Stretch forming is used in producing some automotive body panels and it is important that
the sheet can deform by elongation and uniform thinning. The most appropriate
measure of formability for stretch forming is the strain hardening exponent,
or n value.
s = ken
where k is a constant.
A high value of n is desired if the
strip is to show good stretch formability.
Hot rolled strip steels have values of n
~ 0.1, whereas cold-reduced Al treated low carbon strip steels have n values of 0.2 - 0.25.
