Refer to the spec and log, please see Poor metric results after retraining maskrcnn using TLT notebook - #17 by Morganh and Poor metric results after retraining maskrcnn using TLT notebook - #20 by Morganh
For learning rate, you can track it in training log. There are two phases. First, linear warmup to init_learning_rate. Second, learning rate will be reduced according to the specified learning_rate_steps and learning_rate_decay_levels.
If not using amp, MomentumOptimizer was used.