Photothermal, Structural, and Microstructural Characterization of SAE4320H Automotive Steel
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Photothermal, Structural, and Microstructural Characterization of SAE4320H Automotive Steel Alberto Lara-Guevara, Ignacio Rojas-Rodrı´guez, Ruben Velazquez-Hernandez, David Jaramillo-Vigueras, Karina del A´ngel-Sa´nchez, and Mario E. Rodrı´guez-Garcı´a (Submitted June 29, 2015; in revised form October 6, 2016; published online March 29, 2017) SAE4320H steel was characterized by photothermal radiometry spectroscopy, scanning electron microscopy, x-ray diffraction, and Vickers microhardness, to study metallurgical property changes as a result of the annealing heat treatment. Photothermal radiometry (PTR) images of hot forged and annealed SAE4320H steel were obtained to study the thermal changes, as a consequence of metallurgical microstructure changes that were produced by the heat treatment conditions. X-ray diffraction showed that the annealing process improves the crystalline quality of the SAE4320H steel and releases of any thermal stress. Widmanstatten microstructure was identified as a typical structure after the forging process. The Widmanstatten is a metallographic microstructure transformation to ferrite and pearlite which affected SAE4320H steel hardness and thermal properties. Vickers test showed that the hardness decreases as a result of the annealing process. A positive correlation between Vickers microhardness and PTR amplitude images was found, indicating that the annealing process increases the PTR signal. This methodology allows the determination of the changes in the Vickers microhardness from a non-contact and remote method as in PTR. Keywords
annealing, gear manufacturing, metallurgical microstructure, microhardness, photothermal radiometry
1. Introduction SAE4320H steel is commonly used for gear manufacturing, a process in which pieces are forged and annealed before machining operations. Then, these have to be carburized and hardened. The automotive industry, among others, due to the production volume attempts to simplify the quality assurance inspection steps. Brinell hardness testing and microstructural analyses are typically used to evaluate forged and annealed steel at the production area. However, these techniques are destructive; this fact, unfortunately, delays the production flow. Recently, photothermal radiometry (PTR) based on the measurement of blackbody radiation has been used successfully to characterize semiconductors, as well as metals (Ref 1, 2). In the same manner as PTR, infrared photocarrier radiometry (PCR) has been applied in semiconductor characterization (Ref 3).
Alberto Lara-Guevara, Facultad de Informa´tica, Universidad Auto´noma de Quere´taro, C.P. 76230 Quere´taro, QRO, Mexico; Ignacio Rojas-Rodrı´guez and Ruben Velazquez-Hernandez, Divisio´n Industrial, Universidad Tecnolo´gica de Quere´taro, C.P. 76148 Quere´taro, QRO, Mexico; David Jaramillo-Vigueras, Centro de Investigacio´n e Innovacio´n Tecnolo´gica, Instituto Polite´cnico ´ ngelNacional, C.P. 02250 Mexico, DF, Mexico; Karina del A Sa´nchez, Universidad Tecnolo´gica Gral. Marian
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