Reduction of Fatigue Resistance on Bolts with Threads Rolled after Heat Treatment, as a Result of Superficial Treatment 2003-01-3657
An increase in the fatigue resistance on threaded elements is obtained by thread rolling after heat treatment. This effect is reached by introducing residual compressive stress gotten from the plastic deformation operation to the formation of the threaded fillets.
In critical application bolts, submitted to high work force, as used to assembly connecting rods, main bearing or cylinder head, this additional fatigue resistance is crucial to design joints of low weight and high reliability.
In many of these applications, due to corrosion problems, the fasteners receive as a final operation, superficial treatment of the organometallic kind or electroplated coating, which due to the process of curing or to eliminate hydrogen embrittlement are submitted to temperatures between 200° C - 320° C.
The objective of this paper is to show the influence of the temperature in the final process in the fatigue resistance to fasteners with thread rolled after the heat treatment.
A countless number of fatigue test of bolts submitted to temperature from 140° C to 230° C has been carried out. From the obtained results, empiric equations that determine the relationship between fatigue resistance and temperature were determined.
After analyzing the results we could see that, at a certain level, the temperature of the process performed after the thread rolling, has influences significantly the fatigue resistance on fasteners with thread rolled after heat treatment.