Type 304 stainless steel is one of the most ubiquitous steel grades on the market. Renowned for its excellent corrosion resistance, grade 304 serves a multitude of purposes, from household to industrial applications. Although it may be replaced with 316 stainless steel in extremely corrosive environments–especially when severe pitting and crevice corrosion are an issue–304 stainless remains a go-to solution for engineers and manufacturers worldwide.
Specifying 304 Stainless steel
304 is the SAE International grading for the composition initially branded as Staybrite 18/8; those figures derive from the ratio of chromium and nickel in the alloy. That terminology has persisted, so some still refer to 304 stainless steel as 18/8 steel. However, the content of both chromium and nickel can vary upwards by about 2%. These same general principles apply to other global certifications, so though there’s some variation in vernacular, the different certifications agree on the chemical composition. Hence the 304 stainless steel is equivalent to EN 1.4301 and SU304.
Chemical Composition
| UNS No | S30400 |
| EN | 1.4301 |
| AISI | 304 |
| Carbon (C) | 0.07 |
| Silicon (Si) | 0.75 |
| Manganese (Mn) | 2.00 |
| Phosphorus (P) | 0.045 |
| Sulphur (S) | 0.030 |
| Chromium (Cr) | 17.50 – 19.50 |
| Molybdenum (Mo) | |
| Nickel (Ni) | 8.00 – 10.50 |
| Nitrogen (N) | 0.10 |
304 stainless steel’s composition promotes good resistance to corrosive media, inhibiting both corrosion and oxidation. The low corrosivity of type 304 is largely due to the high chromium content, which forms a protective passivation layer–or patina–on the alloy’s surface. All stainless steel products have this protective layer which self-heals through oxidation, preventing oxidation of the internal structure. Yet grade 304’s higher chromium content increases its durability in the presence of oxidizing agents, meaning 304 stainless steel is unlikely to rust.
Mechanical Properties
| Proof Stress 0.2% (MPa) | 205 |
| Tensile strength (MPa) | 515 |
| Elongation A5 (%) | 40 |
| Hardness | HB: 201HRB: 92 |
Some of the standard mechanical properties of 304 stainless steel are shown in the table above, but we will look into the tensile strength, elongation A5, hardness and yield strength in more detail in the following section.
304 Stainless Steel Tensile Strength
The tensile strength of a property describes the maximum amount of stress the steel can withstand before fracturing or breaking. The tensile strength of 304 stainless steel is at a minimum of 515 MPa and can typical reach 625 MPa as a maximum.
304 Stainless Steel Yield Strength
The yield strength of 304 stainless steel is at 205 MPa. When the steel is placed under stress at 205 MPa or higher it will become permanently deformed. It is therefore important to know this measurement to avoid causing irreversible damage to a steel.
Different Types of 304 Stainless Steel
There are different grades of 304 stainless steel and the two key grades we will cover in this section are 304L and 304H. The L and H grades relate to the carbon content of the 304 forms of steel, each of which has its own benefits and drawbacks.
304L is the low carbon version and has a maximum of 0.3% carbon. When used in temperatures above 425oC, 304L is not as likely to result in carbide precipitation, unlike 304H. It is often used to improve weldability in heavy gauge components.
304H is the high carbon form with a carbon content between 0.04 and 0.1%. 304H stainless steel is often used in the food industry for a number of applications. These include cooking pots, cutlery, kitchen appliances and sinks because of its resistance to corrosion and high tolerance for extreme temperatures. (500 to 800oC)
What is 304 Stainless Steel Used for?
304 stainless steel is used in a variety of applications because of its flexibility and versatility. However, manufacturers might need to make a decision between steel types 304L or 304H depending on the properties they require.
Typical applications for 304 steel are:
- Bolts, screws and springs: Especially in industrial and marine applications where corrosion resistance is important.
- Chemical processes in petroleum refineries: 304H is frequently used to manufacture high-temperature processing equipment and pressure vessels because of its long and short-term strength and ability to withstand extreme temperatures. Additional reasons for using 304H in refineries are its resilience in hydrogen-rich environments and resistance to naphthenic acid attacks.
- Cookware and cutlery: 304L is commonly typically used in cookware and kitchens because of its strong resistance to corrosion and high temperatures. This includes other applications such as sinks, splashbacks, worktops and more. 304H can also be used for larger appliances and sinks.
- Dairy and food production equipment: 304L is used for food processing equipment because of its corrosion resistant properties and ability to withstand high temperatures. It reduces harmful interaction between food products and equipment.
Other applications include:
- Architectural panelling
- Building fascias in the construction industry
- Heat exchangers in the brewing industry
- Tubing
304L stainless steel is most commonly used in applications that present extremely corrosive conditions and operate under high temperatures. Other avantages include rapid hardening after cold forming and resistant to aggressive organic acids. Because of the aforementioned advantages, 304L is a popular choice for manufacturing industry components such as beams, pipe tubes, sheet plates and more.
304H stainless steel is a preferred choice in architectural and industrial processing applications because of it’s durability, high strength properties and reduced need for maintenance. It is especially suited for manufacturing heat exchangers in petroleum refineries.
304 vs 316 Stainless Steel?
The 300 series of stainless steel contain two of the most widely used austenitic stainless steels: 304 and 316. These steels arepopular in the building, food production and pharmaceutical industries because of their lower carbon content, have a austenitic crystalline structure and provide outstanding forming and welding properties.
The differences between these 304 and 316 stainless steels are quite simple in that 304 is made up of 18% chromium and 8% nickel whereas 316 is made up of 16% chromium, 10% nickel and 2% molybdenum. Another difference is their applications.
304 is typically used in food processing environments, including beer brewing and milk and wine processing as well as in petrochemical industries. It is highly resistant to corrosion and common acids and is easily moulded into desired shapes. Due to its good appearance and long service life, 304 can also be used in architectural applications. However, 304 should not be used in marine environments due to its weakness to chloride solutions and saline.
For industrial and marine applications and high-saline environments, 316 is the more appropriate steel. It is robust and can strong withstand powerful acids and chemicals that could cause corrosion. Additionally, 316 is used to manufacture equipment in the pharmaceutical industry, where cleanliness is paramount.
What is the Difference Between 304L and 304H Stainless Steel?
Grade 304 is an austenitic steel which has chromium and nickel as key elements. The inclusion of these elements mean that 304 steel is extremely resistant to corrosion as well as being easy to weld and form. The austenitic structure of this steel means that it can be deep drawn without the need for intermediate annealing and annealing is not required following the welding of thin sections.
Key Attributes of 304L and 304H Stainless Steel
The two key grades of 304 stainless steel are 304L stainless steel, which is the low carbon form, and 304H stainless steel, which is the high carbon form. 304L has a maximum of 0.3% carbon and 304H has between 0.04 and 0.1% carbon which affords it a better strength at higher temperatures.
304 stainless steel does not tend to be a grade for use in very high temperatures, however, it resists oxidisation in constant use up to 925oC and in intermittent use to 870oC. Using 304 stainless steel at temperatures above 425o C can create carbide precipitation and interangular corrosion.
However, 304L has a lower carbon content which means it is less likely to result in carbide precipitation when used at higher temperatures. 304H has significantly higher strength at increased temperatures meaning it is frequently selected when both high-temperature resistance and corrosion resistance are necessary. Often 304H is used in flue gas chimneys in which gases can condense to form aggressive, acidic liquids.
304H stainless steel is frequently used in the food industry due to its resistance to corrosion and is often the material of choice for use in the dairy industry. It is also often used in good quality cutlery and is described as 18/8 referencing the percentages of chromium and nickel. Additionally, it is frequently formed into troughs, sinks and other kitchen appliances and can be spun easily meaning it is well-suited to the production of pots and pans.
304H stainless steel is frequently used in fresh water service as it has a hard oxide layer which does not promote bacterial growth, which can impact fresh water. It is also often used in architectural applications, owing to its low cost compared with other materials.
The heat resistance of 304H stainless steel means it works well in heat exchangers and will not crack or corrode at temperatures between 500°C and 800°C. Additionally, it has a high tolerance for extreme thermal conditions and can be used for situations which cannot be accessed easily as it is a low maintenance material.
What are the application fields of 304 stainless steel?
304 stainless steel is a common steel in stainless steel, also known as 18/8 stainless steel. It is characterized by high temperature resistance, excellent processing performance, good toughness and is often used as a kind of steel. Common in life are 304 stainless steel pipe, 304 stainless steel plate and 304 stainless steel coil and other building materials.
As a very important building material, 304 stainless steel is widely used in industry, construction, home decoration industry and food and medical industry, and is one of the indispensable materials for life! So what items in our lives are made of 304 stainless steel? Let’s take a look together!
Automotive The application of 304 stainless steel pipe in the automotive industry is the fastest developing, and in recent decades such as buses, subways, high-speed railway cars, family cars and other public transportation vehicles, stainless steel pipe materials have been widely used!
Compared with traditional steel, because 304 stainless steel can ensure a high enough strength and weight ratio, but also has good plasticity, toughness, formability and weldability. It is the first choice for making car frames. Superior stainless steel can produce lightweight and impact-resistant, high-safety and long-life cars that are recycled for secondary use. Not only do you save costs, but you also save resources. And some other parts of the car parts are also made of stainless steel. Stainless steel has a large potential market in the entire automotive industry!
Bathroom, kitchen
Because the family kitchen and bathroom are in a humid environment for a long time, ordinary steel pipes will rust after a period of use, the service life is not long, and it affects the safety of family drinking water! Therefore, the use of 304 stainless steel pipe here can ensure long-term no rust, and the corrosion resistance and tensile resistance of 304 stainless steel pipe itself. Make 304 stainless steel pipe more and more popular in the field of home decoration!
Water industry
In order to make water not suffer serious pollution in storage and transportation, stainless steel pipes are now generally used to store and transport water, because 304 stainless steel pipes have anti-rust, high temperature and high pressure resistance, and good hygienic performance, So 304 stainless steel pipe slowly began to be used in the industrial field! .
In addition to common scenes in life, 304 stainless steel is also used in some high-end mechanical fields, such as food industry, chemistry, medical equipment, aircraft exhaust pipes, etc. It can be seen that 304 stainless steel has been widely used in heavy industry, light industry, daily necessities industry and building decoration and other industries. Due to the superior performance, the market of 304 stainless steel is destined to be sesame blossoming and high!
Talking about the application range of 304 stainless steel
304 stainless steel is a common material in stainless steel, with a density of 7.93 g/cm3, also known as 18/8 stainless steel in the industry. High temperature resistance of 800 degrees, with good processing performance, high toughness characteristics, widely used in industrial and furniture decoration industry and food and medical industry.
304 stainless steel is the most widely used chromium-nickel stainless steel, as a widely used steel, with good corrosion resistance, heat resistance, low temperature strength and mechanical properties; Good hot workability such as stamping and bending, no heat treatment hardening phenomenon (use temperature -196 °C ~ 800 °C).
304 stainless steel is suitable for food processing, storage and transportation. It has good processing performance and weldability. Plate heat exchangers, bellows, household products (1 and 2 types of tableware, cabinets, indoor pipelines, water heaters, boilers, bathtubs), auto parts (windshield wipers, mufflers, molded products), medical appliances, building materials, chemicals, food industry, agriculture, ship parts, etc. 304 stainless steel is a nationally recognized food-grade stainless steel.
Most of the use requirements are to maintain the original appearance of the building for a long time. When determining the type of stainless steel to be selected, the main considerations are the required aesthetic standards, the corrosiveness of the atmosphere where it is located, and the cleaning system to be adopted. Increasingly, however, other applications seek structural integrity or impermeability. For example, roofs and side walls of industrial buildings. In these applications, the cost of construction may be more important than aesthetics, and it is also possible that the surface is not clean.
The effect of using 304 stainless steel in a dry indoor environment is quite good. However, in the countryside and in cities, if you want to maintain its appearance outdoors, you need to wash it frequently. In highly polluted industrial areas and coastal areas, the surface will be very dirty and even rust.
However, to achieve an aesthetic effect in an outdoor environment, nickel-containing stainless steel is required. Therefore, 304 stainless steel is widely used in curtain walls, side walls, roofs and other building uses, but in highly aggressive industries or marine atmosphere, it is best to use 316 stainless steel. Stainless steel sliding doors, people have fully recognized the advantages of using stainless steel in structural applications. There are several design guidelines that include 304 and 316 stainless steels.
In fact, stainless steel is manufactured in a full standard metal shape and size, and there are many special shapes. The most commonly used products are made of sheet and strip, but special products are also produced from medium and heavy plates, for example, hot-rolled structural section steel and extruded structural section steel. There are also round, oval, square, rectangular and hexagonal welded or seamless steel pipes and other forms of products, including profiles, bars, wires and castings.
What is the difference between 304 stainless steel with BA surface and 2B surface?
There are many different types of surface finish in 304 stainless steel. According to the treatment methods, the surface of 304 stainless steel can be divided into 2B, 2D, BA, hairline, brushing, satin, etc. In this article, we will specify the difference between the surface of BA and surface 2B.
What is BA and 2B finish?
BA (2R)
Cold rolled and glossy annealing. The final appearance is developed by a single light step through a cold mill on highly polished rolls, but also depends on additional molding, such as grinding the surface into an intermediate gauge. The heat treatment is conducted in the oxygen-free atmosphere that takes the steel out of the furnace in the same physical condition.
2B
Cold rolled, heat-treated, pickled, pinched pass. the production of this finish turns out in the same way as the 2D finish, except for the final step which is a light roll pass through polished rollers called skinpass. This last stage consolidates the steel and does not substantially reduce the thickness of the material.
2B comes out of cold rolling with polished rollers and BA is after annealing in an oxygen-free environment. For the same surface roughness, what changes is the thickness and granularity of the surface oxide (which comes from surface passivation, not from the residues of the lamination oxide scale). If you are polishing a 2B surface to the same level as a BA sheet, sheet 2B would then be somewhat thinner (smaller).
What are the typical surface applications of BA and 2B?
Bachelor of Arts
The interior of sinks, dishwashers, dryers and clothes washers, stoves, microwaves, kitchen utensils, profiles, electrical cabinets, laboratory cabinets, tubes, cutlery, stamping parts, commercial kitchens, automotive, boiler, heat exchangers, bicycle tires …
2B
Machines/instruments, buses, railway vehicles, profiles, electrical cabinets, laboratory cabinets, tubes, cutlery, cut parts, press plates, stamping parts, tank construction, commercial kitchens, construction industry, automotive, boiler, smart grippers, surgical instruments, manufacturer pumps, beer kegs, chimney tubes, heat exchangers, sinks, elevators, etc.
Why should 304 stainless steel pipe be annealed?
304 stainless steel pipe is softened by solution treatment. In general, the stainless steel pipe is heated to about 950~1150 degrees and maintained for a period of time, so that the carbides and various alloying elements are completely and evenly dissolved in the304 stainless steel pipe, and then quickly turned off and water-cooled. Carbon and other alloying elements take too long to precipitate, and the pure 304 stainless steel tube structure is obtained, which is called solid solution treatment.
There are three solution treatment functions.
- Make the structure and composition of 304 stainless steel pipe uniform, which is especially important for raw materials, because the rolling temperature and cooling speed of each section of hot-rolled wire rod are different, resulting in an inconsistent structure.
At high temperatures, atomic activity intensifies, the σ phase dissolves, and the chemical composition tends to be uniform. After rapid cooling, a uniform single-phase structure is obtained.
- Eliminate work hardening to facilitate continuous cold work.
Through solution treatment, the distorted network is restored, elongated and broken grains are recrystallized, internal stress is eliminated, the tensile strength of the steel pipe decreases, and elongation increases.
- Restore the inherent corrosion resistance of 304 stainless steel pipes.
Due to carbide precipitation and lattice defects caused by cold work, the corrosion resistance of stainless steel is reduced. After solution treatment, the corrosion resistance of the steel pipe is restored to the best state.
For stainless steel pipes, the three elements of solution treatment are temperature, maintenance time and cooling rate. The temperature of the solution is mainly determined according to the chemical composition.
Generally speaking, for grades with many types of alloying elements and high content, the temperature of the solution should be increased accordingly. Especially for steel with a high content of manganese, molybdenum, nickel and silicon, the softening effect can only be achieved by increasing the temperature of the solution and completely dissolving it.
However, for stabilized steel, such as 1Cr18Ni9Ti, when the solution temperature is high, the carbide of the stabilized element is completely dissolved in the 304 stainless steel tube, and in the subsequent cooling, it will precipitate to the edge of the grain in the form of Cr23C6, causing intergranular corrosion. To prevent the carbides (TiC and NBC) of the stabilizing elements from decomposing and dissolving solidly, the lower limit temperature of the solution is usually adopted.
As the saying goes, 304 stainless steel is steel. which is not easy to rust. In fact, some stainless steels contain both oxidation resistance and acid resistance (corrosion resistance). The oxidation and corrosion resistance of stainless steel is due to the formation of a chromium-rich oxide film (passivation film) on its surface. Among them, oxidation resistance and corrosion resistance are relative.
Experiments have shown that the corrosion resistance of 304 stainless steel pipes in weak media such as atmosphere and water and in oxidizing media such as nitric acid will increase with increasing chromium water content in steel, which is proportional. When the chromium content reaches a certain percentage of level, the corrosion resistance of steel changes abruptly, that is, from easy to rust to not easy to rust, from no corrosion resistance to corrosion resistance.
304 stainless steel tube oxidation reasons and anti-oxidation principle
304 stainless steel tube has been very common in our life. Of course, sometimes we see the oxidation of stainless steel tubes. Speaking of “stainless steel” and “stainless steel”, why does it still rust?
Why can 304 stainless steel pipe rust?
It does not oxidize forever, and the chrome-rich oxide film (protective film) on its surface is resistant to atmospheric oxidation and corrosion resistance in media containing acids, bases and salts. Its anti-corrosion capacity varies with the chemical composition of the steel itself, the form of processing, operating conditions and the type of environment. When the protective film is damaged, it will rust naturally.
The same principle prevents oxidation.
The surface of the stainless steel tube has a very thin, strong, dense and stable chrome-rich oxide film. Stainless steel pipe rust is the reason that this oxide film can prevent oxygen atoms from infiltrating and oxidizing and causing rust. The addition of nickel and chromium in the stainless steel tube changes the structure of high chromium steel and improves the corrosion resistance and process performance of the stainless steel tube greatly. Corrosion or corrosion of stainless steel pipes. It is beneficial to improve its oxidation resistance and corrosion resistance, and is not easy to rust, which is why 304 stainless steel tube is not easy to rust.