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Manufacturing and maintenance procedures in the railway industry regularly implement welding and metal deposition operations to produce joints, coatings and repair structures. During these processes, residual stresses arise through the generation of heat affected zones and plastic deformation. This makes accurate measurements of the internal stresses a critical aspect of manufacturing, monitoring, repair and model validation in the develop new metallic coating and joining technologies. Selection of an appropriate residual stress measurement method has many important factors including component size, resolution and the magnitude and location of internal stresses, often resulting in a combination of techniques required to obtain complete assessment of the stress state. This paper offers a review of residual stress measurement techniques for railway components including rail joints and coatings through comparison of destructive and non-destructive approaches, their measurement capabilities, benefits and limitations. A comprehensive discussion of different applications is provided with a summary of facilities available to both research and industry. [ABSTRACT FROM AUTHOR]

The development of a laser cladding repair strategy is critical for the continued growth of heavy-haul railway networks. Premium hypereutectoid rails have undergone laser cladding using a new martensitic stainless-steel alloy, 415SS, developed for high carbon rails after standard cladding metals were found to be incompatible. Non-destructive neutron diffraction techniques were used to measure the residual stress in different layers generated across a dissimilar metal joint during laser cladding. The internal stress distribution across the cladding, heat-affected zone (HAZ), and substrate was measured in the untempered rail, after 350 °C and 540 °C heat treatment procedures and two surface grinding operations. The martensitic 415SS depositions produce compressive stress in the cladding, regardless of tempering procedures, which may inhibit fatigue crack propagation whilst grinding operations locally relive surface stress. Balancing tensile stresses were recorded below the fusion boundary in the HAZ due to thermal gradients altering the microstructure. The combination of 540 °C tempering and 0.5 mm surface layer removal produced a desirable combination of compression in the cladding deposition with significantly reduced tensile stresses in the HAZ. A comparison with the current literature shows that this alloy achieves a unique combination of desirable hardness, low tensile stress, and compression in the cladding layer. Data obtained during strain scanning has been used to determine the location of microstructural changes at the fusion boundary and HAZ through correlation of the stress, strain, full width at half maximum (FWHM), and intensity profiles. Therefore, neutron diffraction can be used for both the accurate measurement of internal residual stress and to obtain microstructural information of a metallurgical join non-destructively. [ABSTRACT FROM AUTHOR]

Abstract The effects of different cladding materials, processing parameters and heating regimes on the underlying microstructural features and mechanical properties of laser-cladded premium rails were investigated by using a hypereutectoid rail grade as a substrate, which is extensively used in heavy-haul rail systems. Cladding materials of 410L, 420SS, Stellite 6 and Stellite 21 with single and double depositions were considered for the comparative study of different cladding materials and processing parameters. To ensure the constant thickness of the claddings for comparison purposes, transverse speed and powder feed rate were modified concurrently in the ranges of 1000–1200 mm/min and 3–4 RPM, respectively. Two heating conditions, i.e. preheating only (HTA) and a combination (HTB) of preheating and post weld heat treatment (PWHT) were applied after the preferable parameters for each cladding material were obtained. The most suitable cladding material for rail-wheel contact was established by assessing all crucial aspects, i.e. surface defects, hardness, microstructural and mechanical properties. Process parameters for each considered cladding material were determined to achieve no surface defects. For cladding layers, application of HTA was not able to significantly modify the microstructures of the deposits, whereas HTB was observed to cause severe cracks in Co-base alloys, i.e. Stellite 6 and Stellite 21. In the heat affected zones (HAZs), irrespective of the cladding materials, the formation of untempered martensite was not avoided by the application of preheating at 350 °C. Consequentially, cracking in the HAZ was observed. An uncracked and desirable microstructure in the HAZs was established using HTB, regardless of the depositing materials. The addition of a second layer did not change the thickness of the HAZs but refined the HAZ’s microstructures. Shear punch testing (SPT) and Vickers hardness testing were utilized to characterize mechanical properties for the considered cladding materials and good correlations with the obtained microstructural morphologies were shown. [ABSTRACT FROM AUTHOR]

The impacts of preheating conditions and carbon dilution on the microstructural and mechanical properties of laser cladded rails using single and double cladding layers have been investigated for a hypereutectoid steel grades typically used under heavy haul conditions. The microstructures in the HAZ showed that formation of martensite, which has a detrimental effect on behaviour in wheel-rail contact, was successfully inhibited by increasing the length of the preheated region using a preheating temperature of 350 °C. Dilution of carbon from the hypereutectoid substrate was observed and its effect on the microstructures of the 410L ferritic stainless-steel deposits was investigated. The formation of ferrite in the 410L cladding layers was attributed to the very low carbon content, and no carbide formation was observed on boundaries of the ferritic grains. The thickness of dilution band was determined to be approximately equal to the thickness of the first cladding layer. Texture measurement obtained by EBSD showed a random trend owing to the formation of martensite in diluted bands. Strong solidification fibre texture was developed for double deposition, particularly in the second deposit. Mechanical characterization of the 410L deposits undertaken in terms of Vickers microhardness, shear and tensile yield strengths, and ultimate tensile and shear strengths were correlated with the observed microstructural morphologies. [ABSTRACT FROM AUTHOR]

In this study, the effects of cladding direction, preheating and post heat treatment on microstructural and mechanical properties of laser cladded rail repairs are presented. Laser cladding of a premium hypereutectoid rails grade with 410L stainless steel powder were conducted using a fibre laser gun with a powder feeder. Two different cladding directions and different heat treatment regimes were investigated. An excellent microstructural consistency was established across the railhead and its heat affected zone (HAZ) by changing cladding direction and using a heat treatment consisting of pre-heating and post-heating. The microstructure of the cladding layer and HAZ were characterized by optical microscopy and SEM. Phase identification and distribution were investigated by using XRD, EDS, and EBSD. Indications of the mechanical and tribological performance of the cladding layer in wheel-rail contact were obtained via shear punch tests and Vickers indentation, which demonstrated great correlation with the obtained microstructure. [ABSTRACT FROM AUTHOR]

Rapid deterioration of critical rail components due to wear and fatigue is a significant challenge faced by the railway industry. Laser cladding has been applied to straight and curved light rail substrates which are particularly prone to these methods of degradation using a Stellite 21 hardfacing alloy. The influence of multi-layer cladding depositions, grinding-based finishing procedures and substrate rail grade on residual stress was analyzed using non-destructive neutron diffraction techniques. As cladding is a thermal process, microstructural changes from the heat inputs can result in a high internal stress state which reduces the loading capacity whilst a high hardness increases the likelihood of brittle failure. Stellite laser cladding depositions were found to result in low tensile residual stresses within the cladding layer, which become compressive in the heat affected zone (HAZ). Repeated thermal inputs from multi-layer cladding depositions did not negatively impact the hardness or microstructure after double layer laser cladding and increased the residual stress to 100 MPa at the cladding surface after grinding. Laser cladding on a curved rail substrate also produced increased internal stress after cladding due to higher strains resulting from the rail geometry but remained below the yield limit of the cladding and substrate material. These outcomes were compared to current literature indicating this critical combination of low internal strain and a cladding and HAZ hardness complementing the substrate material is difficult to achieve. Therefore, ensuring laser cladding is compatible with a variety of light rail components is essential in developing viable maintenance techniques to recondition critical railway infrastructure to avoid disruptive replacement procedures. [ABSTRACT FROM AUTHOR]

Fatigue life study of structures constructed by laser cladding using two types of hardfacing alloy, Stellite 6 (Co base) and Deloro 40G (Ni base) on AISI 4130 steel substrate was conducted using rotary bending fatigue test at ambient temperature 20 °C. The laser clad specimens showed a reduced fatigue life compared to the specimen without cladding but of the same size due to the presence of residual stresses in substrate and coating regions. The presence of higher compressive residual stresses in substrate region and lower tensile residual stress in coating region of specimen laser clad with Stellite 6 generated longer fatigue life compared to the specimens laser clad with Deloro 40G, at a similar coating thickness level. With the same final structure size, coating thickness produced an inversely proportional effect on fatigue life where thinner coatings result in less reduction of fatigue life compared to thicker coating. The analytical model employed in this study demonstrated that thinner coatings alters axial residual stress by generating lower tensile residual stress in coating region which enhance fatigue life, compared to thicker coatings. This work has demonstrated the influence of coating type, coating thickness and load level on the fatigue life of the laser clad structures. [ABSTRACT FROM AUTHOR]

Residual stress is one of the critical parameters affecting the fatigue behaviour of tribological components, which can be introduced by a thermo-mechanical process such as laser cladding. In this study, the residual stress distribution of laser cladded rails was evaluated using a neutron diffraction technique. The substrate rail for the laser cladding was hypereutectoid rail steel used in Australian heavy-haul railway track, and the cladding materials were 410L (a low carbon content stainless steel alloy) and Stellite 6 (a Co-based alloy). The cladding materials were selected based on their high wear, corrosion and fatigue resistance properties. This study measured the residual stress in full-scale laser cladded rails where the residual stresses were measured in the cladding layer, heat affected zone (HAZ) and substrate zone of the railhead. A new sample preparation strategy was developed to quantify the residual stresses in the full-scale rails with high spatial resolution. Higher compressive residual stress was found in the cladding layer, which may have resulted from the martensitic transformation occurred in that region. Tensile stresses occurred in the HAZ to a depth of 4 mm, which might be mainly caused by thermal contraction and volumetric change in the microstructure. The addition of a second cladding layer did not significantly affect the magnitude of the residual stresses, but the peak tensile residual stress shifted to a deeper location from the surface, which is beneficial in resisting wear. Post-cladding heat treatment significantly reduced the undesirable high residual stress from the cladding layer and HAZ. [ABSTRACT FROM AUTHOR]

Local material properties of the cladding layer, heat affected zone and substrate of laser cladded hypereutectoid steel rails were evaluated by uniaxial tensile tests on miniature specimens. Three laser cladding materials, i.e. 410 L, SS420 and Stellite 6, and two different heat treatment conditions were considered. To examine any possible anisotropic behaviour, specimens machined along the longitudinal and transverse laser cladding directions were tested. All the cladding layers showed similar or higher yield and ultimate tensile strengths, but lower elongation than the non-clad rail. Application of post-heat treatment significantly improved the elongation of all the cladding layer specimens. Elongation increments of 70%, 192% and 90% were respectively obtained from the 410 L, SS420 and Stellite 6 post-heat treated cladding layers. The post-heat treatment also marginally increased the yield and ultimate tensile strengths in this region. The improvement in tensile properties was associated with a more favourable microstructure, which resulted in a more dimpled morphology as depicted in the SEM images of the fractographic analysis of the tested specimens. While other properties are similar, both cladding layer and HAZ specimens showed significant different elongation values between the longitudinal and transverse directions in some cases, which indicates certain anisotropy in those materials' ductility. • Tensile properties of the cladding layer, HAZ and substrate were directly measured using miniature tensile test specimens. • Both cladding layer and HAZ specimens showed certain anisotropy in those materials' ductility. • Cladding layers presented similar or higher tensile strengths, but lower elongation values than the non-clad rail steel. • Application of post-heat treatment significantly improved elongation of the cladding layers. [ABSTRACT FROM AUTHOR]