4140 tool steel

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4140 alloy steel is a highly versatile and popular low-alloy steel that is used across many industries. This steel is alloyed with chromium and molybdenum to give it specific properties. 4140 alloy steel is very tough, with particularly high torsional and fatigue strength. This makes it great for rotating components that experience significant stress, such as axles and shafts. 4140 steel is available in a variety of different forms but is most popular as bars.

What Is 4140 Alloy Steel?

Like all steels, 4140 alloy steel is composed primarily of iron. It is alloyed with carbon, chromium, molybdenum, and other minor components. It is therefore considered a “chromoly” steel. This alloy is tough and resists both wear and corrosion. 

What Is 4140 Alloy Steel Used For?

4140 alloy steel is typically used for rotating components that are placed under high stress such as axles, drive shafts, crankshafts, spindles, and gears. It is also used for static components that operate under high load such as bolts and chain links. The 4140 alloy excels in these situations thanks to its high tensile strength, toughness, and torsional strength.

How Is 4140 Alloy Steel Made?

4140 alloy steel is made using either an electric furnace or a basic oxygen furnace. The base alloy components are added and melted together at temperatures exceeding 1500 °C. The molten steel is then tapped off from the furnace and allowed to cool. It gets annealed through controlled heating and cooling. After annealing, the mill scale is removed by dipping the metal in hydrofluoric acid. Next, the steel is melted once more and cast into billets or slabs. These are then hot-worked or cold-worked — usually using rollers — to the desired finished dimensions.

What Is the Chemical Composition of 4140 Alloy Steel?

The full composition of 4140 alloy steel is given in Table 1 below: