Unlike machining other materials, machining stainless steel requires review of a myriad of aspects prior to beginning work in the machine shop. Not only should cutting tool specialists and coolant specialists be consulted, but machine capabilities should be addressed as well. Furthermore, one must verify that the correct tooling components are being used: cutting tool geometries, substrates, and coatings, type of coolant and coolant pressure among others. Still though, machining stainless comes with many unique challenges because of its low machinability-a machinability rating that needs to be overcome to utilize the many benefits of stainless steel.
Stainless steel is offered in varying grades based on specific properties. These grades are also split into groupings based upon metallurgical qualities. Outlined below are the different families of stainless steel.
• Austenitic –
A rather common material, austenitic steel is identified as the Type 300 series; grades 304 and 316 are the most accessible. While austenitic stainless steel cannot be effectively heat treated, it can be hardened through cold working-the process of changing the shape without the use of heat. Corrosion resistance, low magnetism and good formability are also characteristics associated with this family of stainless.
• Ferritic –
As part of the Type 400 series, ferritic stainless steels are characterized by their corrosion resistance, strong ductility and magnetism and are typically iron chromium alloys. This family can be altered through cold working rather than thermal hardening methods.
• Martensitic –
Similar to ferritic stainless, martensitic are also iron-chromium alloys within the Type 400 series; however, this grade is able to be hardened by heat treatment unlike the ferritic grade. Other characteristics include magnetism, good ductility and corrosion resistance.
• Precipitation -
hardened (PH)–Through the precipitation hardening process, precipitation hardened stainless steel attains more strength in addition to greater corrosion resistance. Additionally, it is similar to martensitic stainless in terms of chemical makeup.
• Duplex –
With a composition made up of nickel, molybdenum and higher chromium levels, duplex stainless steels combine features of ferritic and austenitic stainless, yet this family demonstrates greater strength and high localized corrosion resistance.
Whether machining valve choke bodies for the offshore oil industry (410 stainless), pump covers for the food processing industry (316 stainless steel), bushings for the aerospace industry (17-4 stainless steel) or pumps for the water and wastewater industry (304 stainless steel),