Note: Descriptions are shown in the official language in which they were submitted.
WO 2014/186689 PCT/US2014/038364
High Strength Steel Exhibiting Good Ductility and Method of Production via In-
Line Heat
Treatment Downstream of Molten Zinc Bath
Grant A. Thomas
Jose Mauro B. Losz
[0001]
BACKGROUND
[00021 It is desirable to produce steels with high strength and good
formability
characteristics. However, commercial production of steels exhibiting such
characteristics has been difficult due to factors such as the desirability of
relatively low alloying additions and limitations on thermal processing
capabilities of industrial production lines. The present invention relates to
steel
compositions and processing methods for production of steel using hot-dip
galvanizing/galvanncaling (HDG) processes such that the resulting steel
exhibits
high strength and cold formability.
SUMMARY
100031 The present stool is produced using a composition and a modified
IIDG process
that together produces a resulting microstructure consisting of generally
martcnsite and austenite (among other constituents). To achieve such a
microstructure, the composition includes certain alloying additions and the
HDG
process includes certain process modification, all of which are at least
partially
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related to driving the transformation of austenite to martensite followed by a
partial stabilization of austenite at room-temperature.
BRIEF DESCRIPTION OF THE FIGURES
[0004] The accompanying figures, which are incorporated in and constitute a
part of this
specification, illustrate embodiments, and together with the general
description
given above, and the detailed description of the embodiments given below,
serve
to explain the principles of the present disclosure.
[0005] FIGURE 1 depicts a schematic view of a HDG temperature profile with
a
partitioning step performed after galvanizing/galvannealing.
[0006] FIGURE 2 depicts a schematic view of a HDG temperature profile with
a
partitioning step performed during galvanizing/galvannealing.
[0007] FIGURE 3 depicts a plot of one embodiment with Rockwell hardness
plotted
against cooling rate.
[0008] FIGURE 4 depicts a plot of another embodiment with Rockwell hardness
plotted
against cooling rate.
[0009] FIGURE 5 depicts a plot of another embodiment with Rockwell hardness
plotted
against cooling rate.
[0010] FIGURE 6 depicts six photo micrographs of the embodiment of FIG. 3
taken from
samples being cooled at various cooling rates.
[0011] FIGURE 7 depicts six photo micrographs of the embodiment of FIG. 4
taken from
samples being cooled at various cooling rates.
[0012] FIGURE 8 depicts six photo micrographs of the embodiment of FIG. 5
taken from
samples being cooled at various cooling rates.
[0013] FIGURE 9 depicts a plot of tensile data as a function of
austenitization
temperature for several embodiments.
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[0014] FIGURE 10 depicts a plot of tensile data as a function of
austenitization
temperature for several embodiments.
[0015] FIGURE 11 depicts a plot of tensile data as a function of quench
temperature for
several embodiments.
[0016] FIGURE 12 depicts a plot of tensile data as a function of quench
temperature for
several embodiments.
3
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DETAILED DESCRIPTION
[0017] FIG. 1 shows a schematic representation of the thermal cycle used to
achieve high
strength and cold formability in a steel sheet having a certain chemical
composition (described in greater detail below). In particular, FIG. 1 shows a
typical hot-dip galvanizing or galvannealing thermal profile (10) with process
modifications shown with dashed lines. In one embodiment the process generally
involves austenitization followed by a rapid cooling to a specified quench
temperature to partially transform austenite to martensite, and the holding at
an
elevated temperature, a partitioning temperature, to allow carbon to diffuse
out of
martensite and into the remaining austenite, thus, stabilizing the austenite
at room
temperature. In some embodiments, the thermal profile shown in FIG. 1 may be
used with conventional continuous hot-dip galvanizing or galvannealing
production lines, although such a production line is not required.
[0018] As can be seen in FIG. 1, the steel sheet is first heated to a peak
metal temperature
(12). The peak metal temperature (12) in the illustrated example is shown as
being
at least above the austenite transformation temperature (A1) (e.g., the dual
phase,
austenite + ferrite region). Thus, at the peak metal temperature (12), at
least a
portion of the steel will be transformed to austenite. Although FIG. 1 shows
the
peak metal temperature (12) as being solely above A1, it should be understood
that in some embodiments the peak metal temperature may also include
temperatures above the temperature at which ferrite completely transforms to
austenite (A3) (e.g., the single phase, austenite region).
[0019] Next the steel sheet undergoes rapid cooling. As the steel sheet is
cooling, some
embodiments may include a brief interruption in cooling for galvanizing or
galvannealing. In embodiments where galvanizing is used, the steel sheet may
briefly maintain a constant temperature (14) due to the heat from the molten
zinc
galvanizing bath. Yet in other embodiments, a galvannealing process may be
used
and the temperature of the steel sheet may be slightly raised to a
galvannealing
temperature (16) where the galvannealing process may be performed. Although,
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in other embodiments, the galvanizing or galvannealing process may be omitted
entirely and the steel sheet may be continuously cooled.
[0020] The rapid cooling of the steel sheet is shown to continue below the
martensite
start temperature (Ms) for the steel sheet to a predetermined quench
temperature
(18). It should be understood that the cooling rate to Ms may be high enough
to
transform at least some of the austenite formed at the peak metal temperature
(12)
to martensite. In other words the cooling rate may be rapid enough to
transform
austenite to martensite instead of other non-martensitic constituents such as
ferrite, pearlite, or bainite which transform at relatively lower cooling
rates.
[0021] As is shown in FIG. 1, the quench temperature (18) is below M,. The
difference
between the quench temperature (18) and M, may vary depending on the
individual composition of the steel sheet being used. However, in many
embodiments the difference between quench temperature (18) and M, may be
sufficiently great to form an adequate amount of martensite to act as a carbon
source to stabilize the austenite and avoid creating excessive "fresh"
martensite
upon final cooling. Additionally, quench temperature (18) may be sufficiently
high to avoid consuming too much austenite during the initial quench (e.g., to
avoid excessive carbon enrichment of austenite greater than that required to
stabilize austenite for the given embodiment).
[0022] In many embodiments, quench temperature (18) may vary from about 191
C to
about 281 C, although no such limitation is required. Additionally, quench
temperature (18) may be calculated for a given steel composition. For such a
calculation, quench temperature (18) corresponds to the retained austenite
having
an WL temperature of room temperature after partitioning. Methods for
calculating
quench temperature (18) are known in the art and described in J. G. Speer, A.
M.
Streicher, D. K. Matlock, F. Rizzo, and G. Krauss, "Quenching And
Partitioning:
A Fundamentally New Process to Create High Strength Trip Sheet
Microstructures," Austenite Formation and Decomposition, pp. 505-522, 2003;
and A. M. Streicher, J. G. J. Speer, D. K. Matlock, and B. C. De Cooman,
"Quenching and Partitioning Response of a Si-Added TRIP Sheet Steel," in
WO 2014/186689 PCT/US2014/038364
Proceedings of the International Conference on Advanced High Strength Sheet
Steels for Automotive Applications, 2004.
[0023] The quench temperature (18) may be sufficiently low (with respect
to MO to form
an adequate amount of martensite to act as a carbon source to stabilize the
austenite and avoid creating excessive "fresh" martensite upon the final
quench.
Alternatively, the quench temperature (18) may be sufficiently high to avoid
consuming too much austenite during the initial quench and creating a
situation
where the potential carbon enrichment of the retained austenite is greater
than that
required for austenite stabilization at room temperature. In some embodiments,
a
suitable quench temperature (18) may correspond to the retained austenite
having
an M, temperature of room temperature after partitioning. Speer and Streicher
c-
al. (above) have provided calculations that provide guidelines to explore
processing options that may result in desirable microstructures. Such
calculations
assume idealized full partitioning, and may be performed by applying the
Koistinen-Marburger (KM) relationship twice (jin =1¨ e-1.100-2 (AT)) first to
the
initial quench to quench temperature (18) and then to the final quench at room
temperature (as further described below). The Ms temperature in the KM
expression can be estimated using empirical formulae based on austenite
chemistry (such as that of the well known in the art Andrew's linear
expression):
100241 Ms( C) = 539¨ 423C ¨ 30.4Mn ¨ 7.5S1 +30 Al
10025] The result of the calculations described by Speer et al. may
indicate a quench
temperature (18) which may lead to a maximum amount of retained austenite. For
quench temperatures (18) above the temperature having a maximum amount of
retained austenite, significant fractions of austenite are present after the
initial,
quench; however, there is not enough martensite to act as a carbon source to
stabilize this austenitc. Therefore, for the higher quench temperatures,
increasing
amounts of fresh mattensite form during the final quench. For quench
temperatures below the temperature having a maximum amount of retained
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austenite, an unsatisfactory amount of austenite may be consumed during the
initial quench and there may be an excess amount of carbon that may partition
from the martensite.
[0026] Once the quench temperature (18) is reached, the temperature of the
steel sheet is
either increased relative to the quench temperature or maintained at the
quench
temperature for a given period of time. In particular, this stage may be
referred to
as the partitioning stage. In such a stage, the temperature of the steel sheet
is at
least maintained at the quench temperature to permit carbon diffusion from
martensite formed during the rapid cooling and into any remaining austenite.
Such
diffusion may permit the remaining austenite to be stable (or meta-stable) at
room
temperature, thus improving the mechanical properties of the steel sheet.
[0027] In some embodiments, the steel sheet may be heated above Mc to a
relatively high
partitioning temperature (20) and thereafter held at the high partitioning
temperature (20). A variety of methods may be utilized to heat the steel sheet
during this stage. By way of example only, the steel sheet may be heated using
induction heating, torch heating, and/or the like. Alternatively, in other
embodiments, the steel sheet may be heated but to a different, lower
partitioning
temperature (22) which is slightly below M,. The steel sheet may then be
likewise
held at the lower partitioning temperate (22) for a certain period of time. In
still a
third alternative embodiment, another alternative partitioning temperature
(24)
may be used where the steel sheet is merely maintained at the quench
temperature. Of course, any other suitable partitioning temperature may be
used
as will be apparent to those of ordinary skill in the art in view of the
teachings
herein.
[0028] After the steel sheet has reached the desired partitioning
temperature (20, 22, 24),
the steel sheet is maintained at the desired partitioning temperature (20, 22,
24)
for a sufficient time to permit partitioning of carbon from martensite to
austenite.
The steel sheet may then be cooled to room temperature.
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[0029] FIG, 2 shows an alternative embodiment of the thermal cycle
described above
with respect to FIG. 1 (with a typical galvanizing/galvannealing thermal cycle
shown with a solid line (40) and departures from typical shown with a dashed
line). In particular, like with the process of FIG. 1, the steel sheet is
first heated to
a peak metal temperature (42). The peak metal temperature (42) in the
illustrated
embodiment is shown as being at least above Al. Thus, at the peak metal
temperature (42), at least a portion of the steel sheet will be transformed to
austenite. Of course, like the process of FIG. 1, the present embodiment may
also
include a peak metal temperature in excess of A3.
[0030] Next, the steel sheet may be rapidly quenched (44). It should be
understood that
the quench (44) may be rapid enough to initiate transformation of some of the
austenite formed at the peak metal temperature (42) into martensite, thus
avoiding
excessive transformation to non-martensitic constituents such as ferrite,
pearlite,
banite, and/or the like.
[0031] The quench (44) may be then ceased at a quench temperature (46).
Like the
process of FIG. 1, quench temperature (46) is below M,. Of course, the amount
below Ms may vary depending upon the material used. However, as described
above, in many embodiments the difference between quench temperature (46) and
M, may be sufficiently great to form an adequate amount of martensite yet be
sufficiently low to avoid consuming too much austenite.
[0032] The steel sheet is then subsequently reheated (48) to a partitioning
temperature
(50, 52). Unlike the process of FIG. 1, the partitioning temperature (50, 52)
in the
present embodiment may be characterized by the galvanizing or galvannealing
zinc bath temperature (if galvanizing or galvannealing is so used). For
instance, in
embodiments where galvanizing is used, the steel sheet may be re-heated to the
galvanizing bath temperature (50) and subsequently held there for the duration
of
the galvanizing process. During the galvanizing process, partitioning may
occur
similar to the partitioning described above. Thus, the galvanizing bath
temperature (50) may also function as the partitioning temperature (50).
Likewise,
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in embodiments where galvannealing is used, the process may be substantially
the
same with the exception of a higher bath/partitioning temperature (52).
[0033] Finally, the steel sheet is permitted to cool (54) to room
temperature where at
least some austenite may be stable (or meta-stable) from the partitioning step
described above.
[0034] In some embodiments the steel sheet may include certain alloying
additions to
improve the propensity of the steel sheet to form a primarily austenitic and
martensitic microstructure and/or to improve the mechanical properties of the
steel sheet. Suitable compositions of the steel sheet may include one or more
of
the following, by weight percent: 0.15-0.4% carbon, 1.5-4% manganese, 0-2%
silicon or aluminum or some combination thereof, 0-0.5% molybdenum, 0-0.05%
niobium, other incidental elements, and the balance being iron.
[0035] In addition, in other embodiments suitable compositions of the steel
sheet may
include one or more of the following, by weight percent: 0.15-0.5% carbon, 1-
3%
manganese, 0-2% silicon or aluminum or some combination thereof, 0-0.5%
molybdenum, 0-0.05% niobium, other incidental elements, and the balance being
iron. Additionally, other embodiments may include additions of vanadium and/or
titanium in addition to, or in lieu of niobium, although such additions are
entirely
optional.
[0036] In some embodiments carbon may be used to stabilize austenite. For
instance,
increasing carbon may lower the Ms temperature, lower transformation
temperatures for other non-martensitic constituents (e.g., bainitc, ferrite,
pearlite),
and increase the time required for non-martensitic products to form.
Additionally,
carbon additions may improve the hardenability of the material thus retaining
formation of non-martensitic constituents near the core of the material where
cooling rates may be locally depressed. However, it should be understood that
carbon additions may be limited as significant carbon additions may lead to
detrimental effects on weldability.
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[0037] In some embodiments manganese may provide additional stabilization
of
austenite by lowering transformation temperatures of other non-martensitie
constituents, as described above. Manganese may further improve the propensity
of the steel sheet to form a primarily austenitic and martensitic
microstructure by
increasing hardenability.
[0038] In other embodiments molybdenum may be used to increase
hardenability.
[0039] In other embodiments silicon and/or aluminum may be provided to
reduce the
formation of carbides. It should be understood that a reduction in carbide
formation may be desirable in some embodiments because the presence of
carbides may decrease the levels of carbon available for diffusion into
austenite.
Thus, silicon and/or aluminum additions may be used to further stabilize
austenite
at room temperature.
[0040] In some embodiments, nickel, copper, and chromium may be used to
stabilize
austenite. For instance, such elements may lead to a reduction in the M,
temperature. Additionally, nickel, copper, and chromium may further increase
the
hardenability of the steel sheet.
[0041] In some embodiments niobium (or other micro-alloying elements, such
as
titanium, vanadium, and/or the like) may be used to increase the mechanical
properties of the steel sheet. For instance, niobium may increase the strength
of
the steel sheet through grain boundary pinning resulting from carbide
formation.
[0042] In other embodiments, variations in the concentrations of elements
and the
particular elements selected may be made. Of course, where such variations are
made, it should be understood that such variations may have a desirable or
undesirable effect on the steel sheet microstructure and/or mechanical
properties
in accordance with the properties described above for each given alloying
addition.
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EXAMPLE 1
[0043] Embodiments of the steel sheet were made with the compositions set
forth in
Table 1 below.
[0044] The materials were processed on laboratory equipment according to
the following
parameters. Each sample was subjected to Gleeble 1500 treatments using copper
cooled wedge grips and the pocket jaw fixture. Samples were austenitized at
1100 C and then cooled to room temperature at various cooling rates between 1-
100 C/s.
11
Table 1 Chemical compositions in weight %.
ID Description Al C Co Cr Cu Mn Mo Nb Ni P
Si Sn Ti V
V4037 Lab Material 1.41 0.19
- 0.01 <0.003 1.54 <0.003 <0.003 <0.003 <0.003 0.11 <0.003 0.01 <0.003
-
V4038 Lab Material 1_29 0.22 - 0.20 <0.003 1.68 <0.003
0.02 <0.003 0.02 0.01 <0.003 0.01 <0.003 -
oc
crN
ch
V4039 Lab Material <0.003 0.20 <0.002 0.01 <0.002
2.94 <0.002 0.00 <0.002 0.00 1.57 <0.002 0.01 <0.002
0.00 oc
0
0
IRNO
=
oc
12
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EXAMPLE 2
[0045] The Rockwell hardness of each of the steel compositions described in
Example 1
and Table 1 above was taken on the surface of each sample. The results of the
tests are plotted in FIGS. 3-5 with Rockwell hardness plotted as a function of
cooling rate. The average of at least seven measurements is shown for each
data
point. The compositions V4037, V4038 and V4039 correspond to FIGS. 3, 4, and
5, respectively.
EXAMPLE 3
[0046] Light optical micrographs were taken in the longitudinal through
thickness
direction near the center of each sample for each of the compositions of
Example 1. The results of these tests are shown in FIGS. 6-8. The compositions
V4037, V4038, and V4039 correspond to FIGS. 6, 7, and 8, respectively.
Additionally, FIGS. 6-8 each contain six micrographs for each composition with
each micrograph representing a sample subjected to a different cooling rate.
EXAMPLE 4
[0047] A critical cooling rate for each of the compositions of Example 1
was estimated
using the data of Examples 2 and 3 in accordance with the procedure described
herein. The critical cooling rate herein refers to the cooling rate required
to form
martensite and minimize the formation of non-marten sitic transformation
products. The results of these tests are as follows:
[0048] V4037: 70 C/s
[0049] V4038: 75 C/s
[0050] V4039: 7 C/s
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EXAMPLE 5
[0051] Embodiments of the steel sheet were made with the compositions set
forth in
Table 2 below.
[0052] The materials were processed by melting, hot rolling, and cold
rolling. The
materials were then subjected to testing described in greater detail below in
Examples 6-7. All of the compositions listed in Table 2 were intended for use
with the process described above with respect to FIG. 2 with the exception of
V4039 which was intended for use with the process described above with respect
to FIG. 1. Heat V4039 had a composition intended to provide higher
hardenability
as required by the thermal profile described above with respect to FIG. 1. As
a
result V4039 was subjected to annealing at 600 C for 2 hours in 100% H2
atmosphere after hot rolling, but prior to cold rolling. All materials were
reduced
during cold rolling about 75% to lmm. Results for some of the material
compositions set forth in Table 2 after hot rolling and cold rolling are shown
in
Tables 3 and 4, respectively.
14
C)
n.)
l.0
r-, Table 2 Chemical
compositions in weight %.
o
o 0
1-.
Iv Heat Description c Mn Si
Al Mo Cr Nb B "
0
--,
N.)
1 4=
0 V4037 Lab Material 0.19 1.54
0.11 1.41 0 0.009 0 ' 0.0007 r-r
r-.
r cre
cs=
I V1307 1 Lab Material 0.19
1.53 1_48 0.041 0 0 0 0.0005 ere
I-
0
I V4063 Lab Material 0.19 1.6
0.11 1.34 0 0.003 0 0.0007
r-.
to
V4038 Lab Material 022 1.68
0.007 1.29 0 0.2 0.021 0.0008
V4039 Lab Material 0.2
2.94 1.57 <0.030 <0.002 0.005 0.002 NM
V1305 Lab Material 0_2 294
1_57 0 0 0 0 0.0006
V4107 Lab Material 0.18 4.03
1.63 0.005 0 0 0 I 0.0008
1
V4108 Lab Material 0.18 5.06
1_56 0.004 0 0 0 0.0009
;IN V4060 Lab Material 0.4 1.2
1.97 0.003 0 0.19 0,007 0.0005
_
V4061 Lab Material 0.41 1.2
0_98 0.003 0 0.003 o 0.0004
V4062 Lab Material o.n 1.18
0.012 1.16 0 0.003 o 0.0007
V4078-1 Lab Material 0.2 1.67
0.1 1.41 0.28 0.003 <0.003 0.0007
V4078-2 Lab Material 0.2 1.67
0.1 1.41 0.27 <0.003 0.051 0.0007
V4079-1 Lab Material 0.19 1.94
0.098 1.43 <0.003 <0.003 <0.003 0.0007
1
,
V4079-2 : Lab Material 0.19 1.96 0.099 1.41 <0.003 <0.003
0.051 0.0007
*0
n
1-i
4:-
-a
Ca
00
t.4
0
C) Table 3 - Tensile Data, Post
Hot Rolling
Kt
to
i-. Yield
Strength Total Uniform ...
-
0 UpperYS Lower YS UT
Hardness
o Heat YPE (%) 0.2% Offset
Elongation Elongation 0 H RA
1-.
MPa ksi MPa Etsi MPa ksi MPa ksi (2") % 14
d
N.) V4063 0 N/A N/A N/A N/A 375 54 652 95 26
15 53
4.
n.) 0 N/A N/A N/A N/A 380 55 648 94 26 , 15 ' 53
-...
i--,
0 V4039* 0 _
N/A N/A N/A N/A 640 _
93 1085 157 14
9 67 no
i-. - -
c.,
c,
-.1 V4039* - 0
N/A N/A N/A N/A 603 88 748 109 20
10 61 coo
i (annealed)
to
i 4 k ,
I-. i
1
0 V4060 0.6 645 94
637 92 633
- 92 883 128 20 11 63
I 0.5 610 89 605 88 611 89
876 127 22 12 61
i-. r--
0 N/A N/A N/A 0 496 72 790 115 22 , 11
60
to V4061 0 N/A N/A N/A 0 , 507 74
799 110 20 11 60
1.1 507 _ 74 501
73 , 506 _ 73 _ 712 103 26 ' 12 50
V4062 -
0.7 505 73 502 73 502 73
_. _ 713 103
24 12 57-
V4078-1 0.8 427 , 62 416 80 425
82 694 86 32 18 51
V4078-2 - 0-6 525 I 76 519 - 75 , 525
76 685 99 21 15 55
.._
V4079-1 1.8 364 L_ 53 361 , 52 ,
361 r 52 544 79 30 17 45
V4079-2 1.2 497 72 481 70 489
71 639 93 24 13 52
*Tensile test performed in trans-versc direction for V4039
Table 4 -Tensile Data, Post Cold Rolling
-
Yield
Strength WM 1 Total
Unifr.rm Hardness
' Heat 0.2% Offset Elongation e1on0ation % H RA
MPa ksi 1 MPa ksi (r) %
-
V4037 927 134 _ 971 141 4.8 1.4 64
V4063 1046 152 1101 160 2.4 1.3 65 -
V4038 1001 145 1054 153 5.5 1.6 65
V4039 1149 167 ., 1216 176 4.4 1.5 , 68 -
V4060 1266 , 184 _1393 202 5.4 1.9 , 69
_
V4061 1187 172 1279 186 4.3 1.7 68 IV
_
_ n
V4062 1111 161 _1185 172 4.3 1.7 66 ,-3
V4078-1 1047 152 1105 160 3.6 1_4 - 65 i
V4078-2 1154 167 _ 1209 175
4.2 1.4 66
V4079-1 932 135 975 141 _
4.6 14 64 -, o
'
i--
, V4079-2 1034 150 - 1078 156
3.9 1.3 66 4-
-O"
ta
OD
C.44
dl
"
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EXAMPLE 7
[0053] The compositions of Example 5 were subjected to Gleeble dilatomety.
Gleeble
dilatomety was performed in vacuum using a 101.6x25.4x1 mm samples with a c-
strain gauge measuring dilation in the 25.4 mm direction. Plots were generated
of the
resulting dilation vs. temperature. Line segments were fit to the dilatometric
data and
the point at which the dilatometric data deviated from linear behavior was
taken as
the transformation temperature of interest (e.g., A1, A3, MO. The resulting
transformation temperatures are tabulated in Table 5.
[0054] Gleeble methods were also used to measure a critical cooling rate
for each of the
compositions of Example 5. The first method utilized Gleeble dilatomety, as
described above. The second method utilized measurements of Rockwell hardness.
In particular, after samples were subjected to Gleeble testing at range of
cooling
rates, Rockwell hardness measurements were taken. Thus, Rockwell hardness
measurements were taken for each material composition with a measurement of
hardness for a range of cooling rates. A comparison was then made between the
Rockwell hardness measurements of a given composition at each cooling rate.
Rockwell hardness deviations of 2 points HRA were considered significant. The
critical cooling rate to avoid non-martensitic transformation product was
taken as the
highest cooling rate for which the hardness was lower than 2 point HRA than
the
maximum hardness. The resulting critical cooling rates are also tabulated in
Table 5
for some of the compositions listed in Example 5.
Table 5 ¨ Transformation Temperatures and Critical Cooling Rate from Gleeble
Dilatomety
Critical Cooling Rate
Heat A1 ( C) A3 ( C) M, ( C) (ous)
Gleeble Cileeble/
Dilatometry Hardness
V4037 737 970 469 Inconclusive 65
V4063 720 975 425 70
V4038 791 980 441 65
V4039 750 874 394 <10 6
V4060 725 975 325 30
V4061 675 900 325 40 55
17
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V4062 700 975 375 30
V4078-1 750 925 450 40 55
V4078-2 790 980 425 40
V4079-1 800 1000 430 40
V4079-2 750 990 425 40
EXAMPLE 8
[0055] The compositions of Example 5 were used to calculate quench
temperature and a
theoretical maximum of retained austenite. The calculations were performed
using
the methods of Speer et al., described above. The results of the calculations
are
tabulated below in Table 6 for some of the compositions listed in Example 5.
Table 6¨ Quench Temperature and Theoretical Maximum of Retained Austenite
õ
f(y) Theoretical
Heat QT ( C)
Maximum
V4037 281 0.15
V4063 278 0.15
V4038 270 0.18
V4039 203 0.2
V4060 191 0.35
V4061 196 0.36
V4062 237 0.31
V4078-1 276 0.16
V4078-2 276 0.16
V4079-1 273 0.16
V4079-2 272 0.16
EXAMPLE 9
[00561 The samples of the compositions of Example 5 were subjected to the
thermal profiles
shown in FIGS. 1 and 2 with peak metal temperature and quench temperature
varied
between samples of a given composition. As described above, only composition
V4039 was subjected to the thermal profile shown in FIG. 1, while all other
compositions were subjected to the thermal cycle shown in FIG. 2. For each
sample,
tensile strength measurements were taken. The resulting tensile measurements
are
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plotted in FIGS. 9-12. In particular, FIGS. 9-10 show tensile strength data
plotted
against austenitization temperature and FIGS. 11-12 show tensile strength data
plotted against quench temperature. Additionally, where the thermal cycles
were
performed using Gleeble methods, such data points are denoted with "Gleeble."
Similarly, where thermal cycles were performed using a salt bath, such data
points
are denoted with "salt."
[0057] Additionally, similar tensile measurements for each composition
listed in Example 5
(where available) are tabulated in Table 7, shown below. Partitioning times
and
temperatures are shown for example only, in other embodiments the mechanisms
(such as carbon partitioning and/or phase transformations) occur during non-
isothermal heating and cooling to or from the stated partitioning temperature
which
may also contribute to final material properties.
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Table 7 - Tensile Data, Post Partitioning
Peak
Quench Heat Te 0.2% Ultimate Total
Metal Partitioning Partitioning Elongation x UTS (Mpa
Temp Yield Tensile Elongation
mp Temp ( C)
( C) Strength Strength (%)
( C)
800 250 466 30 419 818 27 22,424
800 250 466 30 416 807 28 22,345
850 250 466 30 553 862 25 21,805
V1307 850 250 466 30 535 847 25 21,336
900 250 466 30 548 854 24 20,144
800 250 400 30 445 898 22 19,675
900 250 466 30 566 856 23 19,594
800 250 400 30 432 889 22 19,478
800 160 466 15 746 1317 23 29,630
800 200 466 15 716 1332 19 25,309
800 250 466 15 718 1403 18 25,115
V4060 800 200 466 15 632 1309 19 24,746
800 250 466 15 701 1379 18 24,407
800 160 466 15 845 1311 18 23,986
850 250 466 15 891 1291 18 23,749
850 250 466 15 735 1223 19 23,729
850 300 466 15 443 657 32 20,763
921 200 466 30 325 612 34 20,633
850 250 466 15 405 696 30 20,543
921 300 466 30 380 591 34 20,090
921 356 466 30 386 592 34 20,078
921 400 466 30 388 588 34 19,937
940 200 466 30 362 598 33 19,906
V4037 850 200 466 15 427 687 28 19,022
940 200 466 30 353 592 32 18,989
980 200 466 30 341 612 31 18,897
900 300 466 15 493 727 26 18,767
850 200 466 15 447 702 27 18,600
850 300 466 15 404 678 27 18,435
980 200 466 30 347 611 30 18,387
940 200 466 30 330 548 33 18,253
980 200 466 30 345 612 29 17,939
850 300 466 15 481 754 26 19,536
918 400 466 30 377 681 27 18,461
918 286 466 30 357 695 26 18,348
V4038
918 200 466 30 363 697 26 18,193
918 300 466 30 354 696 26 17,949
850 300 466 15 457 773 23 17,777
800 250 400 60 821 1299 15 19,225
800 250 400 60 821 1298 15 18,945
V4039 900 250 400 60 923 1273 15 18,593
850 250 400 60 874 1278 14 18,142
900 250 400 60 913 1258 14 17,984
800 160 466 15 746 1317 23 29,630
800 200 466 15 716 1332 19 25,309
800 250 466 15 718 1403 18 25,115
800 200 466 15 632 1309 19 24,746
V406 800 250 466 15 701 1379 18 24,407
0
800 160 466 15 845 1311 18 23,986
850 250 466 15 891 1291 _ 18 23,749
850 250 466 15 735 1223 19 23,729
800 200 466 30 942 1319 17 22,422
850 200 466 15 695 1222 16 19,070
750 250 466 15 553 985 20 19,902
V4061
750 250 466 15 581 918 21 18,996
750 200 466 15 478 813 23 18,778
V4062 750 250 466 15 480 816 22 17,944
750 200 466 15 536 790 23 17,936
V4107 850 250 400 60 776 1382 13 17,824
900 250 400 60 923 1642 11 17,401
V4108
850 250 400 60 952 1620 11 17,337
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V 850 300 466 15 448 783 24 19,016
4078-1
850 300 466 15 492 761 24 17,888
900 250 466 30 713 843 21 17,946
V4078-2 850 300 466 15 689 859 20 17,525
850 300 466 15 671 871 20 17,503
21
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,
1
1
,
WO 2014/186689
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100581 It will be understood various modifications may be made to this
invention without
departing from the scope of it. Therefore, the limits of this
invention
should be determined from the appended claims.
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