INFLUENCE OF TITANIUM ON MICROSTRUCTURES AND TOUGHNESS IN SIMULATED COARSE GRAINED HEAT AFFECTED ZONE FOR TITANIUM MICRO-ALLOYED STEEL WITH DIFFERENT HEAT INPUTS

摘要

Microstructure in coarse grained heat affected zone (CGHAZ) has great effect on the welding properties. The effect of t8/5 on the microstructure at CGHAZ for micro-alloyed steels with different titanium content was studied using Gleeble 3500. The microstructure, hardness, and impact toughness of the samples were analyzed. Results indicated that the structures of CGHAZ for high Ti steel (HTS) were lath-shape bainite and martensite when t8/5 was less than 15 s, and acicular ferrite would form if the t8/5 reached 60 s. The impact toughness was less than 10J once the t8/5 was more than 15 s. The microstructure of low Ti steel (LTS) was resemble with that of HTS. Meanwhile, The influence of Ti content on microstructure, phase transformation temperature, mechanical properties was discussed. More inclusions were formed by addition of titanium. Grain growth was restricted and acicular ferrite was facilitated forming by inclusions. The range of phase transformation temperature reduced with Ti increasing.