Ti-nb Microalloying Deal With The Impact On The Structure And Properties Of Q345b Thick Steel Plate

Nowadays, carbon structure steel Q235 and low-alloy structure Q345 steel are the main steel products in the market of China.but the strength and toughness of the two kinds of steel are low, the plate is also thin,can't meets the market need .therefore,we sould pay more attention on researching and developing the thick and good emprehensive performance low-alloy high strength steel plate of Q345B.This paper researches the CCT curve of the test steel by thermal simulate.We observed the metallurgical, analysed the inclusion, researched the precipition and tested the mechanics performance of Q345B steel plate and the thick Ti-Nb compound treatment Q34SB steel, having a clear mind of the component design,the metallurgy and rolling process of the test plate .it can help to develop large quantity of this kind of steel plate.The research shows that,(1) Because Ti-Nb are put into the test steel,the temperature of the austenite transformation sinks about 100℃. The critical cooling velocity of the bainite transformation is a bit up. The good structure of the steel crystalline grain and performance can be got during the production by this satisfactory controlling condition.(2) The proper cooling velocity after rolling shoud be less than 7℃/s,so that thin and small grain of ferrite+pearlite can be obtained.(3) As Ti-Nb are put into the test steel,the grain size are remarkable fine,the form and structure of the test steel plate are better than the form Q345B plate.(4) According to the shape characterics and size of the grain,it can be judged that the sequence of precipition is mainly that TiN-(Ti,Nb)CN -TiS-TiC .(5) As Ti-Nb makes the grain size of the test plate notable smaller and pures the steel component,the performance of 60mm plate is better than the 40mmQ345B.(6) The pretreatment and LF refining can reduce the inclusion,enhance the purity of the iron metal and improve the microstructure,and help to improve the michanics performance. The test plate may have the excellent structure and performance by proper controlled rolling and air cooling.