Effect of N-bonding elements on dissolution and precipitation of B in micro B-treated ultra-heavy plate steels has been investigated,utilizing Thermo-Calc thermo-dynamic software and experimental test.The calculation results show that Titanium or excessive Aluminum content is effective to bond Nitrogen,preventing BN from forming and thus keeping boron in solid solution in austenite,while Vanadium is not.The experiment has also revealed that slight amount of solution Boron by addition of Ti or a little excessive Aluminum is helpful to improve hardenability of the steels. Effect of N-bonding elements on dissolution and precipitation of B in micro B-treated ultra-heavy plate steels has been investigated, using Thermo-Calc thermo-dynamic software and experimental test. The calculation results show that Titanium or excessive Aluminum content is effective to bond Nitrogen, preventing BN from forming and thus keeping oxygen in solid solution in austenite, while Vanadium is not the experiment has also revealed that a slight amount of solution Boron by addition of Ti or a little excessive Aluminum is helpful to improve hardenability of the steels.