For western type crusty buns in a deck oven, temperature should be at least 220°C for 15-20 minutes, depending on size and oven load. Some bakers preheat to 240°C. Steam is usually only; pre-steam the deck, load, and steam for 30-40 seconds – leave damper closed for first 5 minutes, then open damper. Depending on load and knowing your oven, you might open the damper all the way, some only 1/2 way.
If you are attempting to produce a par-bake product for brown-and-serve; I would suggest trying to preheat to 200°C, steam and drop temperature setting to 175°C. The total bake time will be much shorter. You only need to reach an internal temperature of about 80-85° C. 10-12 minutes for buns might be sufficient. You can read more about starch gelatinization here: https://bakerpedia.com/processes/starch-gelatinization/