Search Results

Fracture split steel connecting rod has been developed for new passenger diesel engines for its advantages in cost saving and better performance. The splitting type of steel con rod is made of high carbon micro-alloyed steel with no additional heat treatment after hot forging. This con rod blank is forged in one-die mold and later fracture splitted. Unlike the conventional types where the rods and caps are separately forged and machined, this steel split con rod needs no additional rod/cap contact face milling which means a substantial savings in machining cost. Besides, a firm contact between rod and cap improves stiffness and compatibility with other crank-train moving parts - a definite merit in engine performance. Our research work focuses on optimizing the two major technologies in this subject - microstructural analysis of controlled cooling (high carbon micro-alloyed steels) and detailed fracture splitting parameters and test results.

A new technique of heat treatment is developed for the bearings of automotive transmission and chassis to maximize their service life under contaminated and severe environments. This study demonstrates an improvement of the microstructure of bearing steels by applying special heat treatments. The microstructure is developed by optimizing various heat treating parameters (temperature, cycle time and gas atmosphere, etc.) as well as by modifying the quenching processes (double quenching and press quenching). We obtained a desirable microstructure of dense and fine martensite with optimum levels of retained austenite and compressive residual stress on the subsurface. The size and distribution of carbides and grains are found to be very fine and homogeneous. The endurance test results show that the specimens with new treatment have an excellent fatigue life compared with the conventional bearing samples.

The banded microstructure of pearlite and ferrite in normalized alloy steel is susceptible to thermal distortion during carburizing process due to its unidirectional orientation parallel to rolling direction. The planetary gears with material of banded microstructure have been experienced in high thermal distortion during carburizing and quenching process and result in uneven surface hardness and effective case depth at the inside of pinion gear after honing. These defects played failure initiation site roles in durability test during development of new automatic transmission. The galling between the contacting components in severe lubricating system was the main failure mechanism. Double normalizing at 920 °C was designed to resolve the banded microstructure of normalized alloy steel. The microstructure and grain size of the double heated steel became equiaxed and fine due to homogenizing and recrystallization through double heat treatment.