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A comparison of microstructure and mechanical properties of laser cladding and laser-induction hybrid cladding coatings on full-scale rail
摘要： With the rapid development of high-speed and heavy-haul trains, the surface damages of rails are becoming more and more severe, and how to promote the surface strength of the rail and prolong its service life with high efficiency are becoming extremely important. Laser cladding (LC), with small heat affected zone (HAZ) and low dilution, is a promising novel way to hardface and repair the rail. However, there are two great barriers for the traditional LC to apply on full-scale rails: one is how to prevent the coating from cracking under the rapid heating and cooling cycle; the other is how to eliminate the martensite structure in HAZ, which may threaten the safety of railway transportation due to its high hardness and low fracture toughness and usually be forbidden in almost all the Railway Standards over the world. In this paper, laser-induction hybrid cladding (LIHC) was innovatively proposed to deposit Ni-based coatings on a full-scale rail. The cracking behaviors, microstructures and mechanical properties of the coatings and HAZs by LC, LIHC with induction pre-heating (pre-LIHC) and LIHC with induction post-heating (post-LIHC) were studied systemically. The results indicate that the cracking and martensite transformation occurred in the HAZ can only be prevented by post-LIHC, where fine pearlite with smaller pearlite block size and lower interlamellar spacing formed instead. Therefore, the abrupt change of microstructure and mechanical properties in the HAZ could be avoided by post-LIHC, and the hardness, strength and toughness of the rails can be improved significantly. The post-LIHC technology shows the potentiality to hardface and repair the full-scale rail.
关键词： Martensite,Microhardness distribution,Toughness,Laser-induction hybrid cladding (LIHC),Full-scale rail,Strength
更新于2025-11-28 14:24:20
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In-situ measurement of surface relief induced by Widmanst?tten and bainitic ferrites in low carbon steel by digital holographic microscopy
摘要： In-situ measurement by digital holographic microscopy (DHM) was employed to clarify the difference between the surface relief effects of Widmanst?tten ferrite (WF) and bainitic ferrite (BF) associated with their transformations from austenite in a low-carbon steel. It was clarified that the evolution of the surface relief is totally different between WF and BF. Only in BF, the observed ratio of the relief height to the plate width converged instantly to the value predicted by the phenomenological theory of martensite crystallography (PTMC). The ratio gradually increased with increasing plate thickness and never reached the value predicted by PTMC in WF.
关键词： Digital holographic microscopy,Phase transformations,Surface relief,Phenomenological theory of martensite crystallography
更新于2025-09-23 15:21:21
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Influence of laser polishing on surface roughness and microstructural properties of the remelted surface boundary layer of tool steel H11
摘要： This work investigates the influence of multi-step laser polishing on microstructural properties of the remelted surface layer of tool steel H11. Four different laser polishing process parameter sets were selected that lead to a significant reduction in roughness. In a sequential process using continuous and pulsed laser radiation (Nd:YAG) a significant reduction of surface roughness was achieved on an initially annealed H11 sample. The remelted layers were analyzed using roughness measurements, white light interferometry, X-ray diffractometry, electron backscatter diffraction, glow discharge emission spectroscopy, and nanoindentation hardness measurements. Laser polishing leads to a grain refinement and a significant increase in hardness. A surface roughness of Ra 50nm was achieved in an Argon process atmosphere with an additional 6vol% CO2. In particular the carbon concentration was more than halved within the remelted layer. The lower carbon concentration is correlated with a decreased maximal surface hardness down to 366HV. High residual tensile stresses of up to 926MPa can be introduced by laser polishing. Overall, high temperature gradients and, in particular, decarburization due to carbon diffusion processes were identified to be the major driving force for significant changes in surface micro-roughness and microstructural properties.
关键词： AISI H11,micro hardness,laser polishing,decarburization,surface roughness,martensite formation
更新于2025-09-23 15:21:01
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Effect of laser patterning on the material behaviour of 22MnB5 steel with induced local strengthening
摘要： When using a supporting laser patterning method, it is possible to adaptively tailor the strength variations and formability of a pre-fabricated single panel. This paper focuses on the effect of line and geometrical laser patterning on the strength enhancement and material behaviour of steel sheets. To validate the performance of the laser patterning specimens, a tensile test for evaluating the in-plane deformation behaviour and a 3-point bending test for out-of-plane have been conducted while maintaining the area fraction for the laser-treated area. Close-type laser patterns, e.g., 0°, auxetic, and honeycomb, not only induce a substantial increase in strength but also enhance bending resistance without sacrificing the springback tendency of the initial sheet material.
关键词： Fibre laser,Martensite,Laser patterning,Local hardening,22MnB5
更新于2025-09-23 15:21:01
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The phase transitions in selective laser-melted 18-NI (300-grade) maraging steel
摘要： Dilatometric studies in 18-Ni steel components fabricated by selective laser melting technique were carried out to determine the influence of heating rate on transitions occurring during the heating cycle. SLM components have been examined in controlled heating and cooling cycles. For analysis, heating of the analysed materials was carried out at heating rates of 10, 15, 20, 30 and 60 °C min?1. During the heating process, two solid-state reactions were identified—i.e. precipitation of intermetallic phases and the reversion of martensite to austenite. A simplified procedure based on the Kissinger equation was used to determine the activation energy of individual reactions. For precipitation of intermetallic phases, the activation energy was estimated 301 kJ mol?1, while the martensite to austenite reversion was determined at the activation energy 478 kJ mol?1.
关键词： Precipitation,Martensite reversion,Phase transitions,Maraging steels
更新于2025-09-23 15:21:01
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Microstructure and Tensile Property of the Joint of Laser-MIG Hybrid Welded Thick-Section TC4 Alloy
摘要： In this paper, thick-section TC4 alloy was welded to itself by laser-MIG hybrid (LAMIG) welding. The microstructure of the welded joints was characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results revealed that α’ and β phases were formed in the weld seam. The effects of heat input (E) on the microstructure and tensile strength of the joints were investigated. With the increase of heat input, the residence time of platelet α’ martensite in the high-temperature phase changing zone became longer and the thickness of platelet α’ martensite increased. Furthermore, the β thickness became large, and tangling dislocations were found to exist in platelet α’. In addition, the increasing heat input could cause a decrease in the tensile strength. The failed dimple pattern experienced a change from equiaxed to tearing, which was harmful to the property of the joint.
关键词： α’ martensite,titanium welding,strength,microstructural analysis
更新于2025-09-16 10:30:52
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[Laser Institute of America ICALEO? 2015: 34th International Congress on Laser Materials Processing, Laser Microprocessing and Nanomanufacturing - Atlanta, Georgia, USA (October 18–22, 2015)] International Congress on Applications of Lasers & Electro-Optics - Hot wire laser cladding for repairing martensite precipitation hardening stainless steel
摘要： Martensite precipitation hardening stainless steel (M-PHSS) is widely used as load-bearing parts because of its excellent overall properties. It is economical and flexible to repair the failure parts instead of changing new ones. However, it is difficult to keep the properties of repaired layer as good as the substrate. Multi-pass layers were cladded on the surface of FV520B by hot wire laser cladding. Response surface methodology (RSM) was used to optimize processing parameters and predict formation quality of multi-pass cladding. Microstructure of the as-cladded layer was non-uniform and divided into quenched and tempered region. For the as-cladded layer, tensile strength was almost equivalent to that of the substrate, while ductility and impact toughness deteriorated much. With using laser scanning, microstructure of the clad layers was tempered to fine martensite uniformly. The ductility and toughness of clad layer were improved to be equivalent to those of the substrate, while the tensile strength was a little lower than that of the substrate. By adding TiC nanoparticles as well as laser scanning, the precipitation strengthening effect was improved and the structure was refined in the clad layer. As a result, the strength, ductility and toughness were all improved further. Finally, high quality clad layers were obtained with equivalent or even superior mechanical properties to the substrate, offering a valuable technique to repair M-PHSS.
关键词： Mechanical properties,Microstructure,Hot wire laser cladding,Martensite precipitation hardening stainless steel,Repair
更新于2025-09-16 10:30:52
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Processing of X65MoCrWV3a??2 Cold Work Tool Steel by Laser Powder Bed Fusion
摘要： Laser powder bed fusion (L-PBF) of forming tools has become of major interest in the tooling industry because of the high geometrical flexibility of this process. During L-PBF, a metallic powder bed is melted selectively by a laser beam, enabling the layer-wise manufacturing of parts from 3D computer-aided design data. The process is characterized by a locally and temporally unsteady heat flow in the solidified part and in the melt pool, causing nonequilibrium solidification and phase transformations. In addition, rapid heating and cooling occur, promoting the formation of microstructural defects, cold cracks, and distortion. Because of the high tendency to form cold cracks, processing of martensitic tool steels is still a challenging task. Tool steel X65MoCrWV3-2 is processed by L-PBF and the resulting microstructure and the associated local properties are investigated by microhardness measurements, nanoindentation, and scanning electron microscopy. It is gathered from the investigations that regions of different microstructures and mechanical properties on both micro- and macroscale are present in the L-PBF-densified steel. The different microstructures and properties are the result of the alternating heat insert at different temperature regimes, forming heat-affected zones in which the tempering processes are triggered and strongly varying properties are generated.
关键词： additive manufacturing,martensite,microstructure formation,laser powder bed fusion,tool steels
更新于2025-09-16 10:30:52
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Laser surface tempering of hardened chromium-molybdenum alloyed steel
摘要： The effect of a laser tempering process, subsequent to a laser hardening treatment, on the microstructure, microhardness, structural composition of phases and residual stresses of a 42CrMo4 steel has been studied. The tempering process has been carried out using a 10 kW diode laser and a galvanometer scanner head. Results show that the subsequent tempering process, after the laser hardening treatment, can be a complementary and effective method to adjust, through the selection of the appropriate process parameters, the desired degree of hardness and tensional state of the processed area, attending to the specific requirements demanded in a component.
关键词： 42CMo4,tempered martensite,laser tempering,martensite,retained austenite
更新于2025-09-12 10:27:22
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Influence of Beam Power and Traverse Speed in Fibre Laser welding of Dual phase steel (590) on Depth of weld zone penetration, Microstructure and Hardness
摘要： The influence of heat input on microstructure, microhardness, and mechanical properties of welded structures of DP 590 (Commercially known as DP 600 grade) grade steel of 1.6 mm thickness sheet has been investigated. The investigation was carried out by using Nd: YAG fibre laser source at a beam power of 1.5 kW and 3.0 kW at a traverse speed of 2 m/min, 4 m/min, and 6 m/min in bead on plate weld configuration. Except at lower beam power and lower traverse speed, at all other combinations of beam power and traverse speed a complete weld penetration has been observed. The weld zone microstructures have been transformed into predominantly martensitic phase due to rapid solidification. The width of the Heat Affected Zone and Weld Zone decreased as the heat input decreased. Hardness values of weld zone has increased to 350 -380 HV from 180-200 HV due to formation of martensite.
关键词： Dual Phase Steel,microhardness,Laser welding,martensite,heat affected zone
更新于2025-09-12 10:27:22