9Ni钢内部自由界面产生原因与修复机制

Formation reason and restoration mechanism of free interfaces in 9Ni steel

研究了9Ni钢锻件偶然存在的原生自由界面缺陷及其产生原因与修复机制。制备了含人工预制真空界面的试样和含原生自由界面的试样,并在不同温度下进行了压缩焊合实验。焊合试样的拉伸实验和断口观测结果表明,若9Ni钢内部自由界面能够完全贴合,则在高温受压变形条件下容易焊合。当断口发生在材料原生的自由界面处时,可在扫描电镜下观察到自由界面上有明显的光亮区域、"围堰状"粘合区和气孔痕迹。以此推断是凝固过程中气体进入熔池内部,形成气团,锻造时随着气团体积减小,气体压力显著增大,阻碍了空洞的焊合,从而形成自由界面。

The formation reason and restoration mechanism of the free interface defects which were occasionally found in 9 Ni steel forgings were investigated.The specimens with artificial prefabricated vacuum interface and with in-situ free interface were prepared,and the compression bonding experiments were carried out at different temperatures.The tensile experiement and fracture observation results of the bonded specimens show that if the free interface in the 9 Ni steel can be fully fitted,it is is easy to bond under the deformation condition of high temperature compression.When the fracture occurs at in-situ free interface of material,there are obvious bright zones,"cofferdam like"bonding zone and air holes penetrating on the free interface under the scanning electron microscope.It can be inferred that the air bubble formed by the air entering into the molten pool during solidification.In the forging process,the air pressure increases significantly with the decrease of the air bubble volume,which hinders the bonding of the voids and thus results in free interface.