Welding of ferritic stainless steel

Many methods of joining stainless steels are able to be applied well to ferritic stainless steels, mainly including.

(1) Melt welding By melting the base material and the filler metal after recrystallization so that the two or more materials separated from each other to achieve a complete bond.

(2) Soft brazing Using the filler metal with a melting point below 450°C, heating it to the brazing temperature (below the melting point of the base metal) to obtain a connection.

(3) Hard brazing Same as soft brazing, but the welding temperature is >450°C.

(4) Mechanical connection Including inlay, rolled edge bonding, riveting and mechanical fastening.

(5) Bonding Achieved by using a bonding agent and applying pressure to a clean and active surface. The bonding agent achieves the joining action by oxygen, water or chemical reaction.

Many welding methods developed for carbon steel can also be used in stainless steel welding, really suitable for stainless steel welding and has become the standard method are arc welding, resistance welding, electron beam welding, laser welding and friction welding.

Although it is said that various arc welding methods can be used to do the welding of ferritic stainless steel, but the welding energy concentration, welding speed should be the preferred method of welding ferritic stainless steel. The use of appropriate welding methods to achieve control of welding line energy, to achieve the purpose of suppressing the ferrite grain overgrowth in the weld zone.

So it seems, the welding method should be selected for high energy plasma arc welding and vacuum electron beam welding is the most appropriate, and to prevent the intrusion of air. In addition to the use of small heat input for welding, the back of the weld can be inert gas protection, and preferably using water-cooled copper pad to reduce overheating and increase the cooling rate; multi-layer welding interlayer temperature should be controlled at about 1000C.

Welding materials for ferritic stainless steel

The selection of welding materials for ferritic stainless steel is undoubtedly very important for the welding of ferritic stainless steel.

Its welding material should ensure that the plasticity and toughness of the welded joint, that is, the problem of embrittlement does not occur, but also to ensure that the welded joint of ferritic stainless steel has the same corrosion resistance as the parent material.

When welding ferritic stainless steel, two welding materials can usually be used.

The same type of welding material as the base material such as 0Crl2, 0Crl3, 0Crl3A1, etc. with 0Crl3Nb wire, 0Crl7, 0Crl7Ti using 10Crl7 (Ti) wire. In the requirement that the weld metal and the parent material has the same electrical conductivity, magnetic conductivity and mechanical properties and surface color should be used when the same material welding materials.

The use of austenitic welding materials or nickel-based alloys The use of austenitic welding materials or nickel-based alloys, essentially heterogeneous steel welding, can improve the toughness of the welded joint, eliminating preheating before welding and post-weld heat treatment. The application of ferritic welding materials is somewhat limited by the low toughness of the deposited metal and the difficulty of effectively transitioning the ferrite forming elements such as added Al and Ti into the melt pool. Although in some examples using the same metal as the wire is successful, but it is best to use low carbon austenitic stainless steel as the filler metal for ferritic stainless steel welds.

Welding techniques for ferritic stainless steels

(1) Using narrow welding channels, such as small welding line energy, faster welding speed, etc.

(2) Keeping the heated end of the welding wire in the shielding gas at all times.

(3) The use of advanced welding techniques, such as plasma arc welding, fusion electrode arc welding, etc.

(4) Continuing to pass shielding gas after arc extinguishment until adequate cooling.

(5) Protect the welding pool with argon gas of high purity.

(6) the back of the weld should be protected by inert gas.

(7) For multi-layer welding, stainless steel brushes should be used to remove interlayer oxides.