INFLUENCE OF SEA-WATER ON THE FATIGUE-STRENGTH AND NOTCH SENSITIVITY OF A PLASMA-NITRIDED B-MN STEEL

Notched and smooth cylindrical plasma nitrided (PN) and quench and tem pered (Q&T) steel specimens made of a B-Mn SS2131( approximate to AISI 15B21H) steel have been exposed to constant amplitude plane reversed bending corrosion fatigue tests (R = -1) at 47 Hz in sea water. S-N cu rves show; that sea water suppresses the fatigue limit and reduces fat igue strength (especially at long lives) of smooth and notched Q&T and PN specimens. Plasma nitriding improves the corrosion fatigue resista nce of Q&T specimens; this is associated with the good corrosion resis tance of epsilon and gamma'-phases, the enhancement of corrosion and f atigue by compressive residual stresses, and the consumption of H+ ion s during reduction of nitrogen. This improvement is more significant f or smooth specimens and for long lives. Notch sensitivity of Q&T and P N specimens decreases with fatigue life. Fitting corrosion, cyclic app lied stress and residual stresses due to plasma nitriding are the main topics of this work. An equation to predict corrosion fatigue strengt h from air fatigue strength of smooth specimens, has been established. (C) 1998 Elsevier Science S.A. All rights reserved.