AISI 4140 alloy steel is similar to AISI4130 in chemical composition. However, its higher carbon content endows it with more outstanding strength and heat treatment performance. However, due to the slight increase in carbon content, its welding performance is slightly inferior to that of AISI4130.

The machinability of AISI 4140 is excellent. For simple shapes, efficient processing can be carried out after normalizing treatment. When it comes to complex shapes, annealing treatment can meet higher processing requirements. At an appropriate carbon level, especially in the annealed state, its processing performance is even more excellent.

Because AISI 4140 alloy steel is harder than ordinary carbon steel, it needs to withstand greater pressure during the forming process. Although this alloy steel can be welded using conventional techniques, if it is welded in a heat-treated state, it will have an adverse effect on its performance. Therefore, it is recommended to carry out appropriate heat treatment after the welding is completed.

It is extensively used in tubular form for downhole tools.