ASTM A959-2004 Standard Guide for Specifying Harmonized Standard Grade Compositions for Wrought Stainless Steels

304 stainless steel is a common stainless steel material with a density of 7.93 g/cm³. It is also known in the industry as 18/8 stainless steel. It is a widely used steel with excellent corrosion resistance, heat resistance, low-temperature strength, and mechanical properties. It also has excellent hot workability in stamping and bending, with no heat-hardening (operating temperature ranges from -196°C to 800°C). It is corrosion-resistant in atmospheric environments. However, in industrial atmospheres or heavily polluted areas, it requires prompt cleaning to prevent corrosion. It is suitable for food processing, storage, and transportation. It has good processability and weldability. It is used in plate heat exchangers, bellows, household items (Class 1 and 2 tableware, cabinets, indoor plumbing, water heaters, boilers, bathtubs), automotive parts (windshield wipers, mufflers, molded parts), medical devices, building materials, chemicals, the food industry, agriculture, ship components, and Xiaomi mobile phones. 304 stainless steel is a nationally recognized food-grade stainless steel. Rusting of 304 stainless steel may occur for several reasons:

Chloride Ions

Chloride ions are widely present, such as in salt, sweat, seawater, sea breeze, and soil. Stainless steel corrodes rapidly in environments with chloride ions, even more rapidly than ordinary mild steel. Therefore, stainless steel must be used in a specific environment and must be frequently wiped, dust-free, and kept clean and dry. (This can lead to a charge of "improper use.") In the United States, a company used an oak container to store a chloride-containing solution. The container had been in use for over a hundred years and was scheduled for replacement in the 1990s. However, due to the inadequacy of the oak material, stainless steel was replaced. Sixteen days later, the container leaked due to corrosion.

Solution Treatment

Alloying elements are not dissolved into the matrix, resulting in a low alloy content and poor corrosion resistance.

Intergranular Corrosion

This material, which does not contain titanium and niobium, is prone to intergranular corrosion. Adding titanium and niobium, combined with stabilization treatment, can reduce intergranular corrosion. Stainless steel is a high-alloy steel that resists corrosion in air and chemically corrosive media. It boasts an attractive surface and excellent corrosion resistance, eliminating the need for surface treatments such as plating, leveraging its inherent surface properties. It is commonly referred to as stainless steel and is used in a variety of applications. Representative high-alloy steels include 13-chromium steel and 18-8 chromium-nickel steel. Metallographically, the chromium content in stainless steel creates a thin chromium film on its surface, which isolates the steel from oxygen intrusion and acts as a corrosion barrier. To maintain the inherent corrosion resistance of stainless steel, the steel must contain at least 12% chromium. It is used in applications requiring welding. A low carbon content minimizes carbide precipitation in the heat-affected zone near the weld, which can cause intergranular corrosion (weld erosion) in certain environments.

Surface Phenomenon

Surface marking refers to linear or pitting defects that occur on the surface of 304 stainless steel after deep processing or grinding of the processed product.

Causes: Foreign matter on the surface or mold surface, or scars on the edge pad surface. Countermeasures: Remove foreign matter and scratches before processing. You can also thoroughly grind to remove orange peel.

Orange peel refers to the appearance of orange peel-like patterns on the surface of 304 stainless steel molded parts during grinding or other processes.

Causes: Insufficient grinding (the orange peel becomes more severe with larger machining processes), coarse raw material grains, and softening during heat treatment.

Countermeasures: Thoroughly grind deep-processed products, select appropriate heat treatment conditions, and control the raw material grain size.