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Stainless Steel for CNC Machining

Stainless steel is a ubiquitous metal critical to a myriad of industries from medical to power generation. Its value lies in its strength, heat resistance, and exceptional corrosion resistance. Indeed, the ability to resist corrosion is the primary thing that distinguishes stainless steel from regular steel

cnc machined stainless steel partscnc machined stainless steel parts

About Stainless Steel for CNC Machining

What sets stainless steel apart from normal steel is the inclusion of chromium in its alloys. All stainless steel chemical compositions contain at least 10.5% chromium. The inclusion of chromium makes these steels more corrosion resistant. The different grades of this material have various alloying elements that serve to further improve corrosion resistance, heat treatability, and machinability. It should be noted that heat treatment can significantly affect the metal’s mechanical properties.

Stainless steels can be classified based on their crystalline structure. This includes Austenitic, ferritic, martensitic, and duplex:

  • Austenitic stainless steel, such as 300- and 200-series stainless, are highly formable and do not work harden. They are also non-magnetic in an annealed condition.
  • Ferritic stainless steels are magnetic and offer better thermal conductivity than austenitic stainless. They cannot be hardened by heat treatment.
  • Martensitic stainless steel such as grade 416 and 420 can be hardened through multiple methods of aging or heat treatments.
  • Duplex stainless steel, also known as austenitic-ferritic, are grades of stainless that are highly specialized for improved corrosion resistance. Duplex steels are typical in industrial and architectural structuring. 

Given its versatility, some form of stainless steel is prevalent in every industry. 

Stainless Steel At a Glance
ApplicationUsed in the automotive, consumer goods, aerospace, and medical industries, primarily in applications that require exceptional corrosion resistance.
AdvantagesGood heat resistance, excellent corrosion resistance, high strength and toughness
DisdvantagesExpensive; can be difficult to machine depending on alloy and heat treatment
Lead TimeMinimum 3 days; potentially longer for complex or internationally manufactured parts.
TolerancesMachining tolerances depend on the exact alloy used. However, a tolerance of 0.005” is generally achievable.
Wall ThicknessMinimum ~0.03” (0.80 mm); may vary depending on the ratio of wall thickness to planar dimension as well as alloy.
Max Part SizeThe maximum size of the part is determined by the machines available and the complexity of the part.

Stainless Steel 15-5

Stainless Steel 15-5 is a precipitation-hardened (PH) metal. The process gives it excellent toughness, strength, and corrosion resistance. Mechanical properties are enhanced by low-temperature heat treatment, making this material ideal for aerospace and nuclear applications.

Stainless Steel 15-5 Properties
Tensile Strength, Yield (MPa)Shear Modulus (GPa)Elongation at Break (%)Hardness (Brinell)Density (g/cm^3)

Stainless Steel 17-4

This precipitation-hardened (PH) steel grade has better corrosion-resistant properties at high temperatures when compared to 15-5 stainless steel. It achieves this increased corrosion resistance by sacrificing mechanical strength. This is also one of the more widely used grades of PH stainless steel. Applications include chemical processing parts and gas turbines.

Stainless Steel 17-4 Properties
Tensile Strength, Yield (MPa)Shear Modulus (GPa)Elongation at Break (%)Hardness (Brinell)Density (g/cm^3)

Stainless Steel 18-8

This grade of stainless steel has an austenitic crystal structure and is one of the most widely used grades. 18-8 is often referred to as 304 stainless steel or SS304, and Xometry quotes 18-8 as SS304, but the two have slight differences in some alloying elements. 18-8 has good corrosion resistance characteristics and is regularly used to create fasteners and pressure piping.

Stainless Steel 18-8 Properties
Tensile Strength, Yield (MPa)Shear Modulus (GPa)Elongation at Break (%)Hardness (Brinell)Density (g/cm^3)

Stainless Steel 303

This grade of austenitic stainless steel was formulated to be easier to machine than SS304 by including sulfur among the alloying elements. This addition, however, makes the alloy less corrosion resistant than SS304. It is ideal for items that require heavy machining like gears and shafts.

Stainless Steel 303 Properties
Tensile Strength, Yield (MPa)Shear Modulus (GPa)Elongation at Break (%)Hardness (Brinell)Density (g/cm^3)

Stainless Steel 304

This grade of austenitic stainless steel has good corrosion resistance properties and is used extensively for fasteners. It is often seen as a low-cost alternative to SS316 while not having the same corrosion resistance. This alloy is very similar to grade 18-8 stainless steel as it has the same amount of chrome and nickel, however, it has improved strength due to a higher level of carbon in the alloy.

Stainless Steel 304 Properties
Tensile Strength, Yield (MPa)Shear Modulus (GPa)Elongation at Break (%)Hardness (Brinell)Density (g/cm^3)

Stainless Steel 316

This austenitic grade of stainless steel contains molybdenum which gives it excellent corrosion resistance. In addition to this, it is highly formable and weldable. Applications include chemical tanks and boat fittings. The low carbon version, 316L, is more resistant to chlorides than the basic formulation.

Stainless Steel 316 Properties
Tensile Strength, Yield (MPa)Shear Modulus (GPa)Elongation at Break (%)Hardness (Brinell)Density (g/cm^3)

Stainless Steel 416

Stainless steel 416 is one of the most machinable stainless steels available. As is the case with other alloys, this improved machinability comes at the cost of corrosion resistance, so it generally rusts easier than its other stainless steel counterparts. Applications include motor shafts and gears.

Stainless Steel 416 Properties
Tensile Strength, Yield (MPa)Shear Modulus (GPa)Elongation at Break (%)Hardness (Brinell)Density (g/cm^3)

Stainless Steel 420

This martensitic stainless steel has a higher carbon content and lower chromium content than the other steels mentioned previously. Due to its lower chromium content, it has only mild corrosion resistance but makes up for that with improved mechanical properties in its annealed state.

Stainless Steel 420 Properties
Tensile Strength, Yield (MPa)Shear Modulus (GPa)Elongation at Break (%)Hardness (Brinell)Density (g/cm^3)

Stainless Steel 440C

Stainless steel 440C has the highest carbon content of the 400 series. This means that 440C has only mild corrosion resistance. However, it has excellent hardness characteristics (which can be further increased with heat treatment) and mechanical strength. Typical applications include bearing housings and surgical instruments.

Stainless Steel 440C Properties
Tensile Strength, Yield (MPa)Shear Modulus (GPa)Elongation at Break (%)Hardness (Brinell)Density (g/cm^3)

Stainless Steel 410

Stainless steel 410 is the most general-purpose steel among the 400 series. It has a low carbon content that gives it improved corrosion resistance. Like other martensitic steels, 410 can be hardened to achieve impressive mechanical strength. 410 stainless steel is typically used for cutlery, fasteners, and machinery parts.

Stainless Steel 410 Properties
Tensile Strength, Yield (MPa)Shear Modulus (GPa)Elongation at Break (%)Hardness (Brinell)Density (g/cm^3)

Finishes and Post-Processing Options

Xometry offers a wide range of surface finishes applicable to stainless steel.

  • As machined (standard): This standard finish leaves the part in its original state after machining. Xometry can achieve 125 Ra or better. Finishing passes can be performed to further refine the surface roughness. This is the most common surface finish for stainless steel.
  • Powder coating: Powder coating creates an excellent and robust surface finish. Stainless steel is corrosion resistant to a wide array of chemicals, but some, like chlorides, still pose a challenge. Powder coating can be used to improve its anti-corrosion properties in these situations.
  • Bead blasting: This process creates a smooth and uniform matte finish by lightly blasting the surface. This surface finish is generally applied for cosmetic purposes.
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Cost-saving Design Tips

To reduce the cost of stainless steel alloys, below are some design tips:

  • Choose the right alloy: Not all stainless steels are equal in price. Make sure that the chosen material is suited to the application. These metals are generally ideal in corrosive environments but not all are resistant to the same chemicals. To learn more, contact a Xometry expert.
  • Machinability: Some stainless steels are more machinable than others. When only mild corrosion resistance is required, consider using free-machining stainless steel to reduce machining costs.
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