Monitoring Heat Treatments in Steels by a Non Destructive Ultrasonic Method

Abstract

In order to determine if heat treatments can be discerned by nondestructive ultrasonic testing, samples of SAE 1045 and SAE 4140 steels were subjected to the classical heat treatments of annealing, normalizing, quenching, and quenching and tempering, and their elastics constants, Young's, shear and Poisson's moduli, were monitored by ultrasound. Results show that the microstructural differences associated to the various heat treatments generate differences on the elastic constants that can be effectively discerned by the use of longitudinal and shear ultrasonic waves. Special attention is given to Poisson's modulus, since for its determination only times of flight of longitudinal and shear ultrasonic waves, and not the distance the waves travel, are required, which is of quite practical importance, since measurements are simplified and a fundamental source of error is eliminated. It is thus shown that the microstructural evolution of a steel part subjected to heat treatments can be monitored by this simple ultrasonic method.

Effect of Annealing Time and Temperature Parameters on the Microstructure, Hardness and Strain-Hardening Coefficients of 42CrMo4 Steel

“…0. These results are in range of hardness expected by the literature of the subject [8,9,15]. Summing up, the hardness results indicate that the annealing scheme no.…”

“…Nevertheless, in industrial conditions, the particularly time-effective measurement of hardness is employed to examine the softening of steel before subjecting the treated steel to metal forming processes. Although in many cases light optical microscopy (LOM) and scanning electron microscopy (SEM) give accurate results of metallographic examination [7,[13][14][15], electron back-scattered diffraction (EBSD) [16,17], transmission electron microscopy (TEM) [1,18] and X-ray diffraction (XRD) [19][20][21] seem to be much more powerful tools for evaluating microstructure development due to plastic deformation or heat-treatment. In [20] the authors employ XRD to study the hardening and tempering behaviour of the En24 steel (ISO equivalent 34CrNiMo6) via X-ray peak profile analysis.…”

“…Although 42CrMo4 steel (AISI 4140) is a popular machine-building material, literature recommends different annealing procedures for softening the material and facilitating its cold working. Not to mention the fact that the literature of the subject gives various annealing parameters [6,8,9,15,37]. In addition, a very important factor in industrial conditions is to obtain the highest steel deformability in optimal time of the annealing process.…”

Effect of Annealing Time and Temperature Parameters on the Microstructure, Hardness, and Strain-Hardening Coefficients of 42CrMo4 Steel

“…Nevertheless, in industrial conditions, the particularly time-effective measurement of hardness is employed to examine the softening of steel before subjecting the treated steel to metal forming processes. Although, in many cases, light optical microscopy (LOM) and scanning electron microscopy (SEM) give accurate results of metallographic examination [7,[13][14][15], electron back-scattered diffraction (EBSD) [16,17], transmission electron microscopy (TEM) [1,18], and X-ray diffraction (XRD) [19][20][21] seem to be much more powerful tools for evaluating microstructure development owing to plastic deformation or heat treatment. In [20], the authors employ XRD to study the hardening and tempering behaviour of the En24 steel (ISO equivalent 34CrNiMo6) via X-ray peak profile analysis.…”

“…Although 42CrMo4 steel (AISI 4140) is a popular machine-building material, the literature recommends different annealing procedures for softening the material and facilitating its cold working, not to mention the fact that the literature of the subject gives various annealing parameters [6,8,9,15,37]. In addition, a very important factor in industrial conditions is to obtain the highest steel deformability in an optimal time of the annealing process.…”