| Rimband is a safety part of TV Picture Tube.Strict properties are required for the steel strip used for making it.For a long time,low carbon steel strip with a typical yield strength of less than 300MPa has been used to make rimbands whereas high strength steel strip with a yield strength of higher than 320 MPa is mainly imported from Japan and other countries.The steel strip for rimband developed by Nippon steel is high cost high stength aluminium plated Ti-IF steel strip.A low cost technological route of microalloyed low carbon Al-killed was used to develop high strength aluminium-zinc alloy plated steel strip in this study.Its relevant reports have not been found in the references.Depending on the existing production conditions of Pangang Group,The low carbon Al-killed base steel was microalloyed with niobium(0.017%Nb and 0.030%Nb,respectively).The hot-rolled bands with different coiling temperatures(550℃,600℃,650℃)were cold-rolled at several levels of reduction(45%,55%,65%and 75%,respectively)and salt bath annealing tests were carried out to investigate the effect of Nb and coiling temperatue on the as hot-rolled microstricture and properties,the effect of Nb,hot coiling temperatue and cold-rolling reduction on the recrystallized behaviour,as well as the microstructure and properties under different annealing conditions.The results showed that,in the case of base steel,the yield strength and ferrite grain size were little affected by coiling temperatue whereas the tensile strength was decreased and the elongation was inproved as a result of the precipitaiton of AlN at high coiling temperatue;the strength and ferrite grain size of 0.017%Nb steel were little affected by coiling temperatue;in comparison with the base steel, the yield strength was increased by about 100MPa and 150MPa and the elongation was decreased by about 3%and 4%for 0.017%Nb steel and 0.030%Nb steel,respectively;The full recrystallization temperature was afftected by coiling temperature for the base steel and a high coiling temperatue will result in a low recrystallization temperature whereas coiling temperature had little effect on the full recrystallization temperature of 0.017%Nb steel and its full recrystallization temperature was increased by about 60℃in comparison with the base steel;The full recrystallization temperature was further increased by adding 0.030%Nb;As the annealing temperature rised,the strength of experimental steels were lowered to different content in such a way that the decrease of strength was caused by increasing recrystallization fraction when the annealing temperature is under the full recrystallization temperature whereas the the decrease of strength of the base steel and the microalloying steels resulted from the coarsening of ferrite grain and the riping of precipitates,respectively; However,the strength was obviously increased and the elongation was decreased as the result of grain refinement and precipitaiton hardening by Nb microalloying and the grain size of the microalloyed steel became finer as the cold rolling reduction was increased.To balance the strength and the ductility of the steel strip for rimband, the niobium should be about 0.017%and the optimized production parameters such as sorking temperature,finishing rolling temperature, coiling temperature,cold rolling reduction ratio and annealing temperature were 1200℃,900℃,600℃,70%and 750℃to 780℃,respectively.According to the laboratory results,pilot production of S320GD + AZ strip for rimband has been carried out.The results showed that,the 0.030%Nb steel exhibits an average yield strength and tensile strength of 410 MPa and 450MPa,respectively,as well as an elongation of 27%to 31%,which didn't meet the tagets of the customers due to higher strength and lower elongation wheareas an average yield strength and tensile strength of 375 MPa and 430MPa as well as an average elongation of 32.5%were obtained in the 0.017%Nb steel,which fully meet the requirements of customers. |
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