A new morphology of retained austenite obtained by intercritical tempering of 13Cr-4Ni martensitic stainless steel

This research investigates the effect of various intercritical tempering in a 13Cr-4Ni stainless steel on the morphology, size, and gamma-stabilizer elements enrichment of the retained austenite, i.e. the austenite retained at room temperature after intercritical heat treatments. A comparative microstructural and chemical composition study was conducted on AISI415 steel using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and micro hardness measurements for three tempering conditions giving the same retained austenite volume fraction (10%). These tempering conditions were: 620 degrees C 1 h, 600 degrees C 4 h, and 580 degrees C 10 h. The intercritical tempering at low temperature does not provide greater gamma-stabilizer elements enrichment of the austenite. In this condition, the morphology of the formed retained austenite can be described as thin hollow particles with short lamellae shapes, which is significantly different than the morphology obtained at higher temperatures; the latter being characterised by thick and long lamellae. The retained austenite produced by tempering at low temperature is surrounded from both internal and external sides by martensite phases. Furthermore, it increases the austenite-martensite interfacial area that contributes to increase the barrier energy to martensitic transformation induced plasticity (TRIP).

本研究探讨了13Cr - 4Ni不锈钢中各种亚临界回火对残余奥氏体（即亚临界热处理后在室温下保留的奥氏体）的形态、尺寸以及γ - 稳定元素富集的影响。针对AISI415钢，在三种回火条件下进行了微观结构和化学成分的对比研究，这三种回火条件下残余奥氏体的体积分数相同（10%），采用了扫描电子显微镜、透射电子显微镜、X射线衍射以及显微硬度测量等方法。这些回火条件分别为：620℃回火1小时、600℃回火4小时以及580℃回火10小时。低温亚临界回火不会使奥氏体的γ - 稳定元素有更大程度的富集。在此条件下，所形成的残余奥氏体的形态可描述为带有短薄片形状的薄空心颗粒，这与在较高温度下获得的形态有显著差异；后者的特征是厚且长的薄片。低温回火产生的残余奥氏体在内外两侧均被马氏体相包围。此外，它增加了奥氏体 - 马氏体界面面积，这有助于提高对马氏体相变诱发塑性（TRIP）的势垒能。