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Everything about CNC Machining Stainless Steel
Due to the excellent machinability and excellent uniformity of stainless steel, CNC machining stainless steel parts is one of the effective manufacturing processes. CNC machining is the process by which computers guide mills, lathes, drills, and other cutting tools to efficiently and cost-effectively manufacture precise, repeatable parts, especially CNC milling stainless steel. With its high strength, high tensile strength, corrosion resistance, wear resistance and eye-catching unique appearance, stainless steel is one of the most popular materials for manufacturing custom parts and prototypes, playing a pivotal role in modern society, and its range of applications From cookware to automotive parts to medical, chemical, marine industry, aerospace and other fields.
What is stainless steel?
The salient feature of stainless steel is that the content of chromium is greater than 11%, the content of nickel is greater than 8%, it has high corrosion resistance in the air or in a corrosive environment, and it also has high corrosion resistance in a high temperature environment (>450°C). Strength of. Stainless steel is not a pure metal, but a kind of alloy steel, there are about 150 kinds. The alloying elements of each stainless steel are different, and its properties are also very different. For example, stainless steel with a chromium content of 16%-18% is called acid-resistant steel. The inclusion of other metallic elements such as nickel stabilizes the crystalline microstructure of iron, and molybdenum or titanium improve the heat and corrosion resistance of stainless steel. When exposed to the outdoor environment, the chromium in stainless steel will form an oxide film, which is called a “passive layer” to prevent further corrosion of stainless steel, prevent rust, and maintain a spotless appearance.
At a glance
Processes | Lead Time | Tolerance | Price | Applications | Grades | Finishiing Services |
CNC Milling CNC Turning | As fast as 1 days | Following drawing: as low as +/- 0.005 mm No drawing: ISO 2768 medium | $$$ | Industrial applications, fittings, fasteners, cookware, medical devices, | 150, AF (13% PTFE Filled), 30% Glass Filled | Black Oxide, Electropolishing, ENP, Media Blasting, Nickel Plating, Passivation, Powder Coating, Tumble Polishing, Zinc Plating |
Classification of stainless steel
There are many types of stainless steel, and different models have different application ranges. The main difference lies in the content of alloying elements. We discuss stainless steel classifications to help you choose the best grade for your CNC machining project. Stainless steel is classified according to the crystal structure, which can be divided into 5 types, namely: austenitic, ferritic, martensitic, duplex and precipitation hardening (PH) grades.
Austenitic stainless steel: Austenitic stainless steel is named for its microstructure in which iron elements are austenite crystals. It is the most popular and widely used stainless steel, accounting for about 70% of all stainless steels. The main alloying element is chromium (content between 18%-39%) and nickel (content between 6%-20%), so austenitic stainless steel is the most corrosion-resistant of all stainless steel series. The alloy still has high strength at high temperature, and its excellent mechanical properties are very suitable for CNC machining. Austenitic stainless steel has no magnetism, high formability and toughness, and can be cold treated, but not heat treated. The most widely known is the 300 series. Typically, CNC machining of austenitic stainless steel can make parts or prototypes such as shafts, valves, bolts, bushings, nuts, aircraft fittings, food equipment, pipes and containers.
Common Austenitic Stainless Steel Grades
Standard grade austenitic stainless steel. Standard grades of austenitic stainless steel have carbon contents up to 0.08%, with no minimum carbon requirement.
Low carbon grade austenitic stainless steel. Low-carbon austenitic stainless steels are usually marked with the letter “L” after the grade (such as 304L, 316L). The carbon content is about 0.03%.
High carbon grade austenitic stainless steel. High carbon grades of austenitic stainless steel have a minimum carbon content of 0.04% and a maximum of 0.10%. High carbon grades can maintain strength at extreme temperatures and are usually identified by the letter “H” after the grade. This grade of stainless steel can be chosen when CNC machined stainless steel parts are ultimately used in extreme environments.
Common Austenitic Stainless Steel Grades
303 stainless steel contains trace elements such as selenium, sulfur and phosphorus to improve the mechanical properties suitable for CNC processing. It is easier to process than SS304 stainless steel, and its corrosion resistance is not as good as SS304. It is very suitable for heavy duty or high surface finish occasions. For example, gears, shafts, valves, bolts, screws, etc.
Tensile strength σb (MPa): ≥520
Conditional yield strength σ0.2 (MPa): ≥205
Elongation δ5 (%): ≥40
Reduction of area ψ (%): ≥50
Hardness: HB≤187HB; HRC≤90HRB;
HV≤200HV
304 stainless steel is one of the most commonly used austenitic stainless steels. It contains 18% chromium, 8% nickel, and the maximum carbon content is 0.07%. It is very suitable for CNC processing and has excellent corrosion resistance, ductility, formability and weldability. 304 or 304L is widely used in cookware, food, chemical, construction, fasteners, etc., and is considered to be a low-cost substitute for SS316.
Tensile strength σb (MPa)≥515-1035
Conditional yield strength σ0.2 (MPa)≥205
Elongation δ5 (%)≥40
Reduction of area ψ (%)≥?
Hardness: ≤201HBW; ≤92HRB; ≤210HV
Density (20°C, g/cm³): 7.93
Melting point (°C): 1398~1454
Specific heat capacity (0~100℃, KJ·kg-1K-1): 0.50
Thermal conductivity (W•m-1•K-1): (100°C) 16.3, (500°C) 21.5
Linear expansion coefficient (10-6•K-1): (0~100°C) 17.2, (0~500°C) 18.4
Resistivity (20°C, 10-6Ω•m2/m): 0.73
Longitudinal modulus of elasticity (20°C, KN/mm2): 193
309.309 stainless steel is famous for its corrosion resistance and heat resistance, with higher chromium and nickel content, it can withstand repeated heating below 980 ℃ without affecting performance. At room temperature, it is stronger than 304 stainless steel, and it is easy to CNC process because it contains sulfur. 309 stainless steel can be cold worked, but not heat treated, and can be welded. It is very suitable for the manufacture of parts in high temperature applications, such as boiler parts, generators, refractory supports, refractory backing plates, etc.
Yield strength/MPa: ≥ 205
Tensile strength/MPa: ≥520 (hardness HB≤187)
Elongation/%: δ5≥ 40
316.316 stainless steel is one of the most commonly used stainless steel grades, second only to 304 stainless steel, which has a chromium content between 16% and 18%, nickel content between 11% and 14%, and at least 2% molybdenum. 316 stainless steel can be called marine grade stainless steel, because of its high molybdenum content and low carbon content, it has high corrosion resistance in marine or chemical environments (strong acid, strong alkali). Under severe temperature, it still cannot affect the corrosion resistance of 316 stainless steel, far exceeding that of 304 stainless steel. 316 stainless steel contains sulfur and is suitable for CNC processing, sheet metal stamping and other processes. It is usually an ideal material for manufacturing marine industry, auto parts, medical equipment, food industry (applicable temperature between -196°C-700°C), and building material parts , of which SS316 is also used in the manufacture of nuclear fuel recovery devices. The cost of CNC machining 316 stainless steel is usually higher than that of 304 stainless steel.
Tensile strength σb (MPa): ≥520
Conditional yield strength σ0.2 (MPa): ≥205
Elongation δ5 (%): ≥40
Reduction of area ψ (%): ≥60
Hardness: ≤187HB; ≤90HRB; ≤200HV
317.317 stainless steel contains 19% chromium, 13% nickel and 3% molybdenum, which is a strong and durable alloy. Because its molybdenum content is higher than stainless steel 316 stainless steel, 317 stainless steel is more corrosion-resistant than 316 stainless steel and tougher than 304 stainless steel. It can be welded, cold-worked and hot-worked, but it cannot be heat-treated. It is easy for CNC processing and is often used in highly corrosive environments. , chemical equipment, pulping equipment, etc. It is an ideal material for manufacturing parts such as engines, absorption towers, valves, pressure vessels, and heat exchange tubes.
Yield strength ≥ 205/MPa,
Tensile strength ≥ 520/MPa,
Elongation ≥ 35%,
Hardness test: HBS≤187, HRB≤90, HV≤200
321．The unique feature of 321.321 stainless steel is that its titanium content is 5 times higher than the carbon content, so as to avoid the formation of chromium carbide due to welding or exposure to high temperature control, with high tensile strength and fatigue resistance, can be used at 1500 Working in a high temperature environment of 100 degrees Celsius, it is easy to creep and break. The mechanical properties of 321 stainless steel are superior to those of 304 stainless steel. It is often used in aircraft equipment, petrochemical, electric power, bridges and automobiles. It is used in the manufacture of aircraft exhaust pipes and manifolds, jet engine parts, boiler shells, heaters, boiler pressure vessels , Furnace pipes, ideal materials for chemical delivery pipes.
Tensile strength σb (MPa): ≥520
Conditional yield strength σ0.2 (MPa): ≥205
Elongation δ5 (%): ≥40
Reduction of area ψ (%): ≥50
Hardness: ≤187HB; ≤90HRB; ≤200HV
348.348 stainless steel contains niobium and tantalum, which can avoid chromium carbide in the welding process, and can still maintain excellent corrosion resistance at a high temperature of 800-1500 degrees Celsius. It is a metal suitable for the nuclear power industry.
Martensitic grade stainless steel.
Martensitic stainless steel is a heat-treatable stainless steel, nickel-free, magnetic, named for the martensitic microstructure of iron. CNC machined martensitic stainless steel parts with excellent surface finish. Compared with austenitic stainless steel, martensitic stainless steel has relatively lower corrosion resistance and is mainly used in environments with high hardness, high strength and wear resistance. It is used in the manufacture of turbine parts, valves, pumps, tableware, surgical instruments, Ideal material for bolts, screws, aircraft parts, guns. Common martensitic stainless steel grades include 410, 414, 416, 420, 431 and 440.
410.410 stainless steel, the most versatile steel in the 400 series, is a low carbon steel with increased corrosion resistance and can achieve impressive mechanical strength when hardened. 410 stainless steel is versatile and is a magnetic, low-cost, heat-treatable stainless steel. It is often used in environments with high hardness and does not require good corrosion resistance to manufacture fasteners, dental and surgical instruments, pipes, valves , nozzles and automotive parts ideal material.
Yield strength: ≥205
Tensile strength: ≥440
Elongation: ≥20
HB: ≤183
HRB: ≤88
HV: ≤200
414 stainless steel .In order to increase its CNC machining performance, 414 stainless steel is usually heated to 650-675 ° C, then soaked and cooled in the air. Containing 2% nickel, it has good corrosion resistance. 414 stainless steel is a good material for manufacturing bolts, nuts, valves, surgical knives, chemical equipment, and fasteners.
416. 416 stainless steel is one of the easiest stainless steels for CNC machining. It is especially suitable for manufacturing batches of CNC milling and CNC turning parts. It can be heat treated, has low carbon content, good corrosion resistance, and low friction coefficient. The strength and CNC machining performance of 416 stainless steel are better than 304 and 316, but the corrosion resistance is not as good as the latter two. 416 stainless steel has a high sulfur content and is not recommended for use in high temperature and sub-zero environments. It is a good choice for manufacturing bolts, nuts, studs, pumps, valves, gears, and washing machine components.
Tensile strength σb (MPa): quenched and tempered, ≥735
Conditional yield strength σ0.2 (MPa): quenched and tempered, ≥540
Elongation δ5 (%): Quenching and tempering, ≥12
Reduction of area ψ (%): Quenching and tempering, ≥40
Impact energy Akv (J): Quenching and tempering, ≥24
Hardness: annealed, ≤235HB; quenched and tempered, ≥217HB
420.420 stainless steel has a smooth surface, high plasticity, toughness and mechanical strength, and is resistant to corrosion by acids, alkaline gases, solutions and other media. It is an alloy steel that is not easy to rust. 420 stainless steel has certain wear resistance and corrosion resistance, high hardness, and its price is the lowest among all stainless steels. Due to the high carbon content of 420 stainless steel, it has high hardness after quenching and has good CNC machinability. It is suitable for precision machinery, transportation machinery, household appliances, instrumentation and other fields. It is an ideal material for manufacturing bearings, electrical appliances, steam turbine blades, springs, nozzles, valve seats, valve bearings, medical equipment and other parts.
Tensile strength σb (MPa): Quenching and tempering, ≥736;
Conditional yield strength σ0.2 (MPa): Quenching and tempering, ≥540;
Elongation δ5(%): Quenching and tempering, ≥12;
Reduction of area ψ(%): Quenching and tempering, ≥40;
Impact energy Akv (J): Quenching and tempering, ≥29.4;
Hardness: annealed, ≤235HB; quenched and tempered, ≥217HB.
431.431 stainless steel is 1.252%. It has excellent corrosion resistance and good CNC machining performance. Its corrosion resistance is better than that of 410 and 430 stainless steel. It is the alloy with the highest corrosion resistance among all hardenable martensitic stainless steels. 431 stainless steel has good resistance to oxidizing acids, most organic acids and aqueous solutions of organic salts. It is often used in the production of nitric acid, acetic acid, light industry, textile and other industries. It is used in the manufacture of valves, pumps, piston rods, and aircraft parts. Good material for components, propeller shafts, marine equipment.
Tensile strength σb (MPa): Quenching and tempering, ≥1080
Elongation δ5 (%): Quenching and tempering, ≥10
Impact energy Akv (J): Quenching and tempering, ≥39
Hardness: annealed, ≤285HB
440.440 stainless steel usually includes 440A, 440B, 440C, 440F (easy to process) and other models, which have good stability. Among them, 440C stainless steel is known for its high corrosion resistance, wear resistance, strength and hardness qualities among all stainless steel alloys, and is one of the hardest stainless steels. Typical applications include surgical instruments such as medical scalpels, scissors, nozzles, bearings, etc.
Hardness: annealed, ≤269HB;
Quenching and tempering, ≥58HRC
Mechanical behavior:
Internal stress (250 N/mm2)
Tensile strength (560 N/mm2)
EL(18%) HB(250
Ferrite stainless steel.
Ferrite stainless steels contain between 10.5% and 30% chromium, are nickel-free, are magnetic, and have higher corrosion resistance than martensite stainless steels but lower than austenitic stainless steels. Ferrite stainless steels can be cold worked but not heat treated, have average corrosion resistance and poor fabrication characteristics, excellent thermal conductivity. Because of the low carbon content, ferrite has excellent ductility. Nickel is not present in the content, so the cost is lower. Usually used in the automotive field, food equipment, petroleum industry, heat exchange, furnaces and other fields. Common ferrite grades include 405, 409, 430, 434, 436, 442 and 446.
405.405 stainless steel contains 12% to 30% chromium, its corrosion resistance, toughness and weldability increase with the increase of chromium content, and contains a certain amount of aluminum elements to avoid hardening, very suitable for welding, with high formability, good weldability Mechanical properties, which have excellent resistance to chloride corrosion, are ideal materials for manufacturing steam turbine impellers, heat exchange, bolts, nuts and other parts.
Tensile strength σb (MPa): quenched and tempered, ≥490
Conditional yield strength σ0.2 (MPa): quenched and tempered, ≥345
Elongation δ5 (%): quenched and tempered, ≥24
Reduction of area ψ (%): Quenching and tempering, ≥60
Hardness: annealed, ≤183HB
409.409 stainless steel contains 11% chromium, which is one of the cheapest stainless steels. It can only be used in critically corrosive environments. It is a good substitute for carbon steel. It has high temperature resistance and fatigue resistance. Ideal material for pipe manifolds, exhaust pipes, catalytic converters, mufflers and tailpipes.
Tensile strength σb (MPa): ≥380
Conditional yield strength 0.2 sigma (MPa): ≥170
Elongation (A/%): ≥20
430.430 stainless steel contains 16.00-18.00% chromium, commonly known as “stainless iron”, has good corrosion resistance, has better thermal conductivity than austenite, but has a smaller thermal expansion coefficient than austenite, and is resistant to corrosion. Thermal fatigue resistance, the added titanium element makes it have good stability, the mechanical properties of the weld are good, and it is easy to CNC process. 430 stainless steel is used in normal temperature or high temperature scenes such as architectural decoration, fuel burner parts, household appliances, home appliance parts, and fuel burner parts.
Melting point: 1427°C
Expansion coefficient: mm/°C (at 20-100°C)
Young’s modulus: kN/mm²
Rigid modulus: kN/mm²
Application Standard: n/a (UNS)
434.434 stainless steel contains 12% to 30% chromium and molybdenum. This determines that it has excellent corrosion resistance, toughness and weldability. In addition, its resistance to chloride corrosion is much better than other types of stainless steel. It is an ideal choice for manufacturing automotive decorations, fasteners and other parts.
Tensile strength σb (MPa): ≥450
Conditional yield strength σ0.2 (MPa): ≥240
Elongation δ: ≥22
Reduction of area ψ (%): ≥50
Hardness: ≤89HRB;
436.436 stainless steel is an improved version of 434 stainless steel, which reduces impurities such as carbon and nitrogen, and adds niobium and titanium to improve its corrosion resistance, heat resistance and formability, and is more durable than 304 stainless steel in harsh environments stress corrosion. Because 436 stainless steel does not contain nickel, it is less expensive than 304 stainless steel and is ideal for manufacturing parts such as coastal atmosphere decoration, sinks, gas burners, dishwashers, range hoods, steam irons, and pans.
Yield strength σ0.2(MPa)≥245
Tensile strength σb (MPa) ≥ 410
Elongation δ5(%)≥20
Hardness: HB≤217; HRB≤96; HV≤230
Specific heat capacity (0~100℃, KJ·kg-1K-1): 0.46
Longitudinal modulus of elasticity (20°C, KN/mm2): 200 Thermal conductivity (W•m-1•K-1): (1000) 25
Linear expansion coefficient (10-6•K-1): (200~1000°C) 10.4
Due to its high chromium content, 442.442 stainless steel has extremely high corrosion resistance, good heat resistance, and anti-fouling properties. It cannot be heat-treated and has a high degree of difficulty in processing. It is suitable for operations in high-temperature environments up to 650°C. 442 stainless steel is easy to crack and its weldability is low. It is an ideal material for manufacturing furnaces, die-casting machines, nitric acid storage tanks, blades, high-temperature bolts, turbine impellers, valves and aircraft parts.
The chromium content in 446.446 stainless steel is as high as 27%, which further improves its corrosion resistance and high temperature resistance. Among the 400 series stainless steels, 446 has the strongest oxidation resistance, and is usually used in the manufacture of equipment or parts that have high requirements for oxidation resistance and corrosion resistance at high temperatures, such as furnaces, boilers, thermocouple protection, melting It is an ideal material for glass welding pressure equipment.
Precipitation hardening (PH) grade. Precipitation-hardening stainless steels can be further strengthened and hardened by heat treatment, and their strength, hardness, and corrosion resistance are superior to martensitic chromium stainless steels, higher than austenitic stainless steels, and can maintain properties at high temperatures. Precipitation-hardening stainless steels contain a higher chromium content and are heat-treated to provide a tensile strength of 850MPa to 1700MPa and a yield strength of 520MPa to 1500MPa or higher—about three to four times stronger than austenitic stainless steels. Precipitation-hardening stainless steels are commonly used in oil and gas, nuclear energy, aerospace, military equipment, and other industries that require high strength, corrosion resistance, and general toughness requirements. Common precipitation hardening stainless steel grades include 17-7 PH, PH 15-7 Mo, 17-4 PH and 15-5 PH.
17-7PH. 17-7PH stainless steel is an unstable austenite structure after solid solution treatment, which has good ductility and processability. The structure transforms into low-carbon tempered martensite with better toughness. This state is the state of use of steel and has good mechanical properties at medium temperature. 17-7PH has better corrosion resistance than ordinary martensitic stainless steel, high strength and hardness, excellent fatigue performance, good formability, and minimal deformation during heat treatment. The alloy is especially suitable for aerospace applications and is an ideal material for manufacturing aircraft casings, structural parts, pressure vessels and components of missiles, jet engine parts, springs, diaphragms, bellows, antennas, fasteners, measuring instruments and other parts.
Tensile strength σb (MPa): solid solution, ≤1030; aging at 565°C, ≥1140; aging at 510°C, ≥1230
Conditional yield strength σ0.2 (MPa): solid solution, ≤380; aging at 565°C, ≥960; aging at 510°C, ≥1030
Elongation δ5 (%): solid solution, ≥20; aging at 565°C, ≥5; aging at 510°C, ≥4
Reduction of area ψ (%): aging at 565°C, ≥25; aging at 510°C, ≥10
Hardness: solid solution, ≤229HB; aging at 565°C, ≥363HB; aging at 510°C, ≥388HB
PH 15-7 molybdenum. The basic performance of PH 15-7 molybdenum stainless steel is similar to that of 17-7PH steel, and its comprehensive performance is better. In the austenitic state, it can withstand various cold forming and welding processes. The highest strength is obtained after heat treatment. It has excellent high temperature strength up to 550°C. It is used to manufacture thin-walled structural parts for aviation, various containers, pipes, springs, valve membranes, ship shafts, compressor discs, reactor parts and various chemical equipment and other structural parts.
Ultimate Tensile Strength: 150 KSI max (1035 MPa max)
Yield Strength (0.2% offset): 55 KSI max (380 MPa max)
Elongation: 20% min
Hardness: Rb 92 max
17-4. 17-4 stainless steel is a chromium-copper precipitation-hardening stainless steel with 17% chromium and 4% nickel added, 4% copper and 0.3% niobium, which has excellent oxidation resistance and corrosion resistance Corrosion resistance, high strength, high hardness, mechanical properties such as ductility and oxidation resistance can be optimized through heat treatment. This grade has better corrosion resistance and weldability than ordinary martensitic stainless steel. Similar to 18-8 stainless steel, the heat treatment process is simple, and the CNC machinability is good, but it is difficult to meet the cryogenic processing. After heat treatment, the mechanical properties of the part or prototype are more perfect, and can reach a compressive strength as high as 1100-1300mpa (160-190ksi). 17-4 stainless steel cannot be used at temperatures higher than 300°C (570F) or at very low temperatures. It has good corrosion resistance to the atmosphere and diluted acids or salts. Its corrosion resistance is the same as that of 304 and 430. It is manufactured Ideal material for valves, shafts, chemical fiber equipment, steam turbines and high-strength parts with certain corrosion resistance requirements.
Tensile strength σb (MPa): aged at 480°C, ≥1310; aged at 550°C, ≥1060; aged at 580°C, ≥1000; aged at 620°C, ≥930
Conditional yield strength σ0.2 (MPa): aged at 480°C, ≥1180; aged at 550°C, ≥1000; aged at 580°C, ≥865; aged at 620°C, ≥725
Elongation δ5 (%): aging at 480°C, ≥10; aging at 550°C, ≥12; aging at 580°C, ≥13; aging at 620°C, ≥16
Reduction of area ψ (%): aging at 480°C, ≥40; aging at 550°C, ≥45; aging at 580°C, ≥45; aging at 620°C, ≥50
Hardness: solid solution, ≤363HB and ≤38HRC; 480℃ aging, ≥375HB and ≥40HRC; 550℃ aging, ≥331HB and ≥35HRC; 580℃ aging, ≥302HB and ≥31HRC; 620℃ aging, ≥277HB and ≥28HRC
15-5. 15-5 stainless steel contains 15% chromium and 5% nickel. Its toughness and mechanical properties are higher than 17-4 stainless steel. It is famous for its ability to withstand corrosion resistance under severe conditions and is widely used in aviation Aerospace, chemical, paper and food processing and other fields.
Grade | Heat treatment | Tensile test | Hardness index | |||||
15-5PH | code | condition | tensile бb | yield б 0.2 | elongation δ 5 | area reduction Ψ | HBW Brookfield | HRC Rockwell
|
| Solid solution | 1020-1060℃ oil cooling | Mpa | Mpa | （%） | （%） | ≤363 | ≤38 |
| H900 | After solution treatment, air cooling at 470-490℃ | ≥1310 | ≥1180 | ≥10 | ≥35 | ≥375 | ≥40 |
| H1025 | After solution treatment, air cooling at 540-560℃ | ≥1070 | ≥1000 | ≥12 | ≥45 | ≥331 | ≥35 |
| H1075 | After solution treatment, air cooling at 570-590℃ | ≥1000 | ≥865 | ≥13 | ≥45 | ≥302 | ≥31 |
| H1150 | After solution treatment, air cooling at 610-630℃ | ≥930 | ≥725 | ≥16 | ≥50 | ≥277 | ≥28 |
| Annealing treatment | heat up to 850°C, keep warm for 2-3 hours (determine the holding time according to the effective thickness of the workpiece and other factors), keep cooling at 20°C/h, when it drops to 600°C, cool down to 300°C with the furnace, and then take out the workpiece Allow to cool in the air. | ||||||
Duplex (ferritic-austenitic) stainless steel
As the latest version of stainless steel, duplex stainless steel has the advantages of both austenitic and ferrite stainless steel. Compared with ferrite stainless steel, it has better plasticity and toughness, and maintains the thermal conductivity of ferrite stainless steel. Roughly twice as strong as austenite and ferrite, the alloy is known for its extreme strength, resistance to stress corrosion cracking, and is easy to heat treat but difficult to cold form. Duplex stainless steel is a class of steel that combines excellent corrosion resistance, high strength, and ease of CNC machining. It is an ideal choice for manufacturing chemical processing equipment, pressure vessels, and heat exchange parts. The cost of duplex stainless steel is relatively high.
UNS S32304 (23Cr-4Ni-0.1N). The alloy contains 23% chromium, 4% nickel, is a molybdenum-free duplex stainless steel, has similar corrosion resistance to 316L, and its mechanical properties are twice that of 304L/316L austenitic stainless steel, with high strength and toughness, stress resistance Corrosion cracking, high thermal conductivity, low thermal expansion, easy to manufacture, etc., but it is not recommended to be exposed to high temperature of 1058°C (570°F) for a long time. It is suitable for pulp and paper industry, caustic solution, organic acid, food industry , pressure vessels, heat exchange, seawater industry, rotors, impellers and shafts, piping systems, etc.
Properties | Metric | Imperial |
Tensile strength | ≥ 600 MPa | ≥ 87000 psi |
Yield strength (@strain 0.200 %) | ≥ 400 MPa | ≥ 58000 psi |
Modulus of elasticity | 200 GPa | 29000 ksi |
Shear modulus (@temperature 20°C/ 68°F) | 75.0 GPa | 10900 ksi |
Poisson’s ratio | 0.333 | 0.333 |
Elongation at break | ≥ 25 % | ≥ 25 % |
Hardness, Rockwell C | ≤ 20.0 | ≤ 20.0 |
Hardness, Brinell | 180 – 230 | 180 – 230 |
UNS S31803 (22Cr-5Ni-3Mo-0.15N).UNS S31803 is a duplex stainless steel with a ferrite-austenitic microstructure, and its corrosion resistance is in the AISI 316L and 6% Mo+N austenitic Between stainless steel and steel. UNS S31803 has excellent resistance to chloride pitting and crevice corrosion compared to 317L stainless steel. The alloy has excellent corrosion resistance to seawater and most concentrations of sulfuric acid. In addition, it also has the ability to resist sulfide stress corrosion cracking, and is often used in the manufacture of chemical industry, marine tools and equipment, seawater desalination plants, food industry, paper making, pulp industry, brewing industry, etc.
Properties | Metric | Imperial |
Tensile strength at break | 621 MPa | 90000 psi |
Yield strength (@strain 0.200 %) | 448 MPa | 65000 psi |
Elongation at break (in 50 mm) | 25.0 % | 25.0 % |
Hardness, Brinell | 293 | 293 |
Hardness, Rockwell c | 31.0 | 31.0 |
UNS32550 (25Cr-6Ni-3Mo-2Cu-0.2N). UNS32550 stainless steel generally contains 25% chromium and a certain amount of molybdenum, nitrogen, copper, and tungsten. Its corrosion resistance is higher than that of 22% Cr duplex stainless steel. It can maintain excellent corrosion resistance in the environment of various corrosive chemicals and chlorides including sulfuric acid, phosphoric acid and nitric acid, and also has excellent ductility, impact resistance and wear resistance, and is suitable for many industries demanding applications. Commonly used in oil and gas industry subsea equipment, chemical processing industry equipment, pollution control scrubbers, marine seals, pumps and valves, bolts and fasteners, food processing equipment, pulp and paper bleaching components, chemical tanks, heat exchange , radiator components and aircraft structures.
Tensile strength, Rm: 700 – 900 MPa
The yield point, Rp0,2: >500 MPa
Elongation, A:> 25%
Modulus of elasticity, E: 200 GPa
Hardness, HB: <270
Thermal capacity, cp: 500 J * kg-1 * K-1
Thermal conductivity, λ: 15 W * m-1 * K-1
Linear expansion coefficient, α: 13.0 * 10-6 K-1
Specific resistance, Ω: 0.8 mkOhm * m
UNS S32750 (25Cr-7Ni-3.7Mo-0.3N). UNS S32750 contains high molybdenum and nitrogen, suitable for harsh environment applications, has good corrosion resistance and mechanical comprehensive properties, comparable to super austenitic stainless steel. This grade is characterized by very good resistance to chloride corrosion, especially suitable for corrosive environments, and is widely used in heat exchange, oil and gas, hydropower, pressure vessels, pulp and paper, structures in offshore oil and gas exploration and production, and petrochemical and chemical processing parts and ship propellers, shafts, impellers, etc.
Yield strength Rp0.2,MPa Tensile strength Rm,MPa Elongation[%] Hardness[HB] Impact, Charpy-V, -46ºC[J] Pre
BAR ≥ 550 ≥ 750 ≥ 25 ≤ 310 ≥ 45 ≥ 40
PLATE CR (COIL) ≥ 550 750 – 1000 ≥ 25 ≤ 310 ≥ 45 ≥ 40
PLATE HR (COIL) ≥ 550 750 – 930 ≥ 25 ≤ 310 ≥ 45 ≥ 40
PLATE (QUARTO) ≥ 550 750 – 930 ≥ 25 ≤ 310 ≥ 45 ≥ 40
CNC machining of stainless steel parts or prototypes
There are many grades of stainless steel, as common as aluminum, which is very suitable for various CNC machining projects because of its good machinability and excellent uniformity, as well as excellent high ductility and formability, which can meet the processing requirements of any project. Stainless steel has proven to be one of the most popular metals for CNC machining projects, increasing the durability and service life of a part or prototype, especially when manufacturing parts for aerospace, automotive, medical, and consumer electronics. CNC machining stainless steel parts or prototypes is the best and fastest manufacturing process, where CNC milling stainless steel has a wider range of applications.
Application of CNC machining stainless steel parts. Stainless steel exists in various industries, not limited to include: automotive, aerospace, mechanical engineering, military equipment, pharmaceuticals, mining, construction, transportation, marine industry and other fields, is the manufacturing of marine parts, medical equipment, automotive parts, chemical containers, engines ideal material for parts.
Advantages of CNC stainless steel parts: very high tensile strength, excellent wear and corrosion resistance, good formability and weldability, hygienic with excellent cleanability, good performance at high/low temperature, High precision and high tolerances ensure high quality stainless steel parts, CNC machining stainless steel parts saves time and money, is fast, allows precise manufacture of ordered products to specified specifications, can process complex stainless steel parts for high-tech industries.
The challenge of CNC machining stainless steel. An important consideration in CNC machining stainless steel parts is to prevent machine vibration and tool chatter. “Chatter” is when the tool moves back and forth erratically while working, which can damage not only the part being machined, but also the tool. To prevent vibration and chatter, we ensure that all surface connections between the tool and tool holder are solid and that the workpiece is held securely in place while also keeping the cutting tool sharp.
Tips for CNC machining stainless steel
Compared with carbon steel, CNC machining of stainless steel is more challenging, and the higher the content of alloying elements, the more difficult it is for CNC machining. As mentioned earlier, when CNC machining stainless steel, the “chatter” of the rotating tool is the biggest difficulty factor. In order to obtain parts or prototypes with more precise tolerances, the skills of CNC machining for stainless steel are summarized.
Rigid machines and tools. As we all know, stainless steel is an extremely hard metal material. Therefore, it is important that the CNC machines and tools are of high quality, extremely strong and rigid. Also, choose better workholding fixtures, because less rigid fixtures can also cause “chatter” during rigorous CNC machining.
Choose the right tool. Be sure to keep your knives sharp, and choose a sharper one, such as a high-speed steel (HSS), such as tungsten or molybdenum. The use of these high speed steel tool materials depends on hardness, wear resistance and strength. Carbide is an excellent alternative to HSS when higher feeds or speeds are required, and using coated carbide tools will help improve wear and reduce breakage. A versatile tool for a variety of applications, the HEV-5 end mill also performs well above average in grooving and conventional roughing. Available in square, corner radius, and long reach styles, this well-rounded tool is an excellent choice for CNC machining stainless steel.
Select the appropriate coolant. Choosing a reputable coolant is very important as coolant affects tool wear, feed, speed, chip evacuation, surface finish, heat dissipation and corrosion resistance. Coolants and lubricants are especially important when CNC machining austenitic stainless steels, for example, because their low thermal conductivity can cause heat to build up at the cutting edge. Coolants can be emulsifiers, mineral oil, and cold air, and it is imperative that everyone in charge of the coolant is intimately familiar with each to ensure stainless steel parts are manufactured correctly.
Surface Treatment of CNC Stainless Steel Parts
CNC machined stainless steel parts typically have a glossier and darker finish than aluminum and can be media blasted, sanded, hand polished, and powder coated to achieve a variety of surface finishes.
After processing (standard): This standard stainless steel part maintains the state after processing, Ra can reach 125, or even better. Generally, CNC finishing stainless steel parts can further improve the surface finish of parts, which is a common surface treatment method for stainless steel parts.
Powder Coating: Powder coating creates an excellent and strong surface finish. Stainless steel is resistant to many chemicals, but some, such as chlorides, still pose challenges. In these cases, powder coatings can be used to improve their anti-corrosion properties.
Sandblasting: This process produces a smooth and uniform matte finish by lightly sandblasting the surface. This surface finish is often used for visual enhancement purposes.
CNC machining stainless steel cost saving skills
Choose the right grade of stainless steel: Not all stainless steels are cheap, make sure the material you choose is suitable for the application. Stainless steel is often ideal in corrosive environments, but not all stainless steels resist the same chemicals. For more information, please contact DDPROTOTYPE.
Machinability: When selecting mildly corrosive applications, stainless steel grades that are easier to CNC machine need to be considered.
Find the ideal stainless steel alloy for every project
There are many different grades of stainless steel, and if you are looking for an extra-strength stainless steel with average corrosion resistance, martensitic stainless steel will be a good choice. Likewise, stainless steels with high strength, high pitting and corrosion resistance are required, and duplex stainless steels are ideal. Determining the right material for a particular part or prototype is a critical part of the product design and production process, and designers should thoroughly review material options. That said, with the help of an experienced manufacturing partner like DDPROTOTYPE, you can easily find the right material for your CNC machining project’s unique requirements. DDPROTOTYPE provides efficient on-demand manufacturing services. Working side by side with customers at every stage of design and production, our experienced team of engineers, designers, consultants and technical experts ensure parts are optimized for manufacturability and ensure the most suitable manufacturing method or combination of methods. DPROTOTYPE helps you manufacture quality parts at competitive prices and fast turnaround times. Contact us today to learn more.
