The topic of peritectic phase transition in steel has been widely studied using various in-situ experimental techniques including visual observation on a surface of a sample in a high temperature microscope and measurement of the thermal response from the bulk of the sample using differential thermal analysis (DTA) and differential scanning calorimetry (DSC). These two different techniques have inherent limitations leading to difficulties in interpretation of the results in the case of complex phase transformations such as the peritectic reaction, and there have been discrepancies among the interpretations from many previous studies of the peritectic transition in steel. A new technique was developed through a spatial combination of a DTA apparatus and a high-temperature laser-scanning confocal microscope to overcome these limitations. Solidification experiments with carbon steels of 0.061, 0.182 and 0.451 wt%C were conducted under conditions typical of conventional thermal analysis experiment, i.e. 90 mg of sample mass and 10 °C/min cooling rate, and the findings of earlier studies were revisited. We concluded that whether or not a peritectic reaction in a steel specimen of peritectic composition occurs, largely depends on the size of the sample used in the experiment. Deep undercooling for austenite nucleation can be experienced, in the absence of the occurrence of a peritectic reaction as a result of constrained nucleation of austenite, due to a limited number of nucleation sites in the small samples used.

钢的包晶相变这一主题已使用多种原位实验技术进行了广泛研究，包括在高温显微镜下对样品表面进行目视观察以及使用差示热分析来测量大部分样品的热响应（ DTA）和差示扫描量热法（DSC）。这两种不同的技术具有固有的局限性，导致在复杂的相变（例如包晶反应）的情况下难以解释结果，并且与钢的包晶转变有关的许多先前研究的解释之间也存在差异。通过DTA设备和高温激光扫描共聚焦显微镜的空间组合，开发了一种新技术来克服这些限制。在常规热分析实验的典型条件下（即90 mg的样品质量和10°C / min的冷却速率），采用0.061、0.182和0.451 wt％C的碳钢进行凝固实验，并重新探讨了先前的研究结果。我们得出的结论是，在包晶成分的钢样品中是否发生包晶反应，很大程度上取决于实验中所用样品的大小。由于使用的小样品中成核位点数量有限，在没有因奥氏体成核受约束而发生包晶反应的情况下，奥氏体成核过程经历了深度过冷。90 mg的样品质量和10°C / min的冷却速率，以及先前研究的结果均得到了重新审查。我们得出的结论是，在包晶成分的钢样品中是否发生包晶反应，很大程度上取决于实验中所用样品的大小。由于使用的小样品中成核位点数量有限，在没有因奥氏体成核受约束而发生包晶反应的情况下，奥氏体成核过程经历了深度过冷。90 mg的样品质量和10°C / min的冷却速率，以及先前研究的结果均得到了重新审查。我们得出的结论是，在包晶成分的钢样品中是否发生包晶反应，很大程度上取决于实验中所用样品的大小。由于使用的小样品中成核位点数量有限，在没有因奥氏体成核受约束而发生包晶反应的情况下，奥氏体成核过程经历了深度过冷。