Casting of spherical sector
 

Hi

I am trying to model the casting process on a spherical sector in Ansys Mechanical.
since, i am new to the ansys, so I imported the geometry in .SAT format,
I am using SOLID90 as the element type and meshing the volume with tet shape.
In the loads I am assuming a fixed temperature at the base and convection at the surface.

While doing the transient analysis, i am not being able to get a solution as it say it is non-convergent.
I tried using different no. of steps and time steps but failed.

Can someone advice on this?

And also, what are the factors in accordance to which the time steps are decided?
Thanks in anticipation.