高氮钢相变及重熔过程的在线观察

In-situ observation of nitrogen release and phase transformation of high nitrogen steels

在高温、低压或真空状态下高氮钢中的氮会释放出来,常压氮气氛中高氮钢的焊接也会引起氮的损失。利用共聚焦激光扫描高温显微镜对几种高氮钢的高温相变以及重熔时氮的释放进行了在线观察。观察到Fe-12Cr-0.276N的γ-δ相变、Fe-20Cr-8Mn-0.853N的α-γ相变、Fe-19Cr-15Mn-0.576N的γ-δ相变,验证了计算相图的正确性。观察到液态高氮钢熔化时氮气泡上浮到钢液表面、游动和破裂。根据观察到的氮气泡最大直径和液态不锈钢的表面张力,估算了气泡破裂前期内部的氮气压力。共聚焦激光扫描高温显微镜的在线观察适于发现热效应小的相变发生,并能测定新相的尺寸变化和气泡直径,可以弥补DTA/DSC等高温热分析手段的不足。

Nitrogen in high nitrogen steels （HNS） will be released at high temperature, low nitrogen pressure or vacuum, and it may also be lost when HNS is welded in nitrogen atmosphere at atmospheric pressure. This paper reports the in-situ observation of the high-temperature phase transformation and nitrogen release of several types of HNS by a confocal laser scanning high-temperature microscope. The γ-δ phase transformation of Fe-12Cr-0. 276N, the α-γ phase transformation of Fe-20Cr- 8Mn-0. 853N, and the γ-δ phase transformation of Fe-19Cr-15Mn-0. 576N are observed, which has confirmed the calculated phase diagrams published in related literatures. The nitrogen bubbles are observed floating out from steel melt to the surface, moving, and cracking. The nitrogen pressure in the bubbles is estimated according to the observed maximum diameters of the bubbles and the calculated surface tension of the liquid steels. These observations confirm that the in-situ observation by a cofocal laser scanning high-temperature microscope is a powerful method to study the nitrogen behavior in HNS during heating and melting.