What are the English terms for the Dutch words "kooktraject" and "smelttraject"

Solution 1:

The term boiling range is used in chemistry and the oil industry. Distillation range is also used, particularly for hydrocarbons.

As an example, a presentation on petroleum science from Penn State says

Complex mixtures such as crude oil, or petroleum products with thousands of different compounds, boil over a temperature range as opposed to having a single point for a pure compound. The boiling range covers a temperature interval from the initial boiling point (IBP), defined as the temperature at which the first drop of distillation product is obtained, to a final boiling point, or endpoint (EP) when the highest-boiling compounds evaporate.