1 Introduction
2 Experimental
2.1 Material
C | Si | Mn | Cr | Mo | V |
---|---|---|---|---|---|
0.7 | 0.2 | 0.5 | 5.0 | 2.2 | 0.5 |
2.2 Heat Treatment
Specimen | Holding Time (h) | |
---|---|---|
As quenched | Q50
| — |
Tempering at 798 K (525 °C) |
T
0.1
| 0.1 |
T
0.5
| 0.5 | |
T
1
| 1 | |
T
2
| 2 | |
T
6
| 6 | |
T
10
| 10 | |
Standard tempering [2 × 2 h at 798 K (525 °C)] |
T
2 × 2 | 2 + 2 |
Tempering at 873 K (600 °C) |
T
30
| 30 |
2.3 Microstructural Characterization
3 Results
3.1 Thermodynamic Calculations
Phase | Volume Percent | C | Cr | Mo | V | Si | Mn | Fe |
---|---|---|---|---|---|---|---|---|
Austenite | 98.80 | 0.61 | 4.62 | 2.20 | 0.40 | 0.20 | 0.50 | bal |
M7C3
| 1.20 | 8.50 | 37.5 | 8.00 | 8.65 | — | 0.35 | bal |
3.2 Microstructure
3.2.1 XRD measurements
Specimen | RA (Vol Pct) | Lattice Parameter (a
γ
) Å |
---|---|---|
Q
| 24 ± 2 | 3.6037 ± 0.0005 |
T
0.1
| 22 ± 2 | 3.6070 ± 0.0005 |
T
0.5
| 17 ± 2 | 3.6032 ± 0.0002 |
T
1
| 12 ± 2 | 3.6020 ± 0.0008 |
T
2
| 5 ± 2 | 3.5998 ± 0.0006 |
T
6
| <2 | — |
T
10
| <2 | — |
T
2 × 2 | <2 | — |
T
30
| <2 | — |
3.3 Dilatometry
3.3.1 Hardening
3.3.2 Tempering
3.3.2.1 Single tempering treatments
3.3.2.2 Cooling after single tempering treatments
Specimen |
M
s
K (°C) |
M
f
K (°C) |
---|---|---|
T
0.1
| — | — |
T
0.5
| 313 (40 ± 5) | — |
T
1
| 393 (120 ± 5) | — |
T
2
| 433 (160 ± 5) | — |
T
6
| 513 (240 ± 5) | 413 (140 ± 5) |
T
10
| 553 (280 ± 5) | 453 (180 ± 5) |
T
30
| — | — |
3.3.2.3 Double tempering treatment
4 Discussion
Heat Treatments | Microstructure | Dilatometry | |||
---|---|---|---|---|---|
Etched Regions | Unetched Blocky Regions | XRD | Tempering | Cooling | |
As quenched | no carbides | blocky regions | 24 pct RA | — | austenite transformed to M and B |
Tempering at 798 K (525 °C) (0.5 to 6 h) | carbides | similar fractions of blocky regions but less than as quenched | RA pct decreased with time | contraction | RA transformed to M |
798 K (525 °C) (10 h) | carbides | very small carbides | no RA | contraction | RA transformed to M |
Tempering at 873 K (600 °C) (30 h) | carbides | more and larger carbides than at 798 K (525 °C) | no RA | initially contraction and later expansion | no visible transformation |
4.1 Microstructure
Heat Treatment | FM + B (Vol Pct) | TM + TB (Vol Pct) | FM (Vol Pct) | RA (Vol Pct) | |
---|---|---|---|---|---|
As quenched | Q | 76 | — | — | 24 |
Single tempering |
T
0.1
| — | 76 | 2 | 22 |
Single tempering |
T
0.5
| — | 76 | 7 | 17 |
Single tempering |
T
1
| — | 76 | 12 | 12 |
Single tempering |
T
2
| — | 76 | 19 | 5 |
Double tempering |
T
2 × 2 | — | 95 | 5 | — |