MICRO-JET TECHNOLOGY IN MACHINE SHAFT SURFACING

Transcription

1 Acta Metall. Slovaca Conf. 98 MICRO-JET TECHNOLOGY IN MACHINE SHAFT SURFACING Tomasz Węgrzyn 1)*, Jan Piwnik 2), Z. Kosmała 3), D. Hadryś 4) 1) Silesian University of Technology, Faculty of Transport, Katowice, Poland 2) Bumech, Katowice, Poland 3) Bialystok University of Technology, Białystok, Poland 4) WSZOP, Katowice, Poland Received: Accepted: * Corresponding author: tomasz.wegrzyn@polsl.pl, Tel.: , Silesian University of Technology, Faculty of Transport, Krasińskiego st. 8, Katowice, Poland Abstract Welding surfacing process used to apply a hard, wear-resistant layer of metal to surfaces or edges of worn-out parts. It is one of the most economical methods of conserving and extending the life of machines, tools, and construction equipment. Surfacing weld is composed of longitudinal and circumferential stringers or weave beads. Surfacing is also known as hardfacing or wearfacing, is often used to build up worn shafts, gears and cutting edges. Regenerated surface properties of various machine elements do not provide good tribological properties. For instance combine mining shafts have a short operating time. Main purpose of that paper was to check absolutely innovate technology (welding with micro-jet cooling) in surface welding. Superficial welding with micro-jet cooling could be treated as new approach for steering of the tribological properties of welds. Results of that experiments are very promising. There were presented metallurgical findings after welding with new method of cooling (possibilities of microstructure steering). There were precisely analyzed amount of martensite in surface weld in terms of various micro-jet parameters. Keywords: welding, micro-jet, metallography, martensite 1 Introduction Generally speaking, welding surfacing process is used to apply hardness and wear resistance. Purpose of that paper was describing possibilities of surfacing welding process with micro-jet cooling. The main reason of it was investigate possibilities of getting varied amount of martensite in surface weld of machine shafts in terms of micro-jet parameters. For getting various amount of martensite in this method it is necessary to determine the main parameters of the process such as. number of jets, diameter of stream of the micro-jet injector, type of microjet gases, micro-jet gas pressure. Micro-jet technology was precisely tested for low alloy welding [1-13]. In the steel weld structure the best mechanical properties of weld correspond with low-oxygen processes (approx. 400 ppm) that have strong influence on metallographic structure [9-11]. Especially an maximal amount of acicular ferrite (AF), the most beneficial phase is translated by role of oxygen in metal weld deposit (MWD). AF in weld is connected with size, density and lattices parameters of oxide inclusion in weld. Having the most optimal inclusions in weld it is only possible to get even 65% of AF in weld, but no more. High amount of AF in MWD has influence on impact toughness of welds [14-18]. It was necessary to develop completely new

2 Acta Metall. Slovaca Conf. 99 welding technology to maximize of ferrite AF content. Micro-jet technology gives chance to obtain artificially high amount of AF in weld that corresponds with better mechanical properties of weld [18-22]. The micro-jet technology was tested for steel welding with various micro-jet cooling conditions. Goal of that paper was to describe possibilities of surfacing welding process with micro-jet cooling where amount of martensite is steered in analogy to various AF amount in low alloy welding. Micro-jet technology can be easly applicant to automotive production. For the vehicle shaft surfacing the precision of production or reparation are strongly important because all kind of unbalance generate various vibration [23-25]. 2 Experimental procedure To obtain much higher amount of acicular ferrite in weld metal deposit it was installed welding process with micro-jet injector (with steam diameter of 40 µm). Weld metal deposit (WMD) was prepared by welding with micro-jet cooling with varied parameters. WMD was prepared by welding with various micro-jet cooling gases (nitrogen, argon, helium) with changing another important micro-jet parameter: gas pressure (0.4 MPa and 0.5 MPa). The main data about parameters of welding were shown in Table 1. Table 1 Parameters of welding process No. Parameter Value 1. Diameter of wire 1.2 mm 2. Standard current 220 A 3. Voltage 24 V Shielding welding gas Kind of tested micro-jet cooling gas Ar Ar + 1.5% O 2 82% Ar + 18% CO 2 1 Ar 2 He 3 N 2 6. Micro-jet gas pressure 0.4 MPa 0.5 MPa Argon, nitrogen and helium were chosen for micro-jet cooling (with diameter of 40 µm of stream). Cooling gas pressure was always 0.4 MPa. MIG welding technology (with micro-jet cooling) was only used in this project. Argon is chosen because of not oxidizing potential as a shield gas. Weld metal deposit was prepared by welding with micro-jet cooling with varied geometrical parameters. 3 Results There were tested and compared various welds of standard MIG welding with new technology: MIG welding with micro-jet cooling. A purpose of the study was to examine the varying structure of the typical surfacing shaft after welding. All tested welding processes were realized with varied micro-jet gases: argon, helium, nitrogen. A typical weld metal deposit had chemical composition in all tested cases. Micro-jet gas could have only influence on more or less intensively cooling conditions, but does not have greater influence on chemical WMD composition (except nitrogen amount in MWD), Fig. 1, Table 2.

3 Acta Metall. Slovaca Conf. 100 Fig. 1 Surface welding cooling conditions (t 800/500 in terms of various micro-jet cooling gases) Table 2 Chemical composition of metal weld deposit No. Element Amount 1. C 0.15% 2. Mn 0.4% 3. Si 0.15% 4. P 0.014% 5. S 0.011% 6. Cr 1.8% 7. Ni 1.9% For standard MIG welding and welding with two micro-jet gases: argon and helium amount of nitrogen was always on the level of 50 ppm (Fig. 2). For welding with nitrogen as a micro-jet gas amount of nitrogen was higher, on the level of 70 ppm. After chemical analyses the metallographic structure was given. Example of this structure was shown in Tables 3-5. Table 3 Martensite in weld (argon used as a micro-jet gas) Micro-jet gas pressure Number of jets Martensite aprox, % nitrides 0.4 MPa MPa Table 4 Martensite in weld (helium used as a micro-jet gas) Micro-jet gas pressure Number of jets Martensite aprox, % nitrides 0.4 MPa MPa

4 Acta Metall. Slovaca Conf. 101 Table 5 Martensite in weld (nitrogen used as a micro-jet gas) Micro-jet gas pressure Number of jets Martensite aprox, % nitrides 0.4 MPa 1 60 traces 0.5 MPa 1 70 traces Heat transfer coefficient of tested micro-jet gases influences on cooling conditions of welds (Tables 3-5). This is due to the similar conductivity coefficients (λ 105), which for Ar and N 2, in the 273 K are not very various, respectively: and 23.74, J/cm s K. Cooling conditions are rather similar when nitrogen and argon are chosen as a micro-jet gas. Helium gives much stronger cooling conditions due to the higher conductivity coefficients (λ 105), which for He is J/cm s K. Surface weld cooling conditions for all cases with various micro-jet gases are evidently different. Cooling time t 800/500 of standard welding is much longer in comparison with Fig. 2 Martensite in MAG weld without micro-jet cooling gases, magnification 200 Fig. 3 Martensite (aprox. 70%) in weld after welding with micro-jet cooling (argon as microjet gas), magn. 500x

5 Acta Metall. Slovaca Conf. 102 cooling time t 800/500 of weld is depended on gas conductivity coefficients, thus helium is treated as the most effective cooling gas for micro-jet technology (Fig. 5, Table 5). Micro-jet cooling does not have greater influence on chemical composition of weld. Only in case with helium micro-jet cooling there were observed traces of nitrides. There was carried out metallographic structures for MIG surfacing with micro-jet cooling in terms on micro-jet parameters (Tables 3-5). In all cases martensite was the main phase that was varied in terms of various micro-jet paramiters; it is shown in Figs Fig. 4 Martensite (aprox. 70%) in weld after welding with micro-jet cooling (nitrogen as micro-jet gas), magn. 500x Fig. 5 Martensite (aprox. 80%) in weld after welding with micro-jet cooling (helium as microjet gas), magn. 500x It is not so easy to count martensite amount such as other typical weld phases: acicular ferrite, grain boundary ferrite, side plate ferrite for low alloy welding [16]. Martensite amount was only estimated. Nevertheless it is possible to present, that micro-jet technology is capable of structure steering (Tables 3, 4, 5). Martensite amount is similar when nitrogen and argon are taken as micro-jet gases. Nitrogen as micro-jet gas could be useful for nitrides formation. Martensite amount is the highest when helium is taken as micro-jet gas (Fig. 7). After microscope

6 Acta Metall. Slovaca Conf. 103 observation a micro hardness was carried out (Figs. 8-9). Standard surface welding could not guaranty high hardness (Fig. 6). Fig. 6 Hardness of standard weld without micro-jet cooling Hardness was decreased in terms of the distance from weld face, the maximum value was much below 500 HV. Much higher hardness values were observed after welding with micro-jet cooling (Fig. 7). Fig. 7 Hardness of weld after micro-jet cooling, argon used as micro-jet gas Welding with micro-jet cooling (by argon) with one jet allowed to excide hardness under 500 HV. A little higher hardness values were observed after welding with nitrogen as a micro-jet gas (Fig. 8). Fig. 8 Hardness of weld after with micro-jet cooling, nitrogen used as micro-jet gas

7 Acta Metall. Slovaca Conf. 104 Welding with micro-jet cooling (by helium) allowed to excide hardness under 550 HV, Fig. 9. Fig. 9 Hardness of weld after micro-jet cooling, helium used as a micro-jet gas The micro-hardness inside the martensitic regions after welding with micro-jet cooling are higher than in standard weld, i.e. between 580 HV than 475 HV compared to 470 HV. 4 Conclusion The micro-jet surfacing technology was tested for surface welding with various micro-jet gases (nitrogen, argon, helium) and another micro-jet parameter (micro-jet gas pressure). Micro-jet technology could be very beneficial during shaft surfacing. Micro-jet injector has many parameters, such as: the diameter of jet, the number of cooling jet, the flow rate and the pressure of the cooling medium, the distance between the micro jet injector and the weld, the angle of inclination between the micro jet injector and the material surface during welding, the distance between the micro jet injector and weld arc, the geometry of the jet cooling layout). In this investigation only some of micro jet parameters were tested: number of jets, gas pressure, and various cooling media (argon and nitrogen). However, the preliminary results shows validity of theoretical assumptions and it will be possible to apply this technology in industry very soon. On the basis of investigation it is possible to deduce that: micro-jet-cooling could be treated as a important element of MIG welding process, it is possible to steer the metallographic structure (martensite, nitrides), it is possible to steer the weld harness by various micro-jet parameters, there is not great difference between the influence of argon and nitrogen on cooling conditions, helium used for micro-jet cooling (instead of argon and nitrogen) is responsible of the highest hardness in all tested there were observed traces of nitrides when nitrogen was used for micro-jet cooling (instead of argon when nitrides were not observed). Further direction in that method of surface welding should be related with study of other materials such as Al, Cu and Ti alloys. References [1] T. Wegrzyn, J. Piwnik, Archives of Metallurgy and Materials Vol 57. No. 2. P [2] R. Burdzik, Z. Stanik, J. Warczek: Archives of Materials and Metallurgy, Vol. 57, 2012, No. 2, p , DOI: /v [3] T. Węgrzyn, D. Hadryś, M. Miros: Optimization of Operational Properties of Steel Welded Structures, Maintenance and Reliability, 2007, No. 3, p

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