Ca Al Mn Si Ti B , what will be the sequence of addition in steel and why?

For addition I assume u are asking about the process during steelmaking.

See first thing we need to note is that many elements like Si is already present in steel we can’t get full rid of from the very first blast furnace process. Other than this we add some purposely for specific application and type of steel we want. Now, I will explain the addition used in most general cases.

• The first element we add is Ca l. no doubt calcium is used in primary Steelmaking process to get desired concentration and refining of steels in BOF or EAF. It’s used in slag making during the process. However, Ca is also added afterwards during laddle desulphurisation or as injection powders for inclusion control.
• Now, Al, Si, Mn can have multiple applications during additions but mostly they are added as deoxidizers. Al being the most powerful deoxidised is added during laddle treatment. This can be either done as synthetic slags or by core wire injection and several methods available. Also, previously we used to add it during tapping and at its vicinity to avoid the floating up of Al and mixing go slag without serving it’s it’s purpose.
• Si and Mn are also added simultaneously with Al as Ferro-Sillicon Ferro-manganese, mostly as synthetic slags. There prominent work is deoxidation. But we need to remember that application matters a lot. Some steels like Hadfield steel has high Mn content. They can be added as directly as powders during laddle and composition is maintained accordingly. Si is also maintain similar way and according to composition we decide whether to add it separately or not.
• Now, Ti is very useful alloying element but it is readily attacked by Oxygen. Ti purpose is to firm carbides and provide grain refinement and secondary hardness for this we need Ti in dissolved form. Due to this Ti is usually added after deoxidation process that is after addition of Al, Si and Mn. Also, they are added after the tapping in laddle  and usually we add a little late after tapping so to avoid as much oxidation of Ti.
• The Boron is last element to be added after the Ti. Boron has similiar purpose but Boron is highly effected by Oxygen and needed to be avoided. Ti takes almost all oxygen after addition. So B is added after Ti so that negligible Oxygen is left. Usually Fe-Boron wires are used and done during the laddle treatment.