Effect Of Al Content On Mechanical Properties Of Grade E Steel And Fracture Mechanism Analysis

In this paper, to study the influence of Al content on the microstructure and mechanical properties of Grade E steel by observe the microstructure and mechanical property test. Through SEM and TEM observe to analysis the morphology and the second phase. To study the effect of high Al content on tissue morphology and fracture morphology and analysis the base cause of fracture mechanism.When Al content was lower than 0.04 %, because Al can deoxidize and a little of Al elements had an effect on grain refining of steel. The Grade E steel strength increased. The impact performance improved in low temperature. When Al content was higher than 0.04 %, the change of Al content had a little influence on strength of Grade E steel. With the increase of Al content, elongation and reduction of area were raised first and then declined.When Al element content was more than 0.09 %, macroscopic fracture began to appear smooth surface. With the increase of Al content, the impact energy declined quickly. It didn't meet the requirements of Grade E steel performance. High levels of Al content increased the tissue inhomogeneity. With the increase of Al content, the fracture toughness value decreased. The role of high Al content made the Grade E steel more sensitive to crack. The ability to resist crack propagation was weakened.With the increase of Al content, the micro fracture changed from ductile fracture to brittle fracture characteristics. When Al content was low, the fracture had a large number of toughening. When Al content reached 0.09 t%, the fracture toughness decreased significantly. When Al content reached 0.13 %, it started to appear the mixed fracture of plastic and brittle. As the Al content continues to increase, fracture surface presented typical cleavage fracture characteristics. In actual production testing, we can get the macroscopic fracture by the way ofthrust. Through the Relationship between macro fracture morphology and Al content to quickly determine whether Al content beyond the standard.The excessive Al is the main reason for the formation of brittle fracture, part of the Al formed Al N with N, Al N separated out from the interface. And part of the elements of Al formed of brittle intermetallic compounds with Fe. It had a pinning effect and appeared on the long straight interface. It partitioned the substrate. These factors made the elongation, reduction of area and the impact energy decrease. Eventually lead to Grade E steel change of fracture types.Considering the Grade E steel material standard and the actual fracture characteristics, I suggest the Al content of the Grade E steel in the range 0.03 %to 0.08 %.