What are Super Stainless Steels?

Super stainless steels may be not a common material to you, which are referred to a special type added with a higher content of Nickel, chromium, molybdenum than conventional stainless steel. This blog will help you to get knowledge of them and determine which one is good for your project.

According to their microstructural characteristics, super inox can be divided into super ferritic stainless steel, super austenitic stainless steel, super martensitic stainless steel and super duplex stainless steel.

Super austenitic stainless steel

On the basis of common austenitic stainless steel, this alloy prevents intergranular corrosion caused by precipitation of Cr23C6 by increasing the purity of the alloy, increasing the number of beneficial elements and reducing the C content, thus obtaining good mechanical properties, technological properties, and local corrosion resistance. These alloys also replace Ti stabilized stainless steel.

Super ferritic stainless steel

This kind of stainless steel inherits the characteristics of ordinary ferritic stainless steel, such as high strength, good oxidation resistance, and excellent stress corrosion resistance. It also improves the ductility-brittleness transition of ferritic stainless steel, the sensitivity to intergranular corrosion and the low toughness of welded state. The application of super ferritic stainless steel in corrosion resistance, chloride pitting corrosion resistance and crevice corrosion resistance has entered a new level by using refining technology, reducing C and N content, adding stabilization and metal toughening elements of weld metal.

Super Duplex Stainless Steel

This kind of steel was developed in the late 1980s. The main grades are SAF2507, UR52N and Zeron100. Its characteristics are low C content, high Mo content and high Ni content. The ferrite phase content in the steel accounts for 40%-45%, and it has excellent corrosion resistance.

Super martensitic stainless steel

Common martensitic stainless steel lacks sufficient ductility and is very sensitive to stress during deformation, so cold forming is difficult. However, by reducing carbon content and increasing nickel content, super martensitic stainless steel can be obtained. This kind of hardening stainless steel can solve the problem of poor strength of ordinary martensitic stainless steel perfectly. The only problem is its poor toughness and weldability. Super martensitic steel has been widely used in oil and gas exploitation, storage and transportation equipment, hydroelectric power generation, chemical industry, and high-temperature pulp production equipment.

Functional stainless steel

With the change of market demand, various stainless steels with special uses and functions are constantly emerging. For example, the new medical Ni-free austenitic stainless steel material is mainly Cr-Ni austenitic stainless steel, which has good biocompatibility. Another kind of anti-bacterial stainless steel containing copper is made by adding 0.5%-1.0% Cu into the stainless steel and adopting special heat treatment to make the stainless steel uniformly disperse the precipitates of epsilon-copper from the surface to the interior, thus playing an anti-bacterial role. This kind of anti-bacterial stainless steel containing Cu is suitable for high-grade kitchen utensils and other products requiring high processability and anti-bacterial properties. Ag antimicrobial stainless steel has a high antimicrobial effect on Escherichia coli and Staphylococcus flavus. Especially when the surface is abraded or processed, this material can always maintain the good antimicrobial effect.

Nitrogen-alloyed stainless steel

The addition of N as an alloying element in stainless steel can improve the austenite stability, balance the proportion of phases in dual-phase steel, improve the strength and corrosion resistance of steel without affecting the plasticity and toughness of steel, and partly replace Ni in stainless steel. In dual-phase steels, N retards the diffusion and precipitation of intermetallic compounds; in martensitic steels, N and other elements form nitrides distributed on grain boundaries, which can improve the hardening ability and prevent the growth of austenite and ferrite grains during tempering at high temperature. Austenitic stainless steel with high N content, i.e. high strength non-magnetic austenitic stainless steel, has been developed in recent years. It has high-temperature strength. It will be widely used as cryogenic superconducting material, high corrosion resistance and non-magnetic material.

High Clean Stainless Steel

At present, the scrap rate of products caused by inclusions in domestic stainless steel plants is over 20%. Therefore, the high cleanliness centered on inclusion control in stainless steel smelting process has attracted more and more attention. In the process of stainless steel smelting, endogenous inclusions are produced during deoxidation, alloying and liquid steel crystallization. External inclusions in finished products are produced in the smelting, casting, and transportation of molten steel. In order to obtain stainless steel with high cleanliness, attention should be paid to raw materials, deoxidizer, deoxidizing system, refining, and continuous casting process.

Among them, the most famous one is the steel containing 6% Mo (254SMo). This kind of steel has excellent local corrosion resistance. It has good pitting corrosion resistance (PI 40) and stress corrosion resistance under the conditions of seawater, aeration, crevice, and low-speed erosion. It is a substitute material for Ni-based and Ti-based alloys.

Secondly, in terms of high temperature or corrosion resistance, 304 stainless steel has a better high temperature or corrosion resistance, which is irreplaceable. In addition, from the classification of stainless steel, the metallographic structure of special stainless steel is stable austenite metallographic structure.

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