October 6, 2022

We all know that martensitic steel is very difficult to weld in Metal Welding Service, so, what should we pay attention to skills?

01

Welding method

Martensitic steel can be welded by all fusion welding methods except gas welding, such as electrode arc welding, submerged arc welding, tungsten argon arc welding, MIAR arc welding, etc.

Due to the high cold crack sensitivity of this steel, it is necessary to strictly clean the welds and dry the electrodes before welding to maintain low or even ultra-low hydrogen welding conditions.

When the constraint of the welded joint is large, it is better to use GTIG or MIG welding.

The tendency of cold crack can be reduced by increasing welding heat input appropriately without overheating embodiment in the near seam area.

02

Welding material

The choice of welding material depends on the type of steel, welding method and working conditions of the joint. In order to ensure the requirements of the performance, the chemical composition of the weld should be close to the composition of the base metal, that is, it is appropriate to select welding materials close to the composition of the base metal.

But in this case, the weld and heat affected zone are easy to harden and become brittle. In order to prevent cold cracking, heat treatment is generally required after welding.

When heat treatment is not allowed, 25-20, 25-13 austenitic steel welding material should be used to form austenitic weld, relax the welding stress, and can more solid hydrogen solution, reduce the cold crack tendency.

Austenitic weld plasticity and toughness, but strength is low, and therefore is only applicable to work under the static load conditions of low stress of welding, and due to the thermal physical properties of weld and differences, when working under high temperature, the joint interface can produce high additional stress and cause joint failure in advance, so also does not apply to work under the high temperature of welding.

Electrode arc welding, usually using low hydrogen electrode, 400 ~ 450℃ drying for two hours before welding. Submerged arc welding should use low silicon, high alkaline or weak acid flux, such as HJ172, HJ173, HJ251, etc. TIG welding is mainly used for the back cover welding and thin welding of multilayer welding.

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Preheat and interlayer temperature

Preheating and maintaining interlayer temperature is an important technological measure to prevent cold crack. The selection of preheating temperature should first consider the carbon content in the steel, then consider the joint constraint, the composition of filling metal and welding method.

Table 1 shows the recommended preheating temperature and heat input according to the carbon content. If the tightness of the joint is large, the preheating temperature and interlayer temperature should be increased accordingly. The interlayer temperature should not be lower than the preheating temperature.

When using austenitic steel welding material, the weldment thickness can not be preheated or low temperature preheating.

04

Post weld heat treatment

Post-welding heat treatment is another important technological measure to prevent cold crack. In the selection of welding materials close to the base material composition, we generally need to carry out post-welding tempering heat treatment. When austenitic steel welding materials are selected, post-welding heat treatment is generally not required.

In order to ensure that Austenite is completely transformed into martensite after welding, it is not allowed to temper immediately after welding. The joint must be cooled to a certain temperature below the Ms point and kept for a certain time before high temperature tempering.

Because if the tempering occurs immediately after welding, the austenite will turn to pearlite and the carbide will precipitate along the grain boundary of austenite. This kind of structure is very brittle.

However, in order to prevent cold cracking, the joint is not allowed to cool to room temperature before high temperature tempering treatment, usually cooled to 100 ~ 150℃ temper treatment.

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