Effect of chromium

The use of chromium in the composition of heat-resistant steels significantly increases their resistance to oxidation. However, the effect of chromium is less effective than that of molybdenum, titanium and vanadium. Ferritic steels, when chromium is added, improve properties such as creep resistance, long-term strength, recrystallization temperature and self-diffusion activation energy. Also chromium in tempering of deformed austenite, allows to keep its crystal lattice distortions. The effect of chromium on the refractory properties of ferritic steel depends on factors such as the chromium content and whether it is alloyed with other elements in equal proportions. In addition, the introduction of chromium changes the crystalline lattice of the y-solid solution. The atomic bonding energy of austenitic steels increases and refractory properties and recrystallization temperature improve. The maximum heat resistance was achieved with the introduction of 15% chromium.

In the case of chromium, the hardening of austenitic steels occurs through the formation of carbon-carbide series that are released in the y-solid solution during aging and quenching. However, the hardening level decreases in proportion to increasing operating temperature, due to coagulation of chromium carbides. This process occurs because of the low resistance of chromium carbides to heat. Therefore, chromium alloying austenitic steels is not the most effective way to increase their heat resistance.

Chromium additives can also change the solubility of the 'y-phase in complex alloys of nickel, titanium and aluminum. Thus the dispersion hardening of these alloys is achieved. And the titanium content in this process will be minimal. However, this result is not always observed. So, in the case of using a significant amount of chromium for rolling complex alloyed heat-resistant steel, the formation of ferritic elements, which dramatically reduces the heat-resistant properties of the alloy.

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