Scale-induced effects on fatigue properties of a cast steel for bogie frames of China railway rolling wagons

A new method is suggested for measuring scale-induced effect on fatigue properties of grade B cast steel for fabricating bogie frames of China railway rolling wagons. One grouped material and three grouped structure-like specimens are machined and fatigued under same stressing amplitude with scale kinetics. Fracture surface observations reveal that fatigue cracks are initiated from weakest material cast shrinking cavity or hot tear. There are distinct fatigue striations, river-like flowers, and second cracks in perpendicular to the fatigue crack growth path on fracture surfaces. Lots of dimples appear in transient fracture zone to indicate a ductile fracture. And more dimples appear for material specimens. The effect is statistically assessed on a phase of specified fatigue strength by comparing random fatigue lives. Interactive effect of the scale and surface quality are taken into account involving in scale change. And then, this effect is extensively employed to cover entire fatigue strength range and, additionally, to address structural scale kinetics.