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At present, the corrosion resistance of stainless steel is mainly judged through standardized testing + auxiliary observation verification. The core relies on professional equipment and standard methods. Preliminary judgments can also be made through simple observation. The specific methods are as follows: 1. Professional standardized testing method (accurate judgment) This is an authoritative judgment method common in the industry, which can quantitatively evaluate corrosion resistance. Commonly used methods are:: Salt spray test (the most commonly used accelerated evaluation) simulates the ocean/high-salt environment, places the sample in a 5% sodium chloride salt spray environment for continuous testing, and observes the time when corrosion occurs to determine the grade. For example, the qualification standard for 304 stainless steel is no red rust for 48-72 hours, and no corrosion for hundreds of hours after passivation. The test cost is low and the cycle is short, making it suitable for preliminary screening. Chemical composition analysis uses a spectrometer to detect the content of key alloy elements such as chromium, nickel, and molybdenum in stainless steel.: Chromium content ≥10.5% is the basis of stainless steel. The higher the chromium, molybdenum and nickel content, the stronger the corrosion resistance. For example, 304 contains 18-20% chromium and 8-10% nickel, and its corrosion resistance is far better than low-chromium fake stainless steel. Electrochemical testing accurately and quantitatively evaluates the corrosion rate and mechanism by measuring electrochemical parameters such as corrosion potential and corrosion rate. It is a common method for in-depth research and high-precision material selection. The immersion test completely immerses the sample in the corrosive medium (acid, alkali, salt solution) in the actual use scenario. After immersing for a certain period of time, the corrosion resistance is evaluated through weight loss and surface corrosion, which is closer to the actual use situation. The disadvantage is that the test cycle is longer. The intergranular corrosion test is aimed at the unique intergranular corrosion risk of stainless steel. According to * * Conduct tests in accordance with the standard GB/T 4334 to detect corrosion sensitivity at grain boundaries and determine whether the material is qualified for heat treatment and whether the composition meets the standards. Special standard testing (medical scenario) Medical stainless steel instruments must comply with YY/T 0149-2006 industry standards, and grade corrosion resistance through boiling water test, sodium chloride solution test, and citric acid solution test to ensure medical safety. 2. Daily preliminary judgment method When there is no professional equipment, preliminary screening can be done through simple methods: Surface observation method is used to check whether the stainless steel surface is smooth and flat, and whether there are rust spots, pits, and color differences.: Inferior stainless steel will quickly develop rust spots in a humid environment, while qualified stainless steel has a uniform surface without rust. Magnetism assists in judging that austenitic stainless steel (commonly used 304, 316) is non-magnetic, while ferrite and martensitic stainless steel are magnetic. ； But you cannot judge based on magnetism alone - cold-processed 304 stainless steel will also have weak magnetism, and this method can only be used as a rough reference. The special testing liquid sold in the stainless steel testing liquid market can quickly distinguish the approximate grade.: Different brands will show different colors after dripping. The content of alloy elements can be preliminarily determined by comparing the color card. It can only be roughly distinguished and cannot be used as a basis for accurate judgment.