Stainless Steel 440C

Because of high difficulty in machining, most stainless steel parts are produced by precision casting. Otherwise, the limitation of design geometry and other defects will result in unsatisfactory tolerance and surface roughness. Therefore, metal injection molding (MIM) is the most suitable fabrication technology for stainless parts. It can make complex parts with excellent properties at low price.

However, in reason of technical difficulties, there are few MIM manufacturers can apply MIM technology for 440C materials. ZCMIM has concentrated in the research of MIM 440C debinding and sintering, and successfully produced different MIM 440C part

Metal injection molding technology can manufacture the high-strength and high-hardness of stainless steel 440C. Otherwise, different process parameters in MIM process will result in significant alternation in final mechanical properties and micro-structures. In MIM 440C process, there are three key parameters: sintering atmosphere & temperature, powder loading, carbon addition.

Normally, the higher sintering temperatures give rise to slight higher densities of sintered 440C parts in both pure hydrogen and partical vaccum atmospheres. In addition, the parts sintered in pure hydrogen is also denser than that in partial vacuum atmosphere. From the following optical micro-structures of sintered 440C parts at different sintering temperature. Although higher temperature sintering attain higher densification stage, there are still continuous carbide network on micro-structure.

After heat treatment, the morphology of 440C matrix is composing of martensitic phase, finely primary carbide distribution, secondary carbide network, and retain austenite phase. We can find the micro-structure in the following picture.

In addition, the hardness of 440C parts increase at least 50% after heat treatment. Comparatively, the SS 440C parts achieve lower performance in pure hydrogen than in partial vacuum.

In the following picture, high powder loading of 64% will increase the density simply. Sine there is lesser space between metal powder particles to be densified during MIM sintering process.

Since the high oxygen concentration in the initial powders, the average loss of carbon concentration for sintered parts is approximate 0.25 %. Carbon addition can anticipate and compensate this amount of loss. Once add 0.4% of activated carbon powder(ACP) to base 440C powders, the final sintering density will increase 2.5%, and final hardness can reach to as high as 63 HRC.