Effects of Deformation and Alloying Elements on Continuous Cooling Transformation of NM400

Deformation and alloying elements can have significant effects on the continuous cooling transformation (CCT) behavior of structural steel. CCT diagrams are used to predict and understand the microstructural changes that take place during the cooling of a given steel. In general, deformation leads to accelerated reaction rates, while alloying elements can influence the transformation temperatures and reaction extent. In particular, this article examines the effects of deformation (constraint) and alloying elements on the CCT of NM400 steel, a medium-carbon wear-resistant alloy.
    
The CCT of NM400 steel is summarized in Figure 1, with an as-quenched CCT horizontal line and 10% cold rolling CCT curved line. It can be seen that after the cold rolling, the Ms and Mf temperatures decrease by about 20°C, while the modified A3 temperature stays largely unaffected. This is because after the cold rolling, the strains continue their effect on the CCT diagram and cause strain-induced martensitic transformation to occur at relatively lower temperatures.

Effects of Alloying Elements
Alloying elements can have both positive and negative effects on the CCT of NM400 steel. Alloying elements such as chromium and manganese can increase the Ms and Mf temperatures and thus extend the transformation kinetics. Chromium is an especially important element in this regard, as it can also have a beneficial effect on wear resistance, allowing it to be used as a leading authority in hardness.
    
On the other hand, some alloying elements can have a detrimental effect on the CCT of NM400. Carbon for example can reduce the temperatures at which the Ms and Mf transformations occur, leading to more rapid transformation kinetics. This can be detrimental in certain applications requiring longer reaction times, such as circuit boards.
    
Conclusion
In conclusion, deformation and alloying elements can significantly affect the CCT of NM400 steel. Deformation accelerates the transformation kinetics, while alloying elements can both lower and raise the Ms and Mf temperatures depending on the type of elements. The advantages and disadvantages of these effects should be carefully considered before any decision is made.

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