Abstract: A thermal treatment installation for treating and quenching pieces (22) of small dimensions comprises a treatment line (LT) including a treatment furnace (2) for bringing the pieces to treatment temperatures, a quenching cell (4) located downstream from the furnace, and a transport apparatus for displacing the pieces along the treatment line. The pieces to be treated are placed in baskets (20) and the baskets are grouped into charges or distinct lots forming a volume (V) having a height (H) substantially less than the other dimensions (L1, L2) of the volume. The transport apparatus comprises several driving devices (DE1, DE2, DE3, DE3' AND DE4) which are individually regulated by a regulation circuit (UC) to at least three speeds including an input speed (V1), a treatment speed (V2) and an output speed (V3) to divide the treatment line into sectors so that locally along the treatment line the baskets move at different speeds.