4140 steel: Surface Condition Under Different Processing Techniques

Have you ever had customers ask what the surface of 4140 steel looks like? Do they ask if the surface finish will affect subsequent processing? Could you provide a photo of the surface for their reference?Are these requests frequently made by customers? We believe everyone has their own answer.

The surface condition of 4140 alloy steel varies significantly depending on the processing technology, directly affecting its suitability for subsequent machining. Next,we will discuss this topic in more detail.

4140 Steel Surface Condition After Forming

The hot and cold forming processes for 4140 steel include hot forging, hot rolling, and cold drawing.

4140 steel surface codition after hot forged

4140 Hot Forged Surface

Tolerance:+3 to +10mm

4140 steel surface codition after hot rolled

4140 Hot Rolled Surface

Tolerance:+0.5 to +2mm

4140 Cold Drawn Surface

Tolerance:Best H11

Based on experience, hot-forged 4140 steel has the roughest surface and the most oxide scale. Hot-rolled 4140 steel is relatively better, containing a small amount of oxide scale. Cold-drawn 4140 steel has a high surface finish and no oxide scale.

4140 Steel Black Surface Condition After Quenched and Tempered

4140+QT surface after hot forged condiiton

4140+QT Forged Surface

4140+QT surface after hot rolled condiiton

4140+QT Rolled Surface

4140 steel quenched and tempered surface after cold drawing

4140+QT Cold Drawn Surface

As we can see from the image above, the forged 4140 steel exhibits significant oxide scale after quenching and tempering. The rolled 4140 steel also shows some oxide scale after medium-frequency induction hardening. However, the cold-drawn 4140 round steel, after medium-frequency induction hardening, shows almost no oxide scale.

4140 Steel Surface Condition After Heat Treatment

4140 steel surface codition after tempered

4140 Tempered Surface

4140 Annealed Surface

4140 Normalized Surface

As we can see from the image above, tempered 4140 steel contains a small amount of oxide scale. The oxide scale is quite severe in both annealed and normalized 4140 steel. The difference is that the oxide scale in annealed 4140 steel is tightly adhered to the surface, making it difficult to remove manually. However, the oxide scale in normalized 4140 round steel has gaps between it and the surface, allowing it to be slowly chipped away with tools.

4140 Steel Surface Condition After Machining

4140 steel surface codition after rough turned

4140 Rough Turned Surface

4140 Peeled Surface

4140 Polished Surface

4140 Grinded Surface

As shown in the image above, the surface roughness of roughly machined 4140 steel is the worst, with heavy tool marks, while the surface roughness of polished and ground 4140 steel is good, reaching a mirror finish.

Furthermore, in terms of surface precision, the rough-machined 4140 steel can be controlled to +1 to +2 mm, while the precision of peeling and polishing can reach h11, and the highest precision of grinding can reach h9.