What is weld decay? Where do we find its common features?
What is weld decay? Where do we find its common features?
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Weld decay is a form of intergranular corrosion, usually of stainless steels or certain nickel-base alloys, that occurs as the result of sensitization in the heat-affected zone during the welding operation. The corrosive attack is restricted to the heat affected zone (HAZ). Positive identification oRead more
Weld decay is a form of intergranular corrosion, usually of stainless steels or certain nickel-base alloys, that occurs as the result of sensitization in the heat-affected zone during the welding operation.
The corrosive attack is restricted to the heat affected zone (HAZ). Positive identification of this type of corrosion usually requires microstructure examination under a microscopy although sometimes it is possible to visually recognize weld decay if parallel lines are already formed in the heat affected zone along the weld.
As in the case of intergranular corrosion, grain boundary precipitation, the chromium carbides in stainless steels, is a well recognized and accepted mechanism of weld decay. In this case, the precipitation of chromium carbides is induced by the welding operation when the heat affected zone (HAZ) experiences a particular temperature range (550°C~850°C). The precipitation of chromium carbides consumed the alloying element – chromium from a narrow band along the grain boundary and this makes the zone anodic to the unaffected grains. The chromium depleted zone becomes the preferential path for corrosion attack or crack propagation if under tensile stress.
Weld decay can be prevented through:
1.Use low carbon (e.g. 304L, 316L) grade of stainless steels
2.Use stabilized grades alloyed with titanium (e.g. type 321) or niobium (e.g. type 347). Titanium and niobium are strong carbide- formers. They react with the carbon to form the corresponding carbides thereby preventing chromium depletion.
3.Use post-weld heat treatment (PWHT).
See lessDuring the welding process in nickel alloys and austenitic stainless steels, where chromium is added for corrosion resistance, local sensitized zones often develop. Sensitization is due to the formation of chromium carbide along grain boundaries, resulting in the depletion of chromium in the regionRead more
During the welding process in nickel alloys and austenitic stainless steels, where chromium is added for corrosion resistance, local sensitized zones often develop. Sensitization is due to the formation of chromium carbide along grain boundaries, resulting in the depletion of chromium in the region adjacent to the grain boundary. This chromium depletion produces localized galvanic cells. If this depletion drops the chromium content below the necessary 12 wt% that is required to maintain a protective passive film, the region will become sensitized to corrosion, resulting in an intergranular attack.
This condition occurs when the material is heated to temperatures around 700°C (1290°F) for too long and often happens during welding or improper heat treatment. When such localized galvanic cells form due to welding, the resulting corrosion is known as weld decay.
Methods for preventing weld decay include:
1. Using low carbon grade stainless steels alloyed with stabilized grades of titanium or niobium, which are strong carbide formers. They react with the carbon to form the corresponding carbides, thereby preventing chromium depletion.
See less2. Using post-weld heat treatment
3. Using laser beam surfacing
Any stainless stool contains 13% or higher chromium. Because of the large amount of chromium, stainless steels are kept tree from corrosion due to the chromium oxide forming a rigid membrane on their surfaces when subjected to such corrosive media as air or oxidizing acids (e.g. nitric acid).This phRead more
Any stainless stool contains 13% or higher chromium. Because of the large amount of chromium, stainless steels are kept tree from corrosion due to the chromium oxide forming a rigid membrane on their surfaces when subjected to such corrosive media as air or oxidizing acids (e.g. nitric acid).This phenomenon is called weld decay. Its common features mainly found in 18/8 austenitic stainless steel undergoing sensitization.
See lessHello, I would like to add some points in @suvam During welding of 18-8 SS, in HAZ region the temperature reaches in temperature range 500-800 oC where this sensitization problem exists. This temperature helps to form Cr23C6 along the grain boundaries (GB) and thus Cr depletes near to grain boundaryRead more
Hello,
I would like to add some points in Suvam
- During welding of 18-8 SS, in HAZ region the temperature reaches in temperature range 500-800 oC where this sensitization problem exists.
- This temperature helps to form Cr23C6 along the grain boundaries (GB) and thus Cr depletes near to grain boundary.
- Since, GB has higher energy, the precipitate starts forming at that location.
- Due to composition difference there is formation of galvanic cell and when it is exposed to corrosive environment then weld decay takes place.
See lessThe crude stainless steel contains 0.1%C, which must be reduced to<0.01%C. 18/8 SS carries ~0.01%C and as an elcrode it will form good joint but later due to intergranular corrossion Cr3C27 is precipitated along grain boundary which leads to weld decay. In rural area hawkers sell utensils made ofRead more
The crude stainless steel contains 0.1%C, which must be reduced to<0.01%C. 18/8 SS carries ~0.01%C and as an elcrode it will form good joint but later due to intergranular corrossion Cr3C27 is precipitated along grain boundary which leads to weld decay.
See lessIn rural area hawkers sell utensils made of crude SS for cheap price, later they crack/tear alond the curves/edges for the above mentioned reason.
All the answers are well trie. Greetings.