Papers by Keyword: Local Strengthening

Abstract: The research shows the possibility of increasing the structural strength of the weld joints of EP517 steel and 36NKhTYu iron-nickel alloy as applied to the combined bandage of the high-speed rotor of an electric machine, due to the effect of local strengthening of the soft interlayer. The technology of electron-beam welding of 36NKhTYu alloy to EP517 steel with free root formation, which allows to obtain narrow welds, is described. The results of metallographic researches and mechanical tests of weld joints with different weld widths are presented, which showed that the structure and properties of the weld metal on samples with different weld widths are almost identical. The tension test results of weld joints demonstrate a significantly greater ultimate tensile stress, compared to the ultimate tensile stress of the weld metal. Also, it was established that, due to the local strengthening phenomena the smaller the weld width, the stronger the welded joint is. In addition, the use of heat treatment after welding allows us to increase the strength properties of the weld metal and the heat-affected zone of the 36NKhTYu alloy, due to the formation of the hardening γ’-phase. The possibility of increasing the ultimate tensile strength of the weld up to 98% of the ultimate tensile stress value of EP517 steel (as the less durable of both welded materials), due to heat treatment and reducing the weld width, is demonstrated.

Abstract: Comparison tests of needles made in abroad and domestic on chemical composition, microstruture , mechanical property and so on, the main influence factors of the wear resistance were analysed. Approaches of improving the wear resistance of needles are given,such as hot process,surface treatment ,local strengthening. Combined with finite element analysis, the stress and the strain of the needle hook were analysed. Comparative results of both abroad and domestic show that the carbide in the microstructure and structural design of needles are regarded as the main influence factors of the wear resistance.

Abstract: A lot of innovations in molding and casting technology and also simulation techniques have made ductile iron more and more competitive and it even competes meanwhile against steel forgings. A successful substitution of steel forgings for example is the wheel carrier for a high volume car with the Georg Fischer new ductile iron material 'SiboDur', a ductile iron family with high strength and high elongation at the same time. But there is still a great potential for ductile iron castings to substitute steel forgings, in particular in the automotive industry. One example is the crankshaft for the engine: Quite a lot of gasoline engines are equipped with ductile iron crankshafts, but for instance most of the diesel engines are still running with forged steel cranks. The reason is mostly the belief of design engineers that it is not possible to get similar fatigue limit with castings com-pared to forged steel. This belief may often be correct, but using local strengthening technologies, such as roller burnishing of bearing fillets or inductive hardening of highly stressed areas can raise the fatigue limit of casted crankshafts dramatically. The paper presents studies which show that using the right ductile iron material and optimized roller burnishing conditions can raise the fatigue limit of cast crankshafts to values even higher than forged steel ones (material 38MnVS6). But even quenched and tempered forged steel crankshafts are in the focus to be substituted by castings. It is well known that ductile iron also can be induction hardened, but the induction hardening of ductile iron is still an empirical technology. This leads to the second part of the paper: In a cooperation of Georg Fischer and RWP a research project was carried out to develop a simulation technology to predict the residual stresses in a cast crankshaft due to induction hardening under different condi-tions. The results are very encouraging and enable us today to predetermine the induction hardening conditions to get optimized fatigue behavior of ductile iron crankshafts. Of course, the findings can also be used for other applications than crankshafts.

Abstract: The advantages of low heat joining techniques, such as low distortion and little influence on the local material properties due to the low introduced amount of heat, shall be made usable for the manufacture of high strength structures by increasing the process reliability. The dependency between the parameters of the joining process, the seam geometry, the type of solder, the load type und the fatigue life especially of soldered structure with local strengthening shall be examined to allow a calculative estimation of the part’s life.