INFLUENCE OF HOT-DIP GALVANIZING ON FATIGUE AND CORROSION-FATIGUE RESISTANCE OF A B-MN STEEL

In this study, the effects of hot dip galvanizing on fatigue and corro sion fatigue resistance of smooth and notched quenched and tempered (Q &T) specimens were investigated. Constant stress amplitude plane rever sed bending fatigue tests (R=-1) at 47 Hz in air and sea water were co nducted using cylindrical hot dip galvanized (HDG) and Q&T steel speci mens made of a B-Mn SS2131(-AISI 15B21H) steel with K-t=1.05 and 1.7. The results are compared with those obtained for plasma-nitrided (PN) and laser-hardened (LH) specimens. The S-N curves show that hot dip ga lvanizing slightly decrease the air fatigue limit of smooth (-9%) and notched (-10%) specimens. In sea water, smooth and notched HDG specime ns exhibit corrosion fatigue limits (at 2x10(7) cycles) with values a little lower than the corresponding air fatigue limits. The corrosion fatigue strength of HDG specimens is also superior to the fatigue stre ngths resulting from other surface treatments (plasma nitriding and la ser hardening). It has been shown that the small cracks formed in the coating during galvanizing could be the cause of the slight decrease i n air fatigue. Physical and electrochemical corrosion protection by ho t dip galvanizing are the causes for the good corrosion fatigue proper ties obtained.