A few thoughts on the formation – or prevention – of cold cracks during welding

Hydrogen, and not necessarily the molecular hydrogen H2, but its atomic form, plays a decisive role when it comes to welding fine-grained steels, for example.

The effect: the individual water atom is the smallest thing you can imagine. If there are such atoms in the weld metal, they move back and forth through the crystal lattice over time. If two atoms meet, something dramatic happens. An H2 molecule recombines from two individual H atoms. However, this molecule requires considerably more space than the individual atoms. The consequence of this is a not inconsiderable explosive effect, which manifests itself in corresponding cracks in the weld metal.

What is particularly unpleasant about this is that a visual inspection at the end of the weld or a correspondingly more in-depth examination reveals a perfect result! The hydrogen needs time for its diffusion process. The cracks only appear after one or even several days.

The question now arises as to where the hydrogen comes from. It should be clear that it does not occur as a tramp alloy element in the base or filler material. In this case, we are dealing with an existing supply of WATER (H2O) and, for example, an electric arc that is capable of splitting the water – which leads to the free hydrogen atoms.

So how can you make sure that the available water supply is as small as possible? Well, first of all, you should make sure that the raw material is not standing in the rain and gets really wet. Imagine, however, that a steel beam is stored absolutely dry in a covered outdoor storage area at temperatures close to 0°C. Now it is brought into the hall for processing. Now it is brought into the hall for processing. The mechanism that now sets in can best be compared to a slightly open freezer door: All of a sudden, all the water vapor from the surrounding air irresistibly finds its way to this new, coldest place. In practice, you can see how the wearer really ‘sweats’. This effect occurs immediately and with brute force as soon as the workpiece is the coldest point in the room.

The remedy: the effect is immediately reversed when our steel becomes warmer than the surroundings. Mind you, 10K more than the ambient temperature would already ensure that no more water condenses. And if you wait long enough, any moisture present will be magically attracted to the new, coldest point in the hall. For example, from a window pane that is not so well insulated. The greater the temperature difference, the faster this process takes place.

Bringing heat into the material is therefore exactly what helps to reduce the amount of water on the steel.