Weldability features of Inconel alloy 625
Outstanding weldability was one of the basic goals in the alloy development programs. While the composition developed a matrix that was necessarily a solid-solution kind, the presence of a relatively high content of niobium and its participation in a prolonged aging reaction caused concern for resistance to strain induced cracking while post-weld exposure to moderate temperatures. To evaluate this feature, pierce-miller patch weld tests were performed with outstanding outcomes. The restrained circular welds were subjected to 1000 hours at 649oC or 1200oF, repair welded and then provided additional exposures to 649oC or 1200oF and 704oC or 1300oF without cracking. Field experience above the last quarter century strengthens the observation that Inconel alloy 625 is one of the highly weldable materials among the family of super alloys. Moreover, its competency to tolerate dilution by various elements has established it as a premier exclusive welding material.
For several years, Inconel alloy 625 welding materials have been utilized to weld 9% nickel steel structure that are employed in the cryogenic applications because of the excellent strength, ductility and impact strength of the austenitic kind welds and the toleration of dilution from 9% nickel steel.
Simply from the composition of the Inconel alloy it was found that these should have excellent corrosion features in the various conditions even though the initial lab tests were limited to boiling nitric acid. Early evidence of pitting corrosion resistance was received from the tests at Francis L Laque corrosion laboratory at Wrights vills Beach NC. The entire corrosion data was produced from the comparison test coupons of different corrosion resistant alloys that are subjected to the various conditions.
As an alloying agent, Nickel increases resistance to the different corrosive conditions, specifically to the reduction conditions, neutral salt solutions and alkalis. It is extremely helpful in avoiding stress corrosion cracking. On the other side, chromium provides resistance to the non-oxidizing conditions like hydrochloric acid and also offers excellent resistance to oxidizing solutions like nitric acid. Molybdenum increases the mechanical strength as a matrix stiffener, significantly increases the corrosion resistance in the reducing conditions and provides pitting resistance. The critical temperature for pitting increases with increase in the content of molybdenum and chromium. The anti-pitting property of molybdenum is described by 2.4 multiplier contained in the composition.
Applications of Inconel alloy 625
While outstanding strength, oxidation resistance and fabricability of Inconel alloy 625 added to its selection for aerospace applications, its excellent corrosion resistance has led to outstanding success in the different industries. Navy and sea water applications are high due to the combination of high strength and resistance to pitting and stress corrosion cracking. Specifically, the alloy is used in the crucial submarine applications where reliability in seawater with crevice conditions is required.
The Inconel alloy 625 welding products are commonly used to overlay steel power drive shafting due to their excellent wear features and resistance to sea water pitting and crevice corrosion. In production of nitric acid, Inconel alloy 625 is commonly used as catalyst grid supports. In the power production plants, alloy 625 has been used for several years in the scrubber systems and stack liners. Various other corrosion based applications have received advantage of Inconel alloy 625’s excellent and flexible corrosion resistance properties.