Research And Controlling On Surface Quality Of GF08 Low Carbon Steel Under Ultrafast Cooling

Using GF08 low carbon steel as the raw material,Through searching development of different techniques to explore the influence factors to the surface quality of low carbon steel.By adjusting the subsequent process and increasing the hydrogen reduction to find the acid pickling substitution process for the possibility of acid-free.After the cold-rolling phase,the samples are subjected to box-type furnace without protected gas to observe the effect of different surface microstructures on the surface morphologies of the annealed samples.The main conclusions are as follows:(1)The effects of different final rolling temperature,final cooling temperature,coiling process and so on were observed.The results showed that the oxide scale was divided into two layers:outer layer Fe3O4 Layer and inner FeO layer.The effect of different processes on the outer layer Fe3O4 has little effect on the composition of Fe3O4,but it has influence both on the thickness and eutectoid degree of FeO.(2)The reduction temperature set the reduction temperature in 700℃,800℃,900℃ and the reduction time are 5min,10min,15min respectively.The reduction degree,microstructure and defects of the samples were observed.It was found that the decarburization layer appeared on the surface of the sample after reduction,and the grain growth degree and grain growth speed were different at different reduction time,and the grain at 800℃ was on the highest growth degree.(3)The reduction sample subjected to the cold-rolling process,compared to the cold-rolling sample without reduction process,the internal decarburization layer,the microstructure,the size of grains,the surface continuous and defects was observed.Through observation,the surface of cold rolling sample with reduction process is complete and continuous.Since the presence of decarburization in the cold-rolling stage,the internal grains are generally smaller than those in the cold-rolled sheet without reduction process.The mechanical properties of the cold rolled samples after reduction were found to be better than that the cold rolled sheets without reduction process.(4)In the laboratory box-type annealing furnace for unprotected gas annealing test,observed and analyzed the degree of oxidation on the annealed plate,find the optimal oxidation layer organization and determine the optimal reduction process,to determine the possibility for free pickling process.