Experimental Study On Boron And Boron-Nickel Treated Q345E H-beams By Thermal-Mechanical Simulation Technology

High strength low alloy (HSLA) H-section steel, which is one of the most economical and environmental steels, has the advantages of good mechanics performance, easy assembly, lightweight, saving in materials, and so on. The HSLA H-section steels are widely used in many aspects of modern industrial world such as offshore drilling platforms, bridges, ships, mechanical equipments, large construction projects and so on. Presently, hot-rolled high-greed H-section steels have become one of the prime focuses in this field, especially, the H-section steels with advanced low temperature impact toughness properties are required, as the exploration of scientific and energy resources in the Polar Regions and high latitude regions.Thermal simulation technology is an advance useful method which can reproduce the thermal and mechanical process of the materials in the hot-working process, while only small specimens are required in the thermal simulation test process. The thermal simulation technology, which can reflect the regularity of the phase transition of the materials in the hot-working process, can provide theoretical guidance and technical basis to make reasonable processing technique and develop new materials.The subject was taken from Q345E-based H-beam of Laiwu Iron and Steel Group Co., Ltd.. The purpose of this study is to determine how the hot-working process exert influence on the changes of the phases and microstructure of the materials, and to find the best rolling parameters of the experimental steels. In this study a comparative study of boron and boron-nickel treated materials was also made to determine the different effects of boron and boron-nickel on the Q345E-based steels.In this study both the boron-treated and the boron-nickel-treated Q345E steels which were exerted different cooling rate and different deformation were studied by using of thermal simulation technology. Based on the analysis of the thermal simulation results and the metallographic analysis, the CCT (Continuous Cooling Transformation) diagram of the two experimental steels were determined. A basic knowledge about how the cooling rate and the deformation affects the phase transition temperature and the microstructure were also acquired.The study indicates that a faster cooling rate and the addition of nickel can bring a decrease of austenitic phase transition temperature. Because of the decrease of the austenitic phase transition temperature, the rolling in the austenite non-recrystallization region is easy to operate. Therefore, the steel with fine grain structure and mechanical properties can be obtained. As for the dynamic phase transition, the austenitic phase transition temperature will experience growth as the deformation increases.The production process was made based on the thermal simulation results and was checked in the production practice. It indicates that the simulation results can reflect the actual production processing. As the deformation was exerted to the austenite in its non-crystallization region, the deformation accumulation can be retained. It can produce a finer ferrite-pearlite structure in the subsequent phase transition process, and as a result the mechanical properties especially the low temperature impact properties of the steels were improved as well. This would help to expand the range of application of H-beams in the cold environment.