Stainless Steels used in the CNC Machine Shop
Introduction
Stainless steel is a versatile and widely used material known for its corrosion resistance, strength, and durability. Among the various stainless steel alloys, 17-4, 303, 304, 316, 416, and 440C stand out for their unique compositions and applications. Let's delve into the characteristics and use cases of these stainless steel alloys.
17-4 Stainless Steel: The Precipitation Hardening Stainless
Composition:
Carbon (C): 0.07%
Chromium (Cr): 15%-17.5%
Nickel (Ni): 3%-5%
Copper (Cu): 3%-5%
Manganese (Mn): 1%
Silicon (Si): 1%
Phosphorus (P): 0.04%
Sulfur (S): 0.03%
Iron (Fe): Remainder
Physical Properties (Annealed):
Rockwell 85 HRB Hardness
Hardened up to 45 HRC
Ultimate tensile strength of 160 ksi
Yield tensile strength of 145 ksi
Use Cases:
Valves
Fasteners
Shafts
Bushings
Bearings
Parts that require strength and corrosion resistance
17-4 stainless steel is a precipitation-hardening (age-hardening) alloy known for its excellent combination of high strength, corrosion resistance, and ease of hardening. 17-4 is widely used in aerospace, chemical, and petrochemical industries for applications requiring high strength and corrosion resistance.
303 Stainless Steel: The Go-To Stainless for CNC Machined Parts
Composition:
Carbon (C): 0.15%
Chromium (Cr): 17% - 19%
Nickel (Ni): 8% - 10%
Manganese (Mn): 2%
Silicon (Si): 1%
Phosphorus (P): 0.2%
Sulfur (S): 0.15% (max)
Iron (Fe): Remainder
Physical Properties (Annealed):
Rockwell 84 HRB Hardness
Ultimate tensile strength of 90 ksi
Yield tensile strength of 35 ksi
Use Cases:
Fasteners
Couplers
Shafts
Bushings
Flanges
General Hardware
303 stainless steel is very similar to 304, but it contains added sulfur and to enhance machinability. This alloy offers good corrosion resistance, excellent machinability, and is non-magnetic. 303 is commonly used for machined components that do not need to be Food Safe.
304 Stainless Steel: The Common Stainless Steel
Composition:
Carbon (C): 0.08%
Chromium (Cr): 18% - 20%
Nickel (Ni): 8% - 10.5%
Manganese (Mn): 2%
Silicon (Si): 0.75%
Phosphorus (P): 0.045%
Sulfur (S): 0.03%
Iron (Fe): Remainder
Physical Properties (Annealed):
Rockwell 80 HRB Hardness
Ultimate tensile strength of 85 ksi
Yield tensile strength of 35 ksi
Use Cases:
Food Processing Equipment
Kitchen Appliances
Surgical Equipment
Pipes/Tanks
Fasteners and Fittings
General Fabrication
304 stainless steel is a versatile and widely used alloy that exhibits excellent corrosion resistance, good formability and is non-magnetic. 304 is used for kitchen equipment, chemical containers, architectural applications, and general-purpose components. 304 is used in general applications that are required to be Food Safe.
316 Stainless Steel: The Marine-Grade Stainless
Composition:
Carbon (C): 0.08%
Chromium (Cr): 16% - 18%
Nickel (Ni): 10% - 14%
Molybdenum (Mo): 2% - 3%
Manganese (Mn): 2%
Silicon (Si): 0.75%
Nitrogen (N): 0.1%
Phosphorus (P): 0.045%
Sulfur (S): 0.03%
Iron (Fe): Remainder
Physical Properties (Annealed):
Rockwell 80 HRB Hardness
Ultimate tensile strength of 85 ksi
Yield tensile strength of 35 ksi
Use Cases:
Marine Propellers
Marine Shafts
Marine Fittings & Couplers
Chemical Processing pipes, tanks, fittings, etc
Surgical instruments and implants
Parts that require extreme corrosion resistance
316 stainless steel is similar to 304 but contains molybdenum for enhanced corrosion resistance. This alloy is widely used in marine applications, chemical processing, and medical devices. It is used when corrosion resistance takes priority.
416 Stainless Steel: The Free-Machining Stainless
Composition:
Carbon (C): 0.15%
Chromium (Cr): 12% - 14%
Manganese (Mn): 1.25%
Silicon (Si): 1%
Phosphorus (P): 0.06%
Sulfur (S): 0.15% (min)
Iron (Fe): Remainder
Physical Properties (Annealed):
Rockwell 82 HRB Hardness
Hardened up to 43 HRC
Ultimate tensile strength of 75 ksi
Yield tensile strength of 40 ksi
Use Cases:
Fasteners
Shafts
Structural members
416 stainless steel is a martensitic alloy with added sulfur and reduced nickel content for improved machinability. This alloy offers good corrosion resistance and high machinability. Most often used in architecture and construction applications
440C Stainless Steel: The High-Hardness Stainless
Composition:
Carbon (C): 0.95% - 1.2%
Chromium (Cr): 16% - 18%
Manganese (Mn): 1%
Silicon (Si): 1%
Phosphorus (P): 0.04%
Sulfur (S): 0.03%
Molybdenum (Mo): 0.75%
Iron (Fe): Remainder
Physical Properties (Annealed):
Rockwell 97 HRB Hardness
Hardened up to 50 HRC
Ultimate tensile strength of 110 ksi
Yield tensile strength of 65 ksi
Use Cases:
Knives and Blades
Tooling and Molds
Bearings
Valve Components
Valve Seats
440C stainless steel is a high-carbon martensitic alloy with chromium for corrosion resistance. It exhibits high hardness, good corrosion resistance, and wear resistance, and responds well to heat treatment. 440C is often used for manufacturing bearings, surgical instruments, cutting tools, and other components requiring high hardness and wear resistance.
Conclusion
In conclusion, each stainless steel alloy, including 17-4, 303, 304, 316, 416, and 440C, offers a unique set of characteristics that cater to specific applications. Understanding the properties of these alloys is crucial for selecting the right material for a given task, whether it be in aerospace, manufacturing, medical, or other industries. Stainless steel's versatility makes it a cornerstone material in engineering and manufacturing processes worldwide.
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*Physical Property values based on Machinery’s Handbook 31