Bar Rolling Mills Water Cooling Technology for Low-Temperature Reinforcement Bars
With the continuous growth of the world economy and energy consumption, natural gas as high-quality and efficient energy is widely used in various fields. China’s LNG (liquefied natural gas) consumption is currently growing at a rate of 10% per year. LNG is small in size, convenient for economical and reliable long-distance transportation, and stored in atmospheric pressure LNG tanks. However, the LNG tank is a composite multi-layer structure. The inner tank is welded by 9% Ni steel plate. The concrete close to the inner tank is cast with low-temperature steel bars. The outer concrete is cast with ordinary steel bars HRB355 and HRB400. Therefore, bar rolling mills low-temperature reinforcement for inner concrete requires not only high strength and good toughness at low temperature but also high defect resistance sensitivity.
According to the characteristics of water cooling process of low-temperature steel bars, the convective heat transfer coefficients of different specifications of low-temperature steel bars during water cooling process are obtained by using field measured data and theoretical analysis. The cooling process of low-temperature steel bar through water was studied by using MSC Marc finite element software and field trial production results. The effects of bar rolling mills cooling water flow rate, finishing rolling temperature and water penetration time on temperature field and microstructure evolution of low-temperature steel bars were studied. The simulation results show that when the cooling water flow rate is 120 m3/h, pearlite transformation begins to occur in the steel core; when the cooling water flow rate is 400 m3/h, there is no ferrite transformation in the steel core; when the cooling water flow rate is 160-200 m3/h, the obtained structure is acicular ferrite and bainite. The surface temperature and reddish temperature of steel bar increase about 10 C and 30 C after finishing rolling at 50 C. The core structure of the steel bar is acicular ferrite and fine bainite when cooling for 1.2 s at 200 m3/h water flow rate and finishing rolling at 1050 C. Under the same water pressure and flow rate, with the increase of water penetration rate, the depth of the hardened layer decreases and the reddish temperature increases.
