It's the same metal, that's called Columbium in the USA and Niobium in Europe and here in Brazil. Correct symbols are Cb (not CB, as you wrote) for columbium and Nb (not NB, as you wrote) for niobium.
So, don't worry, Cb and Nb written on a specification are the same thing.
By the way, Wolframium (symbol W) and Tungstenium or Tungsten (symbol Tg) are also the same metal, so if someone says WIG instead of TIG, they're referring to the same welding method (joking, in my almost 50 years dealing with welding I've never heard someone saying WIG)
Giovanni S. Crisi
Sao Paulo - Brazil
There is not a CB on the Periodic chart, at least that I can remember
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