I would almost bet that you have one or both front wheels out of balance. Sometimes the wheel weights will shift and you can then feel the vibration in the steering wheel. When there is steering wheel vibration that is present at certain speeds and then disappears at slower and higher speeds, it almost always is a wheel balance problem.
Take your car to a tire shop that does high speed spin balancing and tell them your problem. It will almost certainly be corrected by rebalancing the front wheels. Fred.