Creep-induced heterogeneous precipitation of Laves phase with two morphologies in tempered martensite ferritic steels

Figures & data

Figure 1. Two independent paths and associated morphologies of Laves phase during creep process. (a–c) Elongated-shaped Laves phase formed by the isolated nucleation and coalescence. (d–f) Blocky-shaped Laves phase formed adjacent to the M₂₃C₆.

Figure 2. The crystallographic characteristics among Laves phase, M₂₃C₆ and ferrite. (a) Phase map showing the M₂₃C₆ and Laves phase indicated by green and blue, respectively. (b) IPF map along axis X, where the Laves phase adjacent to the M₂₃C₆ is highlighted by the red arrows. (c) Color legends of M₂₃C₆, ferrite, and Laves phase. (d) PFs for Laves phase, M₂₃C₆, and ferrite showing three types of ORs of ($110$)_M//($10\overline{1}3$)_L and [$1\overline{1}3$]_M//[$2\overline{1}\overline{1}\overline{1}$]_L, ($110$)_M//($1\overline{1}1$)_F and [$1\overline{1}1$]_M//[110]_F, ($110$)_F//(0001)_L and [$1\overline{1}1$]_F//[11$\overline{2}0$]_L.

Table 1. Summary of reported ORs between ferrite and Laves phase.

	OR		Methods	Type	References
1	[$\overline{1}\overline{1}$2]F//[1$\overline{2}$10]L, [111]F//[0$\overline{1}$10]L	($\overline{1}$10)F//(000$\overline{1}$)L	TEM	Isolated	[27]
2	[1$\overline{1}$0]F//[0001]L, [113]F//[$\overline{1}\overline{1}$20]L	($\overline{3}\overline{3}$2)F//(1$\overline{1}$00)L
3	[31$\overline{7}$]F//[4$\overline{5}$10]L	(211)F//(0001)L	TEM	Isolated	[30]
4	[0$\overline{1}$1]F//[$\overline{2}$110]L, [$\overline{1}$11]F//[01$\overline{1}$0]L	(211)F//(0001)L
5	[$\overline{1}$11]F//[11$\overline{2}$0]L	(110)F//(0001)L	TEM	Isolated	[29]
6	[$\overline{1}$01]F//[0$\overline{1}$10]L	(111)F//(10$\overline{1}$0)L	TEM	Isolated	[28]
7	[$\overline{1}$13]F//[2$\overline{1}\overline{2}$]L	(110)F//(02$\overline{1}$)L	TEM	Isolated	[25]
8	[$\overline{1}$13]F//[0$\overline{1}$0]L	(110)F//(103)L
9	[$\overline{1}$13]F//[03$\overline{1}$]L	(110)F//(013)L
10	[$\overline{1}$13]F//[3$\overline{3}$1]L	($\overline{1}\overline{1}$0)F//(10$\overline{3}$)L
11	[$\overline{1}$13]F//[11$\overline{2}$1]L	(110)F//(0$\overline{1}$13)L	TEM	Isolated	[26]
12	[$\overline{1}13$]F//[$2\overline{1}\overline{1}\overline{1}$]L,[$\overline{1}$13]F//[1$\overline{2}$10]L	(110)F//(10$\overline{1}$3)L	TKD	Isolated	Our study
13	[$\overline{1}$13]F//[01$\overline{1}$0]L	(110)F//($\overline{2}$110)L	TEM	Isolated
14	[1$\overline{1}$1]F//[11$\overline{2}$0]L	(110)F//(0001)L	TKD	Nearby
				M23C6
15	[$110$]F//[$2\overline{1}\overline{1}\overline{1}$]L	(1$\overline{1}$3)F//(10$\overline{1}$3)L

Figure 3. Multi-element segregation and thermodynamic calculations of the creep-deformed samples. (a) Typical bright-field TEM graph, (b) corresponding elemental composition line scans of the 9Cr-3W-3Co steel at 923 K and 140 MPa for 1045 h, showing the multi-element segregation (i.e. Cr, Mn, Si, and W) takes place at GBs before Laves phase nucleation. The influence of alloying elements on the stability of Laves phase at 923 K: (c) Si, (d) Cr, and (e) Mn. Notably, a line from the upper left to the lower right of the figure separates two fields. The field on the left of the line represents a three-phase region, with ferrite, MX and M₂₃C₆, and on the right is a four-phase region, with ferrite, MX, M₂₃C₆ and Laves phase.

Figure 4. Plots of r⁴ vs. t (a) and r² vs. t (b) of Laves phases at two formation paths (Laves phase next to M₂₃C₆ and isolated Laves phase) during creep process. Note that the fitting parameters R² are also given.

Figure 5. Schematic of the heterogeneous precipitation mechanisms of Laves phase with two morphologies. Path 1: the isolated Laves phase; Path 2: Laves phase next to the M₂₃C₆.

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