Ultrahigh-strength high-ductility steel sheet having excellent yield strength, and manufacturing method therefor
AssigneePosco
InventorsKyoo-Young LEE, Joo-Hyun RYU, Sea-Woong LEE
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Abstract
Provided is an ultrahigh-strength high-ductility steel sheet having excellent yield strength, comprising, by wt %, 0.04-0.18% of C, 2% or less of Si, 4-10% of Mn, 0.05% or less of P (except 0%), 0.02% or less of S (except 0%), 0.5% or less of Al (except 0%), 0.02% or less of N (except 0%) and the balance of Fe and the other inevitable impurities, wherein Si+Mn satisfies 6-10% and the microstructure comprises, by volume fraction, 12% or more of retained austenite and 60% or more of annealed martensite.
Claims17
An ultrahigh-strength high-ductility steel sheet having excellent yield strength, comprising:
- carbon (C):
- 0.04 wt % to 0.18 wt %, silicon (Si):
- 2 wt % or less, manganese (Mn):
- 4 wt % to 10 wt %, phosphorous (P):
- 0.05 wt % or less (excluding 0 wt %), sulfur (S):
- 0.02 wt % or less (excluding 0 wt %), aluminum (Al):
- 0.5 wt % or less (excluding 0 wt %), nitrogen (N):
- 0.02 wt % or less (excluding 0 wt %), and the balance of iron (Fe) and other inevitable impurities,
- wherein Si+Mn satisfies 6 wt % to 10 wt %, and
- a microstructure includes, by volume fraction, retained austenite of 12% or more and annealed martensite of 60% or more.
A method for manufacturing an ultrahigh-strength high-ductility steel sheet having excellent yield strength, comprising:
- heating a slab, which includes carbon (C):
- 0.04 wt % to 0.18 wt %, silicon (Si):
- 2 wt % or less, manganese (Mn):
- 4 wt % to 10 wt %, phosphorous (P):
- 0.05 wt % or less (excluding 0 wt %), sulfur (S):
- 0.02 wt % or less (excluding 0 wt %), aluminum (Al):
- 0.5 wt % or less (excluding 0 wt %), nitrogen (N):
- 0.02 wt % or less (excluding 0 wt %), and the balance of iron (Fe) and other inevitable impurities, and in which Si+Mn satisfies 6 wt % to 10 wt %, within a temperature range of 1100° C. to 1300° C.;
- obtaining a hot-rolled steel sheet by hot finish rolling the heated slab within a temperature range of Ar3 to 1000° C.;
- coiling the hot-rolled steel sheet at a temperature of 720° C. or less;
- heat-treating the coiled hot-rolled steel sheet within a temperature range of Ac1 to Ac1+(Ac3−Ac1)/2 for 30 minutes or more;
- obtaining a cold-rolled steel sheet by cold rolling the heat-treated hot-rolled steel sheet;
- primary annealing for cooling after the cold-rolled steel sheet is maintained at a temperature of Ac3 or more for 30 seconds or more;
- and
- secondary annealing for cooling after the primary annealed cold-rolled steel sheet is maintained within a temperature range of 580° C. to Tmax for 10 seconds to 5 minutes,
- where Tmax=667.64+129.1C−6.51Mn+38.52Si+29.3Al1.6, and, in the formula, each element symbol represents the content of each element in wt %.
Dependencies are inferred from the claim text.