High manganese steel having superior low-temperature toughness and yield strength and manufacturing method thereof

1. High manganese steel, consisting of:

by wt %, 0.3 to 0.45% of C, 20 to 25% of Mn, 0.01 to 0.14% of Mo, 3% or less of Al, including 0%, 0.1 to 3% of Cu, 0.06% or less of P, excluding 0%, and 0.005% or less of S, including 0%, one or more selected from between 8% or less of Cr, including 0%, and 0.1 to 3% of Ni, and other inevitable impurities and a remainder of Fe,

wherein Mo and P satisfy the following Relational Expression (1),

4.5≤2*(Mo/93)/(P/31)≤9   [Relational Expression 1]

where a microstructure comprises austenite having a grain size of 19 μm to 29 μm, and

wherein the high manganese steel has an impact toughness value of 115 J to 146 J, measured by a charpy impact test at −196° C.,

wherein the high manganese steel has room temperature yie;d strenght of 380 MPa to 481 MPa.

2. A method of manufacturing the high manganese steel as recited in claim 1 , the method comprising:

reheating a slab at 1000 to 1250° C., the slab consisting of, by wt %, 0.3 to 0.6% of C, 20 to 25% of Mn, 0.01 to 0.3% of Mo, 3% or less of Al, including 0%, 0.1 to 3% of Cu, 0.06% or less of P, including 0%, and 0.005% or less of S, including 0%, one or more selected from between 8% or less of Cr, including 0%, and 0.1 to 3% of Ni, and other inevitable impurities and a remainder of Fe, where Mo and P satisfy the following Relational Expression (1),

1.5≤2*(Mo/93)/(P/31)≤9   [Relational Expression 1]

obtaining a hot-rolled steel sheet by primarily hot-rolling the heated slab, terminating the primary hot-rolling at 980 to 1050° C., secondarily hot-rolling the hot-rolled slab in a non-recrystallization region at a rolling reduction rate of 3% or less, and terminating the secondary hot-rolling at 800 to 960° C.;

water-cooling the hot-rolled steel sheet to a cooling terminating temperature of 350 to 600° C.; and

coiling the cooled hot-rolled steel sheet; thereby producing the high manganese steel of claim 1 .