Common CNC machining stainless steel

Posted on :On May 31th,2024 By GREFEE

Stainless steel has a variety of characteristics in the environment over a wide temperature range, such as Stainless steel has characteristics such as corrosion resistance, scaling resistance, acid resistance, impact resistance, and toughness.

Under different conditions, it can provide various grades and surface smoothness to make the components be the best option for many applications. The chromium in steel can form a rough, invisble, and corrosion resistant chromim oxide film on the surface of the steel.

If the material is chemically or mechanically damaged, the film can repair itself (with O2). Its 100% recycled advantage provides a new method to environmental friendly material.

Therefore, stainless steel has been widely applied into heavy industry, light industry, daily necessities industry, and building decoration industry.

Austenitic Stainless Steel

The most common austenitic alloy is iron chromium nickel steel, referred to as the 300 series, including chromium (about 18% -30%) and nickel (about 6% -20%). Due to its high chromium and nickel content, austenitic stainless steel is the most corrosion-resistant among stainless steel groups.

Meanwhile, it has outstanding mechanical performance, and still maintain high toughness under high temperature with good formability. Also, it allows cold processing but no heat processing, which is commonly used for manufacturing shafts, valves, bolts, bushings, nuts, aircraft accessories, brewing equipment, and low-temperature containers.

“L” level is used to improve the corrosion resistance after welding. The letter “L” after the stainless steel grade indicates low-carbon (such as 304L). The carbon content should be below 0.03% to prevent carbide precipitation. Because the temperature encountered during the welding process may cause carbon deposition), the “L” grade is normally used. Generally speaking, stainless steel rolling mills can provide dual certification for these stainless steel grades, such as 304/304L or 316/316L.

The minimum carbon content of the stainless steel “H” grades is 0.04%, and the maximum is 0.10%.  High content of carbon is helpful in maintaining strength under extreme whether conditions. The letter “H” after the stainless steel grade indicates these grades. This grade should be used when encountering extreme temperature conditions.

304

A type of commonly used (austenitic) stainless steel grade with 18% chromium, 8% nickel basic composition, maximum carbon content is 0.07%, also being called by A2 stainless steel.

304 stainless steels have great corrosion resistance and is easy to process, which has excellent formability after CNC machining. he 304/304L model has excellent formability and excellent welding performance, making it an ideal choice for various household and commercial applications.

It is very suitable for manufacturing processing equipment used in the chemical (mild chemistry), food/dairy, and beverage industries, for its high chromium and nickel content.

309

The higher chromium and nickel content enhances corrosion resistance and high-temperature fouling resistance, making it suitable for high-temperature applications up to 1900F with strong corrosion resistance. 309 aollows cold processing but not heat processing. It is weldable and relatively easy to process.

This alloy is commonly used for furnace components, thermocouple sleeves, boiler pipe hangers in power plants, generators, paper mills, refineries, brazing fixtures, bolts, refractory brackets, and furnace linings.

PA66 is widely used in the automotive industry, instrument casings, and other products that require impact resistance and high strength.

316

316 is the second most widley used steel after 304 with 16%~18% chromium, 11%~14% nickle and minimum 2% molybdenum. The combination of these elements can enhance corrosion resistance, especially molybdenum is helpful to control corrosion pitting, This level can withstand stains at temperatures up to 1600F.

It is used in chemical processing, pulp and paper industry, food and beverage, surgical equipment, processing and distribution, and corrosive environments. It is also used in the marine industry as it is more resistant to chloride corrosion than 304. SS316 is commonly used in nuclear fuel recovery equipment. 18/10 grade stainless steel typically meets this application level.

317

If the content of molybdenum is higher than that of 316, then molybdenum content of this grade should be higher than 3%. This alloy can be welded and easy to process, allowing cold and heat processing. However, it can not be heat treated.

It is often applied into high corrosion environment and air pollution control scrubber systems. It is also the ideal material for manufacturing generators, absorption towers, boilers, condenser tubes, heat exchanger tubes, pressure vessels, chimney fittings, and valves.

The 317L model limits the maximum carbon content to 0.030%. The silicon content can reach up to 0.75% to increase corrosion resistance.

321

The titanium content should be minimum five times of the carbon content. This is to reduce or eliminate the chromium carbide precipitation caused by welding or exposure to high temperatures.

It is applicable to environment with temperature over 1500 Fahrenheit degree, which is prone to creeping and cracks. It has high resistance to elongation and vibration fatigue. Mainly used for manufacturing aircraft exhaust pipes and manifolds, jet engine parts, boiler casings, heaters, etc.

318

The combination of niobium and tantalum content with carbon helps to prevent chromium carbide precipitation during the welding process. It shows outstanding corrosion resistance when exposed to temperatures between 800-1500 ° F.

Martensitic stainless steel

Martensitic stainless steel grades is a group of stainless steel alloy with corrosion resistance and hardenability (using heat treatment). The martensitic grade is pure chromium steel without nickel.

They have magnetism, can be hardened by heat treatment, and are not as corrosion-resistant as austenitic stainless steel. Martensite grades are mainly used in areas where hardness, strength, and wear resistance are required.

It is commonly used to manufacture pump shafts, bolts and screws, valves, liners, rivets, coal cans, cutlery, jet engine parts, aircraft parts, mining equipment, rifle barrels, and fire extinguisher inserts. Common levels include 410, 414, 416, 420, 431, and 440.

410

The basic martensitic grade has the lowest alloy content among the three basic stainless steels (304, 430, and 410). Low cost, universal, heat-treatable stainless steel. Stainless steel 410 contains at least 1.5% chromium, making it particularly resistant to the erosion of many chemicals and acids, which has been widely used in areas with less severe corrosion (air, water, certain chemicals, food acids).

It has been used in components that require a combination of strength and corrosion resistance, such as fasteners.

Compared to 410, the carbon content of 410s is lower and more easy to weld, but difficult to be hardened. 410s is a type of universal corrosion-resistant and heat resistant chromium steel, recommended for corrosion-resistant appliactions.

414

2 percent of nickel improves the corrosion resistance. The applications include bolts and nuts, pressure plates, valve components, surgical instruments, and refineries. Typical applications include springs and tableware.

416

The phosphorus and sulfur are special variants of 410, which can improve cutting performance and allows heat treatment. Typical applications include threaded machine parts.

The carbon improves the mechanical properties, which makes it can be heat treated to a Brinell hardness of approximately 500. Also, it has maximum corrosion resistance after hardening.

It is suitable for various precision machinery, bearings, appliances, equipment, measuring tools, instruments, transportation vehicles, household appliances, etc. Mainly used for manufacturing parts that are resistant to air, water vapor, water, and oxidative acid corrosion.

The nickel content is 1.252%, and the chromium content increases leads to high corrosion resistance and mechanical properties, and the corrosion resistance is better than 410 and 430 steel.

It has the highest corrosion resistance in hardenable martensitic stainless steel. It through hot and cold treatment, its hardness level can reach to 40HRC. Typical applications include valves, pumps, aircraft components, propeller shafts, and ship equipment.

440

440 stainless steel B includes three different grades: 440A, 440B, 440C, and 440F (easier for machine types). More chromium and carbon enhances the hardness and corrosion resistance of this grade. The hardness can reach to 58HRC which is one of the hardest stainless steel. Typical applications include scalpel, scissors, nozzles, and bearings.

Ferritic stainless steel

Same as martensitic steel, ferritic stainless steel is a pure chromium steel without nickel, which has corrosion resistance and oxidation resistance. Meanwhile, it has stress resistance and cracking resistance. These steels have magnetism, but cannot be hardened through heat treatment, only cold processed.

Also, it can be softened through annealing. Although they have higher corrosion resistance than martensitic grades, but are not as good as austenitic grades. They are commonly used for decorative strips, sinks, and certain automotive applications, such as exhaust systems. Common levels include 405, 409, 430, 434, 436, 442, and 446.

405

Contains 12% chromium and aluminum. After cooling from high temperature, this chemical composition helps prevent hardening, which is suitable for welding applications. Advanced shape, easy to process. Typical applications include heat exchangers, turbine materials, hardened parts, etc.

409

The content of chromium is 11%, which is the lowest in all stainless steels. This is the least amount of passivation surface facial mask that forms the corrosion resistance of stainless steel. It is one of the cheapest stainless steel grades.

This type can only be used for internal or external parts in non-severely corrosive environments. Typical applications include silencers.

409 alloy has better corrosion resistance than carbon steel and can replacement of carbon steel in less corrosive environments. Due to its high corrosion resistance and high-temperature oxidation resistance, it has advantages.

403

430 stainless steel is a general steel with great corrosion resistance, better thermal conductivity than austenite, smaller coefficient of thermal expansion than austenite, resistance to thermal fatigue, added stable element titanium, which has excellent mechanical properties in welds. 430 stainless steel is used for building decoration, fuel burner parts, appliances, and appliance parts.

430F is a type of steel with better cutting performance to 430 steel. Mainly used for automatic lathes, bolts, and nuts. Adding Ti or Nb to 430 for 430LX to reduce C content and improve treatment and welding performance. Mainly used in hot water tanks, water supply systems, bathroom appliances, durable household appliances, bicycle flywheels, etc.

413

It contains 12% to 30% chromium and molybdenum is added to improve corrosion resistance. Its corrosion resistance, toughness, and weldability increase with the increase of chromium content, and its ability to resist chloride stress corrosion is superior to other types of stainless steel. 434 is an improved grade of 430 steel, which is more salt resistant than 430 steel and is commonly used in automotive decorative parts and fasteners.

436

436 is improved steel on the base of 434. This grade has niobium that enhances corrosion resistance and heat resistance, which is applied into deep drawing parts, gas burners, dishwashers, kitchen ventilator, steam irons, frying pans, etc.

442

Due to its high chromium content, excellent heat resistance and scale resistance, it has excellent corrosion resistance. However, due to the inability to heat treat, it is difficult to process. Applications include furnaces and combustion components, zinc die-casting machines, nitrogen fixation components, and nitric acid storage tanks.

446

High chromium content (27%) can further improve corrosion resistance and oxidation resistance at high temperatures. The combustion chamber is resistant to high temperature and corrosion, and has no peeling oxide skin below 1082 ℃.

Precipitation Hardening (PH) Stainless Steel

Like martensite, precipitation hardened stainless steel can also be strengthened and hardened through heat treatment. Its strength, hardness, and corrosion resistance are superior to martensitic chromium stainless steel. It is usually stronger and at higher temperatures than austenitic stainless steel.

It can retain most of its power. Commonly referred to as PH stainless steel, both contain high chromium content and are used in the manufacturing of military equipment and aerospace structural components. Common grades include 17-7PH, PH15-7Mo, 17-4PH, and 15-5PH.

17-7

After solid solution treatment, 17-7PH stainless steel forms an unstable austenite structure with good ductility and processability. After quenching and tempering, the composition of austenite precipitates and carbides changes.

After martensitic transformation treatment, most of the microstructure transforms into a more ductile low-carbon tempered martensite. This state is the usage state of steel, which has good mechanical properties at moderate temperatures. The corrosion resistance of 17-7PH is better than that of ordinary martensitic stainless steel.

PH15-7 molybdenum

This is a steel grade developed using 2% molybdenum instead of 2% chromium in 0Cr17Ni7Al steel of which the basic performance is similar to 17-7PH steel, but has better overall performance. In its austenitic state, it can withstand various cold forming and welding processes.

After heat treatment, the highest strength is achieved. Excellent high-temperature strength below 550 ℃ makes it often used for manufacturing aircraft thin-walled structural components, various containers, pipelines, springs, valve membranes, ship shafts, compressor discs, reactor parts, various chemical equipment and other structural components.

17-4

Alloy 17-4 is a chromium copper precipitation hardened stainless steel with excellent oxidation resistance and corrosion resistance. Heat treatment can optimize mechanical properties such as strength, ductility, and oxidation resistance.

This brand can be heat trated  at various temperatures. Generate a wide range of finished product characteristics. This level should not be used at temperatures above 300 ° C or very low.

15-5

This is a variant of the older 17-4 chromium nickel copper precipitation hardened martensitic stainless steel. The toughness of 15-5 alloy is higher than that of 17-4. Compared to other similar martensitic stainless steels, it is used for applications that require better corrosion resistance and lateral performance.

Dual phase (ferrite austenite) grade

Dual phase stainless steel is a modern stainless steel that combines austenite and ferrite materials, which is famous for the extremely high strength and resistance to stress corrosion cracking. The strength of these grades is approximately twice that of austenitic and ferritic grades.

It has better toughness and ductility than ferritic steel, but lower the level of austenitic steel. Heat treatment is easy, but cold forming is difficult. It is usually used to manufacture chemical processing equipment, pressure vessels, and heat exchanger components.

Duplex stainless steel is divided into four categories

Type I is a low alloy steel representing the UNSS32304 (23Cr-4Ni-0.1N) grade, which does not contain molybdenum and has a PREN value of 24-25. It can replace AISI304 or 316 in terms of stress corrosion resistance.

Type II is medium alloy type, represented by the grade UNSS31803 (22Cr-5Ni-3Mo-0.15N), with a PREN value of 32-33, and corrosion resistance between AISI316L and 6 percent of Mo+N austenitic stainless steel.

Type III is high alloy type with 25 percent of Cr, as well as molybdenum and nitrogen, and some also contain copper and tungsten. The standard grade is UNSS32550 (25Cr-6Ni-3Mo-2Cu-0.2N), with a PREN value of 38-39. The corrosion resistance of this type of steel is higher than that of 22 percent Cr duplex stainless steel.

Type IV is the super duplex stainless steel with high molybdenum and high nitrogen content, of which standard grade UNSS32750 (25Cr-7Ni-3.7Mo-0.3N). Some also contain tungsten and copper. Under harsh moderate conditions, the PREN value exceeds 40, exhibiting excellent corrosion resistance and overall mechanical properties comparable to super austenitic stainless steel.

Stainless steel parts have outstanding corrosion resistance even when buried underground due to the thin and dense chromium rich oxide film on the surface of stainless steel. They have excellent corrosion resistance in all water quality, including soft water. It can be safely used for a long time at temperatures ranging from -270 ℃ to 400 ℃, with no harmful substances precipitated at high or low temperatures, and the material properties are very stable.

The material is safe, non-toxic, non-corrosive, non-lixiviating, odorless, and non-muddy, and has no secondary pollution to water quality. It is effective in maintaining pure and hygienic water quality, and ensure adequate hygiene and safety.

It has the characteristics of corrosion resistance, increased strength, less deformation and fracture of steel, environmental protection, less rusting, good ductility and toughness. Suitable for harsh environments (indoor and outdoor environments such as humidity, acidity, and alkalinity).

For more details, please contact GREFEE for the suitable steel type for you.

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