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Some fundamental research on alloy design of the new titanium alloy and process design such as forging and surface treatment were carried out in order to develop new titanium alloy connecting rods. Free machining Ti-3Al-2V alloy is the best alloy for connecting rods because it has mechanical properties equivalent to quenched and tempered medium carbon steels, a popular material for connecting rods. The alloy can be machined at higher speed than the most popular titanium alloy Ti-6Al-4V. Forging in the β phase temperature range is desirable to enable one heat forging of connecting rods and to eliminate crack initiation. New technology such as induction heating in forging, pickling after forging and coating on large ends were developed. As a result of this research, new titanium alloy connecting rods which can be applicable to mass production have been developed.

In recent years, the use of aluminum die cast parts in automobile manufacturing has increased due to greater demand for automotive weight reduction. For even wider application, it is necessary to reduce manufacturing costs and improve product quality. Finite element method (FEM) analysis suggested that a new material, featuring 50% improved thermal conductivity within the working temperature of the die compared to the conventional 5% chromium hot work tool steel AISI-H13 (H-13), would decrease thermal stress on the die surface and lower the maximum surface temperature. As a result, the reduced stress should increase the die service life with respect to heat checks. At the same time, the reduced surface temperature should increase the cooling rate of die cast products, which will in turn improve product quality due to finer structure formation.

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.

Although shot peening is an old technology, it has been revived in the Japanese automotive industry as a means to enhance the fatigue durability of steel components. Particular emphasis is on the application of “hard shot peening”. “Hard shot peening” is a high intensity peening technology which results in a higher magnitude of compressive residual stress and, therefore, greater fatigue resistance than conventional shot peening. The first area of development was in high performance carburizing steels suitable for hard shot peening. Desirable traits were enhanced by reducing the carburizing anomalies resulting from intergranular oxidation and by the enhancing case toughness. Further improvement of fatigue resistance has been accomplished by dual peening, first with hard shot followed by smaller diameter steel shot at a lower intensity. This paper also describes the development of long life shot media for hard shot peening.

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.

The cold forging process is one of the most popular in the manufacture the automotive parts such as gears and shafts, cold forging saves material and machining costs by near-net shape the principle of forming. However, abnormal austenite grain growth sometimes occurs when the cold forged parts are heated for surface carburizing without a prior normalizing process. The size of the coarse grains can be large, sometimes ASTM Grain Size Number -2 to -4. The abnormal grain growth may cause post-carburizing distortion and is harmful to both fracture toughness and fatigue strength of the parts [1]. The purpose of our research was to develope new steels which would keep the fine grains during the carburizing treatment without normalizing. First, we studied the influence of elements on the grain growth property of case hardening steels and Naiobum (Nb) was selected as the element to control the grain growth. Secondly, we developed an ultra fine grain steel containing a small amount of Nb.

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.

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.

A new variable compression turbo (VC-Turbo) engine, which has a multi-link system for controlling the compression ratio from 8:1 to 14:1, requires high axial force for fastening the multi-links because of high input loads and the downsizing requirement. Therefore, it was necessary to develop a 1.6-GPa tensile strength bolt with plastic region tightening. One of the biggest technical concerns is delayed fracture. In this study, quenched and tempered alloy steels were chosen for the 1.6-GPa tensile strength bolt.