The term Resulphurisation is indeed used rather than sulphurisation, and there’s a specific reason for this terminology:

1. Prefix “Re-“:
   The prefix “re-” in this context doesn’t mean “again” as it often does in English. Instead, it’s derived from the Latin “res,” meaning “thing” or “matter.”
2. Historical Context:
   In the early days of steelmaking, sulphur was considered an impurity that needed to be removed. The process of removing sulphur is called “desulphurisation.”
3. Intentional Addition:
   When metallurgists discovered the benefits of sulphur for machinability, they began intentionally adding it back into certain steels. This process was seen as contrary to the traditional desulphurisation.
4. Terminology Evolution:
   The term “resulphurisation” emerged to distinguish this intentional addition of sulphur from both:
   a) The natural presence of sulphur in steel
   b) The process of removing sulphur (desulphurisation)
5. Meaning:
   In this context, “resulphurisation” essentially means “concerning the matter of sulphur” or “dealing with sulphur content,” emphasizing the deliberate control and adjustment of sulphur levels.
6. Industry Standard:
   This term has become the standard in the steel industry to specifically refer to the intentional addition of sulphur to improve machinability in free-cutting steels.
7. Differentiation:
   “Sulphurisation” typically refers to the formation of sulphur compounds on a material’s surface, often as a form of corrosion or chemical reaction. This is different from the metallurgical process of adding sulphur to the steel composition.
8. Global Usage:
   The term “resulphurisation” is used consistently across the global steel industry, in technical literature, and in metallurgical education.

In essence, “resulphurisation” in steelmaking doesn’t mean “to sulphurise again,” but rather “to deliberately adjust the sulphur content,” usually by increasing it. This terminology reflects the historical context of sulphur in steelmaking and the specific nature of the process in producing free-cutting steels like En1a.

This linguistic nuance highlights the evolution of metallurgical processes and how our understanding of elements like sulphur in steel has changed over time. What was once considered only an impurity became a crucial additive for certain steel grades, and the terminology evolved to reflect this change in perspective and practice.