Porosity can be a problem with the nickel alloys, the main culprit being nitrogen. As little as 0.025% nitrogen will form pores in the solidifying weld metal. Quite light draughts are capable of disrupting the gas shield and atmospheric contamination will occur resulting in porosity. Care must be taken to ensure that the weld area is sufficiently protected and this is particularly relevant in site welding applications. With the gas shielded processes, gas purity and the efficiency of the gas shield must be as good as possible. Gas hoses should be checked for damage and leaks at regular intervals and, with the TIG process, as large a ceramic shroud as possible should be used together with a gas lens. It goes without saying that gas purging of the root is essential when depositing a TIG root pass.
A small amount of hydrogen (up to 10%) added to the argon shield gas has been found to reduce the problem. Start and finish porosity is a problem when MMA welding. The weld start should be carried out by welding back over the arc strike position, remelting any porosity that has formed due to the poor gas shielding at the start of the weld. Care also needs to be taken at the weld end, with the arc length reduced and travel speed increased slightly to reduce weld pool size.
Oxygen is also a cause of porosity in certain circumstances when it combines with carbon in the weld pool to form carbon monoxide. Consumable manufacturers generally overcome this problem by ensuring that sufficient deoxidants (primarily manganese, aluminium and titanium) are present in the filler metal.
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On Friday, March 15, 2019 at 10:02:03 AM UTC-5, CLV wrote:Please suggest to overcome porosity problems observed during Monel 400 welding with CuNi-7 wire.Porosity is generally the result of inadequate cleaning of the filler wire and groove area and / or loose Argon connections. Check all your Argon connectionsfrom the torch to your regulator on the tank. All you need is one loose connection to suck a little air into your hose when you start to weld. Also check the hose proper by pressurizing the hose and submerging it in a water tank. Use some 'SNOOP' which is the brand name of a specific soap like liquid which you spray on connections to see if they are leaking. You might also want to use a Argon / Helium mixture. Their are other reasons that can cause porosity. These are just two that I have had more experience with. Also try a search for 'Monel Welding' or 'Monel Porosity' on google.
https://materials-welding.blogspot.com/
https://www.linkedin.com/groups/122787
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