1 Introduction
2 Materials and methods
2.1 Production of Mo-added PM steel
Alloys | Graphite (%wt) | Mo (%wt) | Fe (%wt) |
---|---|---|---|
0.55 graphite + Fe | 0.55 | - | Balanced |
0.55 graphite + Fe + 1Mo | 0.55 | 1 | Balanced |
0.55 graphite + Fe + 2Mo | 0.55 | 2 | Balanced |
0.55 graphite + Fe + 3Mo | 0.55 | 3 | Balanced |
0.55 graphite + Fe + 4Mo | 0.55 | 4 | Balanced |
0.55 graphite + Fe + 5Mo | 0.55 | 5 | Balanced |
2.2 Microstructural preparation
2.3 Machinability process
Symbols | Parameters | 1st level | 2nd level | 3th level |
---|---|---|---|---|
M | Material | 0.55C 3Mo Fe | ||
T | Drill quality | HSS (uncoated) | HSS (TiAlN coated) | |
V | Cutting speed (m/min) | 15 | 20 | 25 |
f | Feed rate (mm/rev) | 0.05 | 0.1 | 0.15 |
3 Results and discussion
3.1 Microstructure and mechanical properties of Mo-added PM steel
Chemical composition | Theoretical density (gr/cm3) | Post-sintered density (gr/cm3) | Relative density (%) | Porosity (%) |
---|---|---|---|---|
0.55 graphite + Fe | 7.8292 | 7.3714 | 94.15 | 5.85 |
0.55 graphite + Fe + 1Mo | 7.8536 | 7.3845 | 94.02 | 5.98 |
0.55 graphite + Fe + 2Mo | 7.8780 | 7.3575 | 93.39 | 6.61 |
0.55 graphite + Fe + 3Mo | 7.9024 | 7.3696 | 93.25 | 6.75 |
0.55 graphite + Fe + 4Mo | 7.9268 | 7.4176 | 93.57 | 6.43 |
0.55 graphite + Fe + 5Mo | 7.9512 | 7.3524 | 92.46 | 7.54 |
Alloy | Ultimate tensile strength (MPa) | Elongation (%) | Hardness (Hv 0.5) |
---|---|---|---|
0.55 graphite + Fe | 290 | 14 | 103 |
0.55 graphite + Fe + 1Mo | 479 | 8.9 | 121 |
0.55 graphite + Fe + 2Mo | 632 | 8.3 | 163 |
0.55 graphite + Fe + 3Mo | 718 | 8 | 241 |
0.55 graphite + Fe + 4Mo | 680 | 7.5 | 172 |
0.55 graphite + Fe + 5Mo | 485 | 6.3 | 128 |
Fe-C | Fe-C-3Mo | ||||
---|---|---|---|---|---|
Element | Result | Unit | Element | Result | Unit |
C | 0.35 | %wt | C | 0.33 | %wt |
Si | 0.005 | %wt | Si | 0.001 | %wt |
Mn | 0.164 | %wt | Mn | 0.189 | %wt |
P | 0.005 | %wt | P | 0.023 | %wt |
Pb | 0.001 | %wt | Pb | 0.006 | %wt |
Cr | 0.064 | %wt | Cr | 0.086 | %wt |
Mo | 0.011 | %wt | Mo | 2.88 | %wt |
Ni | 0.046 | %wt | Ni | 0.078 | %wt |
Al | 0.001 | %wt | Al | 0.0015 | %wt |
Cu | 0.095 | %wt | Cu | 0.098 | %wt |
Co | 0.008 | %wt | Co | 0.006 | %wt |
S | 0.003 | %wt | S | 0.003 | %wt |
Fe | Balanced | %wt | Fe | Balanced | %wt |
3.2 Machinability results of 3% Mo-added PM steel
3.2.1 Assessment of experimental thrust force
Source | Degree of freedom | Sum of square | Mean square | F | P | PCR (%) |
---|---|---|---|---|---|---|
C | 1 | 641467 | 641467 | 513.420 | 0.000 | 56.53 |
V | 1 | 705 | 705 | 0.560 | 0.472 | 0.06 |
f | 1 | 354320 | 354320 | 283.590 | 0.000 | 31.22 |
C*C | 1 | 6834 | 6834 | 4.350 | 0.061 | 0.60 |
V*V | 1 | 3062 | 3062 | 2.450 | 0.152 | 0.27 |
f*f | 1 | 4312 | 4312 | 3.450 | 0.096 | 0.38 |
C*V | 1 | 6440 | 6440 | 5.150 | 0.049 | 0.57 |
C*f | 1 | 106408 | 106408 | 85.170 | 0.000 | 9.38 |
V*f | 1 | 8 | 8 | 0.010 | 0.938 | 0.00 |
Error | 9 | 11245 | 1249 | 0.99 | ||
Total | 17 | 1134801 | 100.000 |
3.2.2 Assessment of surface roughness and chip formation
Source | Degree of freedom | Sum of square | Mean square | F | P | PCR (%) |
---|---|---|---|---|---|---|
C | 1 | 2.1291 | 2.12913 | 104.46 | 0.000 | 17.02 |
V | 1 | 4.599 | 4.59896 | 225.63 | 0.000 | 36.75 |
f | 1 | 5.4586 | 5.45862 | 267.81 | 0.000 | 43.62 |
C*C | 1 | 0.0133 | 0.0133 | 0.65 | 0.564 | 0.11 |
V*V | 1 | 0.0929 | 0.09291 | 4.56 | 0.062 | 0.74 |
f*f | 1 | 0.0265 | 0.02646 | 1.3 | 0.284 | 0.21 |
C*V | 1 | 0.0022 | 0.00217 | 0.11 | 0.752 | 0.02 |
C*f | 1 | 0.0053 | 0.00532 | 0.26 | 0.622 | 0.04 |
V*f | 1 | 0.0027 | 0.00272 | 0.13 | 0.723 | 0.02 |
Error | 9 | 0.1834 | 0.02038 | 1.47 | ||
Total | 17 | 12.513 | 100.00 |
4 Conclusions
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Perlite ratio of powder metal steel with Fe-C composition sintered at 1400 °C increased with the addition of alloying element. At the same time, the perlite ratio increased while the ferrite ratio decreased.
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Generally, it has been observed that the tensile and yield strength increases, and the percent elongation decreases with the increase in the amount of molybdenum up to a certain level. The reason for the rise in strength is attributed to the increase of perlite amount of nickel in the microstructure and also to the bainite and martensite phases formed in the structure.
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EDS analysis of PM steels reveals that Mo, C, and N elements and precipitates such as CrC (N) and MoC (N) formed by these elements are in the iron matrix.
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It has been observed that steels with alloying element added have superior mechanical properties compared to PM steels that are not added. The reason for this is presumed to be related to the strong carbide builder of alloying elements or to transform the microstructure into a harder phase. Refining of grain size and precipitation hardening during sintering or cooling after sintering increase the strength of steel.
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For each cutting speed, the increase of thrust force was calculated by an average of 74.6% and 30% for uncoated and coated cutting inserts, respectively, by increasing the feed rate from 0.05 to 0.1 mm/rev.
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In the increase of cutting speed from 15 to 25m/min, decrease of Ra was obtained as 19.8% and 36.6%, respectively.
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The most important factors on the Fz and Ra are the coating condition and the feed rate with 56.53% and 43.62% PCR, respectively.
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The chip shape becomes erratic due to the increase in the feed rate and it is evident that the form of the chip is disrupted while no observable change with the rise in speed. The explanation for the increase of Ra is clarified by this circumstance.