Non-magnetic steel material having excellent hot workability and manufacturing method therefor
Provided according to one embodiment of the present invention are a non-magnetic steel material and a method for manufacturing the same. The steel material comprises 15-27 wt % of manganese, 0.1-1.1 wt % of carbon, 0.05-0.50 wt % of silicon, 0.03 wt % or less (0% exclusive) of phosphorus, 0.01 wt % or less (0% exclusive) of sulfur, 0.050 wt % or less (0% exclusive) of aluminum, 5 wt % or less (0% inclusive) of chromium, 0.01 wt % or less (0% inclusive) of boron, 0.1 wt % or less (0% exclusive) of nitrogen, and a balance amount of Fe and inevitable impurities, has an index of sensitivity of 3.4 or less, the index of sensitivity being represented by the following relational expression (1): [Relational expression 1]—0.451+34.131*P+111.152*Al−799.483*B+0.526*Cr≤3.4 (wherein [P], [Al], [B] and [Cr] each mean a wt % of corresponding elements), and contains a microstructure with austenite at an area fraction of 95% or greater therein.
1. A non-magnetic steel material, the non-magnetic steel material comprising manganese (Mn): 15 wt % to 27 wt %, carbon (C): 0.1 wt % to 1.1 wt %, silicon (Si):
0.05 wt % to 0.50 wt %, phosphorus (P): more than 0 wt % and 0.03 wt % or less, sulfur (S): more than 0 wt % and 0.01 wt % or less, aluminum (Al): 0.021 wt % to 0.050 wt %, chromium (Cr): 5 wt % or less, boron (B): 0.01 wt % or less, nitrogen (N): more than 0 wt % and 0.1 wt % or less, and a balance of iron (Fe) and inevitable impurities, wherein the non-magnetic steel material has a composition index of sensitivity expressed by Formula 1 below within a range of 3.4 or less,
−0.451+34.131*P+111.152*Al−799.483*B+0.526*Cr≤3.4 [Formula 1]
where each of [P], [Al], [B], and [Cr] is a weight percent (wt %) of a corresponding element,
wherein the non-magnetic steel material has a microstructure comprising austenite in an area fraction of 95% or greater, and
wherein the austenite has an average grain size of 10 μm or greater.
2. The non-magnetic steel material of claim 1 , wherein the non-magnetic steel material comprises 15 wt % to 25 wt % of manganese (Mn).
3. The non-magnetic steel material of claim 1 , wherein the non-magnetic steel material comprises 17 wt % to 25 wt % of manganese (Mn).
4. The non-magnetic steel material of claim 1 , wherein the non-magnetic steel material comprises 0.1 wt % to 1.0 wt % of carbon (C).
5. The non-magnetic steel material of claim 1 , wherein the non-magnetic steel material comprises 0.1 wt % to 0.8 wt % of carbon (C).
6. The non-magnetic steel material of claim 1 , wherein the non-magnetic steel material comprises 0 wt % to 4 wt % of chromium (Cr).
7. The non-magnetic steel material of claim 1 , wherein the non-magnetic steel material comprises 0.001 wt % to 4 wt % of chromium (Cr).
8. The non-magnetic steel material of claim 1 , wherein the non-magnetic steel material comprises 0.0005 wt % or greater of boron (B).
9. The non-magnetic steel material of claim 1 , wherein the non-magnetic steel material comprises 0.001 wt % to 0.06 wt % of nitrogen (N).
10. The non-magnetic steel material of claim 1 , wherein the non-magnetic steel material comprises 0.005 wt % to 0.03 wt % of nitrogen (N).
11. A method for manufacturing the non-magnetic steel material of claim 1 , the method comprising:
preparing a slab, the slab comprising manganese (Mn): 15 wt % to 27 wt %, carbon (C): 0.1 wt % to 1.1 wt %, silicon (S): 0.05 wt % to 0.50 wt %, phosphorus (F): more than 0 wt % and 0.03 wt % or less, sulfur (S): more than 0 wt % and 0.01 wt % or less, aluminum (Al): 0.021 wt % to 0.050 wt % or less, chromium (Cr): 5 wt % or less, boron (B): 0.01 wt % or less, nitrogen (N): more than 0 wt % and 0.1 wt % or less, and a balance of iron (Fe) and inevitable impurities, the slab having a composition index of sensitivity expressed by Formula 1 below within a range of 3.4 or less,
−0.451+34.131*P+111.152*Al−799.483*B+0.526*Cr<3.4 [Formula 1]
where each of [P], [Al], [B], and [Cr] is a weight percent (wt %) of a corresponding element;
reheating the slab to a temperature within a range of 1050° C. to 1250° C.;
hot rolling the reheated slab to obtain a hot-rolled steel material; and
cooling the hot-rolled steel material,
thereby producing the non-magnetic steel material of claim 1 .
12. The method of claim 11 , wherein the hot rolling of the reheated slab is performed at a hot finish rolling temperature of 800° C. to 1050° C.
13. The method of claim 11 , wherein the cooling of the hot-rolled steel material is performed at a cooling rate of 10° C/s to 100° C/s.
14. The method of claim 11 , wherein the cooling of the hot-rolled steel material is stopped at a cooling stop temperature of 600° C. or less.
15. The method of claim 11 , wherein the steel material has a microstructure comprising austenite in an area fraction of 95% or greater.
16. The method of claim 15 , wherein the austenite has an average grain size of 10 μm or greater.