How to improve low temperature toughness of A572 Gr.55 steel plates

ASTM A572 Gr.55 steel plates are low alloy high strength niobium vanadium steel plates. They are widely used in engineering structures, such as construction steel structure, construction machinery, mining machinery, heavy truck, mountainous bridge, pressure vessel. ASTM A572 Gr.55 low alloy high strength niobium vanadium steel plates are especially used to make architectural and engineering machinery parts that have requirements of good weldability and toughness.

In order to improve the low temperature toughness of A572 Gr.55 steel plates, BBN steel increase steel purity while do the grain refinement. The phosphorus and sulfur etc. impurities in the steel especially do harm to toughness of A572 Gr.55 steel plates. The phosphorus adsorption in the grain boundary will reduce the surface energy required by the the crack formation of grain boundary, and reduce the toughness of A572 Gr.55 steel. Therefore, it is conducive to the formation and expansion of intergranular crack. In addition, nitrogen and oxygen exist in A572 Gr.55 steel in molten state, will improve the brittle transition temperature of the steel. The collection of of micro inclusions in A572 Gr.55 steel grain boundary will be extended channel of the crack, and large particles inclusion will become the birthplace of crack. Therefore, during smelting, BBN steel strengthen the operation of removing [P] [S], ensure the vacuum degree of VD furnace,so as to reduce the content of gases and inclusions in A572 Gr.55 steel material. With lower sulfur content, the toughness of ASTM A572 Gr.55 steel plates, especially the transverse toughness will be greatly improved.