Stress Measurement in Carbon Steel by Magnetic Barkhausen Noise Technique

The Magnetic Barkhausen Noise (MBN) technique can evaluate the residual stresses in carbon steel and provide information about the relationship between residual stress level and MBN signal. This research work is based on the analysis of MBN signals obtained from carbon steel samples. ASTM A36 and A516 carbon steel were used to vary the residual stress by heat treatment process with 5 conditions: annealing, normalizing, quenching in oil, quenching in water and quenching in salt water. The microstructure and hardness of samples also were varied by these heat treatment processes. Twelve samples (including base materials) were cut to analyze the microstructure and hardness by the microscope and hardness testing machine. Reference materials from each condition were established to represent the MBN signals. The MBN technique was used to evaluate the residual stresses from heat treatment process on each reference material. Then each sample was prepared to tensile specimen. All specimens were applied static tension load below yield point. The load was increased at 25 N/mm2 (MPa) in increment. Each tensile stress level was measurement by MBN technique at 0 and 90 degree of direction of tension axis. The experimental results found that the MBN signal amplitude changed as the condition of heat treatment changed and the relationship between tensile stress and MBN signal showed linear correlation. This research is useful to understand and guide for establishing the reference materials for residual stress measurement by MBN technique.