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Two important properties in furnace materials
Metal used inside a furnace encounters hot gases, while some components also carry a load. Resistance to surface oxidation and the ability to retain strength at temperature are related but distinct properties. Surface behaviour may be especially important in a thin gas baffle, while mechanical properties have a larger role in a hanger or support. These different duties help explain the variety of heat-resistant stainless steels. 309S, 1.4835 and 1.4818 are three separate grades within this family.
309S: components exposed to hot gases
309S / 1.4833 is an austenitic stainless steel with high chromium and nickel contents. Familiar applications include furnace internals, annealing boxes and hot-gas baffles. Chromium helps form a protective oxide layer on the surface, an important property in components exposed to hot air. The designation 309 is also associated with 1.4828, a separate grade with a different silicon content. It should retain its own EN identity rather than being treated as another designation for 1.4833.
1.4835: equipment experiencing changing temperatures
1.4835 / S30815 is a heat-resistant stainless steel containing silicon, nitrogen and a small cerium addition. It is also known by the trade name 253 MA. Oxidation resistance during repeated heating and cooling is a notable property in furnace components. Silicon and cerium contribute to the behaviour of the protective surface layer, while nitrogen supports strength. Heating tubes, hot-material handling equipment and various furnace elements are applications that benefit from these combined characteristics. Surface behaviour and mechanical duty come together in the same material.
1.4818: a separate heat-resistant grade
1.4818 / S30415 is known by the trade name 153 MA. Its chromium–nickel composition also contains silicon, nitrogen and cerium, supporting applications in furnace and heating equipment. Similar trade names do not make 1.4818 and 1.4835 identical products. Their balances of chromium and other alloying elements differ. Both are associated with surface protection and mechanical strength in hot environments, but they remain separate material definitions. Sheet and plate forms provide examples of their use in broad-surfaced furnace internals.
Their relationship to 310S and ferritic heat-resistant steels
310S belongs to the same broad austenitic heat-resistant family and is known for its higher chromium and nickel contents. Ferritic grades such as 1.4742, 1.4762 and 446 have a different role, including lower thermal expansion and useful properties in particular hot-gas environments. A furnace can therefore contain several different steels. Temperature, gas atmosphere and component duty work together: a protective tube, a broad cover and a load-bearing connection can benefit from different material characteristics within the same plant.