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Technical Paper

Development of Pitting Resistant Steel for Transmission Gears

2001-03-05
2001-01-0827
It was found that pitting resistance of gears is strongly influenced by resistance to temper softening of carburized steel. The investigation about the influence of chemical compositions on hardness after tempering revealed that silicon, chromium and molybdenum are effective elements to improve resistance to temper softening and pitting resistance. Considering the production of gears, molybdenum is unfavorable because it increases hardness of normalized or annealed condition. Developed new steel contains about 0.5 mass% of silicon and 2.7 mass% chromium. The new steel has excellent pitting resistance and wear resistance. Fatigue and impact strength are equivalent to conventional carburized steels. Cold-formability and machinability of the new steel are adequate for manufacturing gears because of its ordinary hardness before carburizing. The new steel has already been put to practical use in automatic transmission gears. Application test results are also reported.
Technical Paper

Development of the Ferritic Stainless Steel Welding Wire Providing Fine Grain Microstructure Weld Metal for the Components of Automotive Exhaust System

2003-03-03
2003-01-0979
Ferritic stainless steel gas metal arc welding (GMAW) wires have been widely using for automotive exhaust system components made of ferritic stainless steels. In order to enhance the high temperature strength of weld metal, it is necessary to make the microstructure of weld metal finer. In this study, the effect of the chemistry of ferritic stainless steel GMAW wire on the weld metal microstructure was investigated and new ferritic stainless steel GMAW wire providing fine grain microstructure of the weld metal was developed to improve high temperature mechanical properties, oxidation resistance, corrosion resistance of the weld metal and weldabiliy of the wire.
Technical Paper

Improvement in Pitting Resistance of Transmission Gears by Plasma Carburizing Process

1994-03-01
940727
The application of both high strength gear steels and shot peening technology has succeeded in strengthening automotive transmission gears. This technology, though, improves mainly the fatigue strength at the tooth root, but not the pitting property at the tooth face. Therefore, demand has moved to the development of new gear steels with good pitting resistance. In order to improve pitting resistance, the authors studied super carburizing which is characterized by carbide dispersion in the case, especially processed with a plasma carburizing furnace. Firstly, the influence of the carburizing temperature and carburizing period on the carbide morphology was investigated and the optimum carburizing conditions were determined. Secondly, the fatigue strength and pitting resistance was evaluated using carbide dispersed specimens.
Technical Paper

High Performance Differential Gear

1989-02-01
890531
Excellent fuel economy and high performance have been urgent in Japanese automobile industries. With increasing engine power, many of the power train components have to withstand higher loads. Differential pinion gear being one of those highly stressed parts, excellent fatigue and shock resistance have been demanded. At first the fundamental study on the fatigue and impact crack behavior of carburized components was studied and the new grade composed of 0.18%C-0.7%Mn-1.0%Cr-0.4%Mo was alloy designed. Furthermore, Si and P is reduced less than 0.15 and 0.015%, respectively aiming at the reduction of intergranular oxidation and improved case toughness. The differential gear assembly test has proved that the new grade shows three times as high impact strength as that of conventional steel, SCM418, and almost the same as that of SNCM420 containing 1.8%Ni.
Technical Paper

A New Iron-Base Superalloy for Exhaust Valves

1981-02-01
810032
For heavy duty gasoline or diesel engines, exhaust valves of 21-2N or 21-4N are generally coated by cobalt-base hard facing alloys, at faces. But the sluggish supply and the spiraling price of cobalt recently forced automakers to adopt valves of high-grade superalloys without hard facing. Candidate superalloys for high-performance exhaust valves are gamma-prime strengthened nickel-base alloys such as Inconel 751 and Nimonic 80A. Unfortunately above-mentioned alloys are too expensive for automobile components. So authors tried to develop a gamma-prime strengthened iron-base alloy, which bears basically 40% Ni-19% Cr-Al-Ti. To optimize Al and Ti contents the effect of the total amount and the ratio of them was examined thoroughly on hardness, strength and corrosion resistance of experimental alloys at elevated temperatures.
Technical Paper

Development of New High Strength Spring Steel and Its Application to Automotive Coil Spring

2000-03-06
2000-01-0098
For the purpose of saving natural resources and energy, the requirements of vehicle weight-saving have been increasing continuously. As for Automotive Suspension Coil Spring, its weight-saving has been achieved by increasing the design stress. Since the increase of design stress requires higher fatigue life and sag resistance, the strength of spring is usually increased. However, in case of the conventional spring steel, the high strength over σB=1900MPa can dramatically reduce the corrosion fatigue life of spring, to decrease the reliability of spring at the actual usage. In this paper, newly developed spring steel material, satisfying higher strength and corrosion fatigue life simultaneously, is proposed, and its application of Automotive Suspension Coil Spring under the appropriate spring manufacturing processes in introduced.
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