中文摘要：

通过稀土化学热处理和第一性原理计算方法研究了纳米化3 J33钢在500℃脉冲等离子体稀土氮碳共渗4h时共渗层的相结构和硬度分布以及共渗相的性质。结果表明,共渗层由厚度约5μm的化合物层和90μm的扩散层组成;共渗相主要由γ′-Fe4N和含碳氮的α′-Fe相组成;与纳米化的3 J33钢相比,渗层表面硬度提高约1倍,基体时效后硬度也有所提高。计算结果表明,在共渗过程中γ′-Fe4N相较α′-Fe相更容易形成,但α′-Fe相更加稳定;γ′-Fe4N相的硬度高于α′-Fe相的硬度的主要原因是γ′-Fe4N相的N-Fe键较α′-Fe相的C-Fe键更强;此外,γ′-Fe4N相的体模量与剪切模量的比值大于1.75,因此该相具有延性。

英文摘要：

The phase structure, mierohardness profile and properties of formed phase in surface layer of nanoerystallized 3J33 steel plasma RE nitrocarburized at 500℃ for 4h were investigated through RE chemical heat treatment and first-principle computation. The results show that RE nitrocarburized layer with a 5 μm thickness compound layer and a 90μm thickness diffusion layer, consists mainly of γ＇-Fe4 N phase and a solid solution α＇-Fe phase with carbon and nitrogen elements. The surface hardness of RE nitroearburized layer is about twice as that of nanoerystallized original 3JJ33 steel, and the hardness of matrix is also enhanced after aging. The calculated results indicate that γ＇-Fe4N phase is easier to form than α＇-Fe during RE nitroearburizing, and α＇-Fe phase is more stable. The hardness of γ＇-Fe4 N phase is higher than that of α＇-Fe phase, which is attributed to the fact that the N-Fe bond in γ＇-Fe4N phase is stronger than C-Fe bond in α＇-Fe phase. Additionally,the calculated ratio of bulk modulus to shear modulus is more than 1.75,thus the γ＇-Fe4N phase is ductile.