Stainless Steel

Essential Design Tips for Stainless Steel Parts: A Guide for Engineers and Designers

About Stainless Steel

In the world of CNC machining, stainless steel has garnered considerable popularity owing to its impressive attributes. This steel alloy contains a minimum of 10.5% chromium, endowing it with exceptional corrosion resistance and durability. Moreover, stainless steel is renowned for its formidable strength, ductility, and toughness, rendering it suitable for a broad spectrum of applications.

A diverse array of stainless steel types is available, each boasting unique properties and applications. Among the commonly utilized stainless steel types in CNC machining are austenitic stainless steel, ferritic stainless steel, and martensitic stainless steel. The mechanical properties and machinability of each type may vary due to their distinct chemical compositions.

On the whole, stainless steel proves to be a versatile material extensively employed across various industries, including automotive, aerospace, and medical, among others. Its ability to endure challenging environments and withstand corrosion positions it as a preferred choice for numerous modern applications.

Subtypes

Stainless Steel 15-5

Stainless Steel 15-5 is a precipitation-hardening stainless steel that contains 15% chromium and 5% nickel. It has excellent corrosion resistance and high strength, making it suitable for aerospace and defense applications. Its disadvantages include lower ductility and impact resistance compared to other stainless steel types.

Stainless Steel 17-4

Stainless Steel 17-4 is a precipitation-hardening stainless steel that contains 17% chromium and 4% nickel. It has excellent strength, hardness, and corrosion resistance, making it suitable for industrial and aerospace applications. However, it has poor weldability and is expensive compared to other stainless steel types.

Stainless Steel 18-8

Stainless Steel 18-8, also known as 304 grade, is a widely used austenitic stainless steel that contains 18% chromium and 8% nickel. It has excellent corrosion resistance, good weldability, and is suitable for a variety of applications, including kitchen equipment and medical devices. Its disadvantages include lower strength and hardness compared to other stainless steel types.

Stainless Steel 303

Stainless Steel 303 is a free-machining austenitic stainless steel that contains 17-19% chromium and 8-10% nickel. It has excellent machinability and is used in applications that require high precision and tight tolerances. Its disadvantages include lower corrosion resistance and toughness compared to other stainless steel types.

Stainless Steel 304

Stainless Steel 304 is a widely used austenitic stainless steel that contains 18% chromium and 8% nickel. It has excellent corrosion resistance, good weldability, and is suitable for a variety of applications, including kitchen equipment and medical devices. Its disadvantages include lower strength and hardness compared to other stainless steel types.

Stainless Steel 316

Stainless Steel 316 is a molybdenum-containing austenitic stainless steel that contains 16-18% chromium and 10-14% nickel. It has excellent corrosion resistance, particularly in harsh environments, and is used in marine, chemical, and medical industries. Its disadvantages include lower machinability and higher cost compared to other stainless steel types.

Stainless Steel 416

Stainless Steel 416 is a martensitic stainless steel that contains 12-14% chromium. It has excellent machinability and is used in applications that require high precision and tight tolerances. Its disadvantages include lower corrosion resistance and toughness compared to other stainless steel types.

Stainless Steel 420

Stainless Steel 420 is a martensitic stainless steel that contains 12-14% chromium. It has excellent hardness and is used in applications that require high wear resistance, such as surgical instruments and cutlery. Its disadvantages include lower corrosion resistance and toughness compared to other stainless steel types.

Stainless Steel 440C

Stainless Steel 440C is a high-carbon martensitic stainless steel that contains 16-18% chromium. It has excellent hardness and wear resistance and is used in applications that require high strength and durability, such as knife blades and bearings. Its disadvantages include lower corrosion resistance and toughness compared to other stainless steel types.

Stainless Steel 410

Stainless Steel 410 is a martensitic stainless steel that contains 11.5-13.5% chromium. It has good corrosion resistance and is used in applications that require high strength and hardness, such as valves and pumps. Its disadvantages include lower toughness and weldability compared to other stainless steel types.

Surface Finishes

As-machined surface finish: The as-machined surface finish of stainless steel is the natural finish that is achieved after CNC machining. This finish is characterized by the tool marks left by the machining process, and it provides a slightly rough and dull appearance. The advantage of this finish is that it is cost-effective and requires no additional processing. However, it may not be suitable for applications where hygiene and aesthetics are critical.

Bead blasting surface finish: The bead blasting surface finish of stainless steel is achieved by propelling small glass or ceramic beads at high velocity onto the surface of the material. This finish results in a matte and uniform appearance and provides excellent resistance to corrosion and wear. The advantage of this finish is that it is cost-effective, easy to clean, and can hide surface imperfections. However, it may not be suitable for applications that require high hygiene standards.

Powder coating surface finish: The powder coating surface finish of stainless steel involves applying a dry powder coating to the surface of the material and then heating it to create a hard and durable finish. This finish provides excellent corrosion resistance, chemical resistance, and aesthetic appeal. The advantage of this finish is that it can be customized to achieve a wide range of colors and textures and is suitable for applications that require high hygiene standards. However, it may not be suitable for applications that require high wear resistance.

Design Tips

Material selection: Select the appropriate grade of stainless steel for the intended application. Different grades have varying levels of corrosion resistance, strength, and machinability.
Wall thickness: Maintain a uniform wall thickness to prevent distortion during manufacturing and ensure consistent performance of the parts.
Fillet radius: Use generous fillet radii to avoid stress concentration and reduce the likelihood of cracking or failure.
Sharp edges: Avoid sharp edges that can cause stress concentration and promote fatigue failure. Instead, use rounded or chamfered edges to distribute stresses evenly.
Surface finish: Consider the intended use and environment of the parts when selecting the surface finish. A smooth surface finish can improve corrosion resistance and aesthetics.
Tolerances: Maintain tight tolerances to ensure that the parts fit and perform as intended. However, avoid overly tight tolerances that can increase the cost of manufacturing and reduce the manufacturability of the parts.
Welding: Avoid welding in areas of high stress or areas that are difficult to access. Also, ensure that the welding process and filler material are appropriate for the grade of stainless steel being used.
Testing: Conduct appropriate testing, such as tensile and corrosion testing, to ensure that the parts meet the required performance standards.

FAQ

Can stainless steel be CNC machined?

Yes, stainless steel can be CNC machined. CNC machining is a common manufacturing process used to create parts from stainless steel due to its excellent corrosion resistance, high strength, and durability. However, machining stainless steel can present some challenges due to its high hardness, toughness, and low thermal conductivity.

What is the best stainless steel for CNC machining?

The best stainless steel for CNC machining depends on the specific application and requirements. However, austenitic stainless steel, such as 304 and 316 grades, are often preferred due to their excellent corrosion resistance, machinability, and weldability. Ferritic stainless steel, such as 430 and 446 grades, are also commonly used for CNC machining due to their low cost and good machinability. It is important to consult with a material expert to select the appropriate stainless steel for a specific application.

Why is stainless so hard to machine?

Stainless steel can be hard to machine due to several factors, including its high hardness, toughness, and low thermal conductivity. Stainless steel has a tendency to work harden during machining, which can cause tool wear and reduce tool life. Additionally, the low thermal conductivity of stainless steel can cause heat buildup during machining, which can lead to thermal expansion and deformation of the workpiece. The high toughness of stainless steel can also cause chip formation problems and make it difficult to achieve high surface finishes. To overcome these challenges, proper selection of cutting tools, machining parameters, and coolant systems is critical.