Austenitic stainless steel having excellent pipe-expandability and age cracking resistance

An austenitic stainless steel comprising, in percent (%) by weight of the entire composition,

• C:
• 0.01 to 0.04%,
• Si:
• 0.1 to 1.0%,
• Mn:
• 0.1 to 2.0%,
• Cr:
• 16 to 20%,
• Ni:
• 6 to 10%,
• Cu:
• 0.1 to 2.0%,
• Mo:
• 0.2% or less,
• N:
• 0.035 to 0.07%, and
• the remainder of iron (Fe) and other inevitable impurities,
• wherein the C+N satisfies 0.06 to 0.1%,
• wherein an Md30 value in equation (1) is −10° C. or less, and an average grain size is 45 μm or more,
• Md30=551−462*(C+N)−9.2*Si−8.1*Mn−13.7*Cr−29*(Ni+Cu)−18.5*Mo (1)
• where, C, N, Si, Mn, Cr, Ni, Cu, and Mo represent the content, % by weight, of each element,
• wherein a product of the Md30 (° C.) value represented by the equation (1) and the average grain size (μm) satisfies less than −500,
• wherein a work-hardening exponent n value in a range of true strain 0.3 to 0.4 satisfies the range of 0.45 to 0.5,
• wherein an aging crack limited drawing ratio of the stainless steel is 2.97 or more, and
• wherein a hole expansion rate (HER) represented by equation (2) is 72% or more
• HER=(Dh−D0)/D0×100 (2)
• where Dh is an inner diameter after fracture and D0 is an initial inner diameter.