Research On Microstructure And Properties Of Low Alloying High Strength Steel At Low Rolling Temperature

Due to its unique performance advantages,micro-alloy high-strength steel plates have been widely used in all walks of life,and our country has conducted a lot of research on them and achieved some results.However,its production process,performance and theoretical research still have some gaps with foreign countries.Therefore,this article focuses on the product rolling process,especially the low temperature rolling of medium and heavy plates,which is lack of research,to provide theoretical data support for actual process production.This article takes microalloy high-strength steel as the research object,and studies the following contents through a combination of experimental research,microstructure observation,performance testing and theoretical analysis.First,the thermal deformation behavior of the material is studied to obtain its thermal deformation characteristics,stress-strain curve changes and dynamic recrystallization rules.Secondly,through comparative analysis,the contribution of low-temperature rolling to the strength and toughness of the material and the effect on the related microstructure and properties were studied.Finally,the tempered structure properties of the steel plate after low temperature rolling were studied to obtain the best tempering process and good microstructure properties.The final research results show:(1)Under different deformation process parameters,the stress-strain curve types include work hardening type,dynamic recovery type and dynamic recrystallization type three curve characteristics.In this experiment,the dynamic recrystallization temperature of steel is 850??950?,and the lower the strain rate and the higher the deformation temperature,the more obvious the dynamic recrystallization process.(2)When the low-temperature finish rolling at 730 ? ? 680 ?,its mechanical properties show directionality.Compared with the high-temperature finish rolling process in the austenite zone,the strength and plastic toughness of the material are improved,especially the low temperature impact toughness greatly improved,impact energy increased by 62.5J.In the vertical rolling direction,the material yield strength value increased by 158 MPa,the tensile strength value increased by 208 MPa,and the elongation increased by 4.3%.The fluctuation of longitudinal mechanical properties is small.(3)In terms of microstructure,the two types of microstructure after rolling are ferrite + bainite + lath martensite.After low-temperature rolling,the structure is more uniformly refined,the ferrite morphology is changed and the number is increased,the ratio of large-angle grain boundaries and the average orientation difference between grains are increased,and the size of precipitate particles is reduced.Therefore,the final organizational properties of the material are improved.(4)After tempering the steel sheet after low temperature rolling,its plastic toughness is further improved compared with that before tempering,but its strength level is reduced.In addition,during the tempering process,the strength and hardness values generally decrease with increasing temperature,and the impact toughness gradually improves.At 450?,the comprehensive structure of the material is good and the tempering process is the best.