Low Cycle Fatigue of G20Mn5 Cast Steel Relation between Microstructure and Fatigue Life

Abstract

Cast steel is commonly used to produce structural and safety parts. Foundry processes allow producing parts from scrap steel directly to the required dimensions without any forming operation. Cast components may, however, exhibit macro- and micro-shrinkage porosities. The combined effect of macro- and micro-shrinkages on the fatigue behavior of cast steel has been characterized in the literature. Macro-shrinkages may nowadays be eliminated by adequate positioning of risers. However, micro-shrinkages will always be present in cast steel components. Present work addresses the influence of micro-shrinkage porosity on a G20Mn5 cast steel. G20Mn5 (normalized) ingots have been cast under industrial conditions, but ensuring the absence of macro-porosities. Solidification leads to two very different microstructures prior to the normalization treatment: columnar dendrites beneath the surface (Skin) and equiaxed microstructures close to the center (Core). First, metallographic observations of the whole ingot revealed the same grain size in both areas. Fatigue samples were extracted, by differentiating two sampling volumes corresponding to columnar (S) and equiaxed solidification (C), respectively. The distribution of micro-porosities was determined on all samples by Micro-CT-scans. Core samples exhibit micro-porosities with volumes 1.7 larger than Skin samples. Low cycle fatigue tests (3 levels of fixed plastic strain) were run on both sample series (C, S). Results follow a Manson–Coffin law. Core specimens exhibit lower fatigue life than Skin specimens. The differences in fatigue life have been related successfully to the differences in micro-porosities sizes.

Special Issue “Fracture Mechanics and Fatigue Damage of Materials and Structures”

“…In the article by Antonin Bermond et al [5], the influence of micro-shrinkage porosity on a G20Mn5 cast steel was presented. G20Mn5 (normalized) ingots were cast under industrial conditions, ensuring the absence of macroporosities.…”

The Role of the Distance between Fine Non-Metallic Oxide Inclusions on the Fatigue Strength of Low-Carbon Steel

“…The results of these works were also confirmed by the author's research. This topic is a relatively new research problem and is worthy of attention [37][38][39][40][41][42][43].…”

Effect of Surface Finishing State on Fatigue Strength of Cast Aluminium and Steel Alloys

“…Moreover, strongly varying microstructural conditions may occur due to changes in local process parameters like local solidification [ 8 , 9 , 10 ]. Such local microstructural conditions lead to varying shape and degree of porosity, affecting the local acting stress field significantly [ 11 , 12 , 13 ]. This results in a severely limited fatigue strength of imperfective cast components compared to the strength of the ideal, defect free material [ 2 , 14 , 15 , 16 , 17 , 18 , 19 ].…”