Research On High Temperature Creep Bending And Straightening Theory Of Steel Continuous Casting

Bending and straightening technology is the key factor to realize steel high-efficient continuous casting.The plastic deformation of steel is usually used to design bending and straightening segment in current casting machine so that the height of casting machine is increased and the cost of construction rises.Internal cracks occur easily because the high temperature creep property of steel isn't fully used in the bending and straightening deformation.So,the high temperature creep property of steel is studied fistly and is used to design the bending and straightening segment of steel continuous casting machine.High temperature creep bending and straightening theory is proposed in this paper.The bending and straightening mechanism of fomer continuous casting machine are changed.Continuous casting slab can be bended or straightened by means of creep deformation not plastic deformation.Thus,some researches on this subject have been done as the following details.Firstly,high temperature mechanical and creep property of Q345 c steel are investigated on the Gleeble3800 machine.Thermophysical parameters and minimum creep strain rate are obtained by uniaxial tensile tests.The high temperature creep constitutive equation is derived by regression analysis method based on testing data.Secondly,High temperature creep bending and straightening theory of steel continuous casting is proposed based on the high temperature creep property of Q345 c steel.The design procedures of roller curves are developed so as to make the creep continuous bending and straightening technology come ture.The relationship between changing rate of curvature and strain rate of slabs are built by finding the strain limit value in continuous bending and straightending curves.Some different curves which make the bending or straightening strain rate less than minimum creep strain rate are chosen to realize the creep continuous bending and straightening technology.After that,the new composite straightening curves which contain four involute lines and one optimized cubic polynomial curve are designed based on the small experimental continuous straightening device.The strain rate of the position which located 15 mm away from upper surface inner the slab can be smaller than the minimum creep strain rate of Q345 c which stressed by less than yield strength at 1200? based on finite element method and formula method.Thus,if only the temperatures of these locations can be above 1200?,there is only creep deformation not plastic deformation in the straightening process.The rollers of the small experimental continuous straightening device are adjusted by the new composite straightening curves.The straightening experiment is carried out in the device in order to calculate the straightening strain rate.The strain rate of the position is also smaller than the minimum creep strain rate as the same as the finite element method and formula method.The experimental results indicate that the finite element method and formula method can be used to identify some cuves whether to be the creep straightening curves.The experimental results also indicate that the creep continuous straightening technology is rational and feasibile.At last,the roller curve of five-point bending and five-point straightening vertical arc slab continuous casting machine in Anshan steel company is redesigned by the creep continuous bending and straightening method.The basic arc segment is cancelled in the new curve so that length of the straightening area can be extended and time of creep behavior can be increased significantly.The slope of bending segment curve is equal to the straightening segment curve at the intersection.The changing rate of curvature varies sinusoidally with arc length in the bending segment and a quintic polynomial without even numbers in exponents curvature function relative to arc length is proposed for straightening segment.The temperature distribution and solidifying shell of the slab are calculated by finite element method in the new casting machine.The strain rate at different locations which is beneath the center of inner arc surface are less than the minimum creep strain rate by the formula mathod when temperature is 1200?.So,the creep continuous bending and straightening technology comes true in the bending and straightening segment of new designing casting machine.Above all,the creep deformation can be fully used to bend and straighten the slab based on high temperature creep bending and straightening theory.It can decrease the strain rate of solifying shell so as to void interal cracks,make the height of casting machine lower and improve the productivity.The creep continuous bending and straightening technology can be applied widely.This study has theoretical and practical significance to improve the level of continuous casting technology,to promote the development of the efficient continuous casting technology and to the technological progress of the steelmanufacturing industry.