WOAH Lakeside -
That is quite a tangent, there was no mention of coatings or SS in the question, It must be the Sam Adams goggles ;-)
CNC Boy
1018 is standard cold rolled steel it is soft. Usually rated in Rockwell B or Brinell hardness scale. I once threw a piece in the hardness tester and I believe it came up -20 Rc on the other hand 4140 HT is an alloy steel and is 28 Rc. This is a huge difference between the two.
The alloy steel will resist corrosion better than CRS.
CRS machines easier.
CRS is less expensive.
To answer which would be better - better for what?
Generally the alloy steel is better but depends on what it is being used for and whether you can justify the difference in cost.
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