LABORATORY SCALE PRODUCTION OF HOT ROLLED DUAL PHASE STEEL FOR FABRICATION OF GAS CILYNDERS

Abstract

Starting  with  a  C-Mn-Si  AWS  70S-6  steel  produced  by  Huachipato  Steel  Company (CSH),  usually employed  to manufacture electrodes for the welding industry, a Dual Phase steel was obtained at the laboratory facilities of USACH by a process of hot rolling and coiling in order to get martensite in a ferritic matrix. The microstructural characterization was complemented by tensile and anisotropy tests. It was determined that the optimum conditions for obtaining the dual phase microstructure from the initial steel are given by an ending rolling temperature near the austenite to ferrite transformation line, followed by quenching to the optimum temperature range of coiling (550 - 600 º C) and furnace cooling. Additionally, three samples were subjected to different heat treatments in order to obtain a dual phase structure in the first specimen; ferrite, bainite and pearlite in the second specimen; and perlite in a ferritic matrix in the third one. Finally, the specimens were MIG welded. The mechanical properties of all the heat affected zones were similar to those of their respective base metals, and hence the dual phase specimen shows the best results. It may be concluded that this dual phase steel meets the mechanical, drawability and weldability requirements established on the Chilean Standard for fabrication of gas cylinders, while having greater resistance than the A45 GL steel presently at use, which turns it into an alternative material for the fabrication of lighter cylinders.