Research On Detection Technology Of Carburized And Hardened Depth Of The Magnetic Coercivity

The processing of aero-engine gear materials all needs surface hardening treatment such as carburizing or nitriding in order to prolong gear fatigue life. Among them, carburizing hardened layer depth is a key technical indicator to reflect the quality of the carburizing material. The traditional method to measure the depth of carburized hardened layer is metallographic method which belongs to destructive sampling with low detection efficiency.This thesis proves that the materials’ related features such as the magnetic coercivity value, the materials’ carbon content as well as the martensitic type and content after being carburized will do no harm to judge the carburized layer’s thickness. This thesis chooses to select 20 Cr Mn Ti as the research object which is commonly used as the materials to process gear, conducts carburization toward a majority of 20 Cr Mn Ti bar samples separately and gets different case depth. Against 20 Cr Mn Ti bar sample, this thesis designs a U-shaped magnetic sensor which programs Micro-Manager plug-in to realize data acquisition, processing and real-time display at the Icy platform in signal processing. Through the study of the saturated hysteresis loop under different carburizing depth and the extraction of coercivity voltage value, the conclusion can be drawn that the remanence decreases with the increase of coercivity value and the signal of coercivity can sensitively reflects the changes of carburized layer depth.This thesis selects the case that the thickness of carbon hardened layer decreases led by tempering grinding burns on the tooth surface commonly seen on aviation gear; extracts coercive force voltage value through research on the saturation hysteresis loop of the normal tooth surface and the tooth surface tempering grinding burns and thus gets the conclusion that the coercivity value without tooth wear burns is much bigger than the coercivity value of the tooth surface tempering grinding burns and the thicker the tooth surface’s grinding burn layer of tempering type is, the smaller the coercivity value detected.The magnetic coercive force testing system designed in this thesis can sensitively reflect the changes of the materials’ carburized layer depth which provides an online and non-destructive method for material’s cementation quality.