STEEL TECHNOLOGIES <STTX> IN JOINT VENTURE Steel Technologies Inc said it signed an agreement with Mitsui and Co Ltd <MITSY> and its subsidiaries to establish a joint venture corporation to be called Mi-Tech Steel Inc. Mitsui, through its subsidiaries, Mitsui and Co USA Inc and Mitsui Steel Development Co Inc, and Steel Technologies each will own 50 pct of the new company, the company said. Mi-tech Steel will construct, own and operate steel service centers. The facilities will be established to serve Japanese and domestic automobile and appliance parts manufactures in the U.S., the company said. The initial processing center will be located near Murfreesboro, Tenn., and is expected to begin operations in the fall of 1987, Steel Technologies said. Daryl Elser, president of Steel Technologies, will be president of the new company, it said.