Topics Covered
Introduction
Chemical Composition
Physical Properties
Mechanical Properties
Thermal Properties
Other Designations
Fabrication and Heat Treatment
Machinability
Forming
Welding
Heat Treatment
Forging
Hot Working
Cold Working
Annealing
Tempering
Hardening
Introduction
Alloy steels comprise different kinds of steels having compositions exceeding the limitations of B, C, Mn, Mo, Ni, Si, Cr, and Va set for carbon steels. They are designated by AISI four-digit numbers.
AISI 4320 alloy steel has high toughness and strength. It contains low carbon content to achieve good welding characteristics.
Chemical Composition
The following table shows the chemical composition of AISI 4320 alloy steel.
|
Element |
Content (%) |
|---|---|
|
Iron, Fe |
95.855 – 96.98 |
|
Nickel, Ni |
1.65 – 2.00 |
|
Manganese, Mn |
0.450 – 0.650 |
|
Chromium, Cr |
0.400 – 0.600 |
|
Molybdenum, Mo |
0.200 – 0.300 |
|
Carbon, C |
0.170 – 0.220 |
|
Silicon, Si |
0.150 – 0.300 |
|
Sulfur, S |
0.0400 |
|
Phosphorous, P |
0.0350 |
Physical Properties
The physical properties of AISI 4320 alloy steel are highlighted in the following table.
|
Properties |
Metric |
Imperial |
|---|---|---|
|
Density |
7.85 g/cm3 |
0.284 lb/in³ |
|
Melting point |
1422°C |
2590°F |
Mechanical Properties
The mechanical properties of annealed AISI 4320 alloy steel are displayed in the following table.
|
Properties |
Metric |
Imperial |
|---|---|---|
|
Tensile strength |
580 MPa |
84100 psi |
|
Yield strength |
425 MPa |
61600 psi |
|
Bulk modulus (typical for steel) |
140 GPa |
20300 ksi |
|
Shear modulus (typical for steel) |
80 GPa |
11600 ksi |
|
Elastic modulus |
190-210 GPa |
27557-30458 ksi |
|
Poisson’s ratio |
0.27-0.30 |
0.27-0.30 |
|
Elongation at break (in 50 mm) |
29% |
29% |
|
Reduction of area |
58% |
58% |
|
Hardness, Brinell |
163 |
163 |
|
Hardness, Knoop (converted from Brinell hardness) |
184 |
184 |
|
Hardness, Rockwell B (converted from Brinell hardness) |
84 |
84 |
|
Hardness, Vickers (converted from Brinell hardness) |
170 |
170 |
|
Machinability (annealed and cold drawn. Based on 100 machinability for AISI 1212 steel) |
60 |
60 |
Thermal Properties
The following table outlines the thermal properties of AISI 4320 alloy steel.
|
Properties |
Metric |
Imperial |
|---|---|---|
|
Thermal expansion co-efficient (@ -18-95°C/-0.400-203°F, condition of specimen unknown) |
11.3 µm/m°C |
6.28 µin/in°F |
|
Thermal conductivity (typical steel) |
44.5 W/mK |
309 BTU in/hr.ft².°F |
Other Designations
Other designations that are equivalent to AISI 4320 alloy steel include:
-
ASTM A29 (4320) -
ASTM A322 (4320) -
ASTM A331 (4320) -
ASTM A519 (4320) -
ASTM A535 (4320) -
ASTM A752 (4320) -
SAE J1397 (4320) -
SAE J404 (4320) -
SAE J412 (4320)
Fabrication and Heat Treatment
Machinability
AISI 4320 alloy steel has good machinability in the annealed condition. However, it is difficult to machine this steel if it is hardened by heat treatment.
Forming
AISI 4320 alloy steel has good forming characteristic in the annealed condition.
Welding
AISI 4320 alloy steel has good weldability.
Heat Treatment
AISI 4320 alloy steel is normalized at 872°C (1650°F) before heat treatment. It is then heat treated at 816°C (1500°F) followed by quenching in oil and tempering to achieve desired hardness.
Forging
AISI 4320 alloy steel is forged at 1038 to 1205°C (1900 to 2200°F)
Hot Working
AISI 4320 alloy steel can be hot worked at 872 to 1205°C (1600 to 1900°F)
Cold Working
AISI 4320 alloy steel can be cold worked using by conventional methods in the annealed condition.
Annealing
AISI 4320 alloy steel is annealed at 872°C (1600°F) followed by slowly cooling in the furnace.
Tempering
AISI 4320 alloy steel can be tempered at 205 to 705°C (400 to 1300°F).
Hardening
AISI 4320 alloy steel can be hardened by cold working, or by teat treatment and tempering.
