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In recent years, efforts for development of high-performance and compact automobile engine are being made more actively than ever before. The connecting rod bolt is one of those parts which are very much required to be compact and light, since its size and weight affect the performance of the engine. However, if it is used under high stress, delayed fracture can be caused. Therefore, it is a common practice to keep the stress below 1177MPa. The developed alloy (HB149) is a precipitation hardening alloy steel of low carbon martensite, composed mainly of 0.35C-1.2Cr-1.0Mo-0.3V. With lowered intergranular inclusions by suppressing impurity elements such as phosphorus and sulfur, and with reduced grain boundary embrittlement by tempering it at a high temperature, this steel is excellent in resistance to delayed fracture. Using this steel, we developed a 1372MPa class (Class 14.9*) high strength connecting rod bolt.

The gears used for motorcycles are required high fatigue strength, high dimensional precision and ease of machining. Therefore, a primary driven gear has been developed using a new nitrocarburized steel. The new Cr-V-Al-B nitrocarburizing steel has made it possible to raise fatigue strength by obtaining a hard and deep nitrocarburized case with a bainite matrix. This paper reports on the new nitrcarburizing steel and the result of its application to gears.

These days, nickel-base superalloy has been applied to reduce the valve weight of motorcycles. Inconel 751 is excellent in performance but expensive in cost. Therefore, we verified the constituents of nickel-base superalloys corresponding to the requirements of valves and we succeeded in developing a new superalloy and applying it to motorcycle exhaust valves. The characteristics are summarized as follows: 1. The basic composition is Fe-46Ni-18Cr-4Ti-1Al-0.3C-0.004B. It is a precipitation-hardened nickel alloy characterized by precipitation of Ni3 (Al,Ti) and, crystallization and dispersion of fine TiC. 2. It has the following distinctive features. (1) Superior to Inconel 751 in wear and heat resistance. (2) Superior to 20-11P steel in resistance to lead oxide corrosion. (3) Applicable to both unleaded and low-lead gasoline. 3.

Production of a relatively inexpensive titanium connecting rod for a mass production motorcycle engine has been achieved. Previously, the high cost of Titanium and other factors limited its usage by the aerospace industry and motor sports racing. As a material for mechanical parts titanium is light in weight and high in strength. In the engines of racing motorcycles the connecting rods, valves, and valve spring retainers which have been fabricated from a titanium alloy enhance the engine's performance.-1, -2 The cost of titanium alloy and its surface treatment is very expensive. -3, -4 Therefore the cost of the material was prohibitive and limited the application of titanium to competition machines. This paper outlines the development of a new surface treatment and application to titanium connecting rods. It was specifically applied to the connecting rods of a 750 cc motorcycle in 1987, the first in this field of industry. -5, -6, -7

A β-titanium alloy wire with a tensile strength of 210 kgf/mm2 (2060 MPa) was made for automotive valve springs. The fatigue of the β-titanium valve springs were heavily affected with the existence of the oxide layer on the surface. The repeated contact of coils to the ends also gives rise to heavy abrasion during the service, indicating the necessity of some measures to prevent it. Through this investigation, technological basis for β-Ti valve springs was established.

In Japanese automotive industry considerable changes have been done in not only design of exhaust train but also materials to be used due to non-leaded gasoline as well as emission controls. Especially application ratio of heat-resisting and stainless steel has increased rapidly and at the same time manufacturing technique and performance improvement of raw-materials have been made for heat-resisting steel for passenger cars. We have explained for the current trend in materials used for exhaust train such as reactor, catalytic convertor, other part of exhaust train, engine valves, valve seat inserts.

A new heat resistant steel wire was developed for automotive valve springs. The purpose of the development is to apply a high temperature carbo-nitriding process to the springs to have a longer fatigue life. The valve spring processed at an optimal temperature was found to have a fatigue life about five times as long as the conventional Si-Cr oil-tempered wire springs processed at a conventional low temperature.

There are strong demands for reduced production costs of ordinary bolts, of which a large number are used throughout automobiles. In addition, there are continued demands for higher performance and lower weight in automobiles. For this reason, there is an increasing trend to develop steel for high strength bolts or to adopt the plastic region tightening method. At present, the principal materials used in high strength bolts of class 10.9 are medium carbon alloy steel. When a low carbon boron steel bolt is used as a class 10.9 bolt under high stress, delayed fracture may occur, so that these cannot always be used for the body and chassis applications. The authors have developed a new low carbon boron steel with increased delayed fracture strength on the same order as that of JIS-SCM435 (equivalent to SAE4135) medium carbon alloy steel. Attention was focused principally on decreasing the amounts of phosphorus and sulfur in the steel.