Copper Precipitation Behavior and Mechanical Properties of Cu-Bearing Ferritic Stainless Steel with Different Cr Addition

doi:10.1007/s40195-025-01814-4

Abstract

Abstract:

The microstructure evolution and mechanical properties of Cu-bearing ferritic stainless steel with different Cr addition (Cr = 12, 15 and 17 wt%) were investigated. The phase transformation behavior under different cooling rate, Cu-rich precipitation behavior and its influence on the mechanical properties under different aging treatment are systematically characterized using dilatometry, differential scanning calorimeter (DSC) and transmission electron microscopy (TEM). The results indicated that the increase in Cr content narrowed the austenite phase region at high temperatures, affecting its microstructure under different cooling rates. The 12Cr-1.5Cu steel exhibited a fully austenitic phase region at high temperature and occurred apparent martensitic transformation after air cooling. Cooling rate significantly influenced the phase transition of the steels, and subsequently affected its mechanical properties. All three investigated steels showed higher strength and lower plasticity in air cooling condition compared to furnace cooling condition, due to the presence of martensite. After aging treatment, high number densities of Cu-rich precipitates were formed in steel matrix and the size of Cu-rich precipitates increased obviously with increasing aging temperature, while the tendency for number density was opposite. Fine and dispersed Cu-rich precipitates formed during low-temperature aging enhanced strength of the steels, while larger Cu-rich phases developed during high-temperature aging endowed greater ductility to the steels. Notably, the Cr content had no significant effect on the precipitation behavior of Cu-rich precipitation. These comprehensive results and analyses could provide a solid foundation for broader applications of Cu-bearing ferritic stainless steels.

Key words: Cu-bearing stainless steel, Mechanical property, Cu-rich precipitate, Microstructure

Yifan Li, Shengyao Ma, Xinrui Zhang, Tong Xi, Chunguang Yang, Hanyu Zhao, Ke Yang. Copper Precipitation Behavior and Mechanical Properties of Cu-Bearing Ferritic Stainless Steel with Different Cr Addition[J]. Acta Metallurgica Sinica (English Letters), 2025, 38(3): 383-395.

Figures/Tables 13

Table 1 Chemical compositions of experimental alloys (wt%)

Alloys	C	Si	Mn	Cr	Cu	Ni	P	S	Fe
12Cr-1.5Cu	0.021	0.35	0.45	12.23	1.52	0.34	0.012	0.005	Bal.
15Cr-1.5Cu	0.019	0.36	0.47	15.32	1.54	0.35	0.013	0.004	Bal.
17Cr-1.5Cu	0.025	0.31	0.44	17.15	1.49	0.32	0.016	0.006	Bal.

Fig. 1 Equilibrium phase diagrams of Cu-bearing ferritic stainless steels with a 12Cr, b 15Cr, c 17Cr. d Volume fraction of Cu-rich precipitation as a function of temperature in different Cr-bearing investigated steels

Fig. 2 Dilatometric curves of Cu-bearing ferritic stainless steels with a 12Cr-1.5Cu, b 15Cr-1.5Cu, c 17Cr-1.5Cu at 10 °C/s and 0.15 °C/s cooling rate

Fig. 3 Non-isothermal DSC curves of investigate steels obtained during heating a, cooling b processes

Fig. 4 Microstructures of Cu-bearing ferritic stainless steel with different Cr addition: a 12Cr-1.5Cu, b 15Cr-1.5Cu, c 17Cr-1.5Cu. The subscripts 1 and 2 represent the air cooling and furnace cooling after solid solution treatment at 950 °C for 0.5 h, respectively

Fig. 5 a Hardness of three investigated steels after air cooling and furnace cooling to different temperature, b tensile stress-strain curves, c ultimate and yield tensile stress, d tensile elongation to failure of investigated steels

Fig. 6 Microstructures of 15Cr-1.5Cu steel after aging treated at different temperature following furnace cooling solid solution: a 500 °C/1 h, b 600 °C/1 h, c 700 °C/1 h, d 800 °C/1 h

Fig. 7 Bright field TEM images of the 15Cr-1.5Cu steel after aging treated at different temperature following furnace cooling solid solution: a 500 °C/1 h, b 600 °C/1 h, c 700 °C/1 h and d 800 °C/1 h

Fig. 8 Hardness of three investigated steels with different aging treatment after air cooling and furnace cooling followed solid solution treatment at 950 °C for 0.5 h

Fig. 9 Engineering stress strain curves of Cu-bearing ferritic stainless steel with different Cr addition after different aging treatment: a 12Cr-1.5Cu, b 15Cr-1.5Cu, c 17Cr-1.5Cu. The subscripts 1 and 2 represent the air cooling and furnace cooling after solid solution treatment at 950 °C for 30 min, respectively

Fig. 10 Bright field TEM images of Cu-bearing ferritic stainless steels after air cooling and furnace cooling (from 950 °C to 400 °C) followed solid solution treatment at 950 °C for 0.5 h

Fig. 11 Bright field TEM images of 12Cr-1.5Cu, 15Cr-1.5Cu and 17Cr-1.5Cu steels aging at 500 °C for 1 h and 800 °C for 1 h, respectively

Fig. 12 TEM performing under high-angle annular dark field mode of the 15Cr-1.5Cu steel after aging at 800 °C for 1 h and XEDS analysis

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