In Situ High Energy X‐Ray Diffraction for Investigating the Phase Transformation in Hot Rolled TRIP‐Aided Steels

Abstract

The phase transformation kinetics of a hot rolled transformation induced plasticity (TRIP) steel is investigated by means of in situ high energy X-ray diffraction. The samples are deformed and annealed according to the parameters of a hot rolling process in a deformation dilatometer installed in the synchrotron beamline. Simultaneously, the phase fraction and the carbon content in the remaining austenite were measured by X-ray diffraction. It is advantageous that the retained austenite (RA) can be measured without sample preparation, which usually results in unwanted strain-induced martensite transformation. This study shows that enough carbon enrichment of austenite can be achieved by forming carbide free bainite. However, too little fraction of the RA for the TRIP effect can be formed without the pre-deformation. The pre-deformation also promotes the decarburization of the bainitic ferrite especially at high temperature. Fig. 6. The change in austenite fraction during quenching from the bainite formation temperature (a) 500°C (b) 475°C (c) 450°C (d) 425°C (e) 400°C (f) 375°C. The solid symbols represent the cases with pre-deformation of 0.6. P. Suwanpinij et al./In Situ High Energy XRD for Hot Rolled TRIP Steel ADVANCED ENGINEERING MATERIALS 2014, 16, No. 8Fig. 8. The relationship between the linear thermal expansion of austenite and the calculated carbon content. P. Suwanpinij et al./In Situ High Energy XRD for Hot Rolled TRIP Steel ADVANCED ENGINEERING MATERIALS 2014, 16, No. 8

In situ synchrotron radiation diffraction study of the role of Gd, Nd on the elevated temperature compression behavior of ZK40

“…High energy X-ray and neutron diffraction has been utilized to investigate various metallic alloys [18][19][20][21][22][23][24][25][26], showing the capabilities of in situ characterization of metallic materials undergoing mechanical loading. In situ high energy X-ray diffraction (HEXRD) is a unique method that can investigate the dynamic microstructural processes that occur during mechanical loading in the bulk of the materials [19].…”

Toward Unraveling the Importance of Deformed Microstructure before TRIP Heat Treatment in Transformation-Induced Plasticity Steels

“…Later, Matsumura et al provided an evidence of this phenomenon is low alloy steels. Since then, TRIP steels have gained widespread recognition as one of the main types of advanced high‐strength steels (AHSSs) . TRIP steels have a microstructure consisting of ferrite, bainite, retained austenite, and sometimes martensite .…”

“…During deformation, the metastable retained austenite transforms to martensite, which is the basis of TRIP effect. This in turn, increases the local strain‐hardening rate and delays necking . The usual route for obtaining TRIP microstructures is performing intercritical annealing (IA) followed by bainitic isothermal transformation (BIT) on a cold‐rolled ferritic–pearlitic sheet as shown in Figure a.…”

“…Since then, TRIP steels have gained widespread recognition as one of the main types of advanced high-strength steels (AHSSs). [3][4][5][6] TRIP steels have a microstructure consisting of ferrite, bainite, retained austenite, and sometimes martensite. [7] During deformation, the metastable retained austenite transforms to martensite, which is the basis of TRIP effect.…”

“…This in turn, increases the local strain-hardening rate and delays necking. [3][4][5][6] The usual route for obtaining TRIP microstructures [7] is performing intercritical annealing (IA) followed by bainitic isothermal transformation (BIT) on a cold-rolled ferritic-pearlitic sheet as shown in Figure 1a. While different aspects of TRIP steels have been extensively studied so far, the importance of the cold-rolling stage before TRIP heat treatment remained largely unclear.…”