热输入对SAF2507超级双相不锈钢焊接接头显微组织及硬度的影响

Effect of heat input on the microstructure and hardness of SAF2507 super duplex stainless steel welded joints

采用显微观察、化学成分分析、硬度测定、EBSD分析的方法,研究了TIG焊接热输入对1.2 mm厚的SAF2507超级双相不锈钢焊接接头显微组织和硬度的影响机理.结果表明,在焊缝中,随着热输入由110 J/mm增加至156 J/mm,铁素体晶粒尺寸由90μm增至200μm,晶粒的粗化减少了奥氏体的形核位置,同时热输入的增加使焊缝中N元素含量由0.25%降低至0.21%,最终导致焊缝中奥氏体含量由28.9%减少至24.3%.在高温热影响区中,当热输入为132 J/mm时,奥氏体含量达到最高值,为36.4%,此时铁素体晶粒中心的Cr;N的析出量最少.焊接热输入由110 J/mm增加至156 J/mm时,焊缝的维氏硬度保持在320不变.这是因为焊缝组织的几何必需位错密度和相界密度都不随热输入的增加而变化,依据金属强化理论可知焊缝硬度不随热输入的增加而变化.

The mechanism of the effect of the heat input in TIG welding on the microstructure and hardness of 1.2 mmthick 2 507 super duplex stainless steel(DSS) welded joints was studied with micro-examination, chemical composition analysis, hardness measurement, and electron backscatter diffraction(EBSD) analysis. According to the results, in the weld seam, as the heat input increased from 110 J/mm to 156 J/mm,the ferrite grain size increased from 90 μm to 200 μm. Grain coarsening reduced the nucleation sites of austenite. In the meantime, increased heat input reduced the N content in the weld seam from 0.25% to 0.21%, eventually resulting in a decrease of the austenite content from 28.9% to 24.3%. In the high temperature heat-affected zone(HTHAZ), the austenite content peaked at 36.4% when the heat input was 132 J/mm, at which point the Cr;N precipitation amount at the center of ferrite grains bottomed. When the welding heat input increased from 110 J/mm to 156 J/mm, the Vickers hardness of the weld seam remained at 320 HV. The reason behind is that both the geometrically necessary dislocation density and phase boundary density of the weld seam remain unchanged with the increase of heat input. According to the metal reinforcement theory, weld hardness won’t change as heat input increases.