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In the current work, the impact of various laser heat inputs on the final microstructure of the nodular graphite cast iron as well as its microhardness values were evaluated. A proper processing window of four different laser powers (600, 1000, 1400, and 1800 W) with four corresponding different laser scanning speeds (1.667, 4.1667, 12.5, and 20.8 mm s−1) was accomplished in this study. Laser hardening, partial melting, and melting processes were achieved as a result of applying different laser heat inputs. The aim was to reach the optimum condition that obtained a free crack microstructure with high hardness values. The microstructure was examined in detail through scanning electron microscopy. Chemical analysis of different zones in the microstructure was analyzed utilizing energy dispersive X-ray (EDX). The results revealed that at low laser heat input (laser hardening) the microstructure consisted of large needle-shaped martensite with retained austenite and undissolved graphite nodules while, at medium laser heat input (partial laser melting), the microstructure contained eutectic ledeburite structure, retained austenite and plate-shaped martensite phase. Whereas, at high heat input (complete laser melting), the structure showed a remarkable refinement of cementite phase and interdendritic eutectic carbides beside the needle-shaped martensite. The heat-affected zone and the overlapped areas have been thoroughly examined as well. The hardened layer measured 250 μm at the lowest value of 9.6 J·mm−2, whereas with increasing the heat input to 144 J·mm−2 the thickness of the deepest melted layer reached ∼1650 μm. The hardness of the modified microstructure significantly increased by almost six-fold higher than that recorded for the as-cast substrate.

The paper addresses the microsegregation of Mn, Mo, Cr, W, V, Si, Al, Cu and P in the white cast iron. Eutectic alloy with the content of 4.25% C was studied. The white cast iron was directionally solidified in the vacuum Bridgman-type furnace at a constant pulling rate v = 83 μm/s and v = 167 μm/s and at a constant temperature gradient G = 33.5 K/mm. The microstructural research was conducted using light and scanning electron microscopy. The microsegregation of elements in ledeburite was evaluated by EDS measurements. Content of elements in ledeburitic cementite and ledeburitic pearlite was determined. The tendency of elements to microsegregation was found dependent on the solidification rate. Microsegregation of elements between pearlite and cementite structural constituents has been specified. The effect of solidification rate on the type and intensity of microsegregation in directionally solidified eutectic white cast iron was observed. A different type of microsegregation was observed in the components of ledeburite in cementite and pearlite.

Unalloyed cast iron materials exhibit low tribological and corrosive resistance. In this respect, nitriding has a wide range of applications for steels. In the case of cast iron, the advantageous properties of nitrided layers are impaired by the presence of graphite. Electron beam remelting of cast iron surfaces prior to nitriding removes graphite. The homogeneous ledeburitic microstructure within the approx. 1 mm-thick remelted layer enables the formation of a dense compound layer during subsequent nitriding. The main objective of this study is to investigate the nitriding mechanism of unalloyed ledeburitic microstructures. Due to the complex relationships, investigations were carried out on both conventional ferritic and pearlitic cast irons and Fe-based model alloys containing one to four additional alloying elements, i.e., C, Si, Mn and Cu. The iron (carbo-)nitride composition (γ', ε) of this compound layer depends on the gas nitriding conditions, the chemical composition of the substrates and the microstructural constituents. As a result, a schematic model of the nitriding mechanism is developed that includes the effects of the nitriding parameters and alloy composition on the phase composition of the nitriding layer. These findings enable targeted parameter selection and a further optimization of both the process and the properties. [ABSTRACT FROM AUTHOR]

The paper addresses the microsegregation of Mn, Mo, Cr, W, V, Si, Al, Cu and P in the white cast iron. Eutectic alloy with the content of 4.25% C was studied. The white cast iron was directionally solidified in the vacuum Bridgman-type furnace at a constant pulling rate v = 83 μm/s and v = 167 μm/s and at a constant temperature gradient G = 33.5 K/mm. The microstructural research was conducted using light and scanning electron microscopy. The microsegregation of elements in ledeburite was evaluated by EDS measurements. Content of elements in ledeburitic cementite and ledeburitic pearlite was determined. The tendency of elements to microsegregation was found dependent on the solidification rate. Microsegregation of elements between pearlite and cementite structural constituents has been specified. The effect of solidification rate on the type and intensity of microsegregation in directionally solidified eutectic white cast iron was observed. A different type of microsegregation was observed in the components of ledeburite in cementite and pearlite. [ABSTRACT FROM AUTHOR]

• Laser cladding of TC4 coating on cast iron, no cracking, max hardness 480.9 HV. • Scan speed 13 mm/s, 500 W 1st layer, 600 W 2nd layer, eradicated ledeburite. • 600 W coating outperforms 800 W & 1000 W in wear resistance at RT & 500 ℃. To enhance the wear resistance of the HT250 surface and eliminate ledeburite formation at the coating-substrate interface, a dual-layer Ti-6Al-4 V coating was created on HT250 surfaces through laser cladding. The influence of varying laser power on the microstructure, hardness, and wear resistance was investigated. The results indicate that a laser power of 600 W for the second layer can eliminate the formation of ledeburite at the coating-substrate interface, fabricating a crack-free cladding layer with a maximum hardness of 480.9 HV. Needle-like TiC was in-situ synthesized in the surface zone when the laser power was set at 600 W and 800 W. The surface hardness at 600 W is 1.1 and 1.4 times higher than that at 800 W and 1000 W, respectively. The optimal wear resistance was achieved at a laser power of 600 W, exhibiting 0.52 and 0.40 times the wear rates compared to those at 800 W and 1000 W, respectively, at 500 °C. At temperatures below 300 °C, the predominant wear mechanisms for all three coatings were abrasive wear and a small amount of oxidative wear. As the temperature increased to 500 °C, oxidative wear became the primary wear mechanism for the coatings. [ABSTRACT FROM AUTHOR]

Unalloyed cast iron materials exhibit low tribological and corrosive resistance. In this respect, nitriding has a wide range of applications for steels. In the case of cast iron, the advantageous properties of nitrided layers are impaired by the presence of graphite. Electron beam remelting of cast iron surfaces prior to nitriding removes graphite. The homogeneous ledeburitic microstructure within the approx. 1 mm-thick remelted layer enables the formation of a dense compound layer during subsequent nitriding. The main objective of this study is to investigate the nitriding mechanism of unalloyed ledeburitic microstructures. Due to the complex relationships, investigations were carried out on both conventional ferritic and pearlitic cast irons and Fe-based model alloys containing one to four additional alloying elements, i.e., C, Si, Mn and Cu. The iron (carbo-)nitride composition (γ’, ε) of this compound layer depends on the gas nitriding conditions, the chemical composition of the substrates and the microstructural constituents. As a result, a schematic model of the nitriding mechanism is developed that includes the effects of the nitriding parameters and alloy composition on the phase composition of the nitriding layer. These findings enable targeted parameter selection and a further optimization of both the process and the properties.