>>10883218>and how often does that happen on current excavators?you would be very surprised, evidently. All heavy equipment is in a constant state of breaking down and being fixed again. Also, what no one has touched on yet is the actual reason you want to use steel no matter what, which is the fact that steel has a fatigue limit. Unlike aluminum, which will eventually develop cracks even under the slightest load strain, steel does not ever develop cracks until a minimum amount of strain is developed in the crystal structure. If you design your beam or arm or whatever to be beefy enough that no part of the steel is brought up to that level of strain, it will literally NEVER crack or break. An aluminum excavator's days are numbered however even if you treat that thing like a newborn baby, and it WILL suffer a catastrophic failure at some point.
Even if your main goal is to reduce weight no matter what, which is an old-space viewpoint and rendered moot anyway by the advent of Starship, you will still want to use steel for all of the load-bearing parts of the equipment you send. The only other option I can think of would be titanium, since it also has a fatigue limit and is significantly lighter for almost the same strength, however building anything big out of titanium is a nightmare and extremely expensive to boot.
