What’s the difference between 304 and 304l?
Stainless steel is a widely-used alloy in various industries and products due to its superior corrosion and weldability.
304 and 304L are two commonly-used stainless steels. However, there are some key distinctions that you should be aware of.
304 is a non-magnetic austenitic stainless steel with at least 18% chromium and 8% nickel content. It offers excellent resistance to atmospheric corrosion and can be easily welded for extra strength.
Corrosion Resistance
Stainless steel offers superior corrosion resistance in both oxidizing and reducing environments, making it a popular material for kitchen appliances, medical equipment, building materials, chemicals, and ship parts. The most widely used alloy is type 304 which contains 18% chromium content. A low carbon version of 304 called 304L also exists for improved weldability.
304 is highly resistant to pitting and crevice corrosion in fresh water with chlorides below 400 mg/L, stress corrosion cracking at temperatures up to 60 degC, moderate organic acids such as acetic acid, but isn’t suitable for marine environments due to its high susceptibility to intergranular corrosion.
Welding of 304 with filler metal can produce coarse chromium carbide particles that are detrimental to corrosion resistance. These can be removed through full annealing to dissolve the carbide and enhance corrosion resistance. Welding that involves hot working may also lead to work hardening of the underlying stainless steel, which may need an intermediate annealing stage in order to alleviate it and avoid tearing or cracking.
The higher carbon levels found in welded 304 alloys can lead to the formation of a thick film of chromium carbide that significantly reduces corrosion resistance. To avoid this issue, welding with lower carbon materials (Type 304L) or using an appropriate filler metal is recommended.
Directed energy deposition 304L microstructures have been reported to possess superior pitting resistance compared to conventionally processed SLM materials, with breakdown potentials (Eb) values in 0.6 M NaCl exceeding those of their wrought counterpart by several mV. This superiority can be attributed to finely dispersed nanoscale oxides and d-ferrite in the microstructure, combined with lack of fusion pores (LOF) that would normally act as crevice sites to control Eb at first order.
Welding and fabrication of 304 stainless steel should not be attempted without the appropriate tooling, work surface and coolant. Fabrication methods such as roll forming, deep drawing or bending should be followed by an intermediate annealing to reduce work hardening and avoid internal stresses that could cause tearing or cracking. After annealing has taken place, quickly cooling the fabricated stainless steel will prevent surface damage while also increasing corrosion resistance.
Weldability
When considering which alloy to weld, manufacturers should take into account their weldability. Both alloys are easily weldable and compatible with most welding processes; the difference lies primarily in their chemical composition: 304l has a lower carbon content than 304, making it easier to weld as well as being suitable for more severe corrosion environments without needing annealing.
304 and 304l are austenitic stainless steels with 18% chromium and 8% nickel content. Due to their superior resistance to atmospheric corrosion, these steels find widespread application in food processing, architectural applications, chemical containers, and heat exchangers.
A common issue when welding these metals is that they become susceptible to chromium carbide precipitation (CCP), which occurs when the base material reaches temperatures of approximately 850 degrees Fahrenheit. Fortunately, this problem can be avoided by employing the correct welding process and alloys.
For stainless steels such as 304 and 304l, it is recommended to use a low P and S content in the weld to minimize hot cracking. Typically, a Creq/Nieq ratio of 1.5-1.9 works well for this purpose; however, higher ranges may be necessary in certain welds with increased primary austenite formation likelihood.
Additionally, when welding an alloy with a high chromium content, it’s best to use gas tungsten arc welding equipment rather than using an MMA welding process as this can lead to more damage than with traditional welds.
When working with stainless steel 304 or 304l, it is essential to maintain sharp cutting edges throughout the work process. Doing so helps avoid work hardening and extends weld longevity. Furthermore, maintaining a cool and dry working environment is key for optimal efficiency.
Alternatively, using a chipbreaker can help ensure that swarf remains within heat-concentrated zones. Doing this prevents it from riding on top of the weld surface and resulting in excessive work hardening.
Strength
Stainless steels are an ideal material for many applications, but selecting the correct type is key. The two most popular varieties are 304 and 304l, both part of the austenitic family which allows them to be readily drawn and formed.
304 is an ideal corrosion-resistant choice due to its high chromium and nickel content, making it suitable for use in both oxidizing and reducing environments such as seawater. Furthermore, 304 exhibits good resistance against moderately aggressive organic acids.
Another significant feature of 304 is its low carbon content. Lowering the carbon content helps avoid the formation of coarse chromium carbide particles at grain boundaries when welding at higher temperatures. Alternatively, you can opt for an ultra-low carbon stainless steel like 304L to minimize sensitization risks and boost component durability.
For tanks containing corrosive liquids, 304L is the preferred material. It has a minimum carbon content of 0.03%, eliminating any risk of chrome carbide precipitation when heated at higher temperatures – particularly important in autoclaves where temperatures can reach 925oC.
Chromium and nickel content in high chrome steel make it a superior material for strength, even at elevated temperatures. It can be utilized to manufacture various products suited for harsh environments and conditions.
That is why 304 is one of the most widely used stainless steels today. It is easily drawn and formed, boasts high ductility, and can be annealed for increased hardness and strength.
AISI 304L (SS304L) is an ultra-low carbon version of the popular 304 grade. It can be used in welding sections 5mm or thicker and helps prevent coarse chromium carbide formation at grain boundaries when exposed to higher temperatures.
The maximum carbon content of 304L is 0.03%, lower than the limit set for 304. This makes it a suitable option for welding parts and equipment that need high strength but may be exposed to extensive corrosive exposure during service.
Cost
If you’re searching for stainless steel with excellent corrosion resistance at an affordable price, 304 and 304l are two great choices. Both alloys are 18-8 chromium-nickel stainless steels with at least 18% chromium and 8% nickel content; additionally, these alloys contain small amounts of carbon and manganese.
304 is an extremely durable alloy with excellent corrosion resistance that can be used in numerous applications. It’s commonly found in appliances, food processing equipment, furniture pieces and architectural trim.
Grade 304 stainless steel is an austenitic chromium-nickel alloy with a tensile strength of about 590 ft-lb (216 J) and yield strength of 600 ft-lb (235 J). It has long been used in food processing equipment and brewery equipment as well as laboratory glassware, test tubes, medical devices, and other specialized items. Additionally, this material has a long history within the pharmaceutical industry where it’s found in laboratory glassware, test tubes, medical devices, and other specialized items.
Food and beverage equipment benefits from easy cleaning, while 304 has excellent oxidation resistance and resistance to corrosive atmospheres. As such, 304 is often employed in plumbing and piping applications where it can handle various corrosive solutions.
In addition to its corrosion resistance, 304 is easy to weld and boasts impressive tensile and yield strengths. It finds widespread application in welded components for chemical, textile, paper, and pharmaceutical industries.
Grade 304l has slightly lower tensile and yield strengths than grade 304, yet it is easier to weld. Furthermore, since no post-weld annealing is necessary, you can save both time and money with this choice.
304L’s lower carbon content makes it ideal for welding in corrosive environments due to its reduced carbide precipitation risk and versatility; it can be welded using various techniques including conventional oxyacetylene welding. When corrosion resistance and/or strength at elevated temperatures are not critical, 304L may be used instead of 304.
Additionally, 304L contains less carbon than 304 and is therefore more resistant to intergranular corrosion. It can be easily welded using conventional techniques without needing post-weld machining, making it an ideal choice for both industrial and home uses.
