Texture Formation And Its Effect On The Mechanical Properties Of High Strength Low Alloy Steel

High strength low-alloy steel refers to steels whose alloying element content is less than 5% in the smelting process.Because of its excellent strength and low temperature toughness,weldability and other characteristics,it is widely used in ships,pipelines,automobiles,power plants and other fields.The high strength low-alloy steel will form deformation texture after rolling,and the texture has great influence on low temperature toughness and tensile properties of steel.However,the relationship between texture and mechanical properties has not been studied yet,so it is necessary to study the texture problem.In order to explore the variation of the mechanical properties of the transverse and longitudinal directions at different positions of the plate thickness,In this experiment,85 mm thick crack arresting steel plates of YP47 grade,code-named "Z30" and "Z28" were selected to study the surface layer,1/4 from the surface and 1/2 from the surface.After characterization analysis,it is found that the microstructure is mainly composed of ferrite grains.As the thickness increases,the ferrite grain size continues to increase,and the tensile properties continue to decrease.The main texture on the surface of the steel plate are{001}<110>,{114}<110>,{112}<110>;the texture at 1/4 is {110}<001>;the main texture components in the center are {001}<110>,{114}<110>,{112}<110>,{332}<113>,the texture of the center is stronger than the surface;There is a large difference of yield strength between the rolling direction and transverse at the surface of the steel sheet;which is due to the anisotropy of tensile properties caused by {114}<110> texture,and the difference of yield strength at the center is obviously weakened,which is related to {332}<113> texture;The low-temperature impact toughness of steel sheet surface is poor because {001}<110>texture is liable to cause cleavage fracture of material.The impact toughness at 1/4 is higher because {110} texture is beneficial to hinder crack propagation.In order to study the effect of rolling direction on texture and mechanical properties,"Z30" was used as raw material to conduct unidirectional rolling and cross rolling at 600?,800?,880? and 960?.It was found that from low temperature to high temperature,the microstructures changed from quasi-polygonal ferrite to lath bainite.The main texture typesin hot rolling are {001}<110>,{223}<110>,{111}<110> and {111}<112>.The texture strength decreases with the increase of hot rolling temperature,which is attributed to the weakening of texture strength by ferrite recrystallization during high temperature cooling.The tensile strength of unidirectional rolling is obviously higher than that of cross rolling from 800?.The impact toughness of cross rolling is significantly lower than that of unidirectional rolling from 600? to 880?.This is related to {001}<110> texture and ?fiber texture.The effect of rolling process on texture and mechanical properties was investigated by controlling the approximation of microstructures.The tensile strength increases with the increase of final rolling deformation under the process of 850? initial rolling+600? final rolling+600? annealing for 18 h.The total deformation is 50% and 60% respectively,the main textures are {001}<110>,{111}<110>,{111}<112>,{110}<001>,{223} and the texture strength is basically the same.The {001}<110> texture is transformed from the recrystallized austenite texture {001}<001>;The {111}<112> texture is transformed by the deformed austenite texture {110}<112>.Cold rolling,1000? initial rolling+650?finishing rolling,1000? initial rolling+850? finishing rolling,three processes at 750?recrystallization annealing 3h,found that the mechanical properties and microstructure of the relationship fully correspond.