engineering parts, it was suggested a tempering treatment for 2 hours at temperatures of 200 or 400ºC. Tensile mechanical testing has shown that welded and tempered coupons presented both yield and maximum strengths comparable to the unwelded material. On the other hand, a maximum elongation of about 4% was obtained, in comparison with 12% from the bulk sample.