High strength and toughness are usually hard to obtain simultaneously because of the trade-off. In this research, cyclic intercritical tempering (IT) was applied to a low-carbon Cu-bearing 7Ni steel to pursue a better strength-toughness balance than what conventional single intercritical tempering can achieve. The mechanical properties and microstructure of cyclic IT and single IT were studied by scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) in addition to dilatometry. It was found that cyclic IT can significantly improve the strength without much sacrifice of toughness. The additional strength comes from dislocation and precipitation strengthening. The mechanism of reverse transformation was studied, and it was found that the mechanism changes from diffusional at single IT or first-cycle IT to a combination of interface-dominated and diffusional at the following cyclic IT. It was suggested that enrichment of Ni after the first cyclic IT is responsible for the mechanism change by thermodynamic calculation. Furthermore, although the Ni content is higher in fresh martensite (FM) after following cyclic IT, no distinct decrease of Ms was found, which is related to the inhomogeneous elemental distribution of FM.

由于折衷，通常难以同时获得高强度和韧性。在这项研究中，将循环临界回火（IT）应用于低碳含铜7Ni钢，以实现比传统的单一临界回火可达到的更好的强度-韧性平衡。除膨胀法外，还通过扫描电子显微镜（SEM），电子背散射衍射（EBSD）和透射电子显微镜（TEM）研究了循环IT和单一IT的机械性能和微观结构。发现循环IT可以显着提高强度，而不会牺牲太多韧性。额外的强度来自位错和降水的加强。研究了反向转化的机理，并且发现该机制从单个IT或第一周期IT的扩散变为接口主导和随后的IT扩散的组合。有人提出，在第一个循环IT之后，Ni的富集是通过热力学计算引起的机理变化的原因。此外，尽管在循环IT后新鲜马氏体（FM）中的Ni含量较高，但未发现Ms明显降低，这与FM的元素分布不均匀有关。