基于多层结构磁滞模型的硬化层深度磁学表征与检测方法

Characterization and Detection Method for Case Depth Evaluation Based on Magnetic Hysteresis Model of Multi-layered Structures

零部件表面经过硬化处理后,一般将形成由硬化层、过渡层和心部组织组成的三层结构,而硬化层深度是表面力学性能的重要评价指标。为将磁测法应用于硬化层深度的定量检测,建立了基于点状磁荷假设的多层结构磁滞模型,预测出三层结构微分磁导率曲线的双峰特性。双峰峰值、峰值比等参数与硬化层深度存在良好线性关系,由此提出一种硬化层深度的磁学无损检测新方法。对具有不同深度高频感应淬硬层的40Cr钢杆试样进行磁滞回线试验测试,分析结果表明:相比矫顽力,微分磁导率曲线的双峰峰值比更适用于硬化层深度的定量表征,其重复测试结果的变异系数小于1%,与硬化层深度的线性拟合确定系数高于0.95。建立的多层结构磁滞模型可为硬化层深度的磁测法提供理论依据,基于微分磁导率双峰曲线的硬化层深度检测方法可推广至平面或曲面构件。

Surface heat treatment can induce micro-structural changes in the components surface to form hardened and transition layer above the core zone, which can be treated as a three-layer structure. The case depth of the hardened layer is an important criteria for evaluating the mechanical properties of the surface material. Magnetic hysteresis model for multilayer structure is established based on point-like magnetic dipole for quantitative evaluation of case depth. Double peaks occur in the predicted differential permeability curve of three-layer structure. The heights of the two peaks and the height ratio almost linearly change as the increasing case depth to produce a new case depth evaluation method. The measured differential permeability curves, which are obtained from high-frequency induction hardened 40 Cr steel rods, show that the peak heights ratio is more suitable for case depth evaluation as compared to coercive force. The variation coefficients among the repeated testing results of the two peak heights are lower than 1%, and the linear regression coefficients are higher than 0.95. The proposed hysteresis model can act as theoretical tool for case depth evaluation using magnetic testing method, and the proposed method can be applied for plat or curved components.