Debinding variables affecting the residual carbon content of injection-molded Fe-2 Pct Ni steels
- PDF / 3,115,354 Bytes
- 10 Pages / 613 x 788.28 pts Page_size
- 60 Downloads / 182 Views
I.
INTRODUCTION
POWDER injection molding is a process route capable of mass-producing high-performance, complexshaped components, m It has widely replaced the other competitive processes in the shape forming of metals and ceramics. A suitable powder is mixed with an appropriate amount of binder. The mixture is then injection molded into a green body. A debinding step at which binder is removed without deteriorating the composition and shape of the component is carefully controlled before the powder is sintered to a high final density. This process proves successful when a powder has a regular shape and a mean particle size in the neighborhood of 10 /~m for metals and 1 /xm for ceramics. Carbonyl-iron powders prove ideal for this route because of the easy molding and sintering arising from its spherical particle shape and its mean particle size of about 5/xm. It is used in molding different ferrous alloys, in which Fe-2 pct Ni is one of the most widely used systems. Carbon content determines the properties of many injection-moldable systems. Soft magnetic materials (Fe-Si, Fe-Ni) and austenitic stainless steels require minimum carbon contents, whereas SiC requires a slightly excessive carbon content. On the other hand, cemented carbides require a stoichiometric quantity of carbon content and ferrous steels require an appropriate quantity. For powder injection molded Fe-2 pct Ni steels, a carbon content in the range of 0.3 to 0.5 wt pct yields an optimal combination of strength and ductility. I2~ Controlling carbon content in powder-injection-molded components has been an intense issue of research, 13-61 primarily due to the difficulty in controlling the reaction kinetics associated with the variations of thermal cycle, process time, and debinding atmosphere. Among the debinding variables, debinding route, 17-1~ thermal cycle, t41 debinding atmosphere, 13,4,5j and the gas flow rate 15,6j are the key issues in carbon control. The solvent-debinding route generally yields a better controlling capability than Y.L. HO, Graduate Student, and S.T. LIN, Associate Professor, are with the Mechanical Engineering Department, National Taiwan Institute of Technology, Taipei, Taiwan, Republic of China. Manuscript submitted September 17, 1993.
METALLURGICAL AND MATERIALS TRANSACTIONS A
single-stage thermal debinding because of the significantly shorter thermal cycling times.[7-1~ In the solventdebinding route, the binder is first partially removed by solvent. Subsequently, a short thermal cycle in the range of 2 to 5 hours is capable of burning off the residual binder without destroying the structural integrity of the partially debound compact. By controlling the process variables, as indicated previously, during the thermal cycle, various residual carbon contents (30 ppm and 1.2 wt pct) can be achieved. During the thermal cycle, carburization or decarburization can occur, depending on the atmosphere. IllJ Ideally, an equilibrium carbon potential can be achieved by using an atmosphere containing carburization- and decarburizatio
Data Loading...
