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Analysis of fracture causes of ferrite-pearlite steel
Oct 13, 2018

Ferritic-pearlite steel accounts for the vast majority of total steel production. They are typically iron-carbons containing between 0.05% and 0.20% carbon and alloys of other small alloying elements added to improve yield strength and toughness.

 

The microstructure of the ferrite-pearlite consists of BBC iron (ferrite), 0.01% C, soluble alloy and Fe3C. In carbon steels with very low carbon content, cementite particles (carbides) remain in the ferrite grain boundaries and grains. However, when the carbon content is higher than 0.02%, most of Fe3C forms a sheet-like structure with some ferrite, which is called pearlite, and tends to be a "grain" and a ball node (grain boundary precipitate). Dispersed in the ferrite matrix. In the microstructure of low carbon steel with a carbon content of 0.10% to 0.20%, the pearlite content accounts for 10% to 25%.

 

Although the pearlite particles are very hard, they are very widely dispersed on the ferrite matrix and are easily deformed around the ferrite. Generally, the grain size of ferrite decreases as the pearlite content increases. Because the formation and transformation of pearlite balls can hinder the growth of ferrite grains. Therefore, the pearlite will indirectly increase the tensile yield stress δy by raising d-1/2 (d is the average grain diameter).

 

From the point of view of fracture analysis, there are two types of steel in the range of carbon content in low carbon steel, and its performance is of concern. First, the carbon content is below 0.03%, carbon exists in the form of pearlite ball joints, and has little effect on the toughness of steel. Second, when the carbon content is high, the toughness and Charpy curve are directly affected by the spheroidal form.


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