Super carburizing is one of the carburizing processes where surface carbon content is increased up to 2 to 4%, extremely higher than that of conventional one. This is characterized by its carbide precipitation in the case and is expected to show superior fatigue durabilities.
At first the effect of plasma super carburizing conditions on the carbide morphology was studied using 0.18%C-0.5%Si-2.25%Cr-0.4%Mo steel. Low temperature carburizing at 1143K was confirmed to be effective to obtain finely and uniformly dispersed carbides. Furthermore, the optimum condition was selected with taking other case properties into account.
The bending and contact fatigue tests were carried out as a next step, and it was revealed that plasma super carburized steel exhibited superior fatigue durabilities to those of conventionaly carburized JIS-SCM 420. The superiority was considered due to its higer surface hardness, finer grain, intergranular oxidation free case and higher elevated temperature hardness.

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The influence of carbon, manganese and chromium contents on the toughness of medium carbon microalloyed steels was investigated by an instrumented Charpy impact testing machine and by the microstructural observation with an electron microscope.
The pearlite area fraction increases when carbon, manganese and chromium contents increase. On the other hand, increasing manganese and chromium contents simultaneously makes the interlamellar spacing of pearlite smaller. Chromium has larger effect than manganese in this respect.
The hardness becomes higher and the toughness becomes lower when increasing the carbon content. However, in the case of manganese and chromium, both hardness and toughness are improved as far as the bainite structure does not appear. This phenomenon is related to the fact that manganese and chromium change the pearlite morphology and increase the crack initiation energy in the impact tests.
Among the steel grades tested in this research, 1.1% manganese and 0.5% chromium is the best combination to get the highest toughness.

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Shot peening is one of the cold working processes performed by projecting hard particles onto the surface of works. In spite of old technology, it has been reconsidered in automotive industries as the means to improve fatigue durability in terms of “Hard shot peening”. Hard shot peening is a high intensity peening technology resulting in larger amount of compressive residual stress and higher fatigue resistance than conventional intensity peening. In hard shot peening process, however, the peak value of the stress is located at the depth of 0.05mm below the surface and the surface value is not so high. To compensate this stress depression at sub-surface, additional beads peening was studied. By applying the additional beads peening further improvement of fatigue resistance has been confirmed. The beads peening process is effective to give residual compressive stress at the surface without surface degradation.

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Some fundamental research on alloy design of 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 the mechanical properties equivalent to quenched and tempered medium carbon steel, 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 and coating on large ends was developed. As a result of this research, new titanium alloy connecting rods which can be applicable to mass production have been developed.

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It is an urgent need in automotive industries to tackle the global enviromental problemes, especially “green house effect”. As carbon dioxide exhausted from vehicles is the main cause, it is strongly required to enhance the fuel efficiency. There is a trend, furthermore, to mount new equipments, especially for the assuring driver safety and easy drivability. Therefore, the weight reduction technology is becoming more and more important, recently.
In this paper, the current technoloby and the future outlook on the power train components, especially by focussing on the materials technology. Although it is the most effective way to apply the light metals such as aluminum and magnesium to reduce the weight, there remains many technical problems to be solved, needless to say its expensive cost.
Therefore, it is still essential to utilize steel materials effectively not only by developing new steels but by innovating the parts producing process.

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Weight reduction is a key technology in order to improve fuel economy and driving performance of automobiles.
Recently, requests for the automobile has been diversified, which are upper-class oriented taste, improvement of safety, noise attenuation and earth environmental problem etc.
These requests cause increase of weight of the automobile. Accordingly, the material technology to reduce weight becomes more and more important.
Furthermore, due to tightening CAFE regulation in the US and the Clean Air Act in California in 1990, it is forced to speed up the development of weight reduction technology.
In this paper, recent materials for weight reduction of gasoline engines are described.

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Induction hardening of cold forged parts have become more popular in automotive industries to simplify the production line. However, carbon steel whose carbon content is higher than 0.4% gives rise to the difficulty in cold forgeability even in spheroidizing annealing condition. When alloy contents are decreased to improve cold forgeability, on the other hand, induction hardenability is deteriorated conversely.
On these backgrounds, the new steel named HAC steel, Hardenability Assured steel for Cold Forging, has been developed to be compatible these two characteristics each other. Ferrite strengthening elements, Si and Mn, are decreased to reduce the flow stress in cold forging and B is added to maintain induction hardenability. HAC steel, the fundamental composition is 0.48∼0.53C-0.05Si-0.25Mn-0.15Cr-B, shows superior cold forgeability to that of conventional JIS carbon steels keeping the same case depth in induction hardening.
HAC steel has been in practical use for constant velocity joint components such as outer race and shaft, and expected to apply to the wide variety of automotive parts.

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Automobile industries have searched for more reliable steel with higher strength. In case of spring steel, much efforts have been made to develop the high strength steel to endure the applied stress of 130kgf/mm².
For this purpose, at first a fundamental study on the alloy designing of ultra-high strength steel was made.
ND 250S (0.4C-2.5Si-0.8Mn-2Ni-0.85Cr-0.4Mo-0.2V) was confirmed to show the great possibility to be applicable to high strength coil spring. Furthermore, the coil spring made of this steel was evaluated in terms of the fatigue properties, sag resistance and delayed fracture property.
The following results are obtained.
(1) The mechanical properties of ND 250S are superior to those of SUP 7 especially in toughness.
(2) The threshold stress intencity factor range of ND 250S is larger than that of SUP 7, which indicate the greater notch toughness.
(3) ND 250S is proved to exhibit superior properties necessary for coil spring to conventional spring steels and to show the potential as the 130kgf/mm² grade high strength coil spring.

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Recently, steel users require the supply of bars which improve machining or forging yield, eliminate some machining processes and can be delivered in a short time. To satisfy the users' requirements, Daido started the study on precision rolling method in 1982 and developed in 1984 the TEKISUN SIZING MILL consisting of three 2-roll stands arranged H-V-H. With this TEKISUN MILL, precision rolling down to a ±0.1mm tolerance, and free size rolling within approx. 1mm range are feasible. In order to establish the BAR TEKISUN technology Daido started the remodeling of Chita Bar Mill in 1987 and completed it in Aug. 1991 under the slogan of “Any size in Any amount at Any time” which brings advantages not only to steel users but also to steel manufacturers themselves.

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A new ausforging equipment and a cooling control equipment for hot forged components without subsequent heat treatment have been developed in Machinery Division, Daido Steel Co., Ltd.
They offer an attractive cost saving due to complete elimination of the conventional production route. We recommend you to try once its unequalled merits and eminent function.

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In recent years, technological innovations in automobiles are so remarkable to obtain high-power, fuel saving and reduction of pollution.
In these current, many engineering parts of automobiles are treated by vacuum equipment. Some kind of vacuum equipments such as investment casting furnace, sintering furnace, plasma carburizing and quenching furnace, ion-plating furnace are introduced. The relationships between these equipments and technological innovations are explained.

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