Before answering this question, we need to know the specific application of 4140 steel.
4140 steel can be very soft, it can reach a surface hardness below 200HB by annealing.Obviously, under this hardness, its application field is also rare.
4140 steel can also be very hard. Usually, the ideal hardness can be achieved through quenching and tempering heat treatment to meet the needs of industrial applications.Usually the hardness can be controlled between 26-60HRC,but in actual production,medium-level hardness 26-34 HRC is widely used.