Steel powder composition and sintered body thereof

Abstract

A powder composition and a sintered body thereof are presented. The powder is a martensitic stainless steel powder for powder injection molding without deformation problems during sintering. The powder composition includes 0.80-1.40 weight percent (wt %) of carbon (C), less than 1.0 wt % of silicon (Si), less than 1.0 wt % of manganese (Mn), 15.0-18.0 wt % of chromium (Cr), 0.10-2.50 wt % of titanium (Ti), and the remainder iron (Fe). The powder can be sintered with a sintering temperature varying within 50° C. and can reach a high density without distortion, and thereby a good dimensional stability is obtained.

Description

FIELD OF INVENTION[0001]The present invention relates to a steel powder composition and a sintered body thereof, and more particularly to a martensitic stainless steel powder composition for metal injection molding, which has an improved dimensional control, and a sintered body thereof.BACKGROUND OF THE INVENTION[0002]Metal injection molding (MIM) includes processes such as mixing a metal powder and a polymer binder, molding with an injection molding machine, debinding, and sintering at high temperatures, to obtain a metal part of near net shape. The technology involves in two fields, that is, powder metallurgy and plastic injection molding. Due to the high strength and hardness requirements for a MIM material, martensitic stainless steel is widely used, for example, steel species such as Japanese SUS410 series, Japanese SUS420 series, and Japanese SUS440C series.[0003]However, the martensitic stainless steel powders generally have problems of poor sinterability, such as poor dimens...

AI Technical Summary

Benefits of technology

[0009]The effect of the present invention lies in that, a titanium-containing composite carbide such as titanium carbide (TiC) or titanium-vanadium carbide ((Ti,V)C) is formed in the process by adding a strong carbide formation element, such as titanium, or by adding a titanium carbide such as TiC or (Ti,V)C, in the steel powder composition, to overcome the disadvantages such as poor dimensional control and low sintered density generated in sintering of the conventional martensitic stainless steel powder.

[0010]Furthermore, the steel powder composition of the present invention may improve the sintering temperature range to 50° C. and still achieve a high sintered density with good shape retention capability, and thereby the production yield is improved.

Problems solved by technology

However, the martensitic stainless steel powders generally have problems of poor sinterability, such as poor dimensional stability, the non-uniform sintered density, inconsistent properties from batches to batches, melting at the surface of sintered work pieces, and even distortion.

The reason lies in that the optimum sintering temperature of the steel species falls within about 10° C. When the temperature is higher than this temperature range, the amount in liquid phase is excessive, and thus a network of liquid phase is formed, and the strength is lowered, and even distortion occurs.

When the sintering temperature is lower than this temperature range, the sintered density is too low.

At present, one of the solutions for solving these problems in sintering of the martensitic stainless steel powder is to control the temperature homogeneity of a sintering furnace within ±5° C. of the optimum sintering temperature, that is, the sintering window is 10° C. However, in that case, a several sets of thermocouples, heaters, and programmed controllers need to be mounted on the sintering furnace, and thus the cost is increased.

However, the production rate is low.

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