M.r. Borhani, S.r. Shoja Razavi, F. Kermani, M. Erfan Manesh, S.m. Barekat, H. Naderi Samani, M. Shahsavari,
Volume 8, Issue 2 (1-2023)
Abstract
The purpose of this research is to laser cladding of stellite6 and stainless steel 17-4PH powders on the substrate of stainless steel 17-4PH, and investigate its solidification microstructure. The results showed that the microstructure of the stellite6 cladding has a cobalt solid solution ground phase with an FCC structure and Cr7C3 and Cr23C6 carbides. Also, the values of the primary dendrite distance and the distance of the secondary dendrite arm have decreased by moving away from the interface; The reason for this is related to the difference in the cooling rate in different parts of the coating. The microstructure of 17-4PH stainless steel coating includes martensitic, ferritic, and austenitic phases; Due to the same chemical composition of the substrate and the cladding, the weight percentage of elements such as iron, nickel, chromium, and copper did not change from the cladding to the interface. It indicates the uniformity of the chemical composition of the cladding and the substrate. The calculated microhardness for the cladding of stellite6, the substrate and the cladding of stainless steel 7-4PH is about 480, 350, and 350 respectively. The reason for the higher microhardness of the cladding is the presence of chromium carbides (Cr7C3 and Cr23C6) formed in the cobalt field and the cobalt solid solution field of the cladding.
A. Adelian, Kh. Ranjbar, M.r. Tavakoli Shoushtari,
Volume 10, Issue 1 (6-2024)
Abstract
This research studied the effect of two-stage over aging treatment on the pitting corrosion behavior and microstructure of the weld metals in the 17-4 precipitation hardening stainless steel. For this purpose, this steel was subjected to solution annealing heat treatment at 1035°C for one hour before welding. Then gas tungsten arc welding (GTAW) was performed using ER630 similar filler metal. Subsequently, a section of the weldment was subjected to two-stage over aging treatment. The microstructure and corrosion resistance of the weld zone after the two-stage over aging treatment were investigated and compared with the weld zone behavior in the as-weld condition. Microstructural studies showed that the two-stage over aging treatment of the weld zone led to the tempering of the martensitic, the formation of more reversed austenite, and the formation of α-ferrite. The volume fraction of austenite in the as-weld condition was approximately %7 and increased to about %30 after two-stage over aging treatment, a four-fold increase. The pitting potential (EPit) of weld metal was -18.15 mv in the as-weld condition and reached 122.54 mv after two-stage over aging treatment, which also signifies an improvement in pitting resistance. The two-stage over aging treatment also reduced the potential differences between the different parts of welding zones reducing the galvanic corrosion occurrence. The assessment of mechanical properties through impact test revealed that impact resistance after
two-stage over aging treatment can be increased by about %66 compared to as-weld condition.
