Hydrogen induced delayed fracture behavior of 4kinds of Mn-B type ultra-high strength steel with different carbon content at quenched and tempered status was studied by means of electrochemical cathodic hydrogen charging,hydrogen thermal desorption spectrometry(TDS)analysis and slow strain rate test.The results show that hydrogen embrittlement susceptibility of tested steels increase with rising carbon content,while the hydrogen embrittlement susceptibility of tested steels is no longer increasing above 0.3...