Abstract��The 45 round steel bar (100 mm specification) was used to produce a kind of hydraulic cylinder piston for excavator in one machinery factory. The straightening fracture occurred during the processing. The 45 round steel and fractured sample were analyzed by chemical composition�� acid pickling test�� fractograph and metallographic structure. The results showed that the mechanical properties and chemical composition of 45 round steel bar for producing piston rod could meet standard requirements. There were few inclusions in the steel�� and the microstructure was normal ferrite��pearlite. The straightening fracture of piston rod belonged to brittle fracture. The rupture source was located on the sample surface�� and the microtopography was rock candy-shaped brittle fracture. After acid pickling test�� many cracks along the circumferential direction as well as deep and thick lathing marks were found on the longitudinal surface of fractured piston rod. The metallographic analysis results indicated that the cracks were intergranular cracks which were formed in medium-frequency hardening process. The hard and brittle structures of tempered martensite existed in crack areas. The straightening fracture cause of the piston rod could be explained as follows�� the hardening intergranular cracks�� which had been formed in medium-frequency hardening process before straightening of workpiece�� were expanded along the matrix until to fracture under the action of straightening stress. The surface hardening cracks could be eliminated by enhancing the degree of surface finish through improving the medium-frequency quenching and tempering processes. The straightening fracture was not observed in the subsequent products.
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LIU Jin-yuan. Straightening fracture cause analysis of the hydraulic cylinder piston for excavator. Chinese Journal of Iron and Steel, 2016, 34(1): 1-6.
2016, Vol. 34 
