Place 3-4 lbs corned beef in bottom of instant pot, pour spices over beef. Add 6 cups of water, or enough to cover beef. Secure lid and set Pressure Release to SEALING.
Select the MEAT/STEW setting and set cooking time for 60 minutes on high pressure. Let pressure release naturally, it may take about 30 minutes. Keep 2 cups of cooking liquid, discard remaining liquid.
While pressure is releasing, chop up 1 small head of green cabbage, 1 lb carrots, and 1 lb red or yukon gold potatoes into similar sized pieces. About an inch thick. Cabbage can be wedged.
Remove beef from pot. Cover with tin foil to keep warm while vegetables are cooking. Place steamer basket in pot, layer potatoes, then carrots, then cabbage into pot. Secure lid and set pressure release to SEALING. Press CANCEL button to reset the system. Select the STEAM setting, and cook 3 minutes on high pressure.
Quick release valve when time goes off. Slice beef and serve with steamed vegetables