Thank you for your elaboration. In this case, for example, I will keep the element size a constant say 0.8mm and run the simulation with a series of time increment experiments by changing the initial and minimum substeps to 1,2,4,8,16 to see the effect of substeps on Accumulated Plastic Strain changes. After a set of time increment experienments are done with 0.8mm elements, I will then proceed to other element size to see if smaller time step is the reason leading to non-convergence of Accumulated Plastic Strain that I faced earlier.
For your information, this is the temperature loading profile of my simulation: