Characterization of aging behaviour in M250 grade maraging steel using eddy current non-destructive methodology (original) (raw)
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Nondestructive Characterization of Thermal Ageing Behaviour at 753 K in M250 Maraging Steel
Maraging steel M250 is widely used in aerospace industry for fabrication of critical rocket motor casings. Specific heat-treatment is given to these parts before they are put into service. Qualification of the heat treatments is presently based on the microscrostructural examination carried out on test coupons, which is indirect tedious, destructive in nature and only limited sampling based. For the complete, faster, accurate and insitu qualification of the actual heat treatment given to the actual component, non-destructive inspection techniques based methodology has been developed. Two NDE techniques, magnetic Barkhausen emission (MBE) and ultrasonic techniques have been used for the characterization of thermal ageing behaviour of the steel at 753 K. The MBE technique has been chosen due to the ferromagnetic nature of the maraging steel. While the MBE technique provides the near surface information, the ultrasonic technique characterizes the bulk of the component. The present study has clearly brought out the complementary nature of these two techniques for the characterization of thermal ageing behaviour in M250 maraging steel. Ultrasonic measurements have been found to be more sensitive to the precipitation of intermetallics, whereas, MBE could clearly identify the onset of austenitic reversion.
Nondestructive characterization of thermal ageing behavior at 753 K in M250 Maraging Steel
Maraging steel M250 is widely used in aerospace industry for fabrication of critical rocket motor casings. Specific heat-treatment is given to these parts before they are put into service. Qualification of the heat treatments is presently based on the microscrostructural examination carried out on test coupons, which is indirect tedious, destructive in nature and only limited sampling based. For the complete, faster, accurate and insitu qualification of the actual heat treatment given to the actual component, non-destructive inspection techniques based methodology has been developed. Two NDE techniques, magnetic Barkhausen emission (MBE) and ultrasonic techniques have been used for the characterization of thermal ageing behaviour of the steel at 753 K. The MBE technique has been chosen due to the ferromagnetic nature of the maraging steel. While the MBE technique provides the near surface information, the ultrasonic technique characterizes the bulk of the component. The present study has clearly brought out the complementary nature of these two techniques for the characterization of thermal ageing behaviour in M250 maraging steel. Ultrasonic measurements have been found to be more sensitive to the precipitation of intermetallics, whereas, MBE could clearly identify the onset of austenitic reversion.
Ultrasonic Characterization of Aging Behavior in M250 Grade Maraging Steel
Metallurgical and Materials Transactions A, 2009
The increase in sound velocities during the aging of M250 maraging steel reported by Rajkumar et al. was analyzed. The present article provides a new perspective on why and to what extent the sound velocities change during aging. The main parameter that affects the elastic moduli and the sound velocities in the early and intermediate stages of aging in maraging steel is the depletion of Ni from the martensitic matrix due to Ni 3 Ti and Ni 3 Mo formation. The issue of sound velocity increase with aging time was addressed here in a few different ways to support the validity of Ni depletion.
A development of swept-frequency eddy current for aging characterization of heat resistant steel
International Journal of Applied Electromagnetics and Mechanics, 2017
This study presents an application of the swept-frequency eddy current (SFEC) technique for characterization of aging conditions of 5Cr-0.5Mo heat resistant steel by a U-shaped, eddy current probe. An optimal eddy current probe was established and employed to investigate the specimens under different simulated service conditions. Sweep frequencies from 500 to 10,000 Hz were generated to measure the impedance changes using a precision LCR meter. As results, the normalized impedances showed the highest differences in each aging condition at the frequency of 3,200 Hz. Microstructural observations were utilized to give details of the differences in microstructures among aged conditions, which related to the carbide precipitation characteristics of the specimens. In addition, a micro-hardness was tested on the carbide colonies in complement the aged conditions. The results showed that the hardness correlated well to the normalized impedances obtained from the swept-frequency eddy current testing.
Journal of Alloys and Compounds, 2009
Maraging steel 350 samples were aged in steps up to 100 h at 470, 510 and 550 • C, which resulted in changes in the microstructure of the samples. The changes in microstructure have been analyzed by X-ray diffraction, scanning electron microscope and optical microscope. Electrical resistivity, Vickers's hardness, and eddy current impedance were also monitored. This study revealed that thermal treatment has no effect on grain size, phase transformation, and electrical resistivity, however, hardness and eddy current impedance response was observed. It establishes that eddy current technique is suitable for the characterization of thermal treatment.
2016
Microstructural changes during thermal ageing of ferromagnetic mater ials can be detected in a rapid and nondestructive way by means of micromag netic methods. The Fraunhofer Institute for Nondestructive Testing (IZFP) proves the suitability of those techniques for the characterization of microstructural ch anges caused by thermal ageing (at different times and temperatures) of the d i fer nt heat resistant ferritic, ferritic/martensitic steels and iron-based alloys. Differing microstructure features and subsequent thermal ageing of high chromium ferritic steels produces populations of strengthening Laves phase precipitates, largely deviating from each other in terms of particle number, size distribution and inter-particle spacing and thus differing mechanical prop erties. The effect of different thermal ageing procedures on the microstructure evolution was characterized by means of micromagnetic techniques. Thermal aged and creep damaged 9-12Cr ferritic/martensitic steel specimens ...
Magnetic properties evaluation of ageing behaviour in water-quenched 5Cr–0.5Mo steel
Journal of Physics D: Applied Physics, 2009
Magnetic Barkhausen emissions and magnetic hysteresis measurements were carried out on water-quenched 5Cr-0.5Mo steel subjected to ageing at 600 • C up to 5000 h. During initial ageing, this steel exhibited magnetic softening, which was attributed to relaxation of quenching stress in the material as well as decrease in dislocation density and migration of interstitial carbon atoms towards the grain boundary. Further ageing resulted in magnetic hardening owing to the restricted movement of the domain wall by the precipitation of carbides such as M 3 C 2 , M 2 C, M 7 C 3 where M stands for Fe, Cr or a combination of them. At longer ageing periods, magnetic behaviour was affected by a change in the composition and morphology of the carbides. Massive M 23 C 6 types of carbides were formed during longer periods of ageing. The coarsening of carbides decreased the pinning density for the domain wall motion and affected the magnetic properties of the steel. The effect of demagnetizing field from voids and non-magnetic massive carbides also affected the magnetic behaviour. Magnetic behaviour and Vickers hardness measurements during ageing have been effectively supported by microstructural evaluations suggesting the capability of the magnetic techniques for assessment of damage during ageing in high temperature 5Cr-0.5Mo steel components.
INFLUENCE OF AGING TEMPERATURE ON MECHANICAL PROPERTIES AND SOUND VELOCITY IN MARAGING STEEL M350
2010
ABSTRACT In the present work, the influence of aging temperature on mechanical properties and sound velocity of Maraging steel M350 was investigated. For this purpose, first, samples were solution annealed at 825 • C for 2 hours and then age hardened at 510 • C-600 • C for 3 hours. Hardness, tensile and impact tests were used for determining mechanical properties and longitudinal ultrasonic velocity was used for determining sound velocity of the samples. The obtained results indicated that hardness, strength and sound velocity of the samples decreases with increase of ageing temperature, whereas, toughness of the samples increases directly with ageing temperature. These results were attributed to the dissolution of Ni 3 (Mo,Ti) and Fe 2 Mo precipitates and also to the formation of reverted austenite which are promoted by the increase of ageing temperature. Optical microscopy of the samples revealed that, in this case, the morphology of reverted austenite is mainly of grain boundary and interlath type. Further, a linear correlation between the mechanical properties and sound velocity of the samples was found that can be used in industrial applications.
Metallurgical and Materials Transactions A, 2008
X-ray diffraction (XRD) studies were carried out to characterize aging behavior of M250 grade maraging steel samples subjected to isothermal aging at 755 K for varying durations of 0.25, 1, 3, 10, 40, 70, and 100 hours. Earlier studies had shown typical features of precipitation hardening, wherein the hardness increased to a peak value due to precipitation of intermetallics and decreased upon further aging (overaging) due to reversion of martensite to austenite. Intermetallic precipitates, while coherent, are expected to increase the microstrain in the matrix. Hence, an attempt has been made in the present study to understand the microstructural changes in these samples using XRD line profile analysis. The anisotropic broadening with diffraction angle observed in the simple Williamson-Hall (WH) plot has been addressed using the modified WH (mWH) approach, which takes into account the contrast caused by dislocations on line profiles, leading to new scaling factors in the WH plot. The normalized mean square strain and crystallite size estimated from mWH have been used to infer early precipitation and to characterize aging behavior. The normalized mean square strain has been used to determine the Avrami exponent in the Johnson-Mehl-Avrami (JMA) equation, which deals with the kinetics of precipitation. The Avrami exponent thus determined has matched well with values found by other methods, as reported in literature.