Abstract
ER70-Ti is a high strength gas shielded welding wire steel, which is suitable for ships, bridges and other structures, and can be used for thick plate welding with high current. In the welding wire industry, ER70-Ti is a high-tech deep-processing product with high added value. In this study, the thermal expansion experiment of ER70-Ti wire rod was carried out. The critical temperature of ER70-Ti phase transformation was measured and the continuous cooling transformation curve (CCT curve) of undercooled austenite was drawn. The microstructure and hardness of the samples under different cooling rates were observed. The results show that Ac1 temperature of ER70-Ti sample was 690 °C, Ac3 temperature was 877°C, and Bs temperature was 575°C. When the cooling rate was low (0.1°C/s~2.5°C/s), the phase transformation products of ER70-Ti were equiaxed polygonal ferrite and granular bainite. With the increase of cooling rate, the grain size of ER70-Ti sample was refined and the bainite content increased from 53% to 85%. When the cooling rate was higher than 5°C/s, all the phase transformation products were bainite. The Vickers microhardness also increased with the increase of cooling rate, from 185HV to 325HV.
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