Studies on laser surface melting of tool steel — Part II: Mechanical properties of the surface (original) (raw)
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Surface & Coatings Technology, 2010
In the present study, the effect of laser surface melting using different proportions of argon and nitrogen as shrouding atmosphere on microhardness and wear resistance properties of a low alloy high carbon tool steel (SAE 52100 steel) has been undertaken. Laser surface melting in argon (Ar) atmosphere significantly refined the microstructure (grain size) with the presence of carbides (both iron and chromium) and martensites and improved microhardness (350-500 VHN) as compared to as-received SAE 52100 steel (280 VHN). Laser surface melting in 100% N 2 atmosphere led to formation of thin nitride (consisting of Fe 4 N and Fe 2 N and Cr 2 N) layer with improved microhardness to as high as 1050 VHN. Wear studies showed a significant enhancement in wear resistance against hardened steel ball, a maximum improvement was achieved when lased using 100% N 2. The mechanism of wear was studied in details.
Gas nitriding, together with gas carburizing and gas carbonitriding, was the most commonly used thermochemical treatment, resulting in many advantageous properties: high hardness, enhanced corrosion resistance, considerably improved wear resistance and fatigue strength. However, an unfavorable increase in the thickness of compound layer (ε þγ′) close to the surface was observed after conventional gas nitriding. This was the reason for undesirable embrittlement and flaking. Therefore, a controlled gas nitriding was developed, reducing the thickness of compound layer. In this study, laser modification with or without re-melting was carried out after the controlled gas nitriding in order to change microstructure and to improve wear resistance. The effects of laser beam power on the dimensions of simple laser tracks were analyzed. It enabled to control the obtained microstructure and to select the laser processing parameters during producing the multiple tracks. Such a treatment was necessary to investigate wear resistance. Laser re-melting resulted in dissolving the majority of nitrides as well as in producing the martensitic structure in re-melted and heat-affected zones. This treatment required argon shielding in order to protect the surface against uncontrolled oxidation. Laser heat treatment without re-melting caused a modification of ε nitrides which became less porous and more compact. Simultaneously, it provided heat-affected zone with the partially martensitic structure of increased hardness below compound zone. Argon shielding was not necessary in this case because of the resistance of nitrides to oxidation during rapid heating and cooling. All the laser-modified layers, irrespective if the nitrided layer was re-melted or not, were characterized by the improved wear resistance compared to the typical gasnitrided layer.
Laser nitriding of tool steel: thermal stress analysis
The International Journal of Advanced Manufacturing Technology, 2010
Lasers can be considered as one of the effective tools to nitride the metallic surfaces. This is because of the precision of operation and the fast processing time. In the present study, laser gas-assisted nitriding of tool steel (H13) is carried out. Temperature and stress fields are predicted using the finite element method. The metallurgical changes in the laser irradiated region are examined using scanning electron microscope (SEM) and X-ray diffraction. The fracture toughness of the surface is determined using the indentation tests. It is found that von Mises stress attains high values in the laser-heated regions. The residual stress predicted is tensile, and it is in the order of 450 MPa. SEM micrographs reveal that surface is free from cracks, and feathery-like compact structures are formed in the vicinity of the surface. The fracture toughness of the surface reduces after the laser treatment process because of the formation of brittle structure in the surface region.
Scripta Materialia, 1999
Laser surface melting (LSM) of tool steels aims to obtain a modified layer with increased wear or corrosion resistance. Laser surface melting produces a very fine dendritic structure, free from defects and large brittle carbides [1], which can result in a significant increase of the hardness and toughness of the material (e.g. ). Though these characteristics are well suited to enhance the wear behaviour of the material, the fact is that, up to now, studies reporting the influence of LSM on the wear resistance of tool steels are scarce and, somehow, contradictory. De Beurs and De Hosson [4] studied the influence of laser surface melting on the abrasive wear behaviour of DIN X210CrW12 steel, and found that the wear resistance of laser melted samples does not differ significantly from the wear resistance of conventionally quenched and tempered samples. On the contrary, Jiandong et al. observed an increase on the abrasive wear resistance of laser surface melted 1 wt.% C tool steel, as compared with the same material with a conventional quenching and tempering treatment. These apparently contradictory results can be due not only to the fact that different wear tests and different materials were used, but also to the fact that the influence of the processing conditions on the microstructure was not considered.
Microstructure and wear resistance of gas-nitrided steel after laser modification
Journal of Achievements in Materials and Manufacturing Engineering, 2017
Purpose: The aim of this work was to study the microstructure and wear resistance of hybrid surface layers, produced by a controlled gas nitriding and laser modification. Design/methodology/approach: Nitriding is well-known method of thermo-chemical treatment, applied in order to produce surface layers of improved hardness and wear resistance. The phase composition and growth kinetics of the diffusion layer can be controlled using a gas nitriding with changeable nitriding potential. In this study, gas nitriding was carried out on 42CrMo4 steel at 570°C (843 K) for 4 hours using changeable nitriding potential in order to limit the thickness of porous e zone. Next, the nitrided layer was laser-modified using TRUMPF TLF 2600 Turbo CO2 laser. Laser tracks were arranged as the multiple tracks with scanning rate vl=2.88 m/min and overlapping of about 86% using the two laser beam powers (P): 0.21 kW and 0.26 kW. Microstructure was observed by an optical microscope. Phase composition was st...
Microstructural and hardness investigation of hot-work tool steels by laser surface treatment
Journal of Materials Processing Technology, 2008
Several techniques can be used to improve surface properties of metals. These can involve changes on the surface chemical composition such as alloying or on the surface microstructure, such as hardening. In the present work, melting of the surface by a 9 kW CO 2 CW laser of wavelength 10.6 μm was used to alter surface features of D2 tool steel. Carbon powder and nitrogen gas were used as sources of alloying elements during laser processing. The effect of various laser parameters (power and speed) on the microstructure and hardness of D2 tool steel was investigated. Laser powers from 1 to 8 kW and laser speeds from 5 to 15 mm/s were employed. It was found that as the laser power increases, the hardness of the melted zone decreases while that of the heataffected zone increases. On the other hand, the depth of both of melted and heat-affected zones increases with power.
Several techniques can be used to improve surface properties of metals. These can involve changes on the surface chemical composition such as alloying or on the surface microstructure, such as hardening. In the present work, melting of the surface by a 9 kW CO 2 CW laser of wavelength 10.6 μm was used to alter surface features of D2 tool steel. Carbon powder and nitrogen gas were used as sources of alloying elements during laser processing. The effect of various laser parameters (power and speed) on the microstructure and hardness of D2 tool steel was investigated. Laser powers from 1 to 8 kW and laser speeds from 5 to 15 mm/s were employed. It was found that as the laser power increases, the hardness of the melted zone decreases while that of the heataffected zone increases. On the other hand, the depth of both of melted and heat-affected zones increases with power.
Metals
Laser heat-treatment and laser nitriding were conducted on an AISI P21 mold steel using a high-power diode laser with laser energy densities of 90 and 1125 J/mm2, respectively. No change in surface hardness was observed after laser heat-treatment. In contrast, a relatively larger surface hardness was measured after laser nitriding (i.e., 536 HV) compared with that of the base metal (i.e., 409 HV). The TEM and electron energy loss spectroscopy (EELS) analyses revealed that laser nitriding induced to develop AlN precipitates up to a depth of 15 μm from the surface, resulting in surface hardening. The laser-nitrided P21 exhibited a superior wear resistance compared with that of the base metal and laser heat-treated P21 in the pin-on-disk tribotests. After 100 m of a sliding distance of the pin-on-disk test, the total wear loss of the base metal was measured to be 0.74 mm3, and it decreased to 0.60 mm3 for the laser-nitrided P21. The base metal and laser heat-treated P21 showed similar ...
Effect of laser surface alloying on structure of a commercial tool steel
International Journal of Microstructure and Materials Properties, 2013
This research project presents the investigation results of laser remelting and alloying especially the laser parameters and its influence on the structure and properties of the surface of the 32CrMoV12-28 hot work steel, using the High Power Diode Laser (HPDL). As a result of the performed research structure changes were determined concerning the grain size and reinforcement ceramic particle distribution in the steel surface layer. The reason of this work was to determine the optimal laser treatment parameters, particularly the laser power applied to achieve good layer mechanical properties for protection of this hot work tool steel from losing their work stability and to make the tool surface more resistant to action in hard working conditions. The remelted layers which were formed in the surface of investigated hot work steel were examined metallographically and analysed using light and scanning electron microscope as well as X-Ray diffraction.