[KISHIKAWA, Hirofumi, YAMASHITA, Masato, KANDA, Atsumu, ONO, Hiroshi] 5-33, Kitahama 4-chome Chuo-ku Osaka-shi Osaka 541;10-73, Minami-Tsukaguchicho 6-chome Amagasaki-shi Hyogo 661;Sumitomo Metal Industries, Ltd. 5-33, Kitahama 4-chome Chuo-ku, Osaka-shi Osaka 541;Sumitomo Metal Industries, Ltd. 5-33, Kitahama 4-chome Chuo-ku, Osaka-shi Osaka 541;Shinto Paint Co., Ltd. 10-73, Minami-Tsukaguchicho 6-chome Amagasaki-shi Hyogo 661;Shinto Paint Co., Ltd. 10-73, Minami-Tsukaguchicho 6-chome Amagasaki-shi Hyogo 661 A surface treating agent of a steel material comprising 0.1 to 15 mass% of chromium sulfate and 10 to 40 mass% of a binder resin containing a butyral resin or a mixture of the butyral resin and a resin compatible with the butyral resin. This surface treating agent can quickly form a rust layer having a protecting function against a severe atmospheric corrosive environment containing a brine such as a coastland area on a steel material.

[Hirofumi Kishikawa, Masato Yamashita, Atsumu Kanda, Hiroshi Ono] c/o Sumitomo Metal Industries, Ltd. 5-33, Kitahama 4-chome,Chuo-ku, Osaka-shi, Osaka,,;c/o Sumitomo Metal Industries, Ltd. 5-33, Kitahama 4-chome,Chuo-ku, Osaka-shi, Osaka,,;c/o Shinto Paint Co., Ltd., 10-73, Minami-Tsukaguchicho 6-chome,Amagasaki-shi, Hyogo,,;c/o Shinto Paint Co., Ltd., 10-73, Minami-Tsukaguchicho 6-chome,Amagasaki-shi, Hyogo,, Disclosed herein is a surface treatment agent for steel, characterized in that, said agent contains 0.1-15% by mass of chromium sulfate and 10-40% by mass of a binder resin containing butyral resin or a mixture of butyral resin with another resin which is compatible with butyral resin.

[Hirofumi Kishikawa, Masato Yamashita, Atsumu Kanda, Hiroshi Ono] JP Osaka Disclosed herein is a surface treatment agent for steel, characterized in that, said agent contains 0.1-15% by mass of chromium sulfate and 10-40% by mass of a binder resin containing butyral resin or a mixture of butyral resin with another resin which is compatible with butyral resin.