The heat resisting austenitics are highly alloyed stainless steel used for their excellent oxidation resistance, high temperature strength and creep resistance in high temperature applications. They are tough and ductile and can be readily fabricated and machined.

U-309S-1.4833 has very good oxidation resistance and this is improved even further with U-309S Si- 1.4828 , which has a higher silicon content.

The U-309S types have a lower nickel content compared to the U-310S types and this improves their resistance to hydrogen sulphide (H2S) attack at high temperatures.

The U-309S types are low carbon grades and are recommended for applications where sensitisation and subsequent corrosion by high temperature gasses or condensates during shutdown may pose a problem.

The U-309S types are used, for example, in applications such as furnace parts, fire box sheets, high temperature containers, catalytic converters, exhaust systems, etc.

The U-310S types have higher chromium and nickel contents to enable them to resist oxidation in continuous service at temperatures up to 1 200°C provided reducing sulphur gases are not present.

The higher silicon content in U-310S Si-1.4841 improves this oxidiation resistance even further.

In intermittent high temperature service, the U-310S types can be used at temperatures up to 1 030°C as they resist scaling and have a relatively low coefficient of expansion differential between the metal and the scale. These stainless steels have superior resistance to both the U-304 types and the U-309S types in carburising and reducing environments.

The U-310S types are used in applications such as furnace parts, muffles, radiant tubes, ammonia converters, etc.