Chromium-Molybdenum Alloy Steel
Chromium-Molybdenum Alloy Steel (Chromium-Molybdenum Alloy Steel, abbreviated as Cr-Mo steel) is a type of medium to high strength alloy structural steel, widely used in high temperature and high pressure environments, pressure vessels, power plants, refining, automotive, aerospace, molds, etc. It is renowned for its excellent strength, heat resistance, and corrosion resistance.
🧪 Main Alloying Elements:
|
Element |
Function Description |
|
Cr (Chromium) |
Increases hardness, oxidation resistance, and corrosion resistance |
|
Mo (Molybdenum) |
Enhances high temperature strength, temper brittleness resistance, and hydrogen corrosion resistance |
🔩 Common Chromium-Molybdenum Alloy Steel Grades (by Standard Classification)
🔹 ASTM / ASME (American Standards)
|
Steel Grade |
Characteristics and Applications |
|
AISI 4130 |
Structural use, good weldability, commonly used in aircraft structures and oil pipes |
|
AISI 4140 |
Medium carbon steel, commonly used for mechanical parts, shafts, and gears |
|
AISI 4340 |
High strength alloy steel, used in aerospace components and heavy-duty machinery |
|
SAE 8620 |
Used for surface hardening applications such as gears and shafts |
|
ASTM A182 F11 |
Pressure fittings and flanges, suitable for high temperature and high pressure environments |
|
ASTM A182 F22 |
Suitable for even higher temperature and pressure, commonly used in power plants and petrochemical industry |
|
ASTM A387 Gr.11 / 22 |
Chromium-molybdenum steel plates for boilers and pressure vessels |
|
ASTM A335 P11 / P22 |
High temperature and high pressure pipe steel used in thermal power plants |
🔹 JIS (Japanese Standards) Equivalent Grades
|
JIS Steel Grade |
Equivalent AISI Grade |
Description |
|
SCM420 |
AISI 4140 |
Chromium-molybdenum steel for mechanical structures, commonly used in gears and shafts |
|
SCM435 |
AISI 4135/4140 |
High strength alloy steel |
|
SCM440 |
AISI 4140 |
Widely used in molds, automotive parts, etc. |
|
SNCM220 |
AISI 8620 |
Alloy steel for carburizing |
🧰 Summary of Characteristics:
|
Characteristic |
Description |
|
High Strength |
Good tensile and yield strength, suitable for heavy load applications |
|
Heat Resistance |
Can withstand high temperatures of 500~600°C without losing strength |
|
Corrosion Resistance |
Chromium and molybdenum provide moderate corrosion resistance (not as good as stainless steel) |
|
Weldability |
Depends on carbon content and cold cracking sensitivity; requires preheating and post-weld heat treatment |
|
Good Heat Treatability |
Can be quenched and tempered to achieve high strength and toughness |
✅ Typical Application Examples:
- High pressure boilers and turbine blades
- Chemical processing equipment (pressure vessels, pipelines)
- Aircraft landing gear and vehicle frames
- Molds (especially plastic injection molds)
- Heavy machinery, gears, and crankshafts