E-mail: [email protected]
Tel: +86-13761906384
Home > News > Content

Industry News

How To Distinguish Whether Stainless Steel Is 304 Or 201

Feb 15, 2021

In daily life, stainless steel is widely used, such as stainless steel gas stoves, stainless steel sinks, stainless steel doors, etc. When purchasing these products, many consumers cannot identify whether the stainless steel is made of 304 or 201. 201 stainless steel It will rust. Many consumers buy fake products because they can’t identify them. Here are a few ways to teach you how to identify genuine and fake stainless steel.

Stainless steel has the characteristics of stainless steel, acid resistance, high temperature resistance, wear resistance and generally non-magnetic austenite. Stainless steel is a common high-grade alloy steel, such as stainless steel knives, stainless steel kitchen utensils, stainless steel building materials, etc. in our daily lives.

The stainless steels we see daily are mostly nickel-chromium stainless steels with the same steel grades as 302 and 304, and chromium stainless steels with 1-4 Cr13 (commonly called "stainless iron"). In my country, there are more than 100 types of stainless steel (steel grades), and the elements and contents of the steel grades are different, and their performance and value are also very different. Therefore, the identification of stainless steel must be carefully studied, to clarify the steel number mark, and comprehensive tests can be used to correctly identify it.

At present, we mainly use the following methods to identify stainless steel:

In fact, the simplest and most intuitive method is to use stainless steel to identify water, also called stainless steel potion;

The source of the whole stainless steel is generally orders from steel mills or imports from abroad, as well as the overstocked processed commodities in the society. The source of stainless steel is different, and its identification method is also different.

1. To identify stainless steel materials ordered by imports or steel mills, generally only need to check the marks on the steel or packaging according to the quality certificate of the import or steel mill.

The quality certificate is the supplier's confirmation and guarantee of the inspection results of the batch of products. Therefore, the quality certificate not only states the name, specification, number of delivered pieces, weight and delivery status of the material, but also must state all the inspection results of the specified guarantee items.

Similarly, in order to facilitate management, avoid confusion and prevent use accidents due to confusion, the manufacturer marks the brand, batch number, status, specification, quantity, and manufacturer code on the materials or packaging. The marked mark should be consistent with the content of the quality certificate. The commonly used marking methods mainly include the following three types: painting (paint the color indicating its brand on the specified part of the material), printing (printing or spray printing on the specified part of the material to indicate the material's brand, specification, furnace pot number, etc. , Often used on thick steel plates or large and medium-sized steel), listing (on bundles or boxes of materials, hanging signs indicating the brand number, batch number, specification, quantity, etc.).

Stainless steel signs are generally used for printing and listing.

2. The society overstocks stainless steel. According to the length of the overstocking time and the quality of storage, there are generally two situations:

One is that the overstocking time is not long, and the storage is good. The processing unit not only keeps the original quality certificate or copy, but also the signs on the steel or packaging are complete and clear. For the identification of this kind of stainless steel, as long as the mark on the steel or packaging is also checked according to the quality certificate.

The other is that the backlog is long and the storage is not perfect. There is no quality certificate, and the marks on the steel or packaging are not obvious or fall off. For the identification of this type of stainless steel, it is mainly necessary to conduct in-depth investigation and research and consult the original documents with the processing unit. Generally speaking, the original documents such as invoices are marked with steel numbers. If there is no record of the steel number, the local price data at the time must be consulted to determine the steel number based on the price. This is a more effective way to determine the steel grade, but it is often easy to show up. Therefore, it is necessary to master the identification method of the physical object.

Physical identification is to determine whether it is stainless steel with the help of simple instruments and the senses based on the inherent physical and chemical properties of the product (including the whole material, residual material, waste, etc.) when the steel type (number) is unknown. And the specific method of which type of stainless steel.

It should be pointed out that sensory identification cannot distinguish specific steel (type) numbers, but can only basically distinguish three major categories of chromium stainless steel, chromium nickel stainless steel and chromium manganese nitrogen stainless steel. The identification methods are as follows:

color identification

The pickled stainless steel has a silvery white and smooth surface color: chromium-nickel stainless steel is silvery white and jade; chromium stainless steel is slightly grayish and weak; the color of chromium-manganese-nitrogen stainless steel is similar to that of chromium-nickel stainless steel. The surface color of stainless steel that has not been pickled: chrome-nickel steel is brown-white, chrome steel is brown-black, and chromium-manganese-nitrogen is black (the three colors refer to the more oxidized colors). Cold-rolled unannealed chromium-nickel stainless steel with silver-white reflective surface.

Use magnetite to identify

Magnet can basically distinguish two types of stainless steel. Because chromium stainless steel can be attracted by magnets in any state; chromium-nickel stainless steel is generally non-magnetic in the annealed state, and some will be magnetic after cold working. However, high manganese steel with higher manganese content is non-magnetic; the magnetic situation of chromium-nickel-nitrogen stainless steel is more complicated: some are non-magnetic, some are magnetic, and some are non-magnetic in the longitudinal plane and magnetic in the transverse plane. Therefore, although magnets can basically distinguish between chromium stainless steel and chromium-nickel stainless steel, it cannot correctly distinguish some special steel grades, let alone specific steel grades.

Identification with copper sulfate

Remove the oxide layer on the steel, put a drop of water, wipe it with copper sulfate, if it does not change color after wiping, it is generally stainless steel; if it turns purple, non-magnetic is high manganese steel, and magnetic is generally ordinary steel or low alloy steel.

For steel grades with special properties, we still need to take the following three methods to identify them.

mill flower identification

grinding pattern identification is to grind stainless steel on a grinder and observe the sparks. If the spark is streamlined and has more dense knots, it is high manganese steel or manganese nitrogen steel with higher manganese content; if there are no knots, it is chromium steel or chromium-nickel stainless steel.

annealing method identification

Cold-worked chromium-nickel stainless steel, if it has magnetism, can take small pieces to boil it red in a fire and let it cool naturally or put it in water (annealing). Generally speaking, the magnetism will be significantly weakened or disappear completely after annealing. However, some chromium-nickel stainless steels, such as Cr18Ni11Si4AlTi steel and Cr21Ni5Ti steel, contain more ferrite elements, and a considerable part of their internal structure is ferrite. Therefore, it is magnetic even in the state of hot working.

chemical qualitative identification

The chemical qualitative method is an identification method to identify whether nickel is contained in magnetic stainless steel. The method is to dissolve a small piece of stainless steel in aqua regia, dilute the acid with purified water, add ammonia to neutralize it, and then gently inject the nickel reagent. If there is a red velvet-like substance floating on the liquid surface, it means that the stainless steel contains nickel; if there is no red velvet-like substance, it means that there is no nickel in the stainless steel (but due to the low nickel content in stainless steel, generally only a few percent, nickel The content is not easy to reveal or determine how much, generally it can be grasped after several experiments with standard samples).

The above identification methods show that the use of sensing tubes to identify stainless steel requires not only a comprehensive test of several methods, but also the test results can only determine a certain type of stainless steel, and cannot determine which alloy elements and specific content the steel contains. Therefore, the method of sensory identification is currently extremely imperfect, and some may be wrong, and there are many physical phenomena that are only known but do not know why, and need to be further explored.