Carbolite/carbolite 103 is bascily hi-tensile steel. There is a 'lightweight' version of this metal. HLE tubing is significantly different.

Peugeots internal/external brazing is incredibly strong. Back in the day we had a customer who T-bones a car and bent the TT and DT in the typical places. The TT metal tore ~1/4" from the internal/external brazed joint.