WELDING OF LOW CARBON STEELS

• Steels having a total carbon content which does not exceed 0.30% are known as Low carbon steels.  These steels can withstand rough treatment during fabrication and its working life. It can be heated to a higher temperature up to red hot color or it can be even white hot color and then quenched with cool water without appreciable embrittlement.
• Low carbon steels canbe welded through any welding processes. Selection of the welding process and welding procedure gives a result of low cost and high welding performance. The factors that are to be considered in order to achieve those are
• Thickness
• Joint design
• Welding Position
• Production required
• Whenever low carbon steel in comparison with high alloy is being welded there is lesser amount of selections to be made and the result is it has wider difference in cost and weld performance. All carbon steels can undergo arc welding readily, if the carbon content is too low they may not be suitable for high speed production welding.
• The steels containing carbon content less than 0.13% and 0.40% manganese cannot be used for high speed production welding because they produce internal porosity in the weld metal. The steels with lower carbon content have lower tensile strength and lower hardness but the ductility and impact strength is higher.
• Low Carbon steels have good weld ability and they can be welded without taking any special precautions. These steels are not capable of developing exceptional mechanical properties by heat treatment and hence forth there no possibility to damage their basic properties by heating to weld or melt them.
• All weld joints should be well ground / machined and be free rust, moisture, dirt, paint etc.
• The welding of low carbon steel with different welding processes is listed below. 

Shielded Metal – Arc Welding:

Most of the welding of low carbon steel in shielded metal arc welding is done manually. There are different types and different grades of electrodes which are used for welding different types of steels. For welding low carbon steel the electrode of E-60xx series can be used for better welding process. The same electrode can also be used for welding medium carbon steel as well.

Submerged – Arc Welding:

The low carbon steels can be welded in both automatic and semi-automatic process. When welded these low carbon steels they make mechanical properties which are equal to the properties which is obtained when welded with coated electrodes. In this process a blanket of flux is covers the welding region and the filled material i.e. the wire is fed mechanically through the torch head and the welding is done. It requires a very high welding current which is six time greater when compared to manual welding processes this results in higher melting rate of electrode and a higher speed of welding. The quality of both automatic and semi-automatic submerged arc welding process is high because the region to be welded is protected covered by flux which protects the weld region from oxidation.

Inert gas Welding:

In this process the weld is being protected by helium or argon gases which act as a blanket for the weld region and protect them from being oxidized. This process for some application is often less economical when compared to other process for welding low carbon steel. But this process is easier for large quantity of production. This process has both consumable electrode welding as well as non-consumable electrode welding of low carbon steel. In general the processes are referred to as MIG and TIG welding. TIG is used for lighter materials where MIG is used for heavier materials. These processes are economical.

Co2 and Vapor Shielding:

In this welding process Co2 is used as a shielding gas in metal arc welding of low carbon steel. This result in improved speed, better penetration and improved quality of weld. The arc which is produced during the process is difficult to control so the electrode selected should act as a deoxidizer in order to ensure good quality of weld. In general the electrode used is of mild steel composition. When flux cored electrode mild steel electrode is used good results are obtained.

Vapor shielded arc welding is always used for high quality welding of carbon steels. They are better than other automatic and semi-automatic processes. The welders with little experience can perform welding with good quality and appearance. Generally the arc is shielded from the atmospheric contamination this permits  following the joint to be easier. It is more effective than Co2 and MIG welding during the cracking which occurs due to high sulphur in the base metal and results in producing sound welds.

Oxyacetylene Welding:

This welding process is made up of both gases acetylene and oxygen. These gases are neutral neither acetylene is excess nor oxygen is excess. A low carbon steel filler rod is used for the deposition of material on the weld region. This process is basically slow when compared to other processes. With the carburizing flame the base metal is heated and now the filler material or the welding rod is introduced into the flame which is melted and casted against the prepared surface. Some amount of carbon is added to the metal because the excess acetylene flame. The resulting weld will have slightly higher strength and lesser ductility when compared to the weld made with neutral flame. Another type of flame which has excessive amount of oxygen and is harmful. It causes excessive foaming and sparking of metal.  

Thermit Welding:

Thermit welding is more of a casting procedure of welding. Welding low carbon steel with thermit welding causes some annealing and some amount of growth of grains in the parent metal happens. The slowly cooled weld metal will have large coarse grains. With low carbon steel it does not matters. The properties of the low carbon steel in casted condition are equal to as that of highly heat treated metals properties and hence the weld quality of joint is satisfactory.

Forge Welding:

This is a solid-state welding process that joins two pieces of metal by heating them to a high temperature and then hammering them together. The process is one of the simplest methods of joining metals and has been used since ancient times. Forge welding is versatile, being able to join a host of similar and dissimilar metals. With the invention of electrical and gas welding methods during the Industrial revolution, forge welding has been largely replaced. Low carbon steel pipes are welded by a roll forge welding process in the mill by lap or butt joint. These welds are strong but the mechanical properties are not equal to that of the base metal because it’s impossible to work all slag and oxide out of the joint.

Welding in cold weather:

The low carbon steels can withstand any kind of weather condition. They can undergo all kind of treatments without any bad effects on its mechanical and physical properties. For example let’s consider the steel is to be welded below the freezing temperature. During the time of welding unusual quick cooling happens which can result in cracking of the material. Hence to avoid such situation the material is preheated before welding in such conditions. Low hydrogen electrodes are supposed to be used. During the welding process the arc must not be struck on the base metal outside the groove, even on the plate edge. These are the reasons for start of cracks and it causes failure or fracture during the service.

 Visit us: www.arcraftplasma.com                                             Email us: salesarcraft@gmail.com

Disclaimer