The invention relates to cold rolled steel sheet.
Cold rolled steel sheet meeting ASTM A1008 HSLAS-F Gr60 typically has a relatively large amount of Niobium, which is relatively expensive.
Forming one aspect of the invention is a cold rolled high strength steel sheet comprising, in weight percent:
N: 0.0001˜0.006
and further comprising iron and incidental impurities, the sheet having: ferrite and pearlite composing 80% or more, in area fraction, of the microstructure; yield strength of 60 ksi or more; elongation of at least 23% and a n-value of at least 0.14.
According to other aspects, the weight percent of Mo is optionally no more than 0.060 and the pearlite content can be 20% or less based on the area fraction.
Forming yet another aspect of the invention is a method for use with a steel slab having, in weight percent:
C: 0.03˜0.10
Si: 0˜0.6
Mn: 0.5˜1.5
Cu: 0˜1.0
Ni: 0˜1.0
Nb: 0 to 0.06
Ti: 0 to 0.1
Mo: 0 to 0.5
Cr: 0˜1.0
Al: 0˜0.06
Ca: 0˜0.006
P: 0˜0.02
S: 0˜0.005
N: 0.0001˜0.006
and further comprising iron and incidental impurities, the method comprising:
According to another aspect, the steel slab can have Mo in a weight percent no more than 0.06.
According to another aspect, the austenite grain size in the rolled sheet can be 50 μm or less.
Non-limiting embodiments of the invention are hereinafter described.
Sheet Material
Sheet material according to a non-limiting embodiment of the invention comprises, in weight percent:
N: 0.0001˜0.006
and further comprising iron and incidental impurities, wherein the sheet
The method is for use with a steel slab having, in weight percent: C: 0.03˜0.10
Si: 0˜0.6
Mn: 0.5˜1.5
Cu: 0˜1.0
Ni: 0˜1.0
Nb: 0 to 0.06
Ti: 0 to 0.1
Mo: 0 to 0.06
Cr: 0˜1.0
Al: 0˜0.06
Ca: 0˜0.006
P: 0˜0.02
S: 0˜0.005
N: 0.0001˜0.006
and further comprising iron and incidental impurities, the method comprising:
Liquid metal having the following composition
C: 0.03˜0.10
Si: 0˜0.6
Mn: 0.5 ˜1.5
Cu: 0˜1.0
Ni: 0˜1.0
Nb: 0 to 0.06
Ti: 0 to 0.1
Mo: 0 to 0.06%
Cr: 0˜1.0
Al: 0˜0.06
Ca: 0˜0.006
P: 0˜.02
S: 0˜0.005
N: 0.0001 ˜0.006
and further comprising iron and incidental impurities, was cast into 78 millimeter (mm) slab at Algoma Steel, Ontario. The slab was cleaned by pickling to remove the oxide layer, then used in the following method to produce fifty two (52) coils. Briefly, the slab is heated to a temperature of 1050° C. to 1150° C. to produce a heated slab; the heated slab if rolled once at a rolling reduction rate of 20% to 80% in a temperature range above the austenite recrystallization temperature to produce a rolled slab; the rolled slab is rolled two or more times at a rolling reduction ratio of 40% to 80% in a temperature range below austenite recrystallization temperature and above Ar3 to produce a rolled sheet; the rolled sheet is cooled at a cooling rate of 20° C. to 50° C. / sec to produce a cooled sheet; the cooled sheet is hot rolled at a temperature of 300° C. to 690° C. to produce a hot rolled sheet; the hot rolled sheet is cold-worked at a reduction rate of 30% to 80% to produce a cold rolled sheet; and the cold rolled sheet is annealed for 10 hours or more at 1300° F. or more.
Each coil was tested for coil chemistry, and the process parameters were monitored during production; details of the same are provided in
Micros were cut in the longitudinal direction of the rolled slab [after cold reduction, preceding annealing] and mounted, ground, polished and Nital etched to reveal the microstructures, as shown in
The finished product was also inspected after Nital etching as shown in
The fifty two (52) rolls produced were tested for mechanical properties against SAE J2340 420X; the results are provided in
Whereas two specific embodiments are herein shown and described, persons of ordinary skill will readily appreciate that variations are possible. Accordingly, the invention should be understood to be limited only by the accompanying claims, purposively construed.
This application depends from and claims priority to U.S. Provisional Application No. 63/143,448 filed Jan. 29, 2021, the entire contents of which are incorporated herein by reference.
Number | Name | Date | Kind |
---|---|---|---|
20150337408 | Schulz | Nov 2015 | A1 |
Number | Date | Country | |
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20220243297 A1 | Aug 2022 | US |
Number | Date | Country | |
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63143448 | Jan 2021 | US |