Correlation between Dynamic Crack Strength, Plastic Deformation Zone and Geometric Dimple Parameters of Structural Steel 09G2S

摘要

In the present paper the profiles of plastic fractures as a result of dynamic tests of 09G2S steel after hardening and tempering at 200, 400, 500 and 650 ℃ are investigated by the Scanning Electron Microscope and optical unit of the automated micro-hardness machine. Micro-dimples geometry is studied, and micro-dimples are classified into three groups according to the width-to-height ratio: flattened one, well-like one and cone-like one. A correlation between the micro-dimples geometry evolution and a rising tempering temperature is found. The size of the Plastic Deformation Zone (PDZ) of high toughness structural steel is evaluated. The PDZ is proved to be not formed at the tip of the initial fatigue crack (concentrator) but rather at some distance ahead within the area of the starting dynamic crack. It is demonstrated that the PDZ grows consistently as the tempering temperature rises from 200 ℃ to 650 ℃. The dynamic crack strength increase implies the PDZ expansion, as well as consolidation of micro-dimples and the macro-dimples area growth within the fracture surface.