I did't find a easy way to upgrade the crucible. I guess I could use my Ceramic crucible to melt Titanium and Niobium together to make a Niobium Titanium crucible.
But I found that I can't gain Titanium before I have Tungsten which Smelter and Extruder need.And I try almost all the way to output melted Rutile in the crucible, but I falied. So now I could only upgrade my crucible by 3 complex ways:
1.Wash thousands of Tantalite Ore or Wolframite Ore to gain Tantalum Nuggets or Tungsten Nuggets.
2.Centrifuge tons of lava to gain Tantalum Nuggets or Tungsten Nuggets.
3.Use Chromium Crucible to melt Iridium. But this two matrials are very rare.
So I want to know that is it a bug or there is another easier way I didn't find? Please.