Journal of Welding Science

In this study, DIN 34CrAlNi7 Nitriding steel in two states before and after nitriding, were welded by tungsten-gas arc welding process using two types of fillers (ER309L and ER312). The aim of this research was to investigate the best conditions for welding (before or after nitriding) and also to choose the best filler metal. The microstructure of the joint was examined using an optical microscope. A tensile strength test was also used to evaluate the mechanical properties. Fracture surfaces were also studied using a scanning electron microscope (SEM). According to the results Welding of these steels with ER309L filler is allowed only in the pre-nitriding state. If the base metal is nitriding, due to microstructural changes in the weld metal, filler metal ER309L cannot be used. However, the results of samples welded with ER312 filler metal show that if the base metal mixing percentage is less than 30%, this filler can be used for welding base metals in both before and after nitriding.

The influence of filler metals on the microstructure and corrosion behavior of AISI 316L welds was investigated. Gas Tungsten Arc welding (GTAW) process was applied to join the AISI 316L plates using ER 316L and ER 312 filler metals. The obtained microstructures were characterized by optical metallography and scanning electron microscope (SEM). Corrosion assessments were conducted in 3.5% NaCl using a three electrode cell.  Open circuit potential and potentiodynamic polarization examinations were conducted on the welds and base metal. Microstructural evaluations indicated that a combination of austenite and ferrite phases was formed in the welds fabricated by both filler metals. Based on the micro hardness tests, the weld fabricated by ER 312 filler exhibited superior harness compared to the ER 316L weld. Corrosion evaluations also show that the weld metal obtained from two filler metals has a lower corrosion rate due to the higher amount of chromium and higher ferrite compared to the base metal. Also, the lower corrosion current of ER 312 weld metal compared to ER 316L weld metal is for this reason. In contrast to the base metal compared to the two welding metals, the result of the two filler metals has shown better pitting corrosion results according to the electrochemical tests and also the examination of the surfaces using an optical microscope after these tests, that these results are due to The presence of two phases of austenite and ferrite in the vicinity of each other in weld metals and the intensification of galvanic corrosion is due to the discharge of the austenite phase from chromium and molybdenum.
 

High entropy alloys are especially suitable for use as filler metals in brazing due to their excellent properties. in the present study, three powders with the composition of CoxCrxCuxFexMnxNix (X atomic percentage of the element) were designed using the criteria of these alloys as well as jmatpro software. in the next step, using mechanical alloying, filler nano powder was synthesized and characterized by X-RAY analysis (XRD) test and the effect of filler composition on the thermal behavior of the alloy was studied. then the filler was used in Inconel 600 super alloy brazing, the single-phase solidification behavior and the absence of boron and silicon in the high entropy filler led to the creation of a continuous microstructure without eutectic components or brittle phases in the brazing interface. thus, the shear strength test was performed and 545 MPa  was the highest shear strength obtained among the three filler compounds. in brazing conventional filler metal, incomplete isothermal solidification and subsequent thermal solidification of the residual liquid results in large grains of chromium-rich boride phase distributed throughout the microstructure. not using compounds that lower the melting point in the filler for the purpose of joining the nickel-based superalloy is considered an important step in reducing the subsequent brazing processes.