cleavage fracture stress model for fractoughness estimation
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Materials Performance andCharacterization
P. R. Sreenivasan1
DOI: 10.1520/MPC20130079
Estimation of ASTM E1921Master Curve of FerriticSteels FromInstrumented ImpactTest of CVN SpecimensWithout Precracking
VOL. 3 / NO. 1 / 2014
P. R. Sreenivasan1
Estimation of ASTM E1921 MasterCurve of Ferritic Steels FromInstrumented Impact Test of CVNSpecimens Without Precracking
Reference
Sreenivasan, P. R., “Estimation of ASTM E1921 Master Curve of Ferritic Steels From
Instrumented Impact Test of CVN Specimens Without Precracking,” Materials Performance
and Characterization, Vol. 3, No. 1, 2014, pp. 285–308, doi:10.1520/MPC20130079. ISSN
2165-3992
ABSTRACT
A semi-empirical cleavage fracture stress (CFS) model, mainly depending on
the CFS, rf, has been derived for estimating the ASTM E1921 reference
temperature (T0) and demonstrated for ferritic steels with yield strength in the
range 400–750 MPa. This requires only instrumented impact test of CVN
specimens without precracking and static yield stress data. The T0 estimate
based on the CFS model, TQcfs, lies within a 620�C band, being conservative
for most of the steels, but less conservative than TQIGC based on the IGC-
procedure (see Nomenclature for definition). Applicability and acceptability of
the present calibration curves for highly irradiated steels need further
examination.
Keywords
Charpy V-notch, instrumented impact test, reference temperature, fracture toughness,
cleavage fracture stress
Manuscript received October 21,
2013; accepted for publication May
14, 2014; published online June 23,
2014.
1
Metallurgy and Materials Group,
Indira Gandhi Centre for Atomic
Resaearch, Kalpakkam,
Tamilnadu-603 102, India,
e-mail: sreeprs@yahoo.co.in
Copyright VC 2014 by ASTM International, 100 Barr Harbor Drive, P.O. Box C700, West Conshohocken, PA 19428-2959 285
Materials Performance and Characterization
doi:10.1520/MPC20130079 / Vol. 3 / No. 1 / 2014 / available online at www.astm.org
Nomenclature
CFS ¼Cleavage fracture stress, rf
CV ¼Energy absorbed by a CVN specimen during animpact test
CVN ¼Charpy V-notchDBTT ¼Ductile-Brittle Transition Temperature. Temperature
corresponding to a fixed CV, lateral expansion, or frac-ture appearance; for example, T28J is a DBTT
d ¼displacement experienced by the CVN specimen dur-ing IIT
IGC-procedureðor IGCAR procedureÞ
¼ a multi-stage correlation procedure to estimate TQIGC,where TQIGC is the estimate of T0 obtained using theIGCAR procedure detailed in Ref. [6]. TQIGC valuesare conservative to the extent of 20�C–30�C.
IIT ¼ instrumented impact testKIC ¼ valid linear elastic fracture toughness as per ASTM
E399 standardKJC ¼ valid linear elastic-plastic fracture toughness as per the
ASTM E1921 standard [5]LTD ¼Load Temperature Diagram; a plot of various loads
from the P-d traces of several CVN specimens testedin the DBTT range plotted as a function of test tem-perature, with the same loads (say, PGY, PF, etc.) joinedby average smooth curves, if possible.
MC ¼ a standard reference fracture toughness curve for fer-ritic steels indexed to reference temperature, T0, as perASTM E1921 standard [5]
P ¼ a general symbol for specimen load; here, experiencedby the CVN specimen during IIT
PA ¼brittle fracture arrest load on the P–d trace of a CVNIIT test record
PF ¼brittle fracture load on the P–d trace of a CVN IIT testrecord
PGY or Pgy ¼ general yield load on the P–d trace of a CVN IIT testrecord
Pmax or PM ¼maximum load on the P-d trace of a CVN IIT testrecord
T0 ¼ reference temperature determined as per ASTM E1921standard
TD ¼ the brittleness transition temperature, end of the grosselastic region in the load-temperature diagram ofinstrumented impact or slow-bend tests and representsalmost end of 100 % cleavage fracture withPF¼ Pmax¼ PGY
TQ ¼Estimated T0 by a non-standard methodTQIGC ¼T0 estimated by the IGCAR-procedure
SREENIVASAN ON CVN SPECIMENS WITHOUT PRECRACKING 286
Materials Performance and Characterization
Introduction
Charpy V-notch (CVN) impact test is very attractive because of its low-cost, sim-
plicity, wide familiarity, and availability [1]. Instrumented impact test (IIT), while
maintaining these advantages—in addition to the conventional Charpy energy
(CV), lateral expansion (LE), and % shear fracture (PSF)—provides additional
load (P)–time (t) or displacement (d) data of the CVN specimen during
deformation and fracture (time can be converted to displacement). Figure 1 shows
the various load parameters obtainable: general yield load-PGY (or Pgy, used inter-
changeably; see nomenclature), initiation load-Pinit (determined by compliance
change or key-curve technique or by acoustic emission or similar sophisticated
instrumentation), maximum load-PM or Pmax, brittle-fracture load-PF and arrest
load-PA, and the corresponding times/displacements— say, for example, dF, the
displacement to PF. The various load parameters plotted against test temperature
(T) provides the load-temperature diagram (LTD) characterizing various regions
of fracture [1,2]; see, for example, Fig. 2 [3]. A typical ferritic steel tested in the
ductile-brittle transition temperature (DBTT) region shows characteristic P–d
traces: at the lower-shelf, the fracture is purely linear-elastic with sudden brittle
TQcfs ¼T0 estimated by the CFS model-TQcfs is the most con-servative of the four, namely, TQcfs1, TQcfs2, TQcfs3, andTQcfs4
TQcfs1 ¼TQcfs obtained from rf/rys (as a function of temperature)and rf/rys*1 ratio
TQcfs2 ¼TQcfs obtained from rf/rys (as a function of temperature)and rf/rys*2 ratio
TQcfs3 ¼TQcfs obtained from rf/ryd (as a function of tempera-ture) and rf/ryd*1 ratio
TQcfs4¼TQcfs obtained from rf/ryd (as a function of temperature)and rf/ryd*2 ratio
TQBT ¼T0 predicted from the empirical correlation of TD withT0
T28J ¼Charpy transition temperature at which Charpyenergy¼ 28 J
T41J ¼Charpy transition temperature at which Charpyenergy¼ 41 J
rf ¼ cleavage fracture stress (CFS) determined from thePF¼ Pmax¼ PGY loads at the temperature TD
rys ¼quasi-static yield stress, dependent on temperatureryd ¼dynamic yield stress, dependent on temperature
ryd-RT ¼dynamic yield stress at room temperaturerys-RT ¼quasi-static yield stress at room temperaturerys*1 ¼rys at (T41J�24)�Crys*2 ¼rys at (T41J�50)�Cryd*1 ¼ryd at (T41J�24)�Crys*2 ¼ryd at (T41J�50)�C
SREENIVASAN ON CVN SPECIMENS WITHOUT PRECRACKING 287
Materials Performance and Characterization
failure occurring at the maximum load, PM (¼PF) corresponding to 100 % cleav-
age, while, at higher temperatures, as the test progresses to the upper shelf, PGYprecedes cleavage fracture. Then PM and PF separate, with substantial ductile
crack extension preceding PF and, at some temperature interval, brittle fracture
started at PF arrests at PA. Ultimately, at the upper shelf, the traces do not show
any brittle fracture: no PF and PA. From the various load parameters, the % shear
fracture (PSF) can be obtained as a function of temperature as also the brittleness
transition temperature (TD), the temperature at which PM (¼PF)¼ PGY [2] and at
higher temperatures, brittle fracture occurs after general yielding. These features
are delineated clearly in Fig. 2. From the PM (¼PF)¼ PGY load at TD, the micro-
cleavage fracture stress, rf, can be calculated. Moreover, from the PGY load values
at various temperatures, the dynamic yield stress, ryd, as a function of tempera-
ture is obtained [1,4]. These data are very important for the present paper, as will
be shown later.
FIG. 1
Characteristic loads marked on
an IIT load-time (t) trace and
energy partitioning related to
fracture surface of a CVN
specimen.
FIG. 2
Load temperature (P–T)
diagram for the 9Cr–1Mo BM
from instrumented CVN impact
tests at V0¼5.12 ms�1.
SREENIVASAN ON CVN SPECIMENS WITHOUT PRECRACKING 288
Materials Performance and Characterization
For obtaining design relevant dynamic fracture toughness (KId), however, test-
ing of fatigue precracked CVN (PCVN) specimens is necessary. This is costly and
time consuming [4]. Moreover, testing of PCVN specimens introduces problems
in data reduction due to superimposed oscillations. To overcome these difficulties,
testing at reduced velocity [3] (say, at� 1ms�1 instead of at the usual impact test
velocity of �5ms�1, with resultant loss of strain rate) or the use of complicated
dynamic analysis methods have been suggested [1]. Nowadays, reactor pressure
vessel (RPV) steels are increasingly being characterized in terms of the reference
temperature T0 and master curve (MC) as per the ASTM E1921 standard [5]. The
present author had previously proposed a multi-stage correlation procedure to esti-
mate TQIGC, where TQIGC is the estimate of T0 obtained using the procedure (IGCAR
procedure) detailed in Ref. [6]. TQIGC values are conservative to the extent of
20�C–30�C. The present paper examines in a new empirical perspective the relation
of rf to fracture toughness and, thereby, tries to derive a methodology to estimate
fracture toughness and master curve from the load-temperature data and Charpy
energy obtained from instrumented impact test (IIT) of CVN specimens without
precracking.
First, the semi-theoretical-empirical basis of the present approach will be
delineated in the light of previous literature. Then the method to obtain the new em-
pirical methodology will be given. The new methodology will be applied to the cali-
bration steels as also to many steels presented in Ref. [6] and others. The results will
be compared with actual T0 or estimated TQ (as a convention, non-standard, i.e., not
following the ASTM E1921 standard for master curve determination, estimates of T0
are designated TQ [6]). In addition to being fast and less costly (as no precracking is
required), the new method, being a single assessment method (compared to the
multi-stage method in Ref. [6]), will simplify the evaluation and hence will be less
error-prone. Moreover, it will enhance the utility and purpose of the IIT of blunt-
notched CVN specimens of ferritic steels. Particularly relevant is the fact that the
new procedure will help obtain more valuable and design relevant master curve
from IIT of irradiation surveillance specimens.
Theoretical-Empirical Basis and Methodology
LITERATURE REVIEW
Based on the concept of brittle cleavage fracture occurring ahead of a crack on the
attainment of a critical cleavage fracture stress (rf) over a critical distance (X0) of
Ritchie et al. [7] and using the stress analysis of Hutchinson [8], Curry [9] related
the cleavage fracture toughness, KIC to rf and rys in the following way:
KIC ¼ b�ðNþ1Þ
2 � X120r
Nþ12
f
rN�12
ys
(1)
where:
b¼ a material dependent constant (mainly a function of Ramberg–Osgood
work-hardening exponent, N, and can be evaluated based on expressions given in
Ref. [8]),
SREENIVASAN ON CVN SPECIMENS WITHOUT PRECRACKING 289
Materials Performance and Characterization
X0¼ the critical distance (depending on the microstructure, it has been related
to 2–3 ferrite grain diameters in ferrite–pearlite steels, or packet or bainite size in
martensitic or bainitic steels or no microstructural feature in certain steels), and
rf¼ independent of temperature and strain rate, and in most cases, even of irra-
diation conditions.
The accurate determination of X0 for various steels is a problem. Later, Hahn
et al. [10] and Kotilianen [11] empirically put KIC to rf and rys relation as:
rf
rys¼ a � KIC
rys
� �c
(2)
where a and c are constants for a particular steel and also depend on the tempera-
ture range of fit. Thus, the above equations have not found universal application;
although Eq 1 is theoretically more satisfying.
Recently, in the mesoscopic (given as mezzo-scopic in the referred paper) analy-
sis of fracture toughness of steels, Miyata and Tagawa [12] simplified the statistical
local fracture criterion approach to fracture toughness analysis of steels by both an
analogous and an empirical approach. Using a two-parameter Weibull stress distri-
bution for predicting fracture probability, they derived the expression relating KIC to
Weibull Stress, rW. Then, using analogy, they replaced the Weibull stress with the
cleavage fracture stress, rc—the fracture stress defined in deterministic terms (the
cleavage fracture stress, rc, is defined as the local maximum principal stress at the
cleavage fracture initiation in round bar tensile specimens with 1mm radius circum-
ferential notch) [12]. Finally, based on both fracture toughness tests and rc tests on a
large number of carbon and low-alloy steels (YS range: 250–1100MPa), they found
the following empirical relation:
KCðMPaffiffiffiffimpÞ ¼ 2:85� 10�3
BðmmÞ14
rCðMPaÞ rC
rys
� �g
(3)
where g is fit constant for a steel (g is represented as a in Ref. [12]).
Since it needs a large number of specimens to obtain the statistical Weibull
parameters compared to the determination of rc, Eq 3 is a simplification. In
Ref. [12], the exponent g was given as a function of T150 temperature. Here, T150 is
the temperature corresponding to a fracture toughness of 150MPaHm. The g-T150plot in Ref. [12] shows high scatter and wide dispersion. Hence, even Eq 3 is not
amenable to practical application. This paper, while retaining the simplicity of the
above methods (rf/rys and rf/ryd ratio or fracture to yield stress ratio method), tries
to overcome their limitations by an empirical procedure.
The features of the above theoretical, semi-empirical, or empirical formula-
tions can be summarized as follows. Basically, at the point of brittle fracture initia-
tion, the local crack tip tensile stress reaches a critical value, namely, the
microscopic cleavage fracture stress, rf or rC (the cleavage fracture stress can be
determined from either notch-tensile tests—many authors denote this as rC—or
three-point bend or instrumented impact tests of Charpy V-notch (CVN) speci-
mens, mostly denoted by rf; based on consideration of differences in sampled and
stressed volume for the two types of specimens, rf; especially determined from
SREENIVASAN ON CVN SPECIMENS WITHOUT PRECRACKING 290
Materials Performance and Characterization
instrumented impact tests, is slightly larger than rC from notch-tensile tests [13])
at a critical distance, usually the distance to the weakest link. In fact, a two- or
three-parameter distribution of Weibull stress distribution is the basis of the mas-
ter curve based on the ASTM E1921 standard [5]. The mesoscopic analysis of
fracture toughness as described in the previous section implies that fracture tough-
ness variation with temperature can be expressed as a function of critical fracture
stress to yield stress ratio.
PRESENT METHODOLOGY
Based on the above considerations, the variation of the ratios, rf/rys or rf/ryd, (ryd,
is the dynamic yield stress determined from instrumented Charpy V-notch speci-
men tests at various temperatures) are related to the relevant static MC fracture
toughness data; i.e., for the same temperature range, at various temperatures, the
ratio, rf/rys or rf/ryd, are evaluated along with the corresponding static MC KJC.
Then the resulting, rf/rys or rf/ryd, values are plotted against the corresponding
static MC KJC and a smooth curve of the following form fitted:
KJC ¼ 20þ a � expðbyÞ(4)
where y ¼ rf=rys or rf=ryd.
Equation 4 is justified because it is general practice to express variation of KJC
with temperature by an equation similar to Eq 4 with rf/ryd replaced by T. Equiva-
lently, T can be replaced by the corresponding rf/ryd (or rf/rys), which depends
only on variation of ryd or rys with temperature as rf is independent of temperature.
The basic methodology adopted in this paper is to fit Eq 4 based on rf/rys and
rf/ryd ratios to the MC data of the 21 calibration steels (with known IIT and T0data as described later) and determine a and b for each steel. For each steel, the 1 in.
MC-KJC data are fitted to Eq 4 in the range of T0 6 50�C, as ASTM E1921 [5] MC is
valid in that range. The MC equation is given by:
KJC ¼ 30þ 70 � expð0:019 � ðT � T0ÞÞ(5)
where T0 is the ASTM E1921 standard reference temperature for the material. Then
an average a (aav) is determined and a second fitting done to Eq 6a or Eq 6b:
KJC ¼ 20þ aavs: exp Brf
rys
� �(6a)
KJC ¼ 20þ aavd: exp Brf
ryd
� �(6b)
where aavs and aavd (corresponding to y¼ rf/rys and rf/ryd, respectively, in Eq 4)
are treated as constants. Then the constant B for various calibration steels based
on aavs is correlated to rf/rys*1 and rf/rys*2 and B for various calibration steels
based on aavd is correlated to rf/ryd*1 and rf/ryd*2, where rys*1 is the rys at
(T41J – 24)�C and rys*2 is the rys at (T41J – 50)�C, ryd*1 is the ryd at
(T41J – 24)�C and ryd*2 is the ryd at (T41J – 50)�C for each steel. rf/rys*1, rf/rys*2,
rf/ryd*1 and rf/ryd*2 are more definitive material identifiers than the simple ratio
of rf/rys-RT, as rys*1, rys*2, ryd*1 and ryd*2 lie on the steeply rising portion of the
SREENIVASAN ON CVN SPECIMENS WITHOUT PRECRACKING 291
Materials Performance and Characterization
T versus rys or T versus ryd curve. Then, there will be four B calibration curves
generated: B1 based on rf/rys*1, B2 based on rf/rys*2, B3 based on rf/ryd*1 and B4based on rf/ryd*2; application of B1 and B2 in Eq 6a generates two sets of MC
KIC values and application of B3 and B4 in Eq 6b generates another two sets of
MC KIC values. Thus, the present methodology ties the constant B indirectly to
the Charpy transition curve (T versus CV)—DBTT-curve.
APPLICATION OF THE NEWMETHODOLOGY FOR ESTIMATING TQ
For a material with known IIT data but with no T0, T0 can be calculated by the
following procedure:
1. Plot the load-temperature diagram (LTD) as in Fig. 2 and determine TD
2. Determine ryd at TD, using Eq 7 and rf using Eq 8The dynamic yield stress of an impact three-point bend (TPB) specimen isgiven by:
ryd ¼ 2:99PGYW
BðW � aÞ2(7)
where W¼B¼ 10mm and a¼ 2mm for a standard (full-size) CVN specimen,and PGY is in N.The micro-cleavage fracture stress, rf is given by [14]:
rf ¼ 2:52ryd(8)
where ryd is the value at TD.Many people have used different values for the multiplication factor (plasticstress concentration factor) on the RHS of Eq 8, which has values 2.18 or2.52, depending on the selected yield criterion, Tresca or von Mises, respec-tively [15]. Some earlier studies even used a value of 2.57 [1,13]. WhileChaouadi and Fabry [15] use an average value of 2.35, in this paper, the fac-tor has been taken as 2.52 and all values of reported rf have been correctedaccordingly. As such, many rf values given here will differ from those givenin the source references.
3. Plot the T versus CV curve and determine (T41J – 24)�C and (T41J – 50)�Ctemperatures. In case of excessive scatter, use a lower bound (LB) curve deter-mined by a fit to the lowest data at various temperatures.
4. Plot the T versus rys and T versus ryd (PGY at various temperatures isconverted to ryd using Eq 7) and obtain rys*1, rys*2, ryd*1 and ryd*2 and thecorresponding rf/rys*1, rf/rys*2, rf/ryd*1 and rf/ryd*2 values.
5. Plot the rf/rys and rf/ryd versus temperature curves.6. By plugging-in the rf/rys*1, rf/rys*2, rf/ryd*1 and rf/ryd*2 values in the B1 ver-
sus rf/rys*1, B2 versus rf/rys*2, B3 versus rf/ryd*1 and B4 versus rf/ryd*2 cali-bration equations generated earlier, determine the B1, B2, B3, and B4 valuescorresponding to the rf/rys*1, rf/rys*2, rf/ryd*1, and rf/ryd*2 values for the par-ticular steel.
7. For each B, for selected values from the rf/rys or rf/ryd curve, calculate KJC
using Eq 6a or Eq 6b (using a spread-sheet program, this can be easilydone for a column of rf/ryd values corresponding to various temperatures).Since calibration was done using MC data of calibration steels, the
SREENIVASAN ON CVN SPECIMENS WITHOUT PRECRACKING 292
Materials Performance and Characterization
generated KJC data are treated as MC curve data. Then select the KJC data inthe 80–120MPaHm and the corresponding temperatures and apply to themulti-temperature equation due to Wallin to obtain the corresponding TQestimate.
0 ¼Xi¼ni¼1
di expf0:019ðTi � T0Þ½31� Kmin þ 77 expf0:019ðTi � T0Þg�
�Xni¼1
ðKJCi � KminÞ4 expf0:019ðTi � T0Þg½31� Kmin þ 77 expf0:019ðTi � T0Þg�5
(9)
where:Kronecker di¼ 1 for valid data and 0 for non-cleavage or censored data (in thepresent case, take di¼ 1 always),Kmin¼ 20MPaHm, andTi¼ the test temperature (temperature corresponding to a particular KJC valuewith the corresponding rf/rys or rf/ryd ratio).
8. Because the new methodology is mainly based on rf, the micro-cleavage stress,T0 estimate, TQ, based on the new methodology will be designated TQcfs, toimply the cleavage fracture stress (CFS) method. Since there will be four esti-mates of TQcfs values corresponding to the four values, B1, B2, B3, and B4, theywill be designated as TQcfs1, TQcfs2, TQcfs3, and TQcfs4, respectively. The crite-rion for selection of the final estimate, TQcfs, will be given later.
Calculated values of TQcfs for the calibration steels and also for other steels will
be compared with actual T0 or other estimates like TQIGC (where T0 is not available).
Material Data
The 21 steels listed in Tables 1 and 2 along with source references (listed in brackets
appropriately) were used for generating the calibration curves as described in the
previous section. All the steels, except the five Said steels, have rf values determined
from either IIT or 4-point bend tests (only for the Lambert steels). All the rf values
have been adjusted as described after Eq 8. The static yield stress data and its varia-
tion with temperature for the 21 calibration steels are experimentally determined.
For the five Said steels, rf values have been determined in the following
two independent ways. Based on Chaouadi’s data, Sreenivasan [6] gave the following
fit:
TQBT ¼ 1:5TD þ 40(10)
where TQBT is the estimate of T0 obtained from TD, with BT representing
brittleness-transition (as TD is called the brittleness-transition temperature). Thus,
putting the actual T0 in Eq 10, an estimate of TD can be obtained. The TD values
listed in Table 2 for the five Said steels were so determined; hence the exact agree-
ment between actual T0 and TQBT (see, Table 2). As mentioned in Ref. [6], although
Eq 10 has a tendency to accuracy, due to various reasons, including the robustness
of the TD measurement from experimental data (especially for steels exhibiting high
scatter), the estimated TQBT can be highly non-conservative as is demonstrated by
the values for the two steels, 16 MND5 and HT9, listed in Table 2. After estimating
SREENIVASAN ON CVN SPECIMENS WITHOUT PRECRACKING 293
Materials Performance and Characterization
the TD, the dynamic yield stress at TD is determined and, then, applying Eq 8, the
corresponding rf value is determined.
It must be mentioned that for the five Said steels and also for the four Lambert
steels in Tables 1 and 2, as IIT data are not available, dynamic yield stress variation
with temperature has been determined using Eq 11 [23].
ryd ¼ rys-RT þ666 500
ðT þ 273Þ � logð2� 1010 � tÞ � 190(11)
where:
rys-RT¼ the room-temperature static yield stress,
T¼ the test temperature in �C, and
t¼ the time in ms (usually 0.1ms is the time to general yielding in IIT). As
such, t can be taken as 0.1 for obtaining the ryd corresponding to standard impact
tests at a strain rate of �103 [1]. Additionally, a scaling can be applied, if the actual
ryd at room or other temperature is known. If, for example, the actual ryd at RT
exceeds that from Eq 11, the absolute difference (of the RT values) can be added to
TABLE 1
(Micro) CFS and other strength properties of calibration steels.
Steel rys-RT (MPa) rf (MPa) T41J (�C) rys*1 (MPa) rys*2 (MPa) ryd*1 (MPa) ryd*2 (MPa)
JAERI Steels [16]
JRQ 488 1873 �25 542 569 718 746
Steel-A 469 2089 �42 536 568 757 813
Steel-B 462 2089 �61 560 607 802 852
SCK–CEN (Report R-4122) Steels [17]
T91 544 2262 �66 620 683 968 1082
E97 557 2488 �72 648 719 934 1037
EM10 495 2310 �96 650 748 937 1024
F82H 562 2293 �65 633 697 888 1005
Lambert-Perlade Steels [18]
BM 433 2065 �84 542 598 832 933
CGHAZ-100s 586 2211 �16 626 645 775 817
ICCGHAZ-100s 534 1755 3 529 537 713 751
CGHAZ-500s 481 1483 29 470 477 648 680
SAID Steels [19]
Steel-1 591 2148 �86 703 766 792 849
Steel-2 493 1856 �60.5 588 633 775 836
Steel-3 266 1280 8.5 315 339 516 547
Steel-4 339 1297 �61.5 411 454 481 543
Steel-5 387 1651 �40 505 556 664 713
Other Steels
DuplxSS [20] 450 2290 �83 676 732 904 944
HT9 [21] 604 2381 �18.5 651 672 802 844
JSPS [15] 461 1701 36 475 479 568 609
20MnMoNi55 [15] 430 2129 �70 496 549 793 892
16MND5 [22] 491 2331 �88 612 675 856 945
SREENIVASAN ON CVN SPECIMENS WITHOUT PRECRACKING 294
Materials Performance and Characterization
those computed using Eq 11 at various temperatures to yield the scaled ryd values. If
the actual ryd at RT is less than that from Eq 11, the absolute difference (of the RT
values) must be subtracted from those computed using Eq 11 at various tempera-
tures to yield the scaled ryd values. If the RT ryd (ryd-RT) is not known, a good way
to estimate ryd-RT is to apply the empirical relation—Eq 12—to obtain the RT
dynamic general yield load (Pdygy-RT, as will be obtained from instrumented Charpy
V-notch tests) from the easily available RT static yield stress (rys-RT). The empirical
equation for estimating Pgy-RT due to Mathy and Greday [24] is as follows:
Pdygy-RTðNÞ ¼ 6300þ 14:8rys-RT(12)
where rys-RT is in MPa and ryd-RT is estimated from the Pdygy-RT using Eq 7. Combin-
ing Eqs 7 and 12 and applying the full-size standard Charpy specimen dimensions
results in the following direct relation:
ryd-RT ¼ 294:33þ 0:691rys-RT(13)
TABLE 2
TQcfs estimates for the calibration steels compared with other TQ estimates
SteelT0 (�C)
(ASTM E1921)TD
(�C)TQ-BT(�C)
TQ-IGC(�C)
TQcfs1
(�C)TQcfs2(�C)
TQcfs3(�C)
TQcfs4
(�C)TQcfs(�C)
JAERI Steels
JRQ �65 �60 �50.0 �47.2 �70 �64 �70 �59 �59Steel-A �76 �80 �80.0 �60.1 �83 �78 �85 �87 �78Steel-B �97 �85 �87.5 �84.3 �96 �101 �106 �106 �96
SCK-CEN (Report R-4122) Steels
T91 �118 �110 �125 �87.4 �100 �109 �106 �116 �100E97 �115 �110 �125 �101.8 �103 �113 �110 �116 �103EM10 �138 �115 �132.5 �101.7 �125 �140 �144 �142 �125F82H �118 �95 �102.5 �95.8 �98 �108 �101 �108 �98
Lambert-Perlade Steels
BM �132 – – �103 �116 �124 �123 �128 �116CGHAZ-100s �45 – – �45 �81 �52 �65 �66 �52ICCGHAZ-100s �12 – – �30 �56 �27 �50 �37 �27CGHAZ-500s �6 – – 18 �23 �5 �29 �19 �5
SAID Steels
Steel-1 �119 �106 �119 �101 �114 �108 �85 �86 �85Steel-2 �103 �95.3 �103 �73 �95 �94 �110 �105 �94Steel-3 �48.5 �59 �48.5 �38 �31 �33 �48 �34 �31Steel-4 �83 �82 �83 �92 �92 �92 �96 �105 �92Steel-5 �78 �78.7 �78 �77 �73 �78 �90 �82 �73
Other Steels
DuplxSS �120 �90 �95 �90.3 �120 �126 �150 �133 �120HT9 �34.8 �112 �128 �33 �71 �50 �64 �58 �50JSPS 5 �40 �20 18 �55 13 �3 �8 13
20MnMoNi55 �126 �105 �117.5 �82 �122 �125 �106 �114 �10616MND5 �95a �133 �160 �94 �120 �128 �126 �133 �120
aValues vary from �85 to �102�C; the mid-value is reported in the table.
SREENIVASAN ON CVN SPECIMENS WITHOUT PRECRACKING 295
Materials Performance and Characterization
Equation 12 is based on the results of low and medium strength steels (mainly of the
ferrite-pearlite type) and, hence, its applicability (as also of Eq 13) to higher strength
steels and to irradiated steels is to be done with caution. However, it can be used,
provided the results are consistent with each other as will be shown when discussing
the results.
Similarly, for estimation of the rys as a function of temperature, the following
equation due to Server [25] can be used:
T� ¼ T95
� �� �þ 32(14a)
rys ¼ 6:895 73:62� 0:0603T� þ ð1:32� 10�4Þ T�ð Þ2�ð1:16� 10�7ÞðT�Þ3� �
(14b)
where T is in �C and rys is in MPa. Equation 14a actually converts �C to �F for use
in Eq 14b. The above equation can also be scaled using known values at one or two
temperatures as discussed after Eq 11 in the case of ryd estimation. As far as possible,
test results are preferred.
One method of estimating rf for the Said steels in Tables 1 and 2 was described
above. The other method is based on the experimental tensile fracture stress results
presented in Said et al. [19]. The fracture stress of a smooth tensile test specimen at
zero-ductility temperature (designated Tsp in Ref. [19]) is related to rf. For the ratio
rf/rf-tension (rf-tension is the fracture stress in a smooth specimen tensile test where
tensile and yield stress coincide at Tsp and is designated Skop in Ref. [19]), Saario
et al. [26] give a value of 1.66 while Said and Talas [27] give a value of 1.71. Taking
the value as 1.71, rf can be computed using the rf-tension values given in Ref. [19].
The results are reported in Table 3 for the five Said steels listed in Table 1. They show
excellent agreement within experimental error with those determined from ryd at
TD (also listed in Table 3) and, hence, a mean value is taken as the rf value for the
steels in Table 3 and the same has been reported in Table 2. Thus, the agreement
between rf values from two independent methods lends confidence to our estimates.
Another point to be mentioned about the Said steels (Tables 1 and 2) is that they
range from low-strength ferrite-pearlite to medium to intermediate strength
quenched and tempered steels, too. The Lambert steels in Tables 1 and 2 pertain to
base metal (BM) and weld heat affected zones including coarse grained heat affected
zone (CGHAZ) material in two cooling conditions and one intercritical CGHAZ
material (ICCGHAZ) in one cooling condition simulated in a Gleeble type test
machine. The other steels are mostly of the reactor pressure vessel (RPV) type
ASTM A533B or similar steels or the 9Cr1Mo type and reduced activation marten-
sitic (RAFM) steels and a Q&T 12Cr martensitic steel, HT9.
The steels used for prediction based on the present CFS model, apart from the
calibration steels in Tables 1 and 2, are listed in Table 4 with source references. The
IGCAR steels consist of a quenched and tempered 9Cr-1Mo martensitic steel
(91BM-IGC) [3], a normalized C-Mn steel A48P2 steel (A48P2-IGC) [28], a service-
exposed 2.25Cr-1Mo steel (21IGC) [2], a post-weld heat treated 9Cr-1Mo weld
(91Wld-IGC) [29], a quenched and tempered ASTM A403 stainless steel (12Cr
martensitic SS) (403SS-IGC) [30] and a normalized and tempered ASTM A203D
3.5 %Ni steel (A203D-IGC) [31]. The ASTM STP 870 steels are old RPV steels of
SREENIVASAN ON CVN SPECIMENS WITHOUT PRECRACKING 296
Materials Performance and Characterization
types similar to ASTM A302B or A212B and their welds and some old A533B steels
also. The ASTM STP 1046 steels are modern RPV steels of the types ASTM A533B
or A508 and their welds tested at BARC, India under an IAEA program. Among the
other steels, HSST-02 is an ASTM A533, Grade B, Class 1 steel well-characterised
under the Heavy Section Steel Technology (HSST) program in both unirradiated
and irradiated (I) conditions [34,35] while the 403SS-DQT steel is an ASTM ASTM
403 SS (12Cr martensitic SS) [36,37] subjected to double quench and tempering heat
treatment to improve toughness. All the Table 4 steels have IIT data available, but
the static yield stress variation with temperature has been estimated mostly using the
relations discussed before.
Results and Discussion
CALIBRATION CURVES ANDTQcfs ESTIMATIONS FOR THE
CALIBRATION STEELS
The values of T41J, rys*1, rys*2, ryd*1, and ryd*2 for the calibration steels are listed in
Table 1 along with rf. As discussed in the Present Methodology, the a and b values
determined based on free fit of rf/rys and rf/ryd in Eq 4 are given in Table 5. as and
bs are values obtained from the fit to the static ratio rf/rys and ad and bd are values
obtained from the fit to the dynamic ratio rf/ryd, respectively. Table 5 also gives the
average values of a and b for both the static and dynamic cases, i.e., aavs and bavs,
aavd and bavd, respectively. Then, keeping the a values as constants at aavs (0.366)
and aavd (1.858), respectively, a second fit was done as described in the
Present Methodology section. The resulting b values (designated B) are shown in
Figs. 3–6; Figs. 3 and 4 display the B values based on fit to Eq 6a against rf/rys*1 and
rf/rys*2, respectively (Figs. 3 and 4 have the same B values as ordinates but abscissae
are different), while Figs. 5 and 6 display the B values based on fit to Eq 6b against
rf/ryd*1 and rf/ryd*2, respectively (Figs. 5 and 6 have the same B values as ordinates
but abscissae are different). The B values based on best fit to the data in Figs. 3–6 are
designated B1, B2, B3, and B4, respectively.
It was found that a cubic fit gives the best fit in all cases. The resulting equations
or calibration curves are given below.
B1 ¼ � 11:0557þ 11:8355rf
rys�1� 3:5165
rf
rys�1
� �2
þ 0:3344rf
rys�1
� �3
(15a)
TABLE 3
Cleavage fracture stress for the five Said steels [19] of Table 1 by two independent methods.
SteelTD fromT0 (�C)
ryd atTD (MPa)
rf from rydat TD (MPa)
TSP
(�C)Skop(MPa)
rf fromSkop¼ 1.71 Skop (MPa)
Meanrf (MPa)
Steel-1 �106 892 2248 �219 1198 2049 2148
Steel-2 �95.3 798 2011 �199 995 1702 1856
Steel-3 �59 572 1441 �180 654 1118 1280
Steel-4 �82 474 1194 �201 819 1401 1297
Steel-5 �78.6 690 1739 �197 914 1563 1651
SREENIVASAN ON CVN SPECIMENS WITHOUT PRECRACKING 297
Materials Performance and Characterization
with correlation coefficient R¼ 0.9153 and validity range for (rf/rys*1)¼ 3.05 to 4.3.
MC KJC data from B1 is given by:
KJC ¼ 20þ 0:366 � exp B1rf
rys
� �(15b)
B2 ¼ � 25:8537þ 25:7755rf
rys�2� 7:8807
rf
rys�2
� �2
þ 0:7858rf
rys�2
� �3
(16a)
with correlation coefficient R¼ 0.8525 and validity range for (rf/rys*2)¼ 2.8 to 3.89.
MC KJC data from B2 is given by:
TABLE 4
(Micro) CFS and other strength properties of test steels.
Steel rys-RT (MPa) rf (MPa) T41J (�C) rf/rys*1 (MPa) rf/rys*2 (MPa) rf/ryd*1 (MPa) rf/ryd*2 (MPa)
IGCAR Steels [6]
91BM-IGC [3] 512 2425 �79 3.9113 3.6631 2.558 2.1032
A48P2-IGC [28] 556 2019 �76.6 2.7695a 2.5428a 2.4682 2.141
21IGC [2] 280 1613 �20.5 4.7949a 4.3128a 2.5767 2.3209
91Wld-IGC [29] 560 2140 8.5 3.5762 3.435 2.5659 2.4318
403SS-IGC [30] 656 2143 34.5 3.2226 3.1376 2.7369 2.6424
A203D-IGC [31] 390 1367 �57.5 2.7672a 2.5744a 2.0252a 1.8374a
ASTM STP 870 Steels [6,32]
M–Y–Wld 453 1907 �36 3.5922 3.4133 2.4799 2.3241
M–Y–Wld–I 703 1926 182 2.9051 2.8877 2.7086 2.6316
M–Y–TL–P 436 1735 �29 3.4909 3.3111 2.4506 2.295
M–Y–TL–P–I 558 1723 77 3.1442 3.0823 2.6549 2.5451
EPRI–EP–24–Wld 350 1890 �29.5 4.621a 4.3349a 2.9905 2.8125
EPRI–EP–24–Wld–I 541 1943 72.5 3.673 3.5783 2.9938a 2.9a
EPRI–EP–23–Wld 367 1824 �11 4.4706a 4.2125a 2.9372 2.7511
EPRI–EP–23–Wld–I 552 1911 72 3.5323 3.4432 2.922 2.8103
A302BRCM–P 432 1695 �12 3.5759 3.3968 2.5148 2.3673
A302BRCM–P–I 599 1801 58 3.0269 2.9573 2.5729 2.4841
ASTM STP 1046 Steels [33]
AP 440 1778 �3.5 3.7669 3.5992 2.6498 2.3519
AP-I 504 1884 28 3.6092 3.575 2.6761 2.3788
FH 467 2343 �88 3.9378 3.6898 2.6355 2.277
FH-I 559 2143 �78 3.1842 3.0141 2.3971 2.1957
GW 478 1895 �60 3.3246 3.1426 2.3927 2.8931a
GW-I 568 1949 �34 3.0887 2.953 2.351 2.1801
JH 459 2190 �80.5 3.7955 3.561 2.6165 2.3224
JH-I 595 2285 �63 3.3116 3.1561 2.5474 2.3777
Other Steels
HSST Plate02 [34,35] 489 1801 6 3.5876 3.4971 2.6761 2.4272
HSST Plate02–I [34] 580 2054 34 3.4932 3.395 2.5934 2.4136
403SS–DQT [36,37] 615 2550 �25 3.8231 3.701 2.9651 2.6927
aThe bold underlined values indicate values outside the permitted range.
SREENIVASAN ON CVN SPECIMENS WITHOUT PRECRACKING 298
Materials Performance and Characterization
KJC ¼ 20þ 0:366 � exp B2rf
rys
� �(16b)
B3 ¼ 2:1566þ 1:1167rf
ryd�1� 0:8441
rf
ryd�1
� �2
þ 0:1263rf
ryd�1
� �3
(17a)
with correlation coefficient R¼ 0.8695 and validity range for (rf/ryd*1)¼ 2.28 to
2.995. MC KJC data from B3 is given by:
TABLE 5
aavs and aavd estimates for the calibration steels.
Steel/Statistics as bs ad bd
JAERI Steels
JRQ 4.11� 10�3 2.9453 4.4571 9.55� 10�4
Steel-A 9.00� 10�3 2.3494 2.4095 0.1092
Steel-B 0.1556 1.7351 2.7429 0.077
SCK–CEN (Report R-4122) Steels
T91 0.8643 1.3824 1.9 1.8084
E97 0.9783 1.2427 1.3052 1.6686
EM10 1.29� 10�68 34.2963 0.922 1.9038
F82H 1.1233 1.3223 3.1518 1.4515
Lambert-Perlade Steels
BM 1.1427 1.2325 2.0854 1.6468
CGHAZ-100s 3.10� 10�5 4.513 7.93� 10�3 3.2716
ICCGHAZ-100s 3.00� 10�21 15.5422 2.47� 10�3 4.1667
CGHAZ-500s 1.46� 10�15 12.2952 3.44� 10�3 4.4864
SAID Steels
Steel-1 0.2736 1.9249 2.3646 0.3507
Steel-2 0.1775 2.0533 2.5768 0.2379
Steel-3 0.4476 1.4149 2.9937 0.0844
Steel-4 0.2687 1.8056 1.5252 1.2825
Steel-5 0.8321 1.4731 2.6979 0.129
Other Steels
DuplxSS 3.47� 10�5 3.9743 4.22� 10�3 3.9731
HT9 8.46� 10�27 18.0926 3.1917 5.51� 10�3
JSPS 0.9407 1.1781 0.1183 2.252
20MnMoNi55 0.1134 1.5854 2.3438 1.5211
16MND5 0.1134 1.5854 2.2129 0.115
STATISTICS
Mean aavs 5 0.3659 bavs¼ 5.4297 aavd 5 1.8579 bavd¼ 1.4544
Median 0.1775 1.8056 2.2129 1.4515
SD 0.423 8.2441 1.2755 1.4717
Standard Error 0.0923 1.799 0.2783 0.3212
95 % Conf 0.1925 3.7527 0.5806 0.6699
99 % Conf 0.2626 5.1192 0.792 0.9139
SREENIVASAN ON CVN SPECIMENS WITHOUT PRECRACKING 299
Materials Performance and Characterization
FIG. 3
B values obtained from fit to
Eq 6a—KJC¼20þ aavsexp
(B*rf/rys) with aavs¼0.366
plotted against rf/rys*1 for each
steel in Table 1.
FIG. 4
B values obtained from fit to
Eq 6a—KJC¼20þ aavsexp
(B*rf/rys) with aavs¼0.366
plotted against rf/rys*2 for each
steel in Table 1.
FIG. 5
B values obtained from fit to
Eq 6b—KJC¼20þ aavdexp
(B*rf/ryd) with aavd¼ 1.858
plotted against rf/ryd*1 for each
steel in Table 1.
SREENIVASAN ON CVN SPECIMENS WITHOUT PRECRACKING 300
Materials Performance and Characterization
KJC ¼ 20þ 1:858 � exp B3rf
ryd
� �(17b)
B4 ¼ 33:7517� 37:5066rf
ryd�2þ 14:713
rf
ryd�2
� �2
� 1:9472rf
ryd�2
� �3
(18a)
with correlation coefficient R¼ 0.8334 and validity range for (rf/ryd*2)¼ 2.09 to
2.82. MC KJC data from B4 is given by:
KJC ¼ 20þ 1:858 � exp B4rf
ryd
� �(18b)
Estmates of T0, based on MC KJC data from Eqs 15b, 16b, 17b, and 18b are desig-
nated TQcfs1, TQcfs2, TQcfs3, and TQcfs4, respectively. Following the procedures
described above, the estimated TQcfs values for the calibration steels are tabulated in
Table 2 along with actual T0 and other estimates like TQIGC and TQBT. The four TQcfs
values show excellent agreement with each other within the error that can be
expected for this. The criterion for choosing the estimate based on the present CFS
model, namely, TQcfs, is the most conservative of the four: TQcfs1, TQcfs2, TQcfs3, and
TQcfs4. The TQcfs values so determined are given in the last column of Table 2.
Figure 7 compares the T0 of calibration steels with the TQcfs estimates tabulated
in Table 2. TQcfs estimates are conservative for most of the calibration steels. This
becomes more apparent in Fig. 8, which plots the residuals (i.e., (T0 – TQcfs) values)
for the 21 calibration steels; only for two steels, the values lie outside the 620�C
band, one being conservative (Steel 1) and the other being non-conservative
(16MND5 steel). For the 16MND5 steel, there is large scatter in the basic T0 data
(see footnote to Table 2) and other estimate TQBT also shows this tendency for non-
conservatism. It must be noted that for the Steel 1 (also, for all the Said Steels in
Tables 1 and 2), as discussed before, the dynamic yield stress has been estimated
using Eqs 11 to 13. There may be some error in this leading to large over conserva-
tism as TQcfs for the Steel 1 is determined by TQcfs3, the value based on ryd and ryd*1.
FIG. 6
B values obtained from Eq 6b—
KJC¼20þ aavdexp
(B*rf/ryd) with aavd¼ 1.858
plotted against rf/ryd*2 for each
steel in Table 1.
SREENIVASAN ON CVN SPECIMENS WITHOUT PRECRACKING 301
Materials Performance and Characterization
Otherwise, based on the results for all other steels, the premise for choosing the
value of TQcfs, namely, the most conservative of the four estimates TQcfs1, TQcfs2,
TQcfs3, and TQcfs4, seems to be sound. Figure 9 compares the TQcfs estimates for the
calibration steels with their TQIGC estimates. TQcfs is less conservative than TQIGC
and, hence, closer to the actual T0. This is to be expected from Fig. 8, which shows
620�C error band for TQcfs whereas TQIGC is mostly conservative to the extent of
20�C–30�C (see the Introduction).
TQcfs ESTIMATIONS FOR THE TEST STEELS
For all the IGCAR steels in Table 6, except for the A48P2-IGC, static yield stress esti-
mates have been made by scaling yield stress data given in literature for similar
steels, instead of Eq 14. For example, for 9Cr-1Mo steels, the data given by Chaouadi
FIG. 7
ASTM E1921 reference
temperature (T0) of calibration
steels compared with TQcfs
estimated using the CFS model.
FIG. 8
Residuals for the calibration
steels based on TQcfs estimated
using the CFS model.
SREENIVASAN ON CVN SPECIMENS WITHOUT PRECRACKING 302
Materials Performance and Characterization
in Ref. [17] has been used with suitable scaling. This makes the static yield stress
estimates closer to actual values. Estimates of TQcfs obtained for the test steels are
tabulated in Table 6 while the strength properties are given in Table 4. In Table 6, the
ratios rf/rys*1, rf/rys*2, rf/ryd*1, and rf/ryd*2 have been given and the values that fall
outside the range specified by Eqs 15a–18a have been highlighted in bold fonts with
underlining. Comparison of highlighted values in Table 4 with the corresponding
TQcfsx (where x stands for 1, 2, 3, or 4, as the case may be) in Table 6 indicates that
when the rf/rys*x or rf/ryd*x value falls outside the specified range, the correspond-
ing TQcfsx prediction is unacceptably large or small and such values have not been
considered for evaluation. In such cases, the largest of the valid values has been
reported as TQcfs in the last column of Table 6. Such behavior occurs mostly for steels
with low-strength, say, rys-RT< 400MPa. For the low-strength IGCAR steel,
A203D-IGC, none of the TQcfsx values are acceptable (vide Tables 4 and 6). Hence,
the present CFS model based on the calibration curves derived in this paper seems
to be applicable to steels with rys-RT in the range of 400–700–750MPa. The require-
ment for strict concurrence of the rf/rys*x or rf/ryd*x values to the validity range
arises from the fact that the calibration curves are cubic equations which will behave
wildly outside their range of fit. For the GW steel, though rf/ryd*2 has been shown
outside the validity range in Table 4, the corresponding prediction in Table 6,
namely, TQcfs4 does not show much difference from other values. This may be due
the fact that rf/ryd*2 value for the GW steel exceeds the upper limit only marginally
and hence does not have any effect on B4 value.
For the HSST-02 plate, Ref. [35] gives a T0 of �28�C which excellently com-
pares with the TQcfs value of �18�C reported in Table 6. For the M–Y Wld, Ref. [38]
gives a T0 of �106�C in the unirradiated condition and a T0 of 106�C in the
irradiated condition (fluence: 6.11� 1011 n cm�2; E> 1 MeV) which also compare
excellently with the TQcfs value of �76�C and 118�C (fluence: 1.3� 1011 n cm�2;
E> 1 MeV) reported in Table 6 for the two conditions, respectively. However, TQIGC
values are very conservative. Finally, Fig. 9 also shows the TQIGC values for the
FIG. 9
TQIGC compared with TQcfs for
the calibration and test steels.
SREENIVASAN ON CVN SPECIMENS WITHOUT PRECRACKING 303
Materials Performance and Characterization
Table 6 test steels plotted against the respective TQcfs values which are in excellent
accord with the trend shown by the calibration steels displayed in the same figure
and discussed in the previous section. Figure 9 also suggests the conclusion that
TQIGC values for steels with high reference temperature (like the highly irradiated
steels) have a tendency to be much more conservative than the corresponding TQcfsvalues as compared to steels having lower reference tempaeratures (i. e., steels near
the left axis of Fig. 9). The implication is that, in such cases, TQcfs values may even
be unacceptably non-conservative. However, the data for HSST-02 and M–Y Wld
do not warrant such a conclusion. Nevertheless, the present data are not sufficient to
draw a definite conclusion. This aspect needs further verification.
TABLE 6
TQcfs estimates for the test steels compared with other TQ estimates.
Steel TQIGC (�C) TD (�C) TQ-BT (�C) TQcfs1 (�C) TQcfs2 (�C) TQcfs3 (�C) TQcfs4 (�C) TQcfs (�C)
IGCAR Steels
91BM-IGC �86.6 �105 �118 �112 �110 �122 �157 �110A48P2-IGC �104.8 �69 �64 277a 232a �91 �69 �6921IGC �56.6 �49 �33.5 2322a 2640a �60 �63 �6091Wld-IGC �26.9 �34 �11 �36 �26 �32 �25 �25403SS-IGC 22.3 �39 �18.5 �20 �8 �9 �4 �4A203D-IGC �70 �86 �89 257a 215a 296a 2142a ––
ASTM STP 870 Steels
M-Y–Wld �52.5 �73 �69.5 �81 �76 �86 �78 �76M–Y–Wld–I 150 71 146.5 113 113 100 118 118
M–Y–TL–P �52.4 �53 �39.5 �69 �65 �73 �65 �65M–Y–TL–P–I 77.8 10 55.0 28 38 23 33 38
EPRI–EP–24–Wld �66 �109 �123.5 2145a �211a �56 �56 �56EPRI–EP–24–Wld–I 70.8 �49 �33.5 39 20 �52a 233a 39
EPRI–EP–23–Wld �39.6 �93 �99.5 298a 2138a �53 �58 �53EPRI–EP–23–Wld–I 72 �39.5 �19.3 �5 34 9 24 34
A302BRCM–P �37.3 �34 �11.0 �57 �51 �61 �53 �51A302BRCM–P–I 67 17 65.5 6.4 34 �16 2.4 34
ASTM STP 1046 Steels
AP �33 �33.3 �9 �46 �33 �35 �42 �33AP–I 24 �4 34 �32 6 �2 �6 6
FH �95 �120 �140 �127 �125 �120 �132 �120FH-I �89 �82.9 �84 �119 �115 �124 �123 �115GW �91 �64.9 �57 �86 �84 �89 285a �84GW-I �58 �32 �8 �46 �40 �63 �60 �40JH �92 �112.8 �129 �119 �117 �117 �123 �117JH-I �64 �91.8 �97 �111 �106 �115 �108 �106
Other Steels
HSST-02 �25 �33.5 �10.3 �36 �18 �31 �36 �18HSST-02-I 37 �2 37 �27 �5 �11 �8 �5403SS-DQT �32.3 �69 �63.5 �45 �33 �46 �60 �33
aValues highlighted and underlined are invalid.
SREENIVASAN ON CVN SPECIMENS WITHOUT PRECRACKING 304
Materials Performance and Characterization
Conclusions
Thus, a semi-empirical formulation of the CFS (cleavage fracture stress) model,
based on the microscopic cleavage fracture stress, rf, for estimating the ASTM
E1921 reference temperature of ferritic steels from instrumented impact test (IIT) of
unprecracked CVN specimens has been established. The relevant calibration equa-
tions necessary for applying the model have been derived and demonstrated for
steels with room temperature yield strength in the range 400–750MPa, including
irradiated steels. However, applicability and acceptability of the present calibration
curves for highly irradiated steels need further examination. The estimate of T0,
based on the present CFS model, TQcfs, lies within a 620�C band, being conservative
for most of the steels, but less conservative than TQIGC based on the IGC-procedure.
Moreover, the CFS model is a single step assessment procedure as compared to the
multi-stage IGCAR-procedure and, hence, less error-prone due to calculation
errors. However, the parameters must strictly meet the validity conditions for the
calibration equations. CFS model enhances the validity and utility of the CVN IIT
by enabling estimation of design-relevant master curve from unprecracked CVN
specimens. Although some researchers have called an approach based on the CFS
mesoscopic (i.e., lying between microscopic and macroscopic scales), at least in
steels, rf operates over microstructural distances. As such, the CFS model or
approach should be the preferred Nomenclature.
ACKNOWLEDGMENTS
The writer acknowledges with thanks the excellent support and encouragement
received from Director, MMG and Director, IGCAR, Kalpakkam, India.
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