Porosity and Nitrogen Content of Weld Metal in Laser Welding of High Nitrogen Austenitic Stainless Steel

Abstract

Some problems such as nitrogen desorption and pores always occur in the weld metal during welding of high nitrogen steel. In order to study the nitrogen content and porosity of the weld metal of high nitrogen steel 1Cr22Mn16N, the steel was welded by CO 2 laser welding, and the influence of the shielding gas composition and heat input on the nitrogen content and porosity of the weld metal was investigated. The experimental results indicate that the weld nitrogen content increases slightly with the increase of the nitrogen content in shielding gas under the same laser welding conditions. The nitrogen content of the weld metal decreases with the increase of the heat input when pure argon is used as the shielding gas, whereas that of the weld metal is improved with the increase of the heat input when some nitrogen is added to the shielding gas. The higher the heat input, the less the porosity in the weld metal, and the more nitrogen in the shielding gas, the less the porosity becomes.KEY WORDS: high nitrogen stainless steel; laser welding; nitrogen content; porosity. used to focus the laser beam to the minimum spot of 0.2 mm in diameter, and the focal point was located just on the plate surface. Full-penetration bead-on-plate welding was carried out under four kinds of welding conditions. The laser power is 2.4 kW, and the welding speed is 1.20, 0.80, 0.60 and 0.48 m · min Ϫ1, which the heat input corresponding to is 120, 180, 240 and 300 J · mm Ϫ1, respectively. For each welding condition, five kinds of shielding gas compositions with gas flow rate of 400 L · h Ϫ1 for axial flow are used, in which the nitrogen content (weight percent) is 0, 5 %, 25 %, 50 % and 100 %, respectively. All the Ar-N 2 mixtures were premixed. After welding, the welds were inspected by Xray radiographic examination taken from the top surface to observe the porosity distribution in the weld, and the diameter of pore that can be detected is not less than 0.1 mm. The nitrogen content in the welds was analyzed by an oxygen and nitrogen analyzer, and the location of the sample in the weld used for the nitrogen analysis is shown in Fig. 2. The specimens of the welds for optical observation were mechanically polished and etched with a 10 % oxalic acid solution at 5 V for 30 s. Figure 3 shows the nitrogen content of the welds under different shielding gas compositions. It can be clearly found that the nitrogen content of the welds changes within the range of 0.53-0.59 %, that is similar with the nitrogen content of the base metal. The nitrogen content in the weld increases slightly with the increase of the N 2 in shielding gas under the same heat input. With pure argon as shielding gas, the nitrogen content of the weld is lower than that of the base metal. When the nitrogen content in the shielding gas is more than a critical value, the weld nitrogen content is higher than that of the base metal. The influence of heat input on the weld nitrogen content can be also found from Fig. 3. The nitrogen content in the weld metal decreases with the increa...

Effect of Brazing Temperature on Microstructure and Mechanical Property of High Nitrogen Austenitic Stainless Steel Joints Brazed with Ni–Cr–P Filler

“…However, nitrogen pores can easily occur in the weld metal during fusion welding of HNS due to the difference of nitrogen gas solubility between molten and solid metals. 28) Thirdly, the brazing process with Ni-Cr-P filler at 1 050°C has no effect on the microstructure and phase composition of HNS substrate. The precipitation of Cr 2 N in the HNS substrate during the cooling process of brazing can be avoided.…”

Nitrogen Steels and High‐Nitrogen Steels: Industrial Technologies and Properties

“…[46,47] Negative effects, such as porosity, hot cracking, and less of N and Mn in the weld joint, [48][49][50] can be prevented through the optimization of laser welding parameters. [47,[51][52][53][54] Sheets (3 or 4 mm in thickness) of two new nitrogen steels (Table 7) and two standard steels after thermomechanical treatment were butt welded at room temperature by a laser according to modes that prevent the formation of defects of the welding seam. [55] According to experimental data and computer, modeling of the laser welding of more thick sheets requires preheating.…”

“…[ 46,47 ] Negative effects, such as porosity, hot cracking, and less of N and Mn in the weld joint, [ 48–50 ] can be prevented through the optimization of laser welding parameters. [ 47,51–54 ]…”

The Influence of Shielding Gases on Keyhole-Induced Porosity and Nitrogen Absorption in SS 304 Stainless Steel Fiber Laser Welds

“…As the high temperature of the laser in the welding area leads to the dissociation of nitrogen from polyatomic molecular nitrogen gas N 2 to the monatomic nitrogen gas N [20], as shown in Eq. 1.…”

“…This means that the solubility limit of nitrogen in molten stainless steel can be increased by raising the partial pressure of the diatomic gas above the melting point. Nevertheless, there are many doubts about Sievert's law's applicability when describing diatomic gas dissolution in molten weld metal in the presence of plasma [20,21,23].…”