PSI - Issue 13

Elena Astafurova et al. / Procedia Structural Integrity 13 (2018) 1129–1134 Elena Astafurova et al. / Structural Integrity Procedia 00 (2018) 000 – 000

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correspond to as-quenched specimens and show round-shaped and elongated particles randomly distributed both on grain boundaries and in grain bodies. The characteristic type, volume fraction and size of precipitates in the specimens are summarized in Table 2.

Table 2. Composition of the precipitates, their size ( d p ) and fraction ( f p ) in CrMnVCN steel depending on QT. Me=Cr, V, Mn, Fe; X=C, N.

d p , nm

f p , %

Element, at. %, based on SEM EDAX analysis

Precipitate type

Treatment

V

Cr

N

C

others

– 3.9 1.3

Me 2 X MeX MeX

6-11

33-47 14-20 11-15

9-21

5-12 6-10

Bal. Bal. Bal.

40±20(width), 530±50 (length)

QT=1100°C

30-32 28-37

24-45 33-39

280±150 420±100

QT=1200°C

3-8

Fig. 1. (a) The effects of QT on XRD patterns; (b) the lattice parameter variation with extrapolation function ( cosθcotθ ) for the steel; (c, d) TEM images on the microstructure of the steel quenched from the temperatures 1100°C and 1200°C respectively.

According to TEM data, the main phase, additional to austenite, is spherical MeX particles on the basis of VN nitrides, is which V and N are partially substituted by Cr and C respectively (Figs. 1c, d, Tab. 2). In addition to MeX particles in specimens quenched after holding at 1100°C, some Cr 2 N-based particles were found (Fig. 1c). These Me 2 X precipitates are non-homogeneously distributed in the structure of the steel and are rarely observed compared to MX particles. According to data in Table 2 and Figures 1c and 1d, increase in QT facilitates partial dissolution of MeX particles (full dissolution of small-sized one, decrease in size of large particles) and full dissolution of Me 2 X precipitates. Therefore, increase in QT decreases volume fraction of MeX phase (Tab. 2). No ferrite was evaluated in CrMnVCN steel structure after both solution-treated regimes.