Abstract
A method for improving mechanical properties of base metal and coarse-grained heat-affected zone (CGHAZ) in ferrite-pearlite steel was proposed. Two steels, with and without special addition of Ti, were fabricated for contrast experiments. Gleeble-3500 simulator was used to simulate CGHAZ. Microstructures were characterized by optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM). Tensile tests and Charpy impact tests were performed. Results show that nano-sized in-situ titanium oxides form in the melt. Compared with those of as-rolled steel without Ti addition, yield strength, elongation and toughness of as-rolled base metal with Ti addition are all promoted. During welding thermal simulation, the coarsened titanium oxides act as nucleation sites for acicular ferrite, which is favourable microstructure in CGHAZs. Toughness in CGHAZ of the steel with Ti addition is nearly ten times that in the CGHAZ of the contrast steel. Evolution of microstructures and mechanical properties was investigated and formation mechanism of titanium oxides was discussed.
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