What are Stainless Steels? 

The stainless steels They are alloys resistant to oxidation and corrosion, with a moderate deformation capacity.

They contain about 11% chromium (Cr), which allows the formation of a thin, protective layer of chromium oxide upon exposure to oxygen.  There are several families of stainless steels based on their crystalline structure and hardening mechanism. The most common families are martensitic and austenitic stainless steels.  

Martensitic Stainless Steels  

Cr can be present between 10.5% and 18%, and carbon (C) can reach up to 1.2%. Martensite is a metastable phase of steels that is formed by rapid cooling of austenite, without diffusion. This phase is characterized by being hard and brittle due to the body-centered tetragonal crystal structure (TCCu) obtained by quenching the steel.  

AISI 420 Courage 

Noted for its:  

• High resistance to corrosion and oxidation.  

• Good machinability and polishing ability.  

• With excellent dimensional stability during quenching.  

It has applications in inserts for high-performance plastic injection molds, exposed to corrosive derivatives of injected plastics, such as PVC. It can replace 303, 304 and 316 stainless steel, improving wear resistance, but sacrificing corrosion resistance.  

AISI 416  

It corresponds to a variation of AISI 410 steel, with the addition of sulfur (S) to improve machinability.  

• High hardenability steel.  

• Good corrosion resistance.  

It is magnetic in any conditions and resists oxidation up to 760°C. With quenching, it can reach a hardness of 42 HRC and allows a wide tempering range to acquire different levels of mechanical resistance and toughness.  

Austenitic Stainless Steels  

In this type of steel, nickel (Ni) is a stabilizing element for austenite. Its composition can have more than 16% Cr, Ni greater than 6% and low levels of C (0.1%). Austenite is obtained by extensive solid solution hardening. These steels have excellent ductility, formability and corrosion resistance. They are not ferromagnetic, which is an advantage for many applications.  

AISI 303  

Austenitic stainless steel not hardenable by conventional quenching. It is a variation of AISI 302 steel, with high S and phosphorus (P) content to improve its machinability.  

• Non-magnetic in annealed condition, although it may present a certain degree of magnetism when cold deformed.  

• Lower thermal conductivity than low alloy carbon steels.  

Used for large production machining of mechanical components exposed to oxidizing agents. It can replace AISI 304, although its resistance to corrosion and oxidation is slightly lower.  

AISI 304  

Austenitic stainless steel not hardenable by conventional quenching. Alloy 304, which contains 18% Cr and 8% Ni, has the widest range of applications within stainless steels. It is worth highlighting its:  

• Good forgeability and weldability characteristics, being less sensitive to intense carbide precipitation during the process. It is important that the cooling rate is rapid once the operation is completed.  

It can be replaced by AISI 416, considering that it is magnetic and has lower resistance to corrosion and oxidation.  

Contributions and Recyclability of Stainless Steels  

Stainless steels have been a great contribution to science for the chemical, pharmaceutical, architectural, food and transportation industries, due to their performance in specific conditions. Furthermore, stainless steel can be easily recycled with a simple separation between magnetic and non-magnetic, contributing to the circular economy.  

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