What is the difference between 4140 and A572 steel?

What is the difference between 4140 and A572 steel?
A572 is a hot-rolled carbon steel that is used where a high strength to weight ratio is desired. A grade such as AISI 4140 offers decent corrosion resistance due to higher chromium and molybdenum content and is commonly used in firearm parts, pressurized gas tubes, and structural tubing for roll cages.1

Is A572 grade 50 or A709 grade 50?
A572 Grade 50 is dual certified to A709 Grade 50. A709-50 material is stocked primarily in flat rolled products, but is also available to a lesser extent in Structural and bar steel products. A709-50 / ASTM A709 is fracture critical and covers the requirements for structural steel for bridges and other structures.

Is A572 better than A36?
ASTM A36 vs. A572: For projects that require more basic structural steel without extreme conditions, A36 is often sufficient. However, for projects that demand higher strength, better durability, and less weight, A572 is the better choice.