SUS 420J1 Stainless Steel: Machinability and Surface Treatment

The manufacturability of SUS 420J1 stainless steel is highly dependent on its material condition, and understanding this relationship is key to efficient fabrication and achieving desired surface qualities. Its performance in machining and the range of applicable surface finishes directly impact the functionality and aesthetics of the final component.
In terms of machinability,SUS 420J1 stainless steel is typically supplied and machined in its annealed state, where it possesses a relatively uniform microstructure and a moderate hardness of approximately 180-220 HB. In this condition, its machinability is considered fair to good, ranking slightly lower than free-machining steels but comparable to many other martensitic stainless grades. Using sharp, positive-rake cutting tools and robust cooling/lubrication is essential to achieve good surface finishes and prevent work hardening. However, once the material undergoes hardening and tempering to achieve high strength (e.g., above HRC 45), conventional machining becomes exceedingly difficult and is not recommended. Machining operations should always be completed prior to the final hardening and tempering process.
For surface treatment, SUS 420J1 stainless steel is an excellent candidate for a variety of finishing processes. Its surface can be polished to a high-gloss, mirror-like finish, which is highly desirable for cutlery, surgical instruments, and decorative hardware. Common industrial finishes include the standard 2B matte finish, a brushed (No. 4) finish, or a bright annealed (BA) surface. Furthermore, components can undergo processes like electroplating or black oxide coating for enhanced corrosion resistance, reduced reflectivity, or specific aesthetic requirements. The ability to be finely polished and treated makes SUS 420J1 a versatile choice where both performance and appearance are critical.