Introduction to 420 Stainless Steel

In the tooling industry, where you are only as good as your last mold, the choice of material can make all the difference. Among the array of materials available, 420 stainless steel stands out as a reliable and versatile option. Widely recognized for its balance of high-hardness and corrosion resistance, 420 stainless steel has become a staple in injection mold tooling, providing essential characteristics required for demanding molding processes, primarily in applications where cleanliness is the driving factor like medical device molding. 

What is 420 Stainless Steel?

420 stainless steel belongs to the martensitic family of stainless steels, characterized by their high carbon content (around 0.15% to 0.40%) and moderate chromium content (12% to 14%). This composition renders 420 stainless steel capable of achieving high hardness levels through heat treatment, making it suitable for injection mold tooling applications where wear resistance and corrosion resistance are essential.

In its annealed state, 420 stainless steel exhibits relatively low hardness and modest strength. However, through processes like quenching and tempering, it can attain impressive mechanical properties, including high hardness, strength, and toughness. These attributes make it a popular choice for injection mold tooling components subjected to demanding conditions, such as high temperatures, pressures, and abrasive materials.

Features and Benefits of 420 Stainless Steel for Injection Mold Tooling

High Hardness and Strength:

Injection mold tooling demands materials with exceptional hardness and strength to withstand the stresses and pressures of the molding process. 420 stainless steel, with its ability to achieve high levels of hardness and strength through heat treatment, is ideally suited for this purpose. By undergoing controlled heating and cooling cycles, it forms a martensitic microstructure that enhances its resistance to wear and deformation, ensuring prolonged tool life and reliable performance.

Excellent Corrosion Resistance:

Corrosion can undermine the integrity of injection mold tooling and contaminate parts during the molding process. Due to the chromium content, 420 stainless steel forms a protective oxide layer on the surface, providing effective corrosion resistance against moisture, chemicals, and corrosive molding materials. This inherent resistance ensures the longevity and reliability of injection mold tools, even in challenging environments. The corrosion resistance makes it an ideal material choice for conformally cooled mold inserts where rust blocking the cooling channels is a concern. 

Surface Finish:

When it comes to surface finish and texturing for injection molding tooling, 420 stainless steel offers remarkable versatility and precision. Through advanced machining and polishing techniques, 420 stainless steel molds can achieve exceptionally smooth surface finishes, crucial for producing high-quality molded parts. Additionally, the inherent machinability of 420 stainless steel allows for intricate texturing patterns to be etched or engraved onto the mold surfaces, imparting unique aesthetics and functional characteristics to the molded parts. Whether seeking a glossy, mirror-like finish or intricate textures for improved part release and surface appearance, 420 stainless steel molds provide the flexibility and precision required to meet diverse molding requirements with precision and reliability.

Why choose 420 stainless steel for your mold?

420 stainless steel emerges as a preferred choice for many mold tooling applications, like medical devices, clean room molding, electronics, lenses, or other scenarios where corrosion and cleanliness are a concern. Another key reason to choose 420 is the surface finish that can be achieved. Whether it is a textured surface or a mirror finish, 420 is often going to be the best choice. Many high-value medical devices, automotive parts, and sealing components are molded using stainless steel plates, cavities, or cores.

Why 3D Print 420 Stainless Steel?

The downsides of choosing 420 stainless steel are the cost and the level of difficulty it takes to machine. On the AISI machinability rating system 420 stainless steel falls around 30% which is a relatively low score. Coupled with a high cost, you are looking at a potential for a volatile project where mistakes can happen and start to add up quickly. For this reason 420 stainless is reserved for the types of projects listed above, but if it were easier and most cost effective would it be used more? The answer is likely yes, and the process to make it more efficient and cost-effective may be here already. 

By utilizing Mantle’s metal 3D printing technology to print 420 stainless steel mold components and cavities can be much more streamlined and without the high stress of low machinability. By taking the machining step out of a manual process and moving it into the printing process, the main drawback of 420 stainless is taken out of the equation. Instead of bogging down your toolmakers with trying to machine 420 stainless steel, you can press a button on the printer and get to work on another job. Conformal cooling and other mold detailing is made much more affordable, accessible, and less of a time suck for the mold makers.