Measures To Control Grain Size

       

Grain refinement is one of the important
ways to improve the mechanical properties of metals. The following methods are
often used in industrial production. In this paper, we introduce the methods of
improving the undercooling of metals and modifying them.

1. Improve the undercooling of metal. The
nucleation rate and growth rate are related to the undercooling degree. With
the increase of the undercooling degree during crystallization, the nucleation
rate and growth rate increase, but the increase rates of the two are different.
The growth rate of the nucleation rate is higher than that of the growth rate,
as shown in Fig. 3. In the undercooling range of general metal crystallization,
the greater the undercooling degree, the greater the N / G ratio and the finer
the grain.

The main measures to increase the
undercooling degree are to improve the cooling rate of liquid metal. For
example, in casting production, metal mold or graphite mold can be used to
replace sand mold, locally increase cold iron, increase the thickness of metal
mold, reduce the preheating temperature of metal mold, reduce the thickness of
coating layer, and adopt water-cooled mold to improve the cooling rate of
castings.

2. Carry out deterioration treatment. Grain
refinement by increasing undercooling is only effective for small or
thin-walled castings. For castings with complex shape, it is often not allowed
to greatly improve the cooling rate. Therefore, modification process is widely
used in production to refine grains.

The so-called modification treatment is to
add inoculant or modifier (nucleating agent) to liquid metal to increase the
number of heterogeneous cores and promote non spontaneous nucleation, so as to
refine grains and improve microstructure. Solid particles with high melting point
are often used as nucleating agent in production. For example, adding titanium
and zirconium to aluminum alloy liquid and adding titanium, vanadium and
zirconium to steel liquid can refine the grain. Adding ferrosilicon or silicon
calcium alloy to cast iron can make the graphite in the structure finer. There
is another kind of modifier, which can not provide the crystallization core,
but can adhere to the crystallization front of the crystal and prevent the
grain growth. Therefore, it is also called growth inhibitor. For example,
adding sodium salt to aluminum silicon alloy can enrich sodium on the surface
of silicon, reduce the growth rate of silicon and hinder the formation of
coarse silicon crystals, so as to obtain fine alloy structure.

For more information about the 3D printing powder, spraying coat powder, or WC based powder,

 you may search online wococarbide. Wococarbide.com provides various products and technical questions and answers.