Corrosion resistance of the welded joints from precipitation hardening steel 17-4 PH

The combination of high strength, high hardness and good corrosion resistance with relatively easy thermal treatment precipitation hardened steel 17-4 PH causes that precipitation hardened steel 17-4 PH is widely used in industrial practice. This kind of steel has also good weldability. proper welded joint can be easy obtained from this steel with appropriate welding procedure. This paper presents results of research on combination of selected parameters of welding and heat treatment after welding on corrosion resistance of the welding joints. High corrosion resistance of this joint found its application in the centrifugal compressor impellers working in the environment containing mist of nitride acid. Welded joints were made with using two welding methods: by hand with rutile coated electrode and semi-automatic with flux cored filler wire. After welding the joints were heat treated as follows: 1) annealing at 620 degreesC - 2 hours 2) solution heat treatment 1040 degreesC - 2 hours and ageing 550 degreesC - 2 hours; 3) solution heat treatment 1040 degreesC - 2 hours and ageing 620 degreesC - 2 hours. After heat treatment the joints were evaluated for corrosion resistance. The tests were carried out in boiling nitride acid with 50% concentration and at the temperature 115 degreesC for 23, 72 and 114 hours. The scanning and light microscopic examinations were performed before and after corrosion test. In addition the strength evaluations of the joints were performed. It was concluded that heat treatment plays an important role in corrosion resistance of the joints obtained with described methods. It was also found that corrosion intensity and distribution depends on both welding method and heat treatment.