Manganese Austenitic Stabilization
The suppression of martensitic transformation through high manganese concentrations, thereby stabilizing the high-temperature phase down to room temperature. This leads to tough, work-hardenable microstructures.
Manganese is a strong austenite former. If you have enough of it in the steel, the structure stays austenitic even at room temperature and doesn't transform into martensite. You know that from manganese Hadfield steels, which are extremely tough and wear-resistant because of this.
When welding, you have to watch out that the heat input isn't too high. Otherwise, precipitations or structural changes can occur in the heat-affected zone, which reduce toughness. Especially with multi-pass welds, you should keep an eye on the interpass temperature.
For practice, that means: cool the part well and weld with as little heat input as possible. If you have the choice, use a filler material that also contains manganese, so that the weld metal matches the base material in composition.