How to Increase the Density of Stainless Steel Powder Metallurgy

(How to Increase the Density of Stainless Steel Powder Metallurgy)

Stainless steel powder metallurgy is prone to pores during manufacturing,
which will affect its use, reduce its mechanical properties, corrosion
resistance and wear resistance, and limit the application of stainless steel
powder metallurgy. These properties of stainless steel powder metallurgy are all
improved with the increase of density. Therefore, it is necessary to increase
the density of stainless steel powder metallurgy. So how to increase the density
of stainless steel powder metallurgy?

Super solid phase wire sintering:

1. Traditional stainless steel sintering generally uses solid phase
sintering. However, a large number of pores will remain in the stainless steel
during solid phase sintering, which will reduce its density and performance. The
super solid phase line liquid phase sintering makes the stainless steel
pre-alloy powder form a liquid phase during sintering, and the liquid phase
fills the pores through flow to improve the density and performance of the
sintered body.

2. Unlike ordinary liquid phase sintering, super solid phase sintering is the
sintering of pre-alloyed powder, and it is always a single phase during the
sintering process. The sintering temperature is between the solid phase line and
the liquid phase line. At temperature, the pre-alloyed powder particles form a
liquid phase in the grains, at the grain boundaries and on the surface of the
particles. The particles are rearranged under the action of the capillary force
of the liquid phase. The places where the surface curvature changes greatly will
be preferentially dissolved and flow through the liquid phase. Mass transfer,
precipitation in the recesses or pores of large particles, to achieve the
purpose of rapid material transfer, so that the sintered body can be
compacted.

3. The density, hardness, wear resistance and corrosion resistance of 316L
stainless steel obtained by super solid phase sintering at 1400 ℃ are higher
than those of solid phase sintering at 1200 ℃. However, because the sintering
temperature is too high, the crystal grains will grow too much and cause
overburning, which should be avoided.

Use suitable additives:

1. Adding certain low-melting alloy elements to the powder can greatly reduce
its porosity through the liquid phase formed during sintering, so that stainless
steel can meet higher performance requirements. For example, adding 2% to 8%
copper-based alloy to 304 stainless steel powder, due to the low melting point
of copper, a liquid phase begins to form at 960 ℃, and all forms a liquid phase
at 1000 ℃. When the temperature is higher than that of copper At the melting
point, the flow of the liquid phase makes the surface pores continue to
spheroidize and shrink; because copper has good wettability to the stainless
steel matrix, it can be evenly distributed on the stainless steel matrix, so
that the sintered body has a significant reduction in pores, and the
microhardness is also obvious. improve. When the additive amount is 8%, the
density after sintering at 1350℃ increases to 7.05g/cm3.

2. The properties of powder metallurgy stainless steel can also be improved
by adding suitable strengthening phases, especially the mechanical properties.
For example, adding 1.5% to 3% (volume fraction) SiC to 316L stainless steel,
due to the interaction between SiC and the stainless steel matrix, forms a low
melting point Fe-SiC phase, which improves the density of the sintered body and
makes it harder And abrasion resistance have been improved.

Compared with stainless steel produced by traditional smelting processes,
stainless steel powder metallurgy has the advantages of producing parts close to
net shape, high dimensional accuracy, high material utilization, and uniform
structure. It has been widely used in machinery, chemicals, ships, automobiles,
and instruments. Instruments and other industries.

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(How to Increase the Density of Stainless Steel Powder Metallurgy)