Page 42 - MetalForming February 2016

The Science of Forming
Both have the same 350-MPa (50- ksi) yield strength but a different tensile strength. During deformation, the DP material exhibits a strong interaction between the ferrite phase and the islands of martensite. This generates an increase in the instantaneous n-value curve that peaks at 3-percent engi- neering strain with an n-value of 0.20,
compared to an n-value of 0.13 for HSLA 350/450. This higher initial n- value increases the stress-strain curve for the DP steel, generating a higher tensile strength. At a strain of 8 percent, the DP steel has exhausted its n-value advantage and the two steels exhibit the same properties.
• What benefit is gained with the
higher n-values at such low strains?
Many parts have areas of localized high deformation called gradients, which contain zones of high stress that create narrow peaks of large deforma- tion. Examples include long character lines, raised channels and localized tight bends. To comply with constancy- of-volume rules, high surface strains also create a corresponding narrow zone of local thinning. Tearing or other failure modes occur early from this forming process. High n-values accel- erate workhardening in these high- strain zones that shut down the gradi- ents as forming begins. DP steels are designed to deal with this gradient problem.
• What are the current primary applications for DP steels?
We find DP steels incorporated into the design of the passenger compart- ment, to absorb crash energy.
• The traditional n-values and forming-limit curves (FLCs) with ini- tial high n-values for DP 350/600 are similar to those for HSLA 350/450. Why?
The higher instantaneous n-value for DP steel is exhausted by a strain of 8 percent. The traditional measure- ment range for n-values is from 10 to 20-percent strain. Therefore, the two steels will have the same values. Like- wise, the FLC depends highly on the terminal n-value just prior to local necking and failure. Again, the two steels will exhibit the same terminal n-values.
• Does the DP steel have a series of steel grades with increased yield- and tensile-strength stress-strain curves similar to HSLA steels?
Yes. Nine DP grades have been pro- duced, as described in “Advanced High- Strength Steels Application Guidelines, Version 5.0.” It’s available as a free download from www.worldau- tosteel.org. In addition to the 250-page guidelines, website visitors also can download another document contain- ing details for 12 case studies describ- ing use of AHSS. MF
KEEP SAFETY AND EFFICIENCY FROM GOING UP IN SMOKE WITH QUINTOLUBRIC® FIRE-RESISTANT HYDRAULIC FLUIDS.
Mineral oils are highly flammable and are a serious source of fire hazard in high temperature environments and applications close to open flames or red-hot metal parts. The risk is further increased
by the rapid and aggressive ignition rate of mineral oils which can cause disruption in production, plant shutdown, increased insurance premiums, and threats to worker safety.
For those who won’t compromise on efficiency or safety, there’s the QUINTOLUBRIC®line of fire-resistant hydraulic fluids. Our solutions keep your machines working at optimal performance with fewer interruptions and a longer life span for a lower total cost of ownership, increased safety and reduced risk.
Our experts work with you to improve operations, process and efficiency, so you’ll keep going strong and keep your workers safe.
QUINTOLUBRIC®– Minimize Risk. Maximize Production.TM
Contact us today.
info@quakerchem.com | quintolubric.com | 1.877.537.1494
© 2016 Quaker Chemical Corporation. All Rights Reserved.
40
MetalForming/February 2016
www.metalformingmagazine.com