采用压力容器常用钢Q345R制作拉伸试件。在拉伸过程中分别进行在线检测和离线检测，研究试件表面磁场强度HP、磁场梯度K及强屈评价因子最大值mmax是否可用来判断试件的弹塑性状态。结果表明，在线检测时，可利用HP曲线形状和mmax大小来判断试件的弹塑性状态;离线检测时，HP信号强度和Kmax大小在屈服前后有较大差别，可作为试件弹塑性状态的判据。

The tensile samples were made of Q345R steel which was used commonly in stress vessel. The variation of low-alloy steels surface magnetic field intensity HP, magnetic field gradient K and mmax according to tensile stress and plastic strain were studied during online and offline tensile testing, so as to examine whether these parameters could be utilized to determine their deformation state. The results suggested that the deformation state could be identified by the shape of HP signals and the magnitude of mmax during online inspection, while the intensity of HP signals and Kmax could be used during offline inspection.