Seek advice on Ni Resist casting 2

arunmrao · Nov 25, 2017

I am planning to cast a ASTM A436 Type 2 ( 20% Ni, flake graphite type), Ni resist casting. This is an impeller bowl casting for a single stage vertical lift pump in sea water. The lifting pump is used as circulating water pump in Thermal power station.

The approximate weight of this casting is 2500 kilos.

My concern is about degassing practice to be adopted for this alloy. I have cast smaller weight castings in shorter melt times and did not experience any Hydrogen gas related issue. This is my first, with this weight of casting.

I shall welcome any advice from experts here in helping me produce a sound casting.

Thanks in anticipation.

"Even,if you are a minority of one, truth is the truth."

Mahatma Gandhi.

EdStainless · Nov 26, 2017

Seawater from near the surface with oxygen in it? NiResist 2 is not the material of option for that application. It works very well in reducing environments, but not so much in oxidizing high Cl applications.

I have never cast NiR2 in anything over about 500kg. We used very standard degassing, but we also made sure that all feedstock was baked out to assure that it was dry.
The biggest issue that I see is related to the wide freezing range and time for full solidification.
The other thing is that we did stress relive all castings, this helps greatly with holding dimensions and resisting SCC.

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P.E. Metallurgy, Plymouth Tube

metengr · Nov 26, 2017

Your use of NiResist 2 will be fine for high velocity applications like in a pump bowl with sea water at a power plant. I would guess this pump will be running nearly continuously, and has been used in similar applications.

arunmrao · Nov 27, 2017

Thanks Edstainless and Metengr for your helpful responses. Always ready to help .

New age pumps use Duplex S.S castings for this application. However, this replacement part has been in service for over 30 years and is now being replaced. Thus, you still find the Ni Resist 2 specification.

I have been considering using metallic chills, but will it cause any white iron formation in those regions? I don't know.

I shall be adopting degassing practice, using Argon gas and Nickel oxide as cover flux.

Stress relieving after rough machining at 600C will be done.

Thanks once again.

"Even,if you are a minority of one, truth is the truth."

Mahatma Gandhi.

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Seek advice on Ni Resist casting 2

arunmrao

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EdStainless

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metengr

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arunmrao

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