This article, in our Material Science section, is about the effect of alloying elements in cast iron. What effects do the alloying elements Cr (chromium), Mo (molybdenum), V (vanadium), and Ni (nickel) have on the corrosion resistance, hardness, machinability, and strength of cast iron, and what advantages do they bring to cast iron?
How Alloying Elements Affect Cast Iron
The manufacturing benefits provided by white and gray cast iron may not be considered sufficient. For such cases, new properties are desired. Generally, to increase strength and corrosion resistance, alloying elements added to cast iron give it new advantages, earning it the name alloyed cast iron. The alloying elements added to cast iron in environments where the alloy composition can be kept under control (electric arc furnaces, Siemens-Martin furnaces) are as follows:
Nickel: Nickel, which can be added to cast iron up to 5%, makes machining easier while also increasing corrosion resistance, hardness, wear resistance, and homogeneity.
Chromium: Chromium, added up to 3%, has the opposite effect to silicon and nickel in cast iron, preventing the formation of graphite. It increases corrosion resistance and hardness.
Nickel-Chromium: Used to create cast irons with a hard internal structure that doesn’t make machining more difficult.
Molybdenum: One of its most important effects is increasing the homogeneity of the internal structure in cases where the cast iron section is thick. It has a positive effect on hardness, wear resistance, and strength. However, it makes machining more difficult. It’s added to cast iron up to a ratio of 1.5%.
Vanadium: This is one of the alloying elements that shows a positive effect even at very low addition amounts. For this reason, it can be added to cast iron up to a ratio of 0.5%. It shows its effects by increasing hardness and strength.
Effect of Silicon
Silicon increases the machinability of cast iron by encouraging graphite formation.
Hardness Increase With Chromium
Adding chromium can significantly increase the hardness and wear resistance of cast iron.
Toughness Increase With Nickel
Nickel is a commonly used alloying element for improving cast iron’s toughness and low-temperature strength.
Related Questions
Nickel both makes machining easier and increases corrosion resistance, hardness, and wear resistance. This multi-faceted contribution is why nickel is frequently chosen in cast iron alloys.
Unlike silicon and nickel, chromium has an effect that hinders, rather than promotes, the conversion of carbon into graphite. Through this effect, chromium contributes to forming a different internal structure that increases the material’s hardness and corrosion resistance.
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