20 questions about welding

Welding is a family of methods used for joining two workpieces; steel in the case of SSAB. Usually a single heat source, normally an electrical arc, locally melts the two workpieces to form a common liquid pool. When the steel solidifies, the pieces are joined. In many cases, a special steel rod or wire (consumable, filler) is melted into the weld pool to get a good weld joint.

The most common welding methods are Shielded Metal Arc Welding (SMAW) more commonly known as MMA or stick welding, Tungsten Inert Gas (TIG), Gas Metal Arc Welding (GMAW) more known as MIG/ MAG welding, submerged arc welding (SAW) and laser welding.

Yes. A typical example can be to weld the root pass with TIG and fill passes with MIG/MAG. 

Yes, but it is more challenging to weld some steels than others, depending on alloying and dimensions.

Welding methods and parameters must be suitable for both steels. Usually, the least weldable steel determines the parameters to be used. 

There is a vast number of consumables. The steelmaker provides advice on these for their different grades. For SSAB steels, see the welding recommendations.

Workpieces can be preheated in a furnace with an oxy-fuel flame, with electrical heating mats or with electrical induction. It is crucial not to exceed the maximum temperatures given in the data sheet for the steel grade to be welded. Too high a temperature may negatively affect the properties of the steel.

Steel workpieces can be preheated in a furnace with an oxy-fuel flame, with electrical heating mats or with electrical induction. It is crucial not to exceed the maximum temperatures given in the data sheet for the steel grade involved. Too high a temperature may negatively affect the properties of the steel.

Source: SSAB Welding Handbook

A rule of thumb is a maximum of 5 ml hydrogen per 100 g weld metal. However, this is in practice not possible to measure. The hydrogen content in solid wires for MAG welding is typically around 1.5-2 ml hydrogen per 100 g weld metal, while cored wires can pick up moisture in the flux which might increase to higher values per 100 g weld metal. Keep all consumables dry and warm, in particular flux-covered and flux-core ones. Packages should be opened shortly before use. 

Shielding gas protects the liquid weld pool from nitrogen and oxygen in the air. Shielding gases are usually different mixtures of argon and carbon dioxide affecting the welding process and result. Shielding gases for Hardox^® and Strenx^® steels are the same as for other low-alloyed steels. 

Source: SSAB Welding Handbook

Hardfacing is a procedure where a harder material is welded to the base metal surface to create a protective layer. The method can be applied to all SSAB steels, but for the hardest ones, a soft buffer layer must first be welded on the base plate to reduce the risk of cold cracking into the base plate. All types of conventional welding processes can be used for both the buffer layer and the hardfacing layer.

Yes, it can. However, the primer will increase the porosity in the welded joint. A high-quality weld calls for complete removal of the primer in the welding area. 

Hardness deterioration is difficult to control. The maximum heating temperatures stated in the data sheets of the steel should always be respected.

The heat-affected zone (HAZ) is close to the welded joint where the temperature has increased temporarily due to the liquid weld pool. HAZ size depends on the heat applied. The mechanical properties of the base steel in the HAZ may change, usually in a negative direction. 

The designer has chosen a suitable plate thickness for the expected structural stresses. A rule of thumb is that the throat thickness is equal to the plate thickness for a one-sided fillet weld. For two-sided fillet welds, the throat thickness should be approx. 0.7 times the plate thickness.

Plate shrinkage in the vicinity of the welded joint will vary due to varying peak temperatures and residual stresses of varying sizes will appear. Thin plates will react with deformation and relaxation of the stresses, while the stresses will prevail in thick plates.  

Too much heat input will alter the mechanical properties of the welded joint (base material in too big a volume) while too little heat input may result in a lack of fusion. SSAB recommends the SSAB WeldCalc app to calculate proper welding parameters.

Hydrogen cracks in welded joints can form due to the concentration of hydrogen in the material close to the weld, as hydrogen embrittles the material. Hydrogen atoms in a hot welded joint will diffuse and collect at “comfortable” spots, e.g. microdefects in the microstructure. Hydrogen gets trapped when the joint cools. Cracks can initiate from those hydrogen traps after hours or even days. The inevitable residual stresses will elongate the cracks. High hardness and alloying make steels more sensitive to hydrogen cracking. 

There are many factors that could cause a welded joint to fail. The most common ones are defects in the form of physical discontinuities, poor microstructure, and residual stresses. There are various reasons behind those factors, including choice of design, joint type, joint geometry, welding process, heat input, preheating, and welding consumables. 

There are many possible welding defects. Some of the more common ones include: 

More information on the above defects can be found in the SSAB Welding Handbook.