Alloy elements refer to elements with a certain content range that are added to stainless steel to obtain the required structure and various properties.
The alloy elements added to stainless steel are mainly metallic elements such as Cr, Ni, Mo, Si, Cu, Mn, W, etc., but there are also non-metallic elements such as C, N.
The main destination and function of the alloying elements added to stainless steel are: the alloying elements act as solutes and enter a solid solution of iron (Fe) as a solvent in an atomic state, forming various matrix structures (solid solutions) of stainless steel; the various alloying elements interact with each other to form various compounds; Some alloy elements (such as Cu, Pb, etc.) can still exist as pure metal phases in the matrix when their content exceeds their solubility in steel; Some relatively active elements and elements with strong binding force with oxygen, sulfur, and other elements in steel can also form various non-metallic inclusions. The alloying elements in stainless steel have various effects on the structure and properties of steel through these effects.
Due to the fact that the structure and properties of stainless steel are mainly determined by the alloying elements in the steel under many conditions, the study of the relationship between composition, structure, and properties in stainless steel has always been of concern.
So, what are the effects of alloying elements on the properties of stainless steel?
Simply put, the performance of stainless steel refers to the behavior of stainless steel under the influence of external chemical, mechanical, physical and other factors. For example, the rust resistance and corrosion resistance of steel under the action of chemical media; Under the influence of mechanical factors, the strength, plasticity, toughness, etc. of steel; under the influence of physical factors, the thermal conductivity, magnetism, etc. of steel.
Adding alloying elements to steel will naturally bring new alloys to which they are added due to their inherent characteristics. As mentioned earlier, adding chromium to steel can make it rust resistant because chromium itself does not rust and has a much stronger passivation ability than iron, which can passivate the steel. When the chromium content in the steel is ≥ 12%, this passivation effect becomes apparent. Adding other alloying elements to stainless steel, the characteristics of these alloying elements (or their combination when multiple elements are present) will also bring to the various types of stainless steel to which they are added.
The influence of alloy elements on the performance of stainless steel is twofold: firstly, the alloy elements directly affect the performance of stainless steel; secondly, the performance of stainless steel is influenced by the previously described changes in the microstructure of stainless steel. Generally speaking, the direct impact of alloy elements is mainly on the stainless steel's rust resistance (although it also affects other properties under certain conditions, such as solid solution strengthening), while the microstructure mainly affects the steel's mechanical, cold and hot workability, welding, physical and other properties (of course, it also affects the stainless steel's corrosion resistance under certain conditions, such as the influence of some compound precipitation). The influence of many properties of steel in stainless steel is often the result of the combined action of the chemical composition and microstructure of the steel.
