MIM has been recognized as a cost-effective way to produce parts for critical applications requiring both high precision and high reliability, as in firearms, automotives, air and power tools. Apart from tensile property, fatigue strength is an important criterion for long-term reliability. Normally, a finer powder can lead to higher strengths of sintered part with more uniform and densified microstructure. Low-alloy steel 4605, which contains 0.4-0.6% carbon and 1.5-2.5% nickel, remains to be the most economic commercial powder for producing structural components that require considerable hardness and strength. It allows a variety of heat treatment process as allowed by wrought carbon steels. In heat treated state, its hardness can reach HRC 55 with UTS ranging up to 1900 MPa.