Austenite is a lamellar microstructure of steel. It is usually a non-magnetic solid solution in which a small amount of carbon is solid-dissolved in rhenium-Fe. The austenite name is from the British metallurgist William Chandler Roberts-Austen. Austenitic Stainless Steel Pipe has good plasticity, low strength, some toughness, and no ferromagnetism. Because austenite is a face-centered cubic, the tetrahedral gap is larger, which can hold more carbon.
Ferrite is an interstitial solid solution in which carbon is dissolved in α-Fe. It has a body-centered cubic lattice, and its carbon dissolving ability is very low. It can dissolve only 0.0008% of carbon at normal temperature, and its maximum carbon dissolving ability is 0.02% at 727 ℃. It is called ferrite or alpha solid solution, and it is expressed by alpha or F. Alpha is commonly used in phase icons, and F is commonly used in the text. Austenite with a sub-eutectoid a component is firstly co-precipitated to form ferrite.
Stainless steel Pipe Ferritic
Stainless steel Pipe Ferritic generally has a pure ferrite structure at room temperature, which is not very high in strength, ductility, and good toughness; if it is heated to high temperatures, a small amount of austenite structure may also appear (lower for chromium Steel) or no austenite the structure appears at all. Therefore, under the effect of thermal cycling during welding, there may be a small or no martensitic structure. Therefore, this type of steel does not have the problem of significantly reduced strength or quench hardening after welding and even a small amount of martensitic structure can be solved by post-weld heat treatment. It can be said that the room temperature strength of this type of steel welded joints is not the main contradiction of welding; furthermore, because its welding thermal expansion problem is far less than that of austenitic stainless steel, its welding hot and cold cracking problems are not very prominent. , Ferritic stainless steel is not as good as austenitic stainless steel, which mainly means that during the welding process, the plasticity and toughness of the welded joint may be reduced, that is, the problem of embrittlement occurs. As with the welding of other types of stainless steel, how to ensure that ferritic stainless steel welded joints have the same corrosion resistance as the base metal, and the embrittlement of welded joints that may occur in long-term service at high temperatures must be paid attention to.
As a Welded Pipe Stainless Steel Supplier, share with you the welding skills of ferritic stainless steel.
1. Welding with narrow beads, such as small welding line energy, faster welding speed, etc.
2. Make the heated end of the welding wire always in the protective gas.
3. Adopt advanced welding technology, such as plasma arc welding, melting electrode arc welding, etc.
After the arc is extinguished, the protective gas should be continued until the cooling is sufficient.
5. Protect the welding molten pool with high purity argon.
6. The back of the weld shall be protected by an inert gas.
7. For multilayer welding, a stainless steel brush should be used to remove interlayer oxides.
Ferritic stainless steel is relatively brittle for three reasons:
1. Grain is coarse. Ferritic stainless steels do not undergo phase transformation during heating and cooling, and cannot use phase transformation recrystallization to refined grains.
2. Brittleness at 475 degrees Celsius. The Cr atoms in the ferrite are ordered to form a Cr-rich body-centered cubic lattice phase, which causes lattice distortion and internal stress. 3. 6-phase brittleness. When ferritic stainless steel stays for a long time at 550-850 ° C, 6 phases will be precipitated. The 6 phases are FeCr intermetallic compounds. The precipitation also is accompanied by a large volume change, and the 6 phases are often distributed along the grain boundaries.
Copyright © Baosteel Special Metals Co., Ltd. (Baowu Group) All Rights Reserved