Heat Treatment

Ferrous PM parts containing 0.3% or higher combined carbon can be quench-hardened and tempered for increased strength, hardness and wear resistance. The percentages of carbon and other alloying elements effectively combined in the material and its density, determine the degree of hardening possible for any given quench condition. Microindentation hardness values of 650 HK 100 gf (56 HRC) and higher can be obtained by quench hardening.

The recommended procedure for heat treatment and/or carburization of ferrous PM parts is with a gas type atmosphere or vacuum. The use of liquid salts is not recommended because of the possibility of surface absorption and subsequent bleed-out of the salts and internal corrosion. Low density parts may carburize throughout while higher density parts (7.0 g/cm3 or higher) may develop a carburized case. Process control is necessary to ensure that specified carbon levels are maintained.

Tempering or stress relief is required after quenching for maximum strength and durability; typically one (1) hour at temperature per 1 inch (25 mm) of section thickness. A compromise between hardness and such properties as impact energy is necessary because the tempering temperature to achieve surface hardness will not necessarily provide optimum strength properties. The tempering temperature is a major factor in determining final hardness.

When selecting materials for a particular application, the cross-section of the component should be taken into account. The listed properties are attained ONLY if the same density and microstructure are present in the PM part as were present in the standardized test specimens used to obtain the mechanical property in question. The hardenability of the material should be appropriate for the cross-section of the part.