|
P-20
Prehardened Mold Steel
 | AISI P-20 is a
chrome-moly-nickel steel, typically supplied at 270-320 Brinell. Typical analysis is shown
in the chart below.
|
| Carbon |
Manganese |
Chromium |
Molyebdenum |
Nickel |
| 0.28%-0.40% |
0.60% - 1.00% |
1.40% - 2.00% |
0.30 - 0.55% |
1.2% |
| AISI P-20 is noted for its good machinability, high purity and
good homogeneity, good polishing characteristics and good uniformity of hardness.
Typical applications are:
 | Plastic Injections Molds |
| Die-casting Molds |
| Forming Tools |
| Structural Components |
P-20 is sold in a prehardened and tempered condition, and may
be used as delivered without additional heat treatment. For higher or lower hardness,
please refer to Heat Treatment Section.
|
| Heat Treatment:
| Forging:
 | Heat steel slowly to 2100°F |
| DO NOT hot work below 1700°F. |
| Cool slowly in ashes or other insulating material. |
|
| Annealing:
| If P-20 must be rehardened, an annealing treatment should be
utilized prior to hardening. |
| Heat to 1425°F, hold steel until uniformly heated through. |
| Cool slowly in furnace. |
| Pack anneal to protect from scaling/decarburization. |
|
| Stress Relief:
| Heat pre-hardened dies to 1075°F, hold at temperature until
heated through, and air-cool. |
| Heat dies in annealed condition to 1250 °F, hold at
temperature until heated through, and air-cool. |
|
| Hardening:
| Preheat temperature: 1110°F |
| Hardening temperature: 1560°F |
| Holding time: 30 minutes |
| Quench in 150°F oil, or martempering bath at 575°F for
maximum 4 minutes, then air-cool. |
| Cooling is complete when steel has reached approximately
210°F. |
| Temper Immediately. |
|
| Tempering:
| Protect against oxidation/decarburization by the following
methods:
| Heat in neutral salt bath |
| pack in spent cast iron chips or paper |
| Protective atmosphere |
|
|
| Welding:
| Annealed - preheat to a minimum of 390°F. |
| Hardened and tempered - preheat to previous tempering
temperature or not less than 390°F. |
| DO NOT preheat higher than original tempering temperature. |
| After welding, allow to cool to approximately 160°F. |
| Soft annealed material should be cooled slowly to 160°F, then
fully soft annealed before hardening and tempering. |
| Hardened and tempered material can be air-cooled to give a
hardening effect in the weld. DO NOT use compressed air: NEVER cool or quench in a liquid.
Retemper hardened and tempered tools. DO NOT exceed the original tempering temperature.
This will reduce the original hardness of the steel. |
| Use chromium-nickel-molybdenum alloy electrodes for welding
structural steels. |
|
| Polishing:
| P-20 has very good polishability in the hardened and tempered
condition. |
|
|
| Mean Thermal Coefficient of Expansion |
| Temperature
Range, °F |
Coefficient x 10-6,
°F |
| 70-100 |
6.7 |
| 70-200 |
6.7 |
| 70-300 |
6.9 |
| 70-400 |
7.1 |
| 70-500 |
7.2 |
| 70-600 |
7.3 |
| 70-700 |
7.5 |
| 70-800 |
7.6 |
| 70-900 |
7.7 |
| 70-1000 |
7.8 |
| 70-1100 |
8.0 |
| 70-1200 |
8.1 |
| 70-1300 |
8.2 |
| 70-1396 |
8.2 |
|
