Alloys 304 (S30400), 304L (S30403), and 304H (S30409) are variants of 18% chromium and 8% nickel austenitic alloys, the most common and commonly used alloys in the stainless steel family.Because these alloys have one or more of the following properties, they can be used for a variety of applications.Attributes include:
• prevent product contamination
• easy to process
• good formability
• beautiful appearance
• easy to clean
• high strength, low weight
• good strength and toughness at low temperature
• multiple product forms already exist
Each alloy is well combined with corrosion resistance and good workability.The combination of good properties is why this alloy is so widely used, accounting for almost half of all stainless steel production in the United States.18-8 stainless steel, mainly 304,304 L, 304H, comes in a variety of forms, including sheets, strips and plates.These alloys are commonly used in the manufacture of equipment and examples of their applications include: food and beverage, hygiene, refrigeration, pressure vessels.Argon oxygen decarburization (AOD) technology achieved low carbon level at low cost, and 304 became the standard alloy.304L is used for welding products which may be exposed to irregular corrosion conditions during operation.
304 h 304 alloy is improved, its carbon content between 0.04 to 0.10, to be exposed to temperatures above 800 ° F parts, using 304 h help to improve the high temperature strength.
ASTM A240 and ASME SA-240:
|Chemical composition||Weight percentages are listed as maximum unless otherwise specified|
|Mechanical properties||ASTM A240 and ASME sa-240Minimum mechanical properties required|
0.2% offsetYield strength,
Ultimate tensile strength,
|Percentage elongation (2 inches or 51mm)||40.0||40.0||40.0|
Austenitic stainless steels are considered the easiest alloy steels to weld, either with all fuses or with resistance welds.304L is a typical austenitic stainless steel.There are two factors to consider when producing welding contacts for austenitic stainless steel:
1) maintaining corrosion resistance and
2) avoiding cracking.
The material is welded to form a temperature ladder, from the melting temperature of the pool to the ambient temperature slightly away from the welding point.The higher the carbon content of the welded material is, the more likely the welding heat cycle will lead to chromium carbide precipitation, which has an impact on the corrosion resistance of the material.In order to maintain the best corrosion resistance of the material, the low carbon material (304L) should be selected for operation in the welded state.Another approach is to use full annealing to dissolve chromium carbide, restoring the standard carbon content of the material to a high level of corrosion resistance.Weld metal with complete austenite structure is more likely to crack during welding operation.Therefore, a small amount of ferrite was added to 304 and 304L alloy to reduce the crack sensitivity of the material and achieve the effect of resolidification.When 18-8 austenite alloys are welded to carbon steel, 309 alloys (23% chromium - 13.5% nickel) or nickel-based solders are usually used.
Austenitic stainless steels can be heat-treated to remove the side effects of cold forming and the chromium carbide that dissolves and precipitates.To fulfill the requirements of the two is the best heat treatment at 1850 ° F to 2050 ° F (1010 ° C to 1010 ° C) of solid annealing temperature range.From the annealing temperature is cooling down 1500-800 ° F (816 ° C to 427 ° C), should be enough to avoid chromium carbide precipitation.These materials cannot be hardened by heat treatment.
Stainless steel surfaces must be kept clean during processing and use, regardless of corrosion.During welding, inert gas is used. Rust and slag formed during welding are removed by stainless steel brush.Ordinary carbon steel brushes will leave carbon steel particles on the surface of the stainless steel, which will eventually cause the surface to rust.In the case of strict requirements, the welding area should be treated with derusting solution (such as nitric acid and hydrofluoric acid mixed solution), which can wash away the rust and slag formed during the welding process.Inland, light industrial materials require less maintenance and only sheltered areas are sometimes cleaned with pressurized water.Heavy industry recommends frequent cleaning to remove accumulated dust, which may eventually cause corrosion and damage to the surface appearance of stainless steel.Stubborn stains and deposits can be scrubbed with a detergent and fiber brush, sponge, or stainless steel wool.The stainless wool will leave permanent scratches on the smooth surface of the stainless steel.Many stainless steels are cleaned and disinfected regularly.Equipment is usually cleaned with caustic soda, organic solvents, and acid solutions (in phosphoric or sulfuric acid).Strong reducing acids (such as hydrofluoric or hydrochloric acid) may cause damage to stainless steel.After the solution is cleaned, rinse the stainless steel thoroughly with water.Proper design helps with cleaning.With round corner, inside corner, seamless equipment, is conducive to cleaning and surface polishing.