The Role of Ferrite in Austenitic Stainless Steel

14/06/2022

Austenitic stainless steel is an important class of stainless steel welding materials, because of its good heat resistance, corrosion resistance, low temperature resistance and good processing and weldability are widely used in various fields, its production accounts for about 70% of the total stainless steel.

 

Mechanism of Formation of Ferrite


All different types of stainless steel are iron-based alloys with Cr content of 12% or more. The organization of stainless steel is determined by the alloying element content (also known as chromium and nickel equivalents).

For stainless steel, alloying elements can be divided into two main categories, namely ferrite forming elements (also known as chromium equivalent elements) and austenite forming elements (also known as nickel equivalent elements), the balance between the two types of elements determines the amount of ferrite content in the tissue. Austenite forming elements are mainly C, N , Mn, Ni, Cu, etc., and ferritic forming elements are mainly Cr, Mo, Si, Nb, Al, Ti, etc.



Ferrite in Austenitic Stainless Steel Advantages and Disadvantages


Beneficial effects:

  • 1. Prevent thermal cracking

  • 2. A small amount of ferrite can improve the corrosion resistance of welded joints, especially intergranular corrosion and stress corrosion rupture resistance.

Disadvantages: 

  • 1. Easy to produce brittle phase, reducing the toughness of the material.

  • 2. Too high ferrite drop caused by austenite resistance to pitting corrosion and corrosion in special media decreased.



Control of Ferrite in Austenitic Stainless Steel Welds


1. In addition to the design of the weld composition (i.e., the Creq/Nieq ratio mentioned earlier).

2. There is also the control of the welding process.


① The height of the arc, the type of shielding gas will significantly affect the N content of the deposited metal, which in turn affects the ferrite content of the weld.

② Welding parameters and process control, will directly affect the melt pool temperature and weld solidification rate, which in turn affects the weld ferrite content.


YUHONG ASTM A312 TP304L STAINLESS STEEL SEAMLESS PIPE

 
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