Magnetic Evaluation of Microstructures and Strength of Eutectoid Steel

Abstract

Microstructures and strength of variously heat treated eutectoid steel were evaluated by magnetic property measurements. Isothermal transformation, continuous cooling or spheroidization heat treatment was performed to produce various microstructures. Microstructural parameters (phase, pearlite interlamellar spacing), mechanical properties (fracture strength) and magnetic parameters (coercivity, remanence, hysteresis loss, saturation magnetization) were measured to investigate the relationships among these parameters. Coercivity and remanence were observed to be high in order of martensite, pearlite and ferrite phase. The linear decrease of coercivity and remanence with the interlamellar spacing and the linear increase of those with fracture strength of pearlitic eutectoid steel were found. Coercivity and remanence were suggested as potential magnetic parameters for discriminating phases and quantitatively assessing the pearlite interlamellar spacing as well as strength of eutectoid steel.

Magnetic Evaluation of Microstructure Changes in 9Cr-1Mo and 2.25Cr-1Mo Steels Using Electromagnetic Sensors

“…For example, irreversible domain wall motion past pinning features in a ferromagnetic material can be detected as a sharp pulse voltage in a search coil wound around the specimen, which is known as Magnetic Barkhausen Emission (MBE) or Barkhausen Noise (BHN) [15]. It has been reported that microstructural changes involving grain size, martensitic lath size, precipitation and dislocation density result in changes in the magnetic properties of steel [12,[16][17][18][19][20][21]. For example, Moothy et al [17,18] correlated grain/lath size coarsening and precipitation in 0.2C steel, 9Cr-1Mo and 2.25Cr-1Mo steels with MBE parameters.…”

“…A maximum MBE peak occurred at an intermediate tempering time (around 10 hours at 923 K (650°C) when there was a certain combination of particle size distribution (affecting magnetic domain pinning strength) and interparticle spacing (affecting mean free path of the domain wall displacement). Dissolution of M 2 C or M 2 X precipitates in 9Cr-1Mo [17, 18] and 2.25Cr-1Mo [12,19] steels was indicated by a large decrease in MBE peak values after a long tempering time. Yamaura [22] found that for pure iron, in which grain boundaries are the predominant domain wall pinning points, the BHN power voltage obeyed a Hall-Petch-type relationship with grain size, which was in agreement with Sakamoto's theoretical prediction [23].…”

Evaluation of thermal degradation of 2.25Cr–1Mo steel by magnetic Barkhausen noise

“…needed because other factor besides carbides coarsening such as shape and spheroidization of carbides [6,11] might affect the measured MBN.…”

“…MBN method has been applied as one of NDE techniques due to its high sensitivity for microstructural changes and convenience [3][4][5][6][7]. Although there were some reports on the usefulness of MBN for the evaluation of residual stress [3], thermal degradation [4], and fracture toughness [5], the correlations between MBN parameters and microstructures and strength are still lacking.…”

Evaluation of microstructures of variously heat treated carbon steel by magnetic coercivity measurement

“…1 Introduction Usual microstructure evaluations of steel products have been performed in a destructive way by cutting, polishing and using microscopical observation, which is selective, time-consuming, and laborious. There are increasing needs to introduce nondestructive evaluation techniques for better time saving and economic quality control of steel products.Magnetic method [1][2][3][4][5][6][7][8][9][10], by which correlations between material properties and magnetic parameters can be obtained, have been applied as one of nondestructive evaluation techniques. Although previous researchers have reported the effect of grain size [3][4][5][6][7], carbon content [4], morphology of carbide particles [8], applied stress [9] and plastic deformation [10] on magnetic coercivity in ferromagnetic steels, the correlations between magnetic coercivity and various microstructures of steels depending on specific heat treatment conditions are still lacking.…”