Effect of helical rolling on structure and fatigue life of 09Mn2Si pipe steel

Abstract

The structure and mechanical properties of ductile ferrite-pearlite 09Mn2Si steel after helical rolling (HR) were studied. It has been shown that five passes of the helical rolling (with a gradual temperature decrease at each pass) resulted in a finely dispersed structure formation in the rod surface layer (up to ∼1 mm thick). This indicated the development of intensive plastic deformation there. At the same time, a lamellar structure consisting of thin elongated ferrite grains has formed in the underlying layers. The largest strain hardening was evident in the surface layer up to 3 mm thick. A yield tooth and plateau were evident on plastic flow curve. The length of the yield plateau was increased up to 2 times compared to as-received steel. This was accompanied with tensile strength increasing by 30%, while the elongation at break decreased. Data of cyclic testing have shown that fatigue life of the HR-treated samples increased by 3.8 times. The highest fatigue durability was characteristic for specimens cut out from the core of HR processed rod.