Stainless steel is a product material that we often see in our daily lives. From stainless steel chopsticks to stainless steel building materials, stainless steel has a wide range of applications. However, stainless steel is just a general term for a type of material. There are many classifications of stainless steel. For example, stainless steel 316 and 304 are the most common stainless steel varieties. So what is the difference between stainless steel 316 and 304? What are the methods to distinguish stainless steel 316 and 304? The following editor has found some related content about stainless steel 316 and 304 for you, let’s take a look!

What is the difference between stainless steel 316 and 304?

1. Grade issue.

The extensions of 304 and 316 are 304L and 316L respectively, and their respective grades are as follows:

304 is 06Cr19Ni10, 304L is 00Cr19Ni10;

316 is 0Cr17Ni12Mo2, 316L is 00Cr17Ni14Mo2.

2. Food grade issues.

I often encounter people who ask if 304 is food grade? In fact, speaking of materials, the material content of 304 has reached food grade. There are probably three common food grade materials in the market: 304, 316 and 430 stainless steel. 304 is commonly found in small household appliances or water cups, 316 is sometimes used in medical equipment, and 430 is often used as stainless steel in knives. But here we also need to clarify a concept. It does not mean that the material is food grade. It also includes whether the manufacturing and other aspects meet food grade standards. For example, Xiyouwo makes stainless steel pipes for decoration, and will There are also stainless steel pipe factories that specialize in producing food-grade stainless steel water pipes, and the required process links are different.

3. Corrosion resistance issues.

316 stainless steel is stainless steel produced by adding some molybdenum to 304 stainless steel to resist pitting corrosion. In various types of water quality (distilled water, drinking water, river water, boiler water, etc.), the corrosion resistance of 304 stainless steel and 316 stainless steel is almost the same, but when the content of chloride ions in the medium is very high, 316 stainless steel is more suitable.

4. Price issue.

Due to the molybdenum and nickel elements added to 316, 316 stainless steel is more expensive than 304 stainless steel.

5. Low-carbon issues.

304L and 316L materials have lower carbon content than 304 and 316, and there is a clear comparison in the material content table. The main reason why stainless steel does not rust is the chromium-rich oxide film formed on the surface. However, when the temperature is too high, intergranular corrosion will occur. Therefore, the low carbon content in 304L and 316L reduces intergranular corrosion. It should be noted that higher intergranular corrosion susceptibility does not mean that non-low carbon content is more susceptible to corrosion. This susceptibility is also higher when in a high chlorine environment.

How to distinguish stainless steel 316 and 304

Identification of color

The surface color of pickled stainless steel is silver-white and smooth: chromium-nickel stainless steel is silver-white and jade-colored; The color of chromium stainless steel is white and slightly gray and has a weak luster; the color of chromium-manganese-nitrogen stainless steel is similar to that of chromium-nickel stainless steel and slightly lighter. The surface color of unpickled stainless steel: chromium-nickel steel is brown-white, chromium steel is brown-black, and chromium-manganese-nitrogen is black (these three colors refer to the colors with heavier oxidation). Cold-rolled unannealed chromium-nickel stainless steel with silvery white surface and reflective surface. ?

Identification with magnets

? Magnets can basically distinguish between 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 become 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 direction but magnetic in the transverse surface. Therefore, although magnets can basically distinguish between chromium stainless steel and chromium-nickel stainless steel, they cannot correctly distinguish some steel types with special properties, let alone specific steel grades. Identification with copper sulfate

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

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

Identification of grinding patterns

Identification of grinding patterns is to grind stainless steel on a grinder and observe the sparks. If the sparks are streamlined and have 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 If the cold-worked chromium-nickel stainless steel is magnetic, you can take a small piece and burn it red in the fire and let it cool naturally or put it in water (annealing). Generally speaking, the magnetism will be significantly weakened or completely disappeared after annealing. However, some chromium-nickel stainless steels, such as Cr18Ni11Si4AlTi steel and Cr21Ni5Ti steel, because the steel contains more ferrite elements, a considerable part of its internal structure is ferrite. Therefore, it is magnetic even in the hot-processed state.

Identification by chemical qualitative method

Chemical qualitative method is an identification method to identify whether magnetic stainless steel contains nickel. The method is to dissolve small pieces of stainless steel in aqua regia, dilute the acid solution with purified water, add ammonia water to neutralize it, and then gently inject 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 because the nickel content in stainless steel is low, generally only a few percent, the nickel content is The content is not easy to reveal or determine. Generally, it can only be grasped after many experiments with standard samples)

The above is what the editor found for you about the difference between stainless steel 316 and 304 and how to identify stainless steel 316 and 304. What are the methods? How about, after reading the editor's introduction, do you have some general understanding of the difference between stainless steel 316 and stainless steel 304 and how to distinguish 316 and 304? What the editor wants to say here is, stainless steel 316 and stainless steel 304 There are still some differences between 304, especially in some special fields. The effects of using 316 and 304 are different, and the two cannot be confused. I hope today’s content will be helpful to you.

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