Improvement of Impact Toughness and Abrasion Resistance of a 3C-25Cr-0.5Mo Alloy Using a Design of Experiment Statistical Technique: Microstructural Correlations after Heat Treatments
Abstract
:1. Introduction
2. Materials and Methods
- Microstructural features being evaluated:
- ○
- Percentage in weight of retained austenite and tempered martensite.
- ○
- Cell unit volume of tempered martensite
- ○
- Percentage in weight of the carbides of the following types M7C3, M23C6 and M2C.
- Mechanical properties tested:
- ○
- The Vickers microhardness of the matrix constituent, with 50gf (0.49N), averaging the results of 24 indentations.
- ○
- The abrasive wear resistance by means of the dry sand/rubber wheel abrasion test, executed in accordance with the ASTM G065-16 standard, with the following test parameters: Rubber wheel diameter: 228.6 mm; Shore A hardness of rubber: 60 ± 2; Silica sand (AF50/70); Sand flow: 300–400 g/min; Rate of revolution: 200 rpm; Test time: 30 min.
- ○
- High strain-rate impact test in a Hounsfield pendulum on un-notched round bars of 8 mm in diameter. The test was conducted on 3 un-notched specs typical for brittle materials for each experiment, and its average value reported.
3. Results
4. Conclusions
- The use of high destabilisation temperatures, around 1050 °C, followed by cooling in hot air at 150 °C. Destabilisation at 1050 °C allows secondary M7C3 carbide precipitation from supersaturated austenite accompanied by partial solubilisation of non-equilibrium eutectic carbides which form during solidification. The after cooling that follows if taking place within an air convection furnace set at 150 °C, seemed to favour further carbide formation in the range of 400–600 °C.
- Abrasion resistance is also favoured by low tempering temperatures (400 °C) and shorter tempering times (2 h). They both seem to favour a fine and dispersed precipitation. From X-ray diffraction analysis, the tempering conditions seemed insufficient for complete ageing of martensite as has been shown by the lattice results which indicate the existence of slender tetragonal lattice remaining after treatment. Thus, its possible contribution to the matrix hardness.
- Quenching in gently stirred oil at ambient temperature has been checked to promote full conversion of destabilised austenite into martensite i.e., to favour the absence of retained austenite after quench. This retained austenite is found to be highly alloyed and with accumulated plastic deformation due to the adjacent presence of tetragonal martensite, thus the need for the absence of residual austenite for better impact response.
- Tempering at 550 °C and long dwell tempering times of around 6 h, helped to complete full ageing of martensite thus the increase of overall toughness.
Author Contributions
Funding
Data Availability Statement
Conflicts of Interest
References
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C | Si | Mn | Cr | Mo |
---|---|---|---|---|
2.7 | 1.2 | 0.8 | 25.1 | 0.5 |
Factors | Levels | ||
---|---|---|---|
Code | Metallurgical Parameter (Factors) | Level −1 | Level +1 |
A | Destabilisation temperature of austenite (°C) for 5h | 950 | 1050 |
B | Cooling media from austenite destabilizing | Air convection within a furnace set @150 °C | gently stirred oil at R.T. |
C | Tempering temperature (°C) | 400 | 550 |
D | Dwell time at tempering temperature (h) | 2 | 6 |
No | A | B | C | D | Restricted Confounding Patterns |
---|---|---|---|---|---|
1 | −1 | −1 | −1 | −1 | A B C D AB + CD AC + BD AD + BC |
2 | +1 | −1 | −1 | +1 | |
3 | −1 | +1 | −1 | +1 | |
4 | +1 | +1 | −1 | −1 | |
5 | −1 | −1 | +1 | +1 | |
6 | +1 | −1 | +1 | −1 | |
7 | −1 | +1 | +1 | −1 | |
8 | +1 | +1 | +1 | +1 |
Experiment | Rietveld Refinement | Phases | Lattice Volume of Martensite (Å3) | wt. % |
---|---|---|---|---|
1 | Rwp = 11.6 Rexp = 7.40 Chi2 = 2.46 | Martensite | 23.58 (±0.006) | 54.64 (±1.99) |
Austenite | - | 5.61 (±0.62) | ||
M7C3 carbide | - | 38.86 (±1.45) | ||
M2C carbide | - | 0.90 (±0.13) | ||
2 | Rwp = 15.6 Rexp = 7.15 Chi2 = 4.79 | Martensite | 23.67 (±0.005) | 20.99 (±0.66) |
Austenite | - | 9.70 (±0.8) | ||
M7C3 carbide | - | 68.83 (±1.82) | ||
M2C carbide | - | 0.48 (±0.09) | ||
3 | Rwp = 10.5 Rexp = 7.84 Chi2 = 1.81 | Martensite | 23.61 (±0.006) | 68.07 (±2.53) |
Austenite | - | 6.22 (±0.34) | ||
M7C3 carbide | - | 25.06 (±0.94) | ||
M2C carbide | - | 0.65 (±0.07) | ||
4 | Rwp = 11.3 Rexp = 7.19 Chi2 = 2.48 | Martensite | 23.64 (±0.01) | 53.85 (±2.30) |
Austenite | - | 18.16 (±0.89) | ||
M7C3 carbide | - | 27.40 (±1.15) | ||
M2C carbide | - | 0.58 (±0.11) | ||
5 | Rwp = 14.4 Rexp = 8.63 Chi2 = 2.78 | Martensite | 23.53 (±0.003) | 69.47 (±3.05) |
Austenite | - | 0.40 (±0.32) | ||
M7C3 carbide | - | 29.50 (±1.26) | ||
M2C carbide | - | 0.63 (±0.13) | ||
6 | Rwp = 11.9 Rexp = 7.35 Chi2 = 2.60 | Martensite | 23.61 (±0.005) | 46.36 (±1.78) |
Austenite | - | 1.12 (±0.39) | ||
M7C3 carbide | - | 52.09 (±1.45) | ||
M2C carbide | - | 0.43 (±0.09) | ||
7 | Rwp = 20.7 Rexp = 9.96 Chi2 = 4.33 | Martensite | 23.56 (±0.001) | 23.69 (±0.38) |
Austenite | - | 0.1 (±0.08) | ||
M7C3 carbide | - | 76.11 (±1.68) | ||
M2C carbide | - | 0.10 (±0.02) | ||
8 | Rwp = 11.8 Rexp = 8.34 Chi2 = 2.00 | Martensite | 23.53 (±0.005) | 64.73 (±2.51) |
Austenite | - | 0.99 (±0.18) | ||
M7C3 carbide | - | 34.03 (±1.14) | ||
M2C carbide | - | 0.24 (±0.09) |
(a) Weight percentage of tempered martensite and retained austenite | |||||||
Experiment Number | Austenite | Martensite | Confounding Pattern | ||||
wt.% | Effects | wt.% | Effects | vol.% | Effects | ||
1 | 5.61 | 5.29 | 54.64 | 50.23 | 23.58 | 23.58 | Average |
2 | 9.70 | 4.41 | 20.99 | −7.49 | 23.67 | 0.04 | A |
3 | 6.22 | 2.16 | 68.07 | 4.72 | 23.60 | −0.01 | B |
4 | 18.16 | −9.27 | 53.85 | 1.68 | 23.64 | −0.07 | C |
5 | 0.40 | −1.92 | 69.47 | 11.18 | 23.53 | −0.01 | D |
6 | 1.12 | 2.01 | 46.36 | 20.90 | 23.6 | −0.04 | AB + CD |
7 | 0.10 | −3.61 | 23.69 | 16.45 | 23.56 | −0.02 | AD + BC |
8 | 1.00 | −2.38 | 64.73 | −18.43 | 23.53 | −0.01 | AC + BD |
(b) Weight percentage of M7C3 and M2C carbides | |||||||
Experiment Number | M7C3 Carbide | M2C Carbide | Confounding Pattern | ||||
wt.% | Effects | wt.% | Effects | ||||
1 | 38.86 | 44.00 | 0.89 | 0.50 | Average | ||
2 | 68.83 | 3.21 | 0.48 | −0.14 | A | ||
3 | 25.06 | −6.67 | 0.65 | −0.22 | B | ||
4 | 27.40 | 7.90 | 0.59 | −0.30 | C | ||
5 | 29.50 | −9.26 | 0.63 | 0.00 | D | ||
6 | 52.09 | −23.08 | 0.43 | 0.17 | AB + CD | ||
7 | 76.11 | −12.95 | 0.10 | 0.11 | AD + BC | ||
8 | 34.03 | 20.95 | 0.24 | −0.14 | AC + BD |
Experiment Number | Wear Loss (30 min) | Confounding Patterns | ||
---|---|---|---|---|
mg | CL (95%) | Effects | ||
1 | 97.08 | ±0.75 | 130.02 | Average A B C D AB + CD AC + BD AD + BC |
2 | 120.30 | ±1.45 | −29.415 | |
3 | 92.35 | ±2.10 | 3.03 | |
4 | 113.00 | ±0.20 | 48.675 | |
5 | 194.33 | ±1.47 | 6.27 | |
6 | 102.31 | ±1.75 | 4.985 | |
7 | 195.15 | ±0.37 | −51.35 | |
8 | 125.64 | ±1.16 | 9.045 |
Experiment Number | Microhardness | Impact Toughness | Confounding Pattern | ||||
---|---|---|---|---|---|---|---|
HV | CL (95%) | Effect | J/cm2 | CL (95%) | Effect | ||
1 | 732 | ±15 | 667.0 | 8.85 | ±1 | 6.8 | Average |
2 | 764 | ±17 | 129.2 | 3.12 | ±0.27 | −1.8 | A |
3 | 664 | ±30 | −51.2 | 1.66 | ±0.18 | 0.5 | B |
4 | 756 | ±23 | −123.2 | 4.73 | ±0.5 | 4.4 | C |
5 | 527 | ±7 | −27.7 | 10.41 | ±1.5 | 0.0 | D |
6 | 749 | ±20 | 2.2 | 3.79 | ±0.4 | 4.4 | AB + CD |
7 | 488 | ±14 | 67.2 | 9.89 | ±1 | −0.5 | AD + BC |
8 | 659 | ±10 | −13.2 | 12.03 | ±1.7 | 3.3 | AC + BD |
Spectrum | C | Cr | Fe | Mo |
---|---|---|---|---|
1 | 45.24 | 4.88 | 23.70 | 26.18 |
2 | 34.27 | 39.12 | 26.61 | - |
3 | 40.62 | 11.51 | 24.18 | 23.69 |
4 | 31.56 | 40.43 | 28.01 | - |
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González-Pociño, A.; Asensio-Lozano, J.; Álvarez-Antolín, F.; García-Diez, A. Improvement of Impact Toughness and Abrasion Resistance of a 3C-25Cr-0.5Mo Alloy Using a Design of Experiment Statistical Technique: Microstructural Correlations after Heat Treatments. Metals 2021, 11, 595. https://doi.org/10.3390/met11040595
González-Pociño A, Asensio-Lozano J, Álvarez-Antolín F, García-Diez A. Improvement of Impact Toughness and Abrasion Resistance of a 3C-25Cr-0.5Mo Alloy Using a Design of Experiment Statistical Technique: Microstructural Correlations after Heat Treatments. Metals. 2021; 11(4):595. https://doi.org/10.3390/met11040595
Chicago/Turabian StyleGonzález-Pociño, Alejandro, Juan Asensio-Lozano, Florentino Álvarez-Antolín, and Ana García-Diez. 2021. "Improvement of Impact Toughness and Abrasion Resistance of a 3C-25Cr-0.5Mo Alloy Using a Design of Experiment Statistical Technique: Microstructural Correlations after Heat Treatments" Metals 11, no. 4: 595. https://doi.org/10.3390/met11040595