Alloy Steels used in the CNC Machine Shop
Introduction
Alloy steels are a versatile class of materials known for their exceptional mechanical properties, making them indispensable in a wide range of industrial applications. Among the plethora of alloy steels, 4130, 4140, 4330, 4340, 8620, and 9310 stand out as high-performance alloys, each tailored for specific applications due to their unique combinations of elements and heat treatments.
4130 Alloy Steel: The Go-To Alloy Steel used for CNC Machined Parts
Composition:
Carbon (C): 0.28% - 0.33%
Manganese (Mn): 0.4% - 0.6%
Phosphorus (P): 0.035%
Sulfur (S): 0.040%
Silicon (Si): 0.15% - 0.35%
Chromium (Cr): 0.8% - 1.1%
Molybdenum (Mo): 0.15% - 0.25%
Iron (Fe): Remainder
Physical Properties (Annealed):
Rockwell 83 HRB Hardness
Ultimate tensile strength of 81 ksi
Yield tensile strength of 52 ksi
Use Cases:
Fasteners
Aircraft Frames
Dies and Molds
High-performance automotive chassis and suspension components
4130 alloy steel is a low-alloy steel containing chromium and molybdenum, offering excellent strength and weldability. This alloy is found in aircraft structures, engine components, landing gear, and more. Its balance of strength and ductility makes it a preferred material for critical applications. 4130 is the most commonly used alloy steel due to its strength, availability, and ease of machining.
4140 Alloy Steel: Versatile and Tough
Composition:
Carbon (C): 0.38% - 0.43%
Manganese (Mn): 0.75% - 1.00%
Phosphorus (P): 0.035%
Sulfur (S): 0.040%
Silicon (Si): 0.15% - 0.35%
Chromium (Cr): 0.8% - 1.1%
Molybdenum (Mo): 0.15% - 0.25%
Iron (Fe): Remainder
Physical Properties (Annealed):
Rockwell 92 HRB Hardness
Ultimate tensile strength of 95 ksi
Yield tensile strength of 60 ksi
Use Cases:
Nuts, Bolts, and other Fasteners
Crankshafts
Connecting Rods
Drill Collars, Drill Rods, and other Downhole Tools
Gears
Shafts
Dies and Molds
4140 is renowned for its high tensile strength and toughness. Chemically, it is very similar to 4130, but with higher carbon contents for added strength. Commonly used in the manufacturing of shafts, gears, and various machine components, 4140 excels in applications requiring high strength, impact resistance, and good fatigue properties.
4330 Alloy Steel: High-Strength Aerospace Grade
Composition:
Carbon (C): 0.28% - 0.33%
Manganese (Mn): 0.4% - 0.6%
Phosphorus (P): 0.035%
Sulfur (S): 0.04%
Silicon (Si): 0.15% - 0.35%
Nickel (Ni): 1.65% - 2.00%
Chromium (Cr): 0.7% - 0.9%
Molybdenum (Mo): 0.2% - 0.3%
Iron (Fe): Remainder
Physical Properties (VAR MOD):
Rockwell 39 HRC Hardness
Ultimate tensile strength of 240 ksi
Yield tensile strength of 190 ksi
Use Cases:
Mine Drill Tooling
Downhole Tools
Turbine Components
Gears
High Performance Dies and Molds
Other Tooling requiring impact/wear resistance
4330 offers increased strength and hardenability compared to 4130 and 4140 due to added nickel contents. 4330 finds its place in critical components like landing gear, structural parts, and other high-stress areas where strength and durability are paramount.
4340 Alloy Steel: Toughness and Wear Resistance
Composition:
Carbon (C): 0.38% - 0.43%
Manganese (Mn): 0.6% - 0.8%
Phosphorus (P): 0.035%
Sulfur (S): 0.04%
Silicon (Si): 0.15% - 0.35%
Nickel (Ni): 1.65% - 2.00%
Chromium (Cr): 0.7% - 0.9%
Molybdenum (Mo): 0.2% - 0.3%
Iron (Fe): Remainder
Physical Properties (Annealed):
Rockwell 96 HRB Hardness
Ultimate tensile strength of 108 ksi
Yield tensile strength of 68 ksi
Use Cases:
Gears
Shafts
Axles
Hydraulic components
High-Performance Connecting Rods & Crank Shafts
High Strength Dies and Molds
4340 exhibits exceptional toughness and wear resistance. Chemically, it is very similar to 4330, but with higher carbon contents for added strength. Commonly employed in aircraft components, automotive parts, and oil and gas industry tools, 4340 excels in applications demanding high tensile strength, fatigue resistance, and impact toughness.
8620 Alloy Steel: Case-Hardening Excellence
Composition:
Carbon (C): 0.18% - 0.23%
Manganese (Mn): 0.7% - 0.9%
Phosphorus (P): 0.035%
Sulfur (S): 0.04%
Silicon (Si): 0.15% - 0.35%
Nickel (Ni): 0.4% - 0.7%
Chromium (Cr): 0.4% - 0.6%
Molybdenum (Mo): 0.15% - 0.25%
Iron (Fe): Remainder
Physical Properties (Annealed):
Rockwell 81 HRB Hardness
Ultimate tensile strength of 78 ksi
Yield tensile strength of 56 ksi
Use Cases:
Gears
Crankshafts
Shafts
Heavy Duty Bushings
Heavy Duty Pins
8620 offers excellent case-hardening properties. This alloy is most often used in gears, cams, and other components requiring high surface hardness and interior ductility. 8620 is popular for its excellent machinability and weldability.
9310 Alloy Steel: Case-Hardening Superiority
Composition:
Carbon (C): 0.08% - 0.13%
Manganese (Mn): 0.45% - 0.65%
Phosphorus (P): 0.025%
Sulfur (S): 0.025%
Silicon (Si): 0.20% - 0.35%
Nickel (Ni): 3.0% - 3.5%
Chromium (Cr): 1.1% - 1.4%
Molybdenum (Mo): 0.08% - 0.13%
Iron (Fe): Remainder
Physical Properties (Annealed):
Rockwell 100 HRB Hardness
Ultimate tensile strength of 119 ksi
Yield tensile strength of 64 ksi
Use Cases:
Heavy Duty Gears
Heavy Duty Crankshafts
9310 is specifically designed for superior case-hardening and heat-treating responses. 9310 is a favored material for gears and other high-stress components where durability, fatigue resistance, and high core strength are crucial.
Conclusion
The world of alloy steels is diverse, and these high-performance alloys, including 4130, 4140, 4330, 4340, 8620, and 9310, showcase the engineering marvels achieved through metallurgy. As industries continue to push the boundaries of performance and reliability, these alloys will likely remain at the forefront of innovation, enabling the development of stronger, more durable, and more efficient components for a wide range of applications.
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*Physical Property values based on Machinery’s Handbook 31