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Testing the Structure and Properties of Steels After Hardfacing and Laser Treatment

Pertek-Owsianna Aleksandra, Wiśniewska-Mleczko Karolina, Panfil Dominika, Bartkowska Aneta

Tribologia

2019

nr 2

97--104

This paper analyses the structure, hardness, and frictional wear resistance of surface layers formed on steels after hardfacing by means of the SSA arc method with self-shielded flux cored welding wire, with a content of carbon 5% and chromium 30% as well as boron alloying with the CO2 laser. S355J2 steel after being hardfaced with one up to three layers is characterized by the martensitic structure with chromium carbides and its surface hardness is 50–55HRC. In the weld deposit zone, with a thickness of up to approx. 2 mm, there is a constant distribution of hardness with the average value of 700 HV0.1, and then the hardness decreases to approx. 160 HV0.1 in the steel substrate. After hardfacing, the carbon content in S355J2 steel (0.23% wt.) increases to a similar content as in steel C90U in the initial state (0.96% wt.). After laser alloying with boron and after rapid cooling, C90U steel obtains distinctive paths with a zone structure and thickness reaching up to approx. 380 μm. In the remelted zone, there is a eutectic structure consisting of a mixture of iron borides and martensite with a hardness of approx. 1200–1800 HV0.1, and beneath it, there is heat affected zone with a martensitic-bainite structure with a hardness of approx. 700HV0.1. Hardfacing and laser heat treatment significantly decrease the frictional wear of the tested steels.

W pracy przeanalizowano strukturę, twardość oraz odporność na zużycie przez tarcie warstw wierzchnich stali po napawaniu metodą łukową SSA drutem proszkowym samoosłonowym o zawartości węgla (5%) i chromu (30%) oraz stopowaniu borem za pomocą lasera CO2. Stal S355J2 po napawaniu jedną do trzech warstw charakteryzuje się strukturą martenzytyczną z węglikami chromu o twardości powierzchni 50÷55HRC. W strefie napoiny o grubości do ok. 2 mm występuje stały rozkład twardości o średniej wartości 700 HV0.1, po czym twardość spada w rdzeniu stali do ok. 160 HV0.1. Po napawaniu zawartość węgla w stali S355J2 (0.23% mas.) wzrasta do podobnej jak w stali C90U w stanie wyjściowym (0.96% mas.). Stal C90U po stopowaniu laserowym borem i szybkim ochłodzeniu uzyskuje charakterystyczne ścieżki o budowie strefowej i grubości dochodzącej do ok. 380 μm. W strefie przetopionej występuje struktura eutektyki będącej mieszaniną borków żelaza i martenzytu o twardości ok. 1100÷1800 HV0.1, a pod nią znajduje się strefa wpływu ciepła o strukturze martenzytyczno-bainitycznej i twardości ok. 700 HV0.1. Napawanie oraz laserowa obróbka cieplna w sposób istotny zmniejszają zużycie przez tarcie badanych stali.

Laser alloying of 316L steel with boron and nickel

Mikołajczak D., Kulka M., Makuch N., Dziarski P.

Journal of Achievements in Materials and Manufacturing Engineering

2017

Vol. 84, nr 1

32--40

Purpose: The aim of the study was to improve the hardness and tribological properties of austenitic 316L steel by laser alloying with boron and nickel. Design/methodology/approach: The relatively low wear resistance of austenitic 316L steel could be improved by an adequate surface treatment. Laser alloying was developed as an alternative for time- and energy-consuming thermo-chemical treatment, e.g. diffusion boriding. In the present study, laser alloying of 316L steel with boron and nickel was carried out as the two-stage process. Firstly, the outer surface of the sample was coated with the paste, consisting of the mixture of boron and nickel powders, blended with a diluted polyvinyl alcohol solution. Second stage consisted in laser re-melting of the paste coating together with the base material. Laser treatment was carried out with the use of the TRUMPF TLF 2600 Turbo CO2 laser. The multiple laser tracks were formed on the surface. The microstructure was observed with the use of an optical microscope (OM) and scanning electron microscope (SEM) Tescan Vega 5135. The phase analysis was carried out by PANalytical EMPYREAN X-ray diffractometer using Cu Ka radiation. Hardness profile was determined along the axis of laser track. Wear resistance was studied using MBT-01 tester. Findings: The use of the adequate laser processing parameters (laser beam power, scanning rate, overlapping) caused that free of cracks and gas pores and the uniform laseralloyed layer in respect of the thickness was produced. In the microstructure, only two zones were observed: laser re-melted zone (MZ) and the substrate. There were no effects of heat treatment below MZ. Heat-affected zone (HAZ) was invisible because the austenitic steel could not be hardened by typical heat treatment (austenitizing and quenching). The produced laser-alloyed layer was characterized by improved hardness and wear resistance compared to the base material. Research limitations/implications: The application of proposed surface treatment in industry will require the appropriate corrosion resistance. In the future research, the corrosion behaviour of the produced layer should be examined and compared to the behaviour of 316L steel without surface layer. Practical implications: The proposed layer could be applied in order to improve the hardness and tribological properties of austenitic steels. Originality/value: This work is related to the new conception of surface treatment of austenitic steels, consisting in laser alloying with boron and some metallic elements.