Modification of Carbon Steel by Laser Surface Melting: Part II: Effect of Laser Beam Power on Microstructural Features and Surface Hardness (original) (raw)
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American Journal of Engineering and Applied Sciences, 2013
The present study aims to improve the surface hardness of carbon steel by application of laser surface melting of effective conditions. The travelling speed of laser beam during this treatment is one of the important treatment conditions. This study aims to investigate the effect of laser surface melting with different beam speeds on macro and microstructure as well as the hardness distribution through the thickness of carbon steel. To achieve this target, three different travelling speeds (1500, 1000 and 500 mm min −1) at a constant beam power of 800 W were chosen in this study. The resulted laser treated specimens were investigated in macro and microscopically scale using optical and scanning electron microscope. Hardness measurements were also carried out through the thickness of the laser treated specimens. The laser treated areas with all used travelling speeds results in melted and solidified zone on the surface of the steel. In the same time, Plates of acicular martensite structure were observed within the upper part of the melted and solidified zone in almost all experimental conditions, while some bainite structure in ferrite grains are detected in its lower part. By increasing the travelling speed, the depth of the laser treated zone was decreases, while travelling speed has much less significant effect on the laser treated zone width. The size of the formed martensite plates was increased by decreasing the travelling speed from 1500 to 500 mm min −1. On the other hand, the travelling speed has a straight effect on the length of the acicular martensite; as the travelling speed increases, the acicular martensite became longer, while it shows fine acicular martensite at lower travelling speeds. The depth that full martensite structure can be reached is increased by increasing travelling speed. At lower travelling speed (500 mm min −1), large amount of bainite structure is observed at the center of the treated zone up to its lower end. The fast travelling speed (1500 mm min −1) show higher hardness on the free surface than that of slow travelling speed (500 mm min −1). On the other hand, the travelling speed has a reverse effect on the depth of this hardness increment; the slower travelling speed give deeper areas of high hardness than that of fast speed. The Heat Affect Zone (HAZ) areas were increased by decreasing the travelling speed. In all conditions, the heat affected zone areas were composed of partially decomposed pearlite in ferrite grains. Finally, the microstructure of the base metal far from the laser treated areas show normal ferrite-sound pearlite microstructure.
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.
Studies on laser surface melting of tool steel — Part II: Mechanical properties of the surface
Surface and 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.
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.
A STUDY ON THE EFFECT OF PROCESS PARAMETERS OF LASER HARDENING IN CARBON STEELS
Surface hardening at functional areas of engineering components is an energy saving process. The components made of En8, En24, En36 and HCHCr steels are hardened in specific areas to meet the functional requirements at effective cost. The formation of martensite structure, leading to hardening, is decided by the composition of the material. Laser beams are used to perform hardening with almost zero deflection. The experimental study is to optimize the process parameters and selecting suitable material for manufacturing components working under critical loads. A 150 W, CO2 continuous wave laser source has been used in the experimental study. Power and scanning speed are the major influencing parameters in hardening process. The results showed that reducing the scanning speed increases hardness and depth due to increased interaction of beam with the work piece. Increasing the power starts melting the surface due to increase in energy. Improved hardness and wear resistance were observed in specimens with higher carbon content.
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.
Laser surface modification of tool steel for semi-solid steel forming
Solid State Phenomena, 2008
This paper presents an analysis of the effect of CO 2 laser processing parameters on the surface modification and heat treatment of steels. The CO 2 laser and sample movement process parameters are presented. The controlled operation of these in conjunction with each other is required to obtain better surface hardness and structure. H13 tool steel samples were rotated at high speeds to keep exposure times below 0.3s. Laser processed samples were analysed using EDX spectroscopy, optical microscopy, Vickers and Martens micro-hardness testing, and X-ray diffraction (XRD). Results show how the hardness profile through the surface is related to the laser treatment and resultant microstructures. Increased surface hardness was noted due to a complete microstructural transformation to an amorphous state in the glazed samples. The usefulness of such coatings on tool steels, in conjunction with other thermal barriers, for the forming of semi-solid steel alloys is presented.
Laser treatment of carbon film coated steel surface
Surface Engineering, 2012
Laser controlled melting in nitrogen of a preprepared steel surface has been carried out. A carbon film formed from a phenolic resin precursor containing 5 vol.-% of TiC particles was first formed at the surface of the steel before the laser treatment. The morphological and metallurgical changes in the laser treated region were examined using scanning electron microscopy and X-ray diffraction (XRD). Temperature and stress fields were predicted in the workpiece using a finite element code. The residual stress at the surface was measured using XRD. The hardness of the workpiece was measured using microindention testing. It was found that the laser treatment results in a dense layer composed of fine grains and TiC particles at the surface, which enhances surface microhardness. The presence of the carbon film at the surface and high pressure nitrogen gas enable the formation of FeN 3 and Fe(N,C) phases at the surface and nitrogen diffusion into the substrate material causes nitride precipitation below the surface. The residual stress measured using the XRD technique at the surface region is 2420 MPa, which is in agreement with the numerical predictions.
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.