The metal cutting industry produces an extremely wide variety of components machined from many different materials. Each material has its own unique characteristics that are influenced by alloying elements, heat treatment, hardness, and other factors. These characteristics influence the selection of cutting tool geometry, grade, and cutting parameters. To simplify this process, workpiece materials are classified into six major groups according to ISO standards, each with unique properties affecting machinability.
Steel (P)
Steel is the most commonly machined material, offering a balance of strength and machinability. It is used in various industries including automotive, construction, and heavy equipment manufacturing. Machinability varies based on carbon content and alloying elements, with low-carbon steels being easier to cut and high-carbon or alloy steels requiring specialized tooling.
Steel Examples:
Carbon Steels – 1005, 1010, 1018, 1020, 1045, 1050, A36, 44W
Alloy Steels – 4130, 4140, 4145, 4340, 8620, 6150, 52100
Stainless Steel (M)
Stainless steel is corrosion-resistant and widely used in medical, food processing, and aerospace industries. However, it presents machining challenges due to its tendency to work harden, causing excessive tool wear. It requires optimized cutting speeds and tool coatings designed to reduce heat buildup.
Stainless Steel Examples:
Austenitic – 301, 302, 303, 304, 304L, 316, 316L
Martensitic – 410, 416, 420, 440C
Ferritic – 430, 446
Duplex – 2205, 2507
Cast Iron (K)
Cast iron is known for its excellent wear resistance and damping properties, making it a preferred material in engine components and industrial equipment. It comes in different types such as gray, ductile, and white cast iron, each requiring different machining strategies due to variations in hardness and brittleness.
Cast Iron Examples:
Gray Iron – ASTM A48 Class 20, Class 30, Class 40
Ductile Iron – ASTM A536 Grade 60-40-18, 65-45-12, 80-55-06
Malleable Iron – ASTM A47 Grade 32510, 35018
Non-ferrous Metals (N)
Non-ferrous metals, including aluminum, copper, and brass, are lightweight and highly resistant to corrosion. They are commonly used in aerospace and electrical applications. Their machinability is generally good, though factors like material softness and built-up edge formation must be managed.
Non-Ferrous Materials:
Aluminum Alloys – 2024, 6061, 6063, 7075
Brass – C36000, C46400
Bronze – C93200 (SAE 660), C95400
Copper – C11000
Titanium – Grade 2, Grade 5 (Ti-6Al-4V)
Heat-resistant Superalloys (S)
Superalloys such as Inconel and titanium alloys are designed to withstand extreme temperatures and pressures, commonly found in aerospace and power generation industries. These materials are difficult to machine due to their high strength and poor thermal conductivity, necessitating specialized tooling and cutting techniques.
Heat Resistant Super Alloys Examples:
Nickel-Based – Inconel 600, 625, 718; Hastelloy C276; Monel 400
Cobalt-Based – Stellite 6, Stellite 21
Iron-Based – A-286
Hardened Materials (H)
Hardened steels are used in tooling and high-strength applications due to their extreme durability. Machining these materials requires advanced cutting tools such as CBN or ceramic inserts to handle the high heat and hardness levels.
Hardened Material:
Tool Steels – D2, A2, O1, H13, M2
Case Hardened Steels – 8620, 9310
Bearing Steels – 52100
Induction Hardened Grades – 1045, 4140