Development And Production Technology Of 500N Australian Standard Steel Bar In Laiwu Steel

500N is a high-strength steel grade in the AS/NZS 4671:2001 standard.It has high strength and good plasticity and weldability.It is widely used in high-rise buildings,bridges,airports and petrochemical industries.Belonging to a kind of material which saves efficient building structure.Speed up the development of the product economy,to open up the Australian market and ease the domestic steel production capacity has a positive significance.This project is based on the present situation of the level of smelting and rolling process equipment of Laiwu steel bar production line.Based on the production of high strength steel bar by hot rolling,the microstructure of the alloy is based on the laboratory The results show that the relevant control points of 500 MPa grade strength and toughness steel controlled rolling and controlled cooling process are obtained,and the field industrial test is carried out,and the key technological parameters required for industrial production of 500 MPa grade hot rolled steel are finally determined.?12-?36 Australian standard steel,the product meets the user's requirements.The development of steel compared to the use of ordinary hot rolling production costs have been greatly reduced for the steel plant has brought good economic benefits.The main achievements of the paper are as follows:(1)In view of the requirement that the carbon standard is low and the control is difficult,the economic composition of vanadium nitrogen microalloying is designed,and the high temperature plasticity behavior of 500N slab is studied according to the composition characteristics.The results show that the temperature range of 750?885? is a high temperature range of 500 ? steel cast.Therefore,in the actual production process,continuous casting straightening surface temperature should be controlled at 885? or more,to avoid the crack prone to the brittle temperature range.(2)The behavior of deformed austenite dynamic and static recrystallization at high temperature of vanadium nitrogen microalloyed high strength steel bar was studied.The results of dynamic recrystallization show that when the 500N high strength steel bars are produced,the strain rate of coarse and middle rolling is 1.0?10s-1,and the rolling temperature is above 1000?.The dynamic recrystallization of ferrite can be achieved.The results of static recrystallization show that the starting temperature of static recrystallization in 500N steel is between 900 and 950?,and the time interval is guaranteed to be at least 5s.According to the actual situation of the production line of Laiwu Steel,the time required for static recrystallization is obviously not satisfied when the continuous rolling time is adopted.Therefore,it can be considered that the temperature range of 900?950? is 500N high strength steel reinforced by vanadium nitrogen microalloying as the starting temperature of the non-recrystallization zone.(3)The dynamic CCT curves of 500N high strength steel bars with vanadium nitrogen microalloying showed that when the cooling rate was higher than 5?/s,the bainite structure began to appear in the steel,and the hot rolled high strength steel bars generally did not Allowing the emergence of bainite and other organizations,requiring rolling steel structure should be ferritic and pearlite composition.Therefore,500N steel bar after cooling the cooling rate should not exceed 5?/s in order to obtain the desired organization.(4)500N steel bars produced by the combination of the pre-finish rolling and the light-through water cooling after the finish rolling are the best after the natural aging,and about 50%of the V alloy can be saved in the case of ordinary hot rolling process.(5)500N steel bars are cooled by the cooling bed temperature between 820?860 ?,after the air-cooled phase transformation of the finished product are F+P tissue,no other abnormal organization,compared to ordinary hot rolling organization is more small Evenly.The results of the second phase test show that the precipitated second V(C,N)particles are fully distributed and dispersed in the steel,which achieves the purpose of improving the strength of the steel.