The role of alloying elements in the 12Cr1MoVG

The role of alloying elements in the 12Cr1MoVG heat resistance steel:
First, chromium (Cr)
The main purpose of adding chromium in the heat-resistant steel is to improve the oxidation resistance and corrosion resistance of steel. Therefore, Chromium is an essential element of heat-resistant steel, with its different content, heat-resistant boiler pipe are divided into four kinds, namely Cr = 1% ~ 5% for the first one; Cr = 8% ~ 9% for the second specie; Cr = 11% ~ 13% for the third one; Cr≥18% for fourth one, respectively used for pressure parts at different temperatures.
Chromium alone has little contributions to improve heat resistance, and it must be matched with other alloying elements. Chromium has the effect of preventing graphitization.
Second, molybdenum (Mo)
Mo can improve the hardenability of steel, but its effect is not as good as C and Cr. Molybdenum can improve the thermal strength properties of steel, when the content is between 1% to 2%, the lasting strength improved significantly.
Alloy steel pipe containing molybdenum alone has rarely been used as pressure parts of boilers.
Third, vanadium (V)
Vanadium can refine the grain, is a strong carbide-forming element, which can reduce the thermal sensitivity of steel.
In the Cr-Mo-V steel, the higher the vanadium content is, the higher sag resistance is, when V / C = 4, it’s with the best long lasting strength. Thus the V / C value is important. When the steel contains niobium or titanium, the best performance of V / C value is not equal to 4.
Vanadium also reduces the ability of carbide ball speed, thus improving the stability under high temperature conditions tissue, which is advantageous. But vanadium during the heat treatment, the thermal sensitivity is low, so that the impact toughness results are scattered, which is unfavorable.
Fourth, G does not stand for the alloying element, is the meaning of boiler steel.