Toughness is dependant both on chemical composition and heat treatment...Knife Guy probably knows and has posted the most on this topic...do a search on his posts as I am sure he did a detailed breakdown on this topic not so long ago.

Certain trace elements can improve rusting...certain others improve strength and durability so the steel would not shatter or break. How high you take a heat treatment also impacts on shatter aspects and durability...and on how hard the steel is to sharpen and how long it may hold an edge. High Rc settings give a harder steel which holds an edge longer and usually to achieve this you need a good high carbon element to the steel...so carbon is very important...but as said above the best "super steel blades" often combine an inner core of high carbon steel and an outer core of a more durable and softer steel to give the blade strength...this is particularly so with powdered base steels which can be used as inner core edge steel for sharpness and then sandwiched either through a damascus process or done by a forge when pressing the steel with another steel for this effect. Most blades though use a singular composition of steel...not a blend...but can be capable of achieving similar effects through differential heat treatment which hardens the edge and inner core steel higher than the outer sides and spine.

In Busse knives SR101 has been given a differential heat treatment on some Swamp blades...Infi however does not seem to need it...although it has an usual composition for a steel and is the only one to contain Nitrogen...this combined with the special heat treatment seems to give a very high level of performance...SR77 is also uncommon in knives as it is usually used in Jackhammer bits...it is usually very hard to get it to take an edge needed on a knife and is designed to simply be tough...a special heat treatment to the steel enables this to be used by Scrapyard for knives but probably accounts for why SR77 holds an edge less well than Infi or SR101.

As to how the trace elements operate to give different "properties" to the steel...I would check some of KnifeGuys posts as he seems to follow this aspect quite well. For me I like a simple "overview" picture and that is how I remember the differences.