Research Of Component-Saving Q345 Production Process

With the emergence of excess of the steel production and the resource crisis, the steel industry is facing unprecedented challenges, mainly because the contradictory between alloy costs rises and corporate profits reduction. In order to meet the requirements of lower production costs and conservation of resources, the amount of the micro-alloying elements in the steel must be reduced.In this paper, relate to the subject of "Research of Component-Saving and Low Alloy Steel Production Process" developed by a plate factory and the RAL laboratory in Northeastern University, on the basis of high-temperature deformation behavior of austenitic steel Q345 and continuous cooling transformation behavior research, using the new generation TMCP technology based on the ultrafast cooling, a low alloy Q345 steel plate is developed, the Mn content can be reduced 0.3%～0.5% without adding Nb, V, Ti. The main work and results are as follows:(1) Experiments carried out with different parameters of single pass compression experiments on the sample steel, studied the influence of deformation temperature, strain and strain rate on the sample steel’s recrystallization behavior and microstructure evolution. The results showed that high temperature and low strain rate deformation beneficial to the austenite’s dynamic recrystallization, deformation resistance mathematical model established by regression.(2) The thermal simulation experiment of Q345 steel is carried on the Gleeble3800 thermal simulation machine. Studied the phase transition behavior of supercooled austenite under continuous cooling conditions, determined the continuous cooling transformation curve by microstructure observation and thermal expansion method, and analyzed the effect of cooling rate and other factors. The results showed that:As the cooling rate increases, the volume fraction of ferrite significantly reduced, the two-phase structure of the ferrite and pearlite gradually transformed to ferrite, pearlite and bainite three phase microstructure, and eventually transformed into ferrite and bainite two-phase structure.(3) Hot-rolled experiment is carried on theΦ450 mill. Through discuss the slab heating system control, rolling temperature system control, deformation system control and cooling system control, combinations of different final rolling temperatures, different final cooling temperatures and different cooling speed etc. systems were used. Under the condition of ultra-fast cooling and controlled cooling, effect of various process conditions on the microstructure and properties of the rolled pieces was compared. It can be a reference for applications of ultrafast cooling technology on Q345 grade steel(4) First, the normal tensile test and normal impact test was carried out obtained under different condition. Obtained yield strength, tensile strength, the elongation and shrinkage fractured and shock absorption energy under 0℃,-20℃,-40℃ and-60℃, and observed the morphology of tensile and impact fracture after SEM, and analyzed the component composition of the fracture’s inclusions. According to the microstructure and SEM microstructure under different process conditions compared regulation at different finish rolling temperature, final cooling temperature and cooling speed. Here’s the conclusion:Sample steel will get a better microstructure and properties when the finishing temperature controlled in 800～820℃, the final cooling temperature controlled in the 590～610℃, the cooling rate controlled at 8～10℃/s.Secondly, after electron probe analysis and EBSD analysis on the surface component, it is understood that Mn almost completely dissolved in the matrix, which has an solid solution strengthening effect. There is a large difference between the grain orientation, and has a high density of HAGB, significantly improved low temperature impact toughness.Finally, through transmittance analysis it can be seen that the nano cementite precipitates have an effect of precipitation hardening.(5) Using the new generation TMCP technology based on the ultrafast cooling industrial test, developed a low-cost, well-organized performance of Q345 grade thick steel plate, and Mn content is reduced 0.3%～0.5%, the cost reduced 30～35 yuan per ton, the first qualified rate increased to more than 99%, steel plate’s back correction rate is reduced to 15% or less, achieved stabilize production.