What Is SUS430? Usage And Precautions

What is SUS430? Usage and precautions

 

What is SUS430? [Composition, specific gravity, weldability, etc.] Usage and precautions
SUS430 is the most common ferritic stainless steel and is widely used in household and industrial parts.

Application of SUS430
SUS430 is the cheapest stainless steel and is used in household items such as sinks and tableware.

Most materials such as spoons and forks that are engraved with "stainless steel" are made of this material. And, because it costs less to make than SUS304 stamped from "18-8 stainless steel," the corrosion resistance is reasonable for a relatively cheap product.

Strength of SUS430
The tensile strength is over 450MPa (*1), which is the same level as low carbon steel.

Like mild steel, it has a well-defined yield point and similar work-hardening properties.

SUS430 is designed in much the same way as using mild steel.

However, please note that embrittlement can occur at low and high temperatures, as shown below.

* 1: JIS G 4303 stainless steel rod

Heat resistance of SUS430
Generally, the upper limit temperature that can be safely used as mechanical parts is about 300°C.

If kept for a period of time in the range of 300°C to 550°C, especially around 475°C, embrittlement will occur (475°C embrittlement), which is divided into high chromium density areas and low chromium density areas.

In addition, even if the temperature is maintained in the range of 600°C to 800°C for a long time, σ phase (brittle compound of iron and chromium) precipitates, causing σ phase embrittlement (σ phase embrittlement).

If embrittlement occurs, it can be restored by heating it above this temperature and quenching it.

At low temperatures, ferrite is brittle because it has a body-centered cubic lattice.

I think it's best to keep it at a low temperature of around -20°C.

Weldability of SUS430
As mentioned above, there is 475°C brittleness and σ phase embrittlement, so welding of SUS430 can cause trouble if not done according to the correct procedure.

SUS430 welding precautions

Place a fixture with good thermal conductivity in close contact with the workpiece to increase the cooling rate.
Weld in the shortest time without overheating
Early cooling is required to prevent σ phase embrittlement and 475°C embrittlement. However, the thermal conductivity of stainless steel is about half that of carbon steel, so heat will be released to clamps made of copper, etc.

In addition, when welding SUS430, hardening caused by the formation of martensite and high-temperature embrittlement caused by coarse grains will occur during the cooling process.

Ferritic stainless steel contains more Cr than martensitic stainless steel, so it is hardened without quenching. However, quenching at 800 to 900°C hardens a limited area, and the toughness and ductility are significantly reduced. (As a post-welding post-treatment, treatment at 760~785℃ will increase the impact value.)

This will not immediately cause problems such as weld cracks due to sigma phase embrittlement, but if this becomes a problem, switching to lower carbon materials can be effective.

SUS430LX is a low-carbon version of SUS430 with added titanium and niobium. Low carbon makes quenching and hardening difficult, and the purpose of titanium and niobium is to prevent grain coarsening.

SUS430 corrosion resistance
The corrosion resistance of SUS430 is not as good as SUS304.

However, since it does not contain nickel, it is less prone to stress corrosion cracking than SUS304.

Magnetic properties of SUS430
Since SUS430 is a ferrite type, it is ferromagnetic like steel.

Unlike austenitic SUS304, it has the characteristics of attracting magnets.

SUS430 price
SUS430 is cheaper than SUS304 because it does not contain expensive nickel.

It depends on the shape and conditions, but you can think of it as an intermediate between steel and SUS304.

Even if the material cap goes up, costs can often be reduced by omitting plating and painting by changing from steel to SUS430.

SUS430 summary
Speaking of SUS, it is easy to write SUS304 on the picture, but is SUS304 level corrosion resistance really necessary?

SUS430 has some things to watch out for such as brittleness, but if used properly it will reduce costs, so I think it's best to check the required specifications before use.