Definition:
Steel containing more than 12% chromium that can resist chemical attacks.
Principle:：
Stainless steel does not mean it won't rust, but rather it is resistant to rusting. The principle involves the addition of chromium, which forms a dense chromium oxide layer on the surface of the steel, effectively preventing further contact between the steel and air. This inhibits the entry of oxygen from the air into the steel, thereby preventing rusting.

Chinese National Standards (CNS), Japanese Industrial Standards (JIS), and the American Iron and Steel Institute (AISI) use three-digit numbers to represent different types of stainless steel, widely referenced in the industry. The 200 series refers to chromium-nickel-manganese austenitic stainless steel, while the 400 series refers to ferritic stainless steel (commonly known as stainless iron), including martensitic and ferritic elements.
Additionally, classification can be based on composition, magnetism, ability to undergo heat treatment hardening, and steel grade numbers, as shown in the table below:：

Magnetism:

All austenitic stainless steel balls are typically non-magnetic; however, some magnetism may be apparent after cold working. Standard: ISO3506 GB/T3098.6 Various materials' ability to be magnetized. Applicable to stainless steel. Complete non-magnetism is only possible under vacuum conditions. The measurement of the magnetic permeability of a material in a magnetic field is relative to the material's magnetic permeability µr in a vacuum. If µr is close to 1, the material has low magnetic permeability. For example: A2: µr ≅ 1.8, A4: µr ≅ 1.015, A4L µr ≅ 1.005, F1: µr ≅ 5.
The strength of magnetism is closely related to the alloy composition of the steel. The following is the formula for calculating magnetism (smaller values indicate lower magnetism): MD30 = 551-462×(C+N)-9.2×Si-8.1×Mn-13.7×Cr-29×(Ni+Cu)-18.5×Mo
Q&A：
Should I choose A2 or A4 stainless steel balls?
Answer: A) Prioritize choosing A2 (commonly known as 304) stainless steel balls, as they generally satisfy most usage environments.
              B) In environments with higher corrosive requirements, such as petrochemicals, chemicals, nuclear power, and coastal areas, consider using A4 (commonly known as 316) stainless steel balls.