The relationship between 51CrV4 end cracking and bainite structure

The main reason for cracking at the end of 51CrV4 spring flat steel is: due to improper cooling after rolling, bainite structure appears in 51CrV4 steel structure, low shear temperature, shear stress and shear deformation cause microcracks in bainite structure. During the storage period of 51CrV4 steel, the residual stress in the deformation zone makes the micro-cracks expand and develop into macro-cracks on the section, resulting in greater residual stress in thick gauges and an increased possibility of end occurrence.

So, how does the bainite structure of 51CrV4 steel mentioned above come into being?

The reason for the formation of bainite structure is: 51CrV4 steel contains more alloying elements such as Cr and Mn. These two elements can significantly improve the hardenability of 51CrV4 steel and significantly delay the transformation of austenite to ferrite and pearlite. The transformation of the bainite structure is obtained in a wide range of cooling rates.