| 1944 Nov. | Established by Asaji Inoue, Representative Director, in Mikunino-mura, Shikama-gun, Hyogo Pref. (currently Himeji City), as a subcontracting factory in the Himeji district, of Kawanishi Aircraft Co., Ltd. |
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| 1945 Aug. | Switched the operation over to the manufacture, and repair of trackwork materials for supply to the Japanese National Railways and private railways. |
| 1958 Sep. | The production of steel castings was started at the Nibuno plant. |
| 1959 Nov. | A 15-ton Heroult electric arc furnace was built inhouse at the Nibuno plant. |
| 1960 Apr. | Construction of a large-size rolling mill at the Nibuno plant was completed. Thus, the company became the only maker of trackwork materials in Japan to operate on a "through" basis-from production of steel ingots to rolling of steel materials and fabrication of final products. |
| 1961 Dec. | A 40-ton electric arc furnace went into operation at the Aboshi plant. |
| 1962 Mar. | Established Yamato Shoji Co., Ltd. |
| 1962 Sep. | Shares listed in the First Section of the Tokyo and Osaka Stock Exchange. |
| 1962 Sep. | The Steel Frame and Bridge Construction Dept. (heavy industries dept.) was established at the main plant. |
| 1966 Nov. | The Nibuno and Ichikawa plants were moved to the site of the main plant to concentrate operations. |
| 1969 Nov. | The Heavy-duty Machining Dept. was newly established and went into operation. |
| 1973 Jun. | The No.1 continuous casting machine went into operation. |
| 1973 Aug. | A 50-ton electric arc furnace went into operation. |
| 1975 Nov. | A universal mill went into operation. |
| 1978 Mar. | No.2 continuous casting machine went into operation. |
| 1987 Feb. | Established Nucor-Yamato Steel Co., Ltd joint venture in America. |
| 1989 Sep. | Established Arkansas Steel Associates LLC joint venture in America. |
| 1991 Oct. | Four strand beam blank/bloom combination type continuous casting machines started operations (upgrade of the No.1 and No.2 casting machines). |
| 1992 Apr. | Established Siam Yamato Steel Co., Ltd joint venture in Thailand. |
| 1996 Apr. | Started use of 130-ton direct current electric arc furnace (upgrade of the 40-ton and 50-ton electric arc furnaces). |
| 2002 Apr. | The trackwork materials department was separated and Yamato Trackwork System Co., Ltd was established. |
| 2002 Nov. | Established Yamato Korea Steel Corporation (currently YK Steel Corporation) in Korea. |
| 2003 Oct. | The steel and heavy industry departments were spun off and Yamato Steel Co., Ltd. was established. Yamato Kogyo Co., Ltd was converted to a holding company. |
| 2009 Feb. | Established United Steel Company (SULB) (currently SULB Company BSC(c)) in Bahrain. |
| 2010 Mar. | The second plant began operations at Siam Yamato Steel Co., Ltd. |
| 2011 Jun. | Established United SULB Company (Saudi Sulb) LLC in Saudi Arabia. |
| 2020 Mar. | Established POSCO YAMATO VINA STEEL JOINT STOCK COMPANY in Vietnam. |
| 2022 Apr. | Shifted from the First Section to the Prime Market in accordance with the reorganization of the market segmentation of the Tokyo Stock Exchange. |
