Stainless steel is an alloy material with iron as its base and a chromium content of not less than 10.5%. With its excellent corrosion resistance, toughness and machinability, it is widely used in the field of CNC machining. Its application scenarios cover many industries such as medical, food, marine, aerospace, industrial automation, and home appliance decoration, ranging from small precision parts and shafts to large pipe flanges and equipment housings.
Highly corrosion-resistant:
Rust-proof, acid and alkali resistant, and resistant to water vapor and salt spray, suitable for harsh environments such as humid, chemical, marine, food, and medical applications.
Good strength and toughness:
High tensile strength and hardness, impact-resistant, and deformation-resistant, suitable for load-bearing structural components.
High-temperature and oxidation-resistant:
Does not easily oxidize or soften at high temperatures, suitable for parts operating in high-temperature conditions.
Excellent dimensional stability:
Minimal deformation after heat treatment, maintaining high precision for a long time after finishing.
Optional non-magnetic/weakly magnetic:
Austenitic stainless steel is non-magnetic, meeting the anti-magnetic requirements of electronics, sensors, etc.
Features: Contains 18%-20% chromium, 8%-12% nickel, ≤0.08% carbon, and no molybdenum. It is a basic grade of austenitic stainless steel with a balanced composition and excellent cost-effectiveness.
Parameters: Tensile strength ≥515MPa, yield strength ≥205MPa, hardness ≤HB201, elongation ≥40%, non-magnetic, resistant to atmospheric, fresh water, and neutral solution corrosion, with moderate corrosion resistance.
Characteristics: Prone to work hardening (surface hardness can increase by 20%-30% after cutting), prone to tool sticking and built-up edge formation during cutting, producing long and tough chips, with moderate chip removal difficulty; however, the process is mature, compatible with conventional CNC tools and parameters, requiring no special equipment, making it the first choice for entry-level CNC stainless steel machining.
Applications: Everyday industrial structural parts, mechanical equipment housings, precision brackets, shafts in non-corrosive environments, household appliance parts, general hardware, etc. It is the stainless steel grade with the highest order volume in CNC machining.
Features: The carbon content is reduced compared to 304 (C≤0.03%), while the chromium and nickel content remains the same. It is molybdenum-free, and the low-carbon design helps prevent intergranular corrosion after welding.
Parameters: Tensile strength ≥485MPa, yield strength ≥170MPa, hardness ≤HB201, elongation ≥40%, non-magnetic, corrosion resistance is basically the same as 304, and weldability is superior to 304.
Characteristics: Machining performance is similar to 304, and it also suffers from work hardening and tool sticking issues. However, due to the lower carbon content, the material has slightly higher toughness, making chips less prone to breakage. More attention needs to be paid to the design of chip breakers. Machining difficulty is comparable to 304, requiring no adjustment to the core process.
Applications: Structural components requiring welding (such as pipes, flanges, equipment frames), food processing equipment (such as conveying pipes and containers), parts in low-temperature environments, and CNC machined parts requiring post-weld corrosion resistance.
Features: Contains 16%-18% chromium, 10%-14% nickel, 2%-3% molybdenum, and ≤0.08% carbon. Molybdenum is its core advantage, significantly improving corrosion resistance.
Parameters: Tensile strength ≥515MPa, yield strength ≥205MPa, hardness ≤HB217, elongation ≥40%, non-magnetic, resistant to acids, alkalis, seawater, and chloride ion corrosion; corrosion resistance is far superior to 304, and high-temperature strength is also higher.
Characteristics: Machining difficulty is higher than 304; the material has higher hardness and toughness, more pronounced work hardening, and more prominent issues of tool sticking and built-up edge; cutting force is 15%-20% greater than 304, requiring higher tool wear resistance; coated carbide or cermet tools are needed, and cutting parameters require appropriately reduced depth of cut and increased spindle speed.
Applications: CNC machined parts in corrosive environments, such as marine engineering equipment (flanges, shafts), chemical equipment (valves, pipelines), ship fittings, and precision parts in moderately corrosive environments.
Features: Carbon content ≤0.03%, chromium, nickel, and molybdenum content consistent with 316 stainless steel. The low-carbon design balances weldability and resistance to intergranular corrosion, making it the preferred grade for high corrosion resistance applications.
Parameters: Tensile strength ≥485MPa, yield strength ≥170MPa, hardness ≤HB217, elongation ≥40%, non-magnetic, corrosion resistance slightly better than 316, no intergranular corrosion after welding, and better toughness than 316.
Characteristics: Machining difficulty similar to 316, but due to the lower carbon content, the material is tougher, resulting in tougher chips and slightly higher chip breaking difficulty. Optimized chip breaker design and enhanced cooling and lubrication are required to prevent tool sticking and workpiece surface scratches. Tool wear is approximately 30% higher than 304 stainless steel.
Applications: High-end corrosion-resistant CNC machined parts, such as medical equipment (surgical instruments, implants, equipment housings), food-grade precision parts (sanitary valves, containers), core components of marine engineering, chemical corrosion-resistant equipment, and high-end electronic equipment housings.
Features: Based on 304 stainless steel, it adds free-machining elements such as sulfur (S) or selenium (Se). Carbon content ≤0.15%, chromium 17%-19%, nickel 8%-10%. These free-machining elements reduce material toughness and facilitate chip breaking.
Parameters: Tensile strength ≥485MPa, yield strength ≥170MPa, hardness ≤HB201, elongation ≥35%, non-magnetic, corrosion resistance slightly lower than 304 (free-machining elements slightly reduce corrosion resistance), but significantly improved machinability.
Characteristics: It is the most machinable grade of austenitic stainless steel, with low cutting force, no significant work hardening, less prone to tool sticking and built-up edge, short and fine chips, smooth chip removal, compatible with conventional tools, and machining efficiency 20%-30% higher than 304, suitable for batch precision machining.
Applications: Precision small parts, shafts, screws, nuts, gears, instrument accessories, etc. produced by CNC turning and milling. It is especially suitable for small machined parts with complex shapes and high precision requirements. It is not suitable for strongly corrosive environments.
Features: Contains 11.5%-13.5% chromium, ≤0.15% carbon, no nickel or molybdenum. Its simple composition and low cost make it the most basic grade of martensitic stainless steel.
Parameters: In the annealed state, hardness ≤HB201, tensile strength ≥480MPa, yield strength ≥275MPa; after quenching and tempering, hardness can reach HRC40-45, with significantly improved strength but decreased toughness.
Characteristics: Machining difficulty is moderate in the annealed state, with slightly lower cutting forces than 304, and less prone to tool sticking, but slight work hardening exists; after quenching, hardness increases significantly, machining difficulty increases dramatically, and tool breakage and wear are more likely. Carbide tools should be used, and cutting parameters should be reduced.
Applications: Cost-sensitive, non-corrosive applications requiring a certain level of hardness, such as valves, faucet valve cores, decorative parts, simple structural components, and low-speed rotating shafts. CNC machining is mostly performed in the annealed state, followed by quenching as needed.
Features: Contains 12%-14% chromium, 0.16%-0.25% carbon, nickel-free, molybdenum-free, and has a higher carbon content than 410. Higher hardness can be achieved through quenching.
Parameters: In the annealed state, hardness ≤ HB223, tensile strength ≥ 520 MPa, yield strength ≥ 305 MPa; after quenching and tempering, hardness can reach HRC45-52, with hardness and wear resistance far superior to 410, and moderate toughness.
Characteristics: Machining difficulty is higher than 410. There is still some work hardening in the annealed state, and burrs are easily generated during cutting, requiring sharp tools. Machining after quenching is extremely difficult, and tool wear is rapid. A typical process is "CNC rough machining → quenching and tempering → fine grinding" to reduce post-quenching machining.
Applications: CNC machined parts requiring high hardness and wear resistance, such as cutting tools (end mills, drill bit holders), mold components, high-precision shafts, valve cores, wear-resistant bushings, etc.
Features: Contains 16%-18% chromium, 0.95%-1.20% carbon, and 0.40%-0.80% molybdenum. Both carbon and chromium content are higher than 420, making it the hardest commonly used grade of martensitic stainless steel.
Parameters: In the annealed state, hardness ≤ HB269, tensile strength ≥ 735 MPa, yield strength ≥ 510 MPa; after quenching and tempering, hardness can reach HRC58-62. It has excellent hardness and wear resistance, and corrosion resistance superior to 410 and 420, but poor toughness.
Characteristics: Extremely difficult to machine. In the annealed state, cutting forces are high, work hardening is severe, and tool breakage and sticking are common. Extremely high requirements are placed on tool rigidity and wear resistance; CBN or diamond-coated tools are required. After quenching, CNC cutting is basically impossible; only fine grinding or polishing is possible.
Applications: Precision parts with high hardness and high wear resistance requirements, such as bearings, balls, high-end cutting tools, mold inserts, and small precision parts that are corrosion-resistant and wear-resistant. CNC machining is only used for roughing and semi-finishing in the annealed state.
Features: Contains 16%-18% chromium, ≤0.12% carbon, nickel-free, molybdenum-free, low cost, and is the most commonly used grade of ferritic stainless steel.
Parameters: Tensile strength ≥450MPa, yield strength ≥205MPa, hardness ≤HB201, elongation ≥22%, magnetic, resistant to atmospheric and freshwater corrosion, but slightly less corrosion resistant than austenitic stainless steel.
Characteristics: Moderate machining difficulty, low toughness, prone to producing brittle chips during cutting, easily chipped, requiring sharp tools, reduced cutting speed, increased feed rate, and avoidance of impact; surface scratches are easily formed after machining, requiring optimization of toolpath and cooling.
Applications: Decorative panels for home appliances, kitchen utensils, outdoor decorative parts, simple structural parts in non-corrosive environments. CNC machining is mainly for planar and simple contours, with significant cost advantages for batch processing.
Features: Contains 15%-17.5% chromium, 3%-5% nickel, 3%-5% copper, 0.15%-0.45% niobium, and ≤0.07% carbon. Strengthening is achieved through the precipitation of copper and niobium, eliminating the need for high-temperature quenching.
Parameters: After aging treatment (holding at 480-620℃), tensile strength ≥1030MPa, yield strength ≥860MPa, hardness up to HRC38-45, corrosion resistance close to 304, combining high strength and good toughness.
Characteristics: High machining difficulty, high material strength, significant work hardening effect, high cutting force, prone to tool sticking and tool wear; requires the use of high-strength cemented carbide or CBN tools, employing high-speed, shallow-depth-of-cut, multi-pass machining processes, enhanced cooling and lubrication, and prevention of workpiece deformation.
Applications: CNC machined parts with high-end precision and high strength requirements, such as aerospace structural parts, precision components of high-end equipment, core parts of medical devices, high-pressure valves, precision molds, etc., which need to be aged after machining to improve strength.
| Grade | Category | Composition | Performance | Machining | Applicables |
|---|---|---|---|---|---|
| 304 / SUS304 | Austenitic | Cr 18%-20%, Ni 8%-12%, C ≤0.08%, Mo-free, high cost-performance ratio | Tensile strength ≥515MPa, hardness ≤HB201, non-magnetic, moderate corrosion resistance | Easy to work harden, prone to sticking to tools, moderate chip removal; mature technology, ideal for beginners | Most commonly used in conventional industrial structural parts, equipment housings, and appliance parts; highest order volume. |
| 304L / SUS304L | Austenitic | Low-carbon version of 304 (C≤0.03%), Mo-free, avoids intergranular corrosion during welding | Tensile strength ≥485MPa, hardness ≤HB201, non-magnetic, weldability superior to 304 | Similar to 304, slightly higher toughness, requires careful chip breaker design | Welded structural components, food processing equipment, low-temperature environment parts |
| 316 / SUS316 | Austenitic | Cr 16%-18%, Ni 10%-14%, Mo 2%-3%, C ≤0.08%, excellent corrosion resistance | Tensile strength ≥515MPa, hardness ≤HB217, non-magnetic, resistant to acids, alkalis, and seawater | High machining difficulty, high cutting force, requires coated tools, reduced depth of cut and increased speed | Parts for corrosive environments such as marine and chemical industries, ship fittings |
| 316L / SUS316L | Austenitic | Low-carbon version of 316 (C≤0.03%), balancing weldability and resistance to intergranular corrosion | Tensile strength ≥485MPa, hardness ≤HB217, non-magnetic, slightly better corrosion resistance than 316 | Similar to 316, but with higher toughness; requires optimization of chip breaking and cooling. | Applications include medical and food-grade precision parts, marine core components, and chemical corrosion-resistant equipment. |
| 303 / SUS303 | Austenitic (Free Machining) | Contains S/Se, C≤0.15%, Cr17%-19%, Ni8%-10% | Tensile strength ≥485MPa, hardness ≤HB201, non-magnetic, corrosion resistance slightly inferior to 304 | Optimal machinability, smooth chip removal, efficiency 20%-30% higher than 304 | Suitable for batch production of small precision parts, shafts, and gears; not suitable for highly corrosive environments. |
| 410 / SUS410 | Martensitic | Cr 11.5%-13.5%, C ≤0.15%, no Ni or Mo, simple composition, low cost | Annealed hardness ≤HB201, after quenching HRC40-45, magnetic, medium strength | Easy to machine after annealing, significantly more difficult after quenching, requires carbide tools | Suitable for cost-sensitive applications, valves, decorative parts, low-speed shafts |
| 420 / SUS420 | Martensitic | Cr 12%-14%, C 0.16%-0.25%, no Ni or Mo, carbon content higher than 410 | Annealed hardness ≤ HB223, quenched hardness HRC45-52, magnetic, excellent wear resistance | Prone to burring after annealing, can only be fine ground after quenching, requires rough machining followed by quenching | Applications: Cutting tools, mold parts, high-precision wear-resistant shafts, valve cores |
| 440C / SUS440C | Martensitic | Cr 16%-18%, C 0.95%-1.20%, Mo 0.40%-0.80%, highest hardness | Annealed hardness ≤HB269, quenched hardness HRC58-62, magnetic, excellent wear resistance | Extremely difficult to machine; annealing requires CBN tools; cannot be cut after quenching | Bearings, high-end cutting tools, mold inserts; CNC machining is only used for roughing after annealing. |
| 430 / SUS430 | Ferritic | Cr 16%-18%, C ≤0.12%, Ni and Mo free, low cost | Tensile strength ≥450MPa, hardness ≤HB201, magnetic, corrosion resistance slightly inferior to austenitic | Easily chipped during machining, requires sharp tools and optimized toolpaths; surface easily scratched | Suitable for simple machining of appliance decorative panels, kitchen utensils, outdoor decorative parts, etc. |
| 17-4PH / SUS630 | Precipitation hardening type | Cr 15%-17.5%, Ni 3%-5%, Cu 3%-5%, C ≤0.07%, age-hardening | Tensile strength after aging ≥1030MPa, hardness HRC38-45, corrosion resistance close to 304 | High machining difficulty, high cutting force, requires high-strength tools and multiple passes | Aerospace structural components, medical core parts, high-end precision molds |
A: 303 stainless steel (free-machining austenitic) is the preferred choice. It contains free-machining elements, resulting in smooth chip removal, high machining efficiency, and low tool wear, making it suitable for mass production of precision small parts. Its only drawback is slightly inferior corrosion resistance compared to 304 and 316.
A: Yes, there is a difference: 316 contains molybdenum, and its corrosion resistance (especially against seawater, acids, and alkalis) is far superior to 304. However, it is more difficult to machine, involves greater cutting forces, and has about 30% higher tool wear than 304. For general applications, choose 304; for corrosive environments (marine, chemical), choose 316/316L.
A: Annealing is required first to eliminate internal stress and reduce hardness. After CNC rough machining, quenching and tempering are performed to increase hardness. After quenching, the hardness is extremely high, making further cutting impossible; only fine grinding is possible. CBN or diamond-coated tools must be used during machining.
A: The purpose is to improve corrosion resistance, prevent oxidation and rust, and optimize the appearance. Common methods include polishing, wire drawing, and passivation; choose according to your needs.
A: Use appropriate fixtures and place soft shims during clamping; control the clamping force to avoid deformation due to excessive tightness or vibration due to excessive looseness; clean chips promptly during machining to prevent surface scratches.
A: Use stainless steel-specific cutting fluid, preferably emulsion or semi-synthetic cutting fluid. Its core functions are cooling, lubrication, and chip removal, reducing tool sticking and tool wear. Ordinary cutting fluids must not be used, as they easily lead to workpiece rust and tool damage.
