Page 39 - MetalForming June 2015

The Science of Forming
properties are given.
• The n-value is commonly measured over the strain
range of 10 to 20 percent.
Analysis—While once suitable for most steels, that strain
range proves insufficient today—many of the higher-strength steels reach maximum load (ultimate tensile strength) at strains less than 20 percent. The onset of this diffuse neck will contaminate the n-value. Other steels have more uniform elongations that exceed 20 percent. Including the extended range of data creates a more valid n-value. The strain for n- value ranges from 10 percent to maximum load.
• I ordered coils of high-strength low-alloy (HSLA) steel with a yield strength of 350 MPa, and received some coils labeled HSLA 350 and others labeled HSLA 450. Is something wrong?
Analysis—No, the coils just came from different parts of the world. North American and European mills label HSLA steel by yield strength, while Asian and Pacific Rim suppliers use tensile strength. The coils labeled HSLA 450 came from Asian or Pacific Rim suppliers. To avoid this confusion, World- AutoSteel, the technical division of WorldSteel, has estab- lished a new classification. In this case, the coils would be labeled HSLA 350/450—identifying the yield and tensile strength of the steel. The metalformers can even obtain the TS/YS ratio and get a feel for its n-value. MF
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