Base material fatigue data for low alloy forged steels used in the subsea industry. Part 1: In air S–N data

• In air fatigue test data for low alloy steel specimens are presented.
• The effect of the surface roughness, mean stress and tensile strength on the fatigue strength have been quantified.
• The scatter in fatigue life has been quantified for the data set consisting of 354 fatigue test results.
• A method for estimating high cycle in air fatigue data for low alloy steels from the tensile strength or the Vickers hardness is presented.

This is the first of two papers presenting fatigue data for low alloy forged steels in a quenched and tempered condition. This paper considers the effect of the surface roughness, mean stress and material strength on the high cycle fatigue crack initiation life on low alloy steels having tensile strengths in the range from 600 to 800 MPa. The scatter in fatigue life has been quantified for the data set consisting of 354 fatigue test results. Fatigue test specimens having surface roughness from Ra=0.3Ra=0.3 μμm (polished surface) to Ra=6.3Ra=6.3 μμm (coarse production surface, resulting for instance from coarse surface grinding). A method for estimating high cycle fatigue data for smooth low alloy steel from the tensile strength or the Vickers hardness is presented. The estimation method has been validated with fatigue test results and compared with other published methods for estimating strain–life fatigue properties. Part 2 of this paper addresses the effect of seawater with cathodic protection on the fatigue crack initiation life for smooth specimens.