关键词: Ti, 大热输入焊接, 焊缝组织, 夹杂物, 针状铁素体

Abstract: Different non-metallic inclusions in electrogas welds containing various titanium contents are compared and the effects of their number, distribution and type are investigated as well for high strength low alloy(HSLA)steel. The results indicate that the inclusions are effectively refined with the titanium contents ranged in 0.028%-0.038%, and acicular ferrite in the welds is obviously promoted owing to the significantly increased percentage of the inclusions with a size smaller than 2 μm. However, the percentage of the inclusions with a size smaller than 2 μm is dramatically decreased with the excessive addition of titanium in the welds and it results in bainite transformation. It is also confirmed that the inclusions in the weld metals mainly consists of oxides in the core and MnS coated outside. Manganese and silicon levels are decreased, whereas aluminum, titanium and oxygen are increased in the inclusions with titanium addition. As a result, oxides in the core are expelled to the edges in an order of MnO, SiO2, Al2O3, MgO, and finally replaced by TixOy. Therefore, the inclusion types are transformed from Mn-Si-O without titanium to Ti-Mn-Al-O and finally to Ti-Al-O with excessive titanium addition. The inclusions are suffering the processing from ineffective to effective and then to ineffective with increasing the titanium content.

Key words: high heat input welding;titanium;microstructure;inclusion;acicular ferrite