304 stainless steel is a common material in stainless steel with a density of 7.93 g/cm3; it is also called 18/8 stainless steel in the industry, which means it contains more than 18% chromium and more than 8% nickel; it is resistant to high temperatures of 800°C and has good processing performance , with the characteristics of high toughness, it is widely used in industrial and furniture decoration industries and food and medical industries. However, it should be noted that compared with ordinary 304 stainless steel, food-grade 304 stainless steel has stricter content indicators. For example: The international definition of 304 stainless steel is that it mainly contains 18%-20% chromium and 8%-10% nickel, but food-grade 304 stainless steel contains 18% chromium and 8% nickel, which is allowed to fluctuate within a certain range, and Limit the content of various heavy metals. In other words, 304 stainless steel is not necessarily food grade 304 stainless steel.
Common marking methods on the market include 06Cr19Ni10 and SUS304. 06Cr19Ni10 generally indicates production according to national standards, 304 generally indicates production according to ASTM standards, and SUS 304 indicates production according to Japanese standards.
Physical properties
Tensile strength σb (MPa)>=515-1035
Conditional yield strength σ0.2 (MPa)>=205
Elongation δ5 (%)>=40
Reduction of area ψ (%)>=?
Hardness: <=201HBW; <=92HRB; <=210HV
Density (20℃, g/cm3): 7.93
Melting point (℃): 1398~1454
Specific heat capacity (0~100℃, KJ·kg-1K-1): 0.50
Thermal conductivity (W·m-1·K-1): (100℃) 16.3, (500℃) 21.5
Linear expansion coefficient (10-6·K-1): (0~100℃) 17.2, (0~500℃) 18.4
Resistivity (20℃, 10-6Ω·m2/m): 0.73
Longitudinal elastic modulus (20℃, KN/mm2): 193
Product ingredients
For 304 stainless steel, the Ni element in its composition is very important, which directly determines the corrosion resistance and value of 304 stainless steel.
The most important elements in 304 are Ni and Cr, but they are not limited to these two elements. Specific requirements are specified by product standards. A common judgment in the industry is that as long as the Ni content is greater than 8% and the Cr content is greater than 18%, it can be considered 304 stainless steel. This is why the industry calls this type of stainless steel 18/8 stainless steel. In fact, the relevant product standards have very clear regulations on 304, and these product standards have some differences for different shapes of stainless steel.
304 stainless steel is the most widely used chromium-nickel stainless steel. As a widely used steel, it has good corrosion resistance, heat resistance, low temperature strength and mechanical properties; it has good hot workability such as stamping and bending, and no heat treatment. Hardening phenomenon (use temperature -196℃～800℃). It is resistant to corrosion in the atmosphere. If it is an industrial atmosphere or a heavily polluted area, it needs to be cleaned in time to avoid corrosion. Suitable for food processing, storage and transportation. Has good processing performance and weldability. Plate heat exchangers, corrugated tubes, household products (Class 1 and 2 tableware, cabinets, indoor pipelines, water heaters, boilers, bathtubs), auto parts (windshield wipers, mufflers, molded products), medical equipment, building materials, chemistry, food industry , agriculture, ship parts, etc. The 304 stainless steel whose content is strictly controlled can also be called food-grade 304 stainless steel.
Most usage requirements are to maintain the original appearance of the building for a long time. When determining the type of stainless steel to choose, the main considerations are the required aesthetic standards, the corrosive nature of the local atmosphere, and the cleaning regime to be adopted. Increasingly, however, other applications are simply seeking structural integrity or impermeability. For example, roofs and side walls of industrial buildings. In these applications, the cost of construction to the owner may be more important than aesthetics, and the surface may not be very clean. The effect of using 304 stainless steel in dry indoor environments is quite good. However, maintaining its appearance outdoors in the countryside and cities requires frequent cleaning. In heavily polluted industrial areas and coastal areas, the surface will be very dirty and even rusty.
But to achieve aesthetic results in outdoor environments, nickel-containing stainless steel is required. Therefore, 304 stainless steel is widely used in curtain walls, side walls, roofs and other construction purposes. However, in severely corrosive industries or marine atmospheres, it is best to use 316 stainless steel. Stainless steel sliding doors, people have fully realized the advantages of using stainless steel in structural applications. There are several design guidelines that include 304 and 316 stainless steel. Because "duplex" stainless steel 2205 has integrated good atmospheric corrosion resistance with high tensile strength and elastic limit strength, this steel is also included in the European standards. Product shape In fact, stainless steel is manufactured in full standard metal shapes and sizes, and there are many special shapes. The most commonly used products are made of thin plates and strips, but medium and thick plates are also used to produce special products, such as the production of hot-rolled structural steel and extruded structural steel. There are also round, oval, square, rectangular and hexagonal welded pipes or seamless steel pipes and other forms of products, including profiles, bars, wires and castings.
Processing method
Etching
The etching processing method uses a screen printing acid-resistant protective film on the stainless steel surface, and then etches it with ferrous chloride liquid to form an artistic pattern.
Spray paint method
The spray color method is to spray color particles after screen printing to form a pear skin-like surface and form an artistic pattern.
Crafting process
The process of spray color art processing of stainless steel products is: stainless steel products → silk screen → etching → alkali treatment → silk screen → oxidation coloring → alkali treatment → finished product.
The process of etching art processing of stainless steel products is: stainless steel products → silk screen → etching → alkali treatment → oxidation coloring → finished product.
The chemical coloring method of stainless steel does not use pigments and dyes. Instead, the stainless steel is soaked in a heated concentrated chromium sulfate solution for chemical coloring. It is characterized by good food resistance. The ink used in this processing method must have very strong acid resistance. Generally, UV vulcanized ink with special properties that is compatible with the processing technology is used.
Stamping processing
For stainless steel products, especially stainless steel strips, many times the original processing method in factories is to use a punch machine to stamp products. Stamping includes two methods: straight punching and stretching. Generally, stretching and bending are used when the hardness is lower than 1/2, and straight punching is used when the hardness is higher than 1/2.
