Redistribution of C and N Atoms in High Nitrogen Martensitic Stainless Steel During Cryogenic Treatment

doi:10.1007/s40195-021-01265-7

Abstract

Abstract:

The redistribution of C and N atoms during cryogenic treatment is crucial for the microstructure evolution and properties of high nitrogen martensitic steel. Here, the distinct redistribution behavior of C and N atoms in a martensitic stainless steel with 0.3 wt% C and 0.5 wt% N after cryogenic treatment were investigated by the atom probe tomography. Carbon clusters begin to form after cryogenic treatment at - 60 °C and gradually increase with the decrease of cryogenic treatment temperature. While Mo-N and Cr-N pairs are homogeneously distributed in the matrix even after cryogenic treatment at -120 °C, and then form enrichment phenomenon when the cryogenic temperature is deeply lowered to - 190 °C. It is found that the distinct redistributions of C and N atoms are associated with the different interaction energy between substitutional atoms and them. The stronger interaction between Cr, Mo atoms and N delays the segregation of N during the cryogenic treatment. Finally, the mechanical properties results confirmed that the deep lower cryogenic treatment is a promising method to improve the hardness and strength in the high nitrogen martensitic stainless steel.

Key words: Interstitial atom, Cryogenic treatment, Martensitic stainless steel, Atom probe tomography

Xin Cai, Xiaoqiang Hu, Leigang Zheng, Dianzhong Li. Redistribution of C and N Atoms in High Nitrogen Martensitic Stainless Steel During Cryogenic Treatment[J]. Acta Metallurgica Sinica (English Letters), 2022, 35(4): 591-595.

Figures/Tables 6

Fig. 1 TEM images illustrating the microstructure after AQ: a martensite and retained austenite, b precipitate and c SAED patterns for analysis

Fig. 2 APT maps demonstrating the atomic distribution after AQ with the box size of 63 nm × 66 nm × 370 nm (a) and after various cryogenic treatments of CT with the box size of 88 nm × 104 nm × 107 nm (b)

Fig. 3 APT maps demonstrating the atomic distribution after SCT with the box size of 35 nm × 38 nm × 230 nm

Fig. 4 APT maps demonstrating the atomic distribution after DCT with the box size of 35 nm × 38 nm × 230 nm

Table 1 Concentrations of different atoms in steel after various cryogenic treatments determined by APT

	C	N	Cr	Mo	Si	Mn	Fe
Bulk	1.347	1.770	15.594	0.561	1.347	0.629	Bal
Quenched	1.026	0.519	13.412	0.558	1.563	0.623	Bal
CT	8.372	0.746	13.461	0.687	1.503	0.596	Bal
SCT	12.033	1.331	13.816	0.792	1.510	0.602	Bal
DCT	14.551	3.362	14.975	1.290	1.508	0.588	Bal

Fig. 5 a Hardness and b yield and tensile strengths with different cryogenic treatments

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