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Effect of TiO x particle on grain refining of HAZ during the welding thermal cycle was analyzed.It shows that HAZ would have better post-welding low temperature toughness if it contains plenty of TiO x particles.This phenomenon can be explained by the following aspects.As we know,welding thermal cycle include a rapid heating process and a cooling process.During the heating-up period,high melting TiO x particles which contains NbC with the size below 1μm can make a stronger pining force on the gain boundary migration than pure NbC ones,this effect restrain the austenite growth and control the austenite grain size to a certain extent.Then,when the cooling process begins,TiO x particles containing MnS with the size between 1 to 3μm act as a nucleation site for the intragranular acicular ferrite (IAF).Although the growth of bainite would extrude the IAF and make the smooth edge of IAF deformed,it still can not grow through the IAF.Just owing to the pining effect of TiO x-NbC particles and the hindering effect of IAF induced by the TiO x-MnS particles,prior austenite grains haven’t undergone a rapid growth during the heating process and these austenite grains are divided into small regions by the IAF finally.
Effect of TiO x particle on grain refining of HAZ during the welding thermal cycle was analyzed. It shows that HAZ would have better post-welding low temperature toughness if it contains plenty of TiO x particles. This phenomenon can be explained by the following aspects. As we know, the welding thermal cycle includes a rapid heating process and a cooling process. During the heating-up period, high melting TiO x particles which contain NbC with the size below 1 μm can make a stronger pining force on the gain boundary migration than pure NbC ones, this effect restrain the austenite growth and control the austenite grain size to a certain extent.Then, when the cooling process begins, TiO x particles containing MnS with the size between 1 to 3 μm act as a nucleation site for the intragranular acicular ferrite (IAF) .Although the growth of bainite would extrude the IAF and make the smooth edge of IAF deformed, it still can not grow through the IAF. Just due to the pining effect of TiO x-NbC particles an d the hindering effect of IA TiO induced by the TiO x-MnS particles, prior austenite grains have not undergone a rapid growth during the heating process and these austenite grains are divided into small regions by the IAF finally.