Dec 17 2012
Topics Covered
Introduction
Chemical Composition
Physical Properties
Mechanical Properties
Thermal Properties
Other Designations
Fabrication and Heat Treatment
Tempering
Annealing
Cold Working
Welding
Forging
Forming
Machinability
Heat Treatment
Applications
Introduction
Low-carbon mold steels or group P steels are of different types that include P2, P3, P4, P5, P6, P20, and P21 steels. Chromium and nickel are the main alloying elements found in group P steels.
P20 tool steels are nitrided or carburized. These steels are capable of being machined into complex and large dies and molds. P20 steels are mostly used in the carburized condition. The presence of chromium and nickel enhances the toughness and hardness of P20 steels.
The sections below provide an overview of P20 tool steels.
Chemical Composition
The chemical composition of P20 tool steels is outlined in the following table..
|
Element |
Content (%) |
|
C |
0.28-0.40 |
|
Mn |
0.60-1.00 |
|
Si |
0.20-0.80 |
|
Cr |
1.40-2.00 |
|
Mo |
0.30-0.55 |
|
Cu |
0.25 |
|
P |
0.03 |
|
S |
0.03 |
Physical Properties
The following table shows the physical properties of P20 tool steels.
|
Properties |
Metric |
Imperial |
|
Density |
7.85 g/cc |
0.284 lb/in3 |
Mechanical Properties
The mechanical properties of P20 tool steels are displayed in the following table.
|
Properties |
Metric |
Imperial |
|
Hardness, Brinell (typical) |
300 |
33 |
|
Hardness, Rockwell C (typical) |
30 |
30 |
|
Tensile strength, ultimate |
965-1030 MPa |
140000-150000 psi |
|
Tensile strength, yield |
827-862 MPa |
120000-125000 psi |
|
Elongation at break (in 50 mm (2")) |
20.0% |
20.0% |
|
Compressive strength |
862 MPa |
125000 psi |
|
Charpy impact (V-Notch) |
27.1-33.9 J |
20.0-25.0 ft-lb |
|
Poisson's ratio |
0.27-0.30 |
0.27-0.30 |
|
Elastic modulus |
190-210 GPa |
27557-30457 ksi |
Thermal Properties
The thermal properties of P20 tool steels are given in the following table.
|
Properties |
Conditions |
|
T (°C) |
Treatment |
|
Thermal expansion |
12.8 x 10-6/ºC |
20-425 |
- |
Other Designations
Equivalent materials to P20 tool steels are:
-
ASTM A681
-
UNS T51620
-
DIN 1.2330
Fabrication and Heat Treatment
Tempering
P20 tool steels are tempered at 482-593°C (900 to 1100°F) for a Rockwell C hardness of 37 to 28.
Annealing
Annealing takes place at 760-788°C (1400 to 1450°F) and then the steels are cooled slowly in the furnace at a temperature less than 4°C (40°F) per hour.
Cold Working
P20 tool steels are capable of being readily cold worked by using conventional tooling methods with the alloy in the annealed condition.
Welding
Conventional methods are used for welding of P20 tool steels.
Forging
P20 tool steels are forged at 1093°C (2000°F) down to 899°C (1650°F). Forging below 871°C (1600°F) is not recommended for these steels.
Forming
P20 tool steels can be readily formed by conventional methods in the annealed condition.
Machinability
P20 tool steels have excellent machinability at about 80% that of water hardening steels.
Heat Treatment
P20 tool steels are heated to 871-899°C (1600-1650°F) in the carburizing medium during the carburizing process. After being carburized, these steels are heated to 816-871°C (1500-1600°F) in order to be hardened and then held for 15 minutes and finally oil quenched.
Applications
P20 tool steels are used for low temperature applications that include injection molds and die casting dies.