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Relationship between yield ratio of steel and plasticity

In recent years, low-carbon steel in the pursuit of high-strength, high toughness, but also the yield ratio as an important indicator because the lower the yield ratio of steel, it means that the high work hardening exponent and a high uniform elongation. If low yield ratio steel used in buildings, it is possible to improve the seismic performance of buildings; if used as automotive sheet, you can significantly improve the cold formability of automotive sheet. For Pipeline steel is, PSL2 level of steel were required to yield ratio. So, people continue by optimizing the chemical composition, controlled rolling and cooling technology designed to study the formation mechanism of low yield ratio steel, and has made certain achievements.

Officially due to the low yield ratio steel has good formability, it has been believed that the lower the yield ratio of steel, the steel plasticity, the better. But it did not, through our trial and denied the claim. Because the uniform elongation is only part of the total amount of plastic deformation, local necked focus extends also will directly affect the plastic deformation of steel. So having a low yield ratio steel sheet does not indicate its total elongation necessarily large. Arguably, if a steel having a low yield ratio, characterizing it only extends even larger, not prone to plastic instability. Low yield ratio steel possesses a greater uniform elongation is due to just the presence of "hard tissue." However, there is advantageous in "hard tissue" is to promote uniform elongation of steel, is to reduce the negative aspects of local necked focus extends This is because when necking occurs, the hole first easy to combine weaknesses and the substrate is formed, and with the increase of external load, holes gradually aggregated into crack, due to "hard tissue" poor plasticity, crack tip dislocation pileup serious, stress relaxation is difficult, prone to cleavage fracture surface, the plastic lower. Therefore, to meet the same chemical composition and yield strength of the premise, lower yield than the plastic below the high yield ratio steel.


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