A New XRD Method to Quantify Plate and Lath Martensites of Hardened Medium-Carbon Steel

Abstract

This paper introduces a new technique to separately measure the volume fraction and tetragonal ratio of co-existing lath and plate martensites in ultrahigh strength steel, and to calculate their different carbon contents. First, the two martensites are assumed to have body-centered tetragonal lattice structures of different tetragonal ratios. X-ray diffraction is then applied to obtain the overlapping {200} diffraction peak, which is subsequently separated as four sub-peaks using a self-made multiple Gaussian peak-fitting method to allow the measurement of the individual lattice parameters c and a. Finally, a modified equation is applied to calculate the carbon contents from the obtained tetragonal ratios. The new technique is then applied to investigate the effect of subsequent tempering on the decarbonization of the as-quenched martensites.

Effect of Austempering Time on the Microstructure and Carbon Partitioning of Ultrahigh Strength Steel 56NiCrMoV7

“…The (200) α diffraction peak was numerically processed more extensively using a newly developed quantitative method. Details of the new method have been described elsewhere [31]. The new analytical method considers martensite in a hardened medium-carbon steel as a mixture of lath-and plate-martensites, whereas the two martensite sub-phases are known to have different tetragonal ratios because of their different carbon contents.…”

“…Firstly, both the overall diffraction peaks (200)α and (211)α were analysed to calculate the lattice strains along the <200> and <211> directions. Then by Gaussian separation of the (200)α peak as sub-peaks, the martensitic or bainitic ferrite was considered as two sub-phases having different tetragonal ratios, namely lath martensite (Mlath) and plate martensite (Mplate) [31]. Consequently the lattice strains of the Mlath and Mplate sub-phases can be estimated.…”

“…Valuable results on the microstructure characteristics have been obtained from the quantitative analyses of these diffraction patterns, including the volume fraction, carbon content and micro-strain of retained austenite and two types of ferritic sub-phases. Detailed consideration of the ferritic subphases can be found in a recent publication [31], namely, that the mixture of martensite and bainite structure have been treated as two martensitic sub-phases (Mplate and Mlath) of different tetragonal ratios; although, a limitation of the method was that it was not capable of separating the austemperinformed bainite and the quenching-formed martensites. Figure 7 shows an example of separation of the ferrite diffraction peak (200)α as four sub-peaks using the Gaussian peak-fitting technique, where peaks 1 and 2 represent the Mplate diffractions and peaks 3 and 4 represent the Mlath diffractions.…”

Effect of Intercritical Annealing and Austempering on the Microstructure and Mechanical Properties of a High Silicon Manganese Steel

“…Those peaks are related to the presence of tetragonal martensite. The presence of a displacement between ferrite and martensite peaks is due to the high carbon content of martensite and the strong distortion of the cell [32].…”

Tribological properties and wear mechanisms of DC pulse plasma nitrided austenitic stainless steel in dry reciprocating sliding tests

“…After stripping the K α2 (λ = 0.1793 nm) and removing the background, a self-developed Gaussian multiple peak fitting process was applied to resolve the diffraction peaks, from which the detailed crystalline structure of each nitrided layer could be determined. The principle and analytical method of the Gaussian peak fitting process can be found in recent publications [25,26] . Fig.…”