With the rapid development of the economy, the loss caused by metal corrosion has gradually increased in various fields such as infrastructure, transportation, energy, and marine engineering. With the rapid development of powder metallurgy, laser additive manufacturing (LAM) technology has shown significant advantages, including short manufacturing cycles and low costs. Powder metallurgy laser additive manufacturing (LAM) technology can not only repair damaged parts, but also enhance the surface properties of the material. Therefore, the LAM technology of powder metallurgy provides a new method for the repair of metal structures and the extension of their service life. In steel, duplex stainless steel has good corrosion resistance and toughness. Duplex stainless steel has the advantages of austenitic and ferritic stainless steel. There are few studies on LAM of duplex stainless steels, which are yet to be developed.
Researchers from Xi'an Jiaotong University conducted a laser cladding experiment based on LAM technology on the widely used SAF2205 duplex stainless steel substrate by using self-made duplex stainless steel powder. On this basis, the structure and properties of the cladding layer and the interface between the cladding layer and the substrate (BM) are thoroughly studied. Related papers were published in Materials and Design with the title "Laser additively manufactured intensive dual-phase steels and their microstructures, properties and corrosion resistance".
Paper link:
https://doi.org/10.1016/j.matdes.2020.108710
In this study, hot-rolled 2205 duplex stainless steel was used as the substrate. Duplex stainless steel powder prepared by electrode induction molten gas atomization (EIGA) is used as a laser cladding deposition material, and the particle size of the powder is in the range of 53-180 μm. The Ni content in the self-made dual-phase steel powder is 2.5% higher than that of the base material.
The study found that after the single-pass laser cladding test, the grain size of the welded joint increased slightly, and most of the austenite precipitated from the boundary of the brown gray ferrite phase. A large amount of dispersed austenite is also precipitated from the inside of ferrite grains, showing different shapes, such as stripe, point and bulk austenite. No pore defects and cracks were found. The microhardness of the cladding layer reaches 330HV, which is about 15% higher than that of BM. This is due to the rapid cooling rate during the laser cladding process. The ferrite content is significantly higher than that of austenite, and the microstructure of the cladding layer Has a higher dislocation density.
Multi-layer and multi-pass laser cladding was carried out on the duplex stainless steel plate, and it was found that the stripe-shaped and feather-shaped white austenite in the cladding layer area was closely distributed in the interior and boundary of black ferrite. The grain size around the cladding layer/BM interface is larger than the grain size at the upper end of the cladding layer. This is because the cooling rate after rapid laser cladding and the upper end of the cladding are preheated by subsequent cladding. The microhardness of the entire coating is in the range of 305-360HV, and the average microhardness is about 328 HV.
The tensile strength and elongation of the cladding along the laser scanning direction are 956 MPa and about 40%, respectively; the tensile strength and elongation of BM are about 760 MPa and 43%, respectively. The tensile strength and elongation in the direction perpendicular to the laser scanning direction are 899 MPa and 37%, respectively; the tensile strength and elongation of BM are about 775 MPa and 39%, respectively. The rapid cooling rate during laser cladding results in a ferrite content that is significantly higher than austenite, and the microstructure of the cladding layer has a higher dislocation density, which makes the cladding layer's tensile strength significantly higher than The tensile strength of the substrate, but the elongation is slightly reduced, all are ductile fracture. Corrosion resistance has also declined.
In summary, the best process parameters obtained through orthogonal experiments are laser power 1300W, scanning speed 480mm/min, and powder feeding speed 12g/min. Compared with the 2205 substrate, the microhardness of the coating prepared with the self-made duplex stainless steel powder is improved, and the average microhardness of the coating is increased by about 15% compared with the 2205 substrate. The proportions of austenite and ferrite phase in the cladding layer are about 47% and 37%, respectively. In this paper, the best process parameters are obtained, which can provide a reference for the subsequent laser cladding of dual-phase steel.