There are no metal alloys stronger than steel at the moment. There are other materials with different combinations of properties (high temperature mechanical strength for example, or strength to density ratios or elastic modulus to density ratios which optimize structures for weight) but there is no metal alloy with a higher tensile strength than steel.
Stronger how? The beautiful thing about steel is there are so many different types all of them behaving differently... some are harder, some more durable, some have higher corrosion resistance... it all depends on the application but there is a reason we still use steel in so many applications, selecting the type of steel to use is what is important. But to answer your question Titanium alloys are very tough and stronger than steel in many applications but also difficult to work with.