Alloy steel grades are classified into low-alloy (5% to 8% alloying elements) and
high-alloy (8% elements) categories, created by adding elements like chromium,
nickel, molybdenum, and manganese to enhance strength, toughness, and wear
resistance.
Common Alloy Steel Grades
 AISI 4130: Chromium-molybdenum steel offering good weldability, toughness, and
moderate strength
 AISI 4140 (42CrMo4): A versatile chromium-molybdenum grade providing high
fatigue, wear resistance, and tensile strength; used for shafts, gears, and spindles.
 AISI 4340 (34CrNiMo6): A nickel-chromium-molybdenum alloy delivering deep
hardenability and superior toughness for heavy-duty forged shafts and critical
structural parts.
 AISI 8620: A nickel-manganese-molybdenum case-hardening steel featuring a tough
core and wear-resistant surface; common in Types of Steel & Steel Grades Chart
automotive gears and pinions.
 AISI 52100: High-carbon chromium steel optimised for extreme wear resistance and
hardness; widely utilised in ball bearings.
Key Alloying Elements & Functions
 Chromium (Cr): Increases hardenability, wear resistance, and high-temperature
corrosion defence.
 Molybdenum (Mo): Elevates tensile strength, creep resistance, and stability at
elevated temperatures.
 Nickel (Ni): Improves impact toughness, low-temperature ductility, and corrosion
resistance.
 Manganese (Mn): Acts as a deoxidiser while boosting baseline strength and
hardenability.