Research On TMCP Process Of A Grade Q390 Type HSLA Steel Plate

Based on the research platform for steel grades design of the state key Laboratory of Rolling and Automation (Northeastern University) and Puyang Steel Corporation (Handan),this paper mainly studied on the controlled rolling and controlled cooling's process parameters of high strength low-alloy steel whose yield strength is 390MPa and the effect of Nb's precipitate on the products'mechanical properties.It was requested that Q390 had not only high strength but also good formability and impact property under low temperature.Reasonable composition is the basis to ensure the property of Q390,The author used microalloy steel containing Nb as the additive,and realized lower flow stress and higher strength by precipitation strengthening and fine grain strengthening in rolling process.This made it possible for mass production in Puyang Steel Corporation.Furthermore, the author studied on the process of Q390's controlled rolling and controlled cooling,established reasonable rolling process suitable for field production and made industrial experiments of 390MPa's steel.The experiments reached expected target,so that Puyang Steel Corporation had the ability to produce various specification of Q390.This paper mainly four items,as follows:(1) In the laborotary,the author researched the cooling speed and final cooling temperature's effect on microstructure and properties of rolled piece.The reasonable rolling process were that:heating temperature was 1180℃;initial rolling temperature of rough rolling was 1050℃;initial rolling temperature of finish rolling was lower and between 840℃and 900℃;final rolling temperature was also lower and about 600℃;laminar cooling speed after rolling was 10～20℃/s,The author could obtain Q390E according to the above process.(2) This paper discussed the relationship between the grain's size and the product's mechanical properties.It found that mechanical properties increased with the decrease of the grain's size.When the cooling speed is in the rang of 10℃/s～20℃/s,the product's microsturcture and properties increased with the increase of cooling speed and increased with the decrease of final rolling temperature and final cooling temperature.Deformation between passes affected the mechanical properties.Therefore,increasing the deformation between passes could improve the austenite grains,refine grain,and improve strength and toughness.These were theoretical basis of producing Q390.(3) Based on two industrial experiments in the field,Puyang Steel Company conduct mass production.Finally,the factory realized the production and updating of Q390 by adding Nb to Q345 and using reasonable process of controlled rolling and controlled cooling.(4) The author adjusted alloying elements,improved the smelting process,and proposed preliminary process from smelting,rolling to producing.This process was used in Puyang Steel Company and made the strength increase up to 380MPa based on the initial composition Q345.This process not only saved the raw material and reduced cost,but also improve the technical level of high strength plate in hot rolling.