Industry News

Performance comparison of various stainless steels

2021-04-30


The so-called duplex stainless steel is that the ferrite phase and the austenite phase in its solid-quenched structure each account for half, and generally the minimum phase content must reach 30%.

Due to the characteristics of the two-phase structure, DSS has the advantages of both ferritic stainless steel and austenitic stainless steel through correct control of chemical composition and heat treatment process.

Compared with austenitic stainless steel, the advantages of duplex stainless steel are as follows:

(1) The yield strength is more than twice that of ordinary austenitic stainless steel, and it has sufficient plastic toughness for forming. The wall thickness of storage tanks or pressure vessels made of duplex stainless steel is 30-50% less than that of commonly used austenite, which is beneficial to reduce costs.

(2) It has excellent resistance to stress corrosion cracking. Even the duplex stainless steel with the lowest alloy content has higher resistance to stress corrosion cracking than austenitic stainless steel, especially in an environment containing chloride ions. Stress corrosion is a prominent problem that is difficult to solve for ordinary austenitic stainless steel.

(3) The corrosion resistance of 2205 duplex stainless steel, which is most commonly used in many media, is better than that of ordinary 316L austenitic stainless steel, while super duplex stainless steel has extremely high corrosion resistance. In some media, such as acetic acid, Formic acid can even replace high-alloy austenitic stainless steels and even corrosion-resistant alloys.

(4) It has good local corrosion resistance. Compared with austenitic stainless steel with the same alloy content, its wear corrosion resistance and fatigue corrosion resistance are better than austenitic stainless steel.

(5) The coefficient of linear expansion is lower than that of austenitic stainless steel, which is close to that of carbon steel. It is suitable for connection with carbon steel and has important engineering significance, such as the production of composite plates or linings.

(6) Whether under dynamic or static load conditions, it has a higher energy absorption capacity than austenitic stainless steel, which is suitable for structural parts to cope with sudden accidents such as collisions and explosions. Duplex stainless steel has obvious advantages and has practical application value. .

Compared with austenitic stainless steel, the disadvantages of duplex stainless steel are as follows:

(1) The universality and versatility of the application are not as good as the austenitic stainless steel, for example, the use temperature must be controlled below 250 degrees Celsius.

(2) Its plastic toughness is lower than that of austenitic stainless steel, and its cold and hot processing technology and forming performance are not as good as austenitic stainless steel.

(3) There is a medium-temperature brittle zone, and the process system of heat treatment and welding needs to be strictly controlled to avoid the appearance of harmful phases and damage performance.

Compared with ferritic stainless steel, the advantages of duplex stainless steel are as follows:

(1) The comprehensive mechanical properties are better than ferritic stainless steel, especially the plastic toughness, which is not as sensitive to brittleness as ferritic stainless steel.

(2) Except for stress corrosion resistance, other local corrosion resistance is better than ferritic stainless steel.

(3) Cold working process performance and cold forming performance are far better than ferritic stainless steel.

(4) The welding performance is also much better than that of ferritic stainless steel. Generally, preheating is not required before welding and no heat treatment is required after welding.

(5) The application range is wider than ferritic stainless steel.

Compared with ferritic stainless steel, the disadvantages of duplex stainless steel are as follows:

The content of alloying elements is high and the price is relatively high. Generally, ferrite does not contain nickel.

In summary, it can be seen in a general way that DSS has an overview of its use performance and process performance. It has won the favor of users with its superior mechanics and corrosion resistance. It has become an excellent resistance to both weight and investment. Eclipse engineering materials.

304 steel will also have magnetism. Whether it is magnetism or not can not judge the quality of stainless steel.

People often think that magnets absorb stainless steel materials to verify their quality and authenticity. They are not attractive and non-magnetic. They are considered to be good and genuine; if they are magnetic, they are considered to be counterfeit products. In fact, this is an extremely one-sided and impractical method of identifying errors.

There are many types of stainless steel, which can be divided into several categories according to the organizational structure at room temperature:

1. Austenite type: such as 304, 321, 316, 310, etc.;

2. Martensite or ferrite type: such as 430, 420, 410, etc.;

Austenite is non-magnetic or weakly magnetic, and martensite or ferrite is magnetic.

The stainless steel usually used as decorative tube sheet is mostly austenitic 304 material. Generally speaking, it is non-magnetic or weak magnetic. However, due to chemical composition fluctuations or different processing conditions caused by smelting, magnetism may also appear, but this cannot be considered as What is the reason for counterfeit or unqualified?

As mentioned above, austenite is non-magnetic or weakly magnetic, while martensite or ferrite is magnetic. Due to component segregation or improper heat treatment during smelting, a small amount of martensite or ferrite in austenitic 304 stainless steel will be caused. Body tissue. In this way, 304 stainless steel will have weak magnetic properties.

In addition, after 304 stainless steel is cold worked, the structure will also be transformed into martensite. The greater the degree of cold working deformation, the more martensite transformation and the greater the magnetic properties of the steel. Like a batch of steel belts, Φ76 pipes are produced without obvious magnetic induction, and Φ9.5 pipes are produced. Because the bending deformation is larger, the magnetic induction is more obvious. The deformation of the square rectangular tube is larger than that of the round tube, especially the corner part, the deformation is more intense and the magnetism is more obvious.

In order to completely eliminate the magnetic properties of 304 steel caused by the above-mentioned reasons, the austenite structure can be restored and stabilized by high-temperature solution treatment, thereby eliminating the magnetic properties.

In particular, the magnetism of 304 stainless steel caused by the above reasons is not at the same level as the magnetism of other materials, such as 430 and carbon steel. That is to say, the magnetism of 304 steel always shows weak magnetism.

This tells us that if the stainless steel is weakly magnetic or not magnetic at all, it should be judged as 304 or 316 material; if it is the same as carbon steel, it shows strong magnetism, because it is judged as not 304 material.