유/무기 하이브리드 용액을 코팅한 냉간압연강판의 내식성 연구

Abstract

In the past a very popular way to reduce the corrosion rate of zinc was the use of chemical conversion layers based on Cr+6. However, there is the important problem that the use of chromium salts is now restricted because of environmental protection legislation. So, earlier researcher investigated the optimum of galvanized steel about organic/inorganic solution with Si. The result showed that the optimum corrosion resistance was at 463K in 5 min. The demand of cold rolled steel(CR) for structural member is gradually increasing. If surface treatment(coating for corrosion resistance) of CR is not conducted, the use is very limited. Because, CR is vulnerable to corrosion. Therefore we need the development of coating solution of high corrosion resistance about CR. In this study, Urethane solution (only Urethane 20 wt.% ; S-700), organic/inorganic solution with Si (Si polysilicate 10 wt.% + Urethane 10 wt.% LR-0317) and organic/inorganic solution with Si and Ti(Si polysilicate 7 wt.% + Urethane 13 wt.% + Ti amorphous 0.5 wt.% ; LR-0727(1), Si polysilicate 7 wt.% + Urethane 7 wt.% + Ti amorphous 0.5 wt.% + epoxy 6 wt.% ; LR-0727(2)) are used for evaluation of corrsion resistance of cold rolled carbon steel under salt spray test. Based on the salt spray test of 7 h, LR-0727(1) and LR-0727(2) had a superior effect for the corrosion resistance on CR steel. The organic/inorganic coating solution with Si and Ti(Si polysilicate 7 wt.% + Urethane 13 wt.% + Ti amorphous 0.5 wt.%; LR-0727(1)) are used for evaluation of corrosion resistance of CR under salt spray test. The specimens with LR-0727(1) coating had heat treatment in the drying oven at 393 ~ 483K for 5 minute. Corrosion resistance was investigated with salt spray test of 7 hours. And adhesive test was conducted, too. The rust shows under heat treatment of 423 K and found no vestiges over 433 K. The specimens with heat treatment of 433 K or more hasn't happened delamination. From these results, it is considered that limited temperature of optimum heat treatment is 433 K considering energy efficiency. When heat treatment time is fixed, the resistance corrosion of LR-0727(1) and LR-0727(2) was improved as heat treatment temperature increased and the optimum minimum temperature was decreased as heat treatment time. And at the optimum heat treatment condition of two coating solutions, heat treatment time of LR-0727(1) solutions was shorter than the thing of LR-0727(2) in same heat treatment temperature. LR-0727(1) coated specimens did not have desquamation and all of the specimens had good adhesive property. But, in case of LR-0727(2) coated specimens, the desquamation occurred. Therefore the adhesive property of LR-0727(1) is superior. Pencil hardness is average 3H without reference to the type of coating solutions and heat treatment conditions. At boiling water resistance test, LR-0727(1) coated specimens were discolored, but LR-0727(2) coated specimens were not. So, moisture proof of LR-0727(2) is superior.