Supplementary material 1

In the sample treated by an isothermal holding at 650 C for 10 s, no

interphase- precipitated carbides can be found. Instead, some randomly precipitated

carbides can be observed. In order to identify the type of these precipitates, analysis

on the orientation relationship was carried out. A TEM bright field (BF) image in

Supplementary Fig. 1a shows the inhomogeneous distribution of the precipitates. The

corresponding dark field (DF) image in Supplementary Fig. 1b was taken from the

selected area diffraction (SAD) spot indicated by the arrow as shown in

Supplementary Fig. 1c. The analysis of SAD pattern, as presented in Supplementary

Fig. 1d, indicated that these precipitates did not obey the Baker-Nutting orientation

relationship (B-N OR) with the ferrite matrix. On the other hand, Supplementary Fig.

1d reveals the Nishiyama-Wassermann orientation relationship (N-W OR); i.e.,

(1 1 0 )α // (1 1 1)MC and [0 0 1]α // [0 1 1 ]MC. For the interphase precipitation and

supersaturated precipitation in ferrite, the MC carbides obey the B-N OR with the

ferrite matrix. On the other hand, if the MC carbides are formed in the supersaturated

austenite, they obey a cube-to-cube orientation relationship with the austenite. With

the decomposition of austenite to ferrite, ferrite may adopt either the Kurdjumov-

Sachs orientation relationship (K-S OR) or the N-W OR with the austenite matrix. As

a result, the K-S or N-W OR is inherited. Thus, the diffraction patterns from the

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carbides that did not display the BN-OR (as shown in Supplementary Fig. 1c and d)

provide evidence to suggest that these carbides originated from strain-induced

carbides in the prior austenite. It should be noted that strain-induced carbides in the

prior austenite are not uniformly distributed, as shown in Fig. 4a and b and

Supplementary Fig. 1a and b.

Supplementary fig. 1. (a) TEM BF showing randomly precipitated MC carbides in small-grained ferrite

in the sample for 10 s holding condition, (b) the corresponding DF image of (a) taken from the

diffraction spot indicated by the arrow in (c), and (d) the diffraction pattern analysis for (c), which

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shows a non-BN orientation relationship.

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