Sumarize the following: 10.5 Varestraint Test 
10.5.1 Scope. The varestraint test is used to evaluate 
base-metal weldability and determine the influence of 
the welding variables on hot cracking of the base metal. 
A means is provided for augmenting conventional 
shrinkage strains to simulate the large shrinkage strains 
found in highly restrained production weldments. 
10.5.1.1 This standard is applicable to the following: 
(1) Qualification of materials and welding procedures, 
(2) Manufacturing quality control, and 
(3) Research and development. 
10.5.1.2 The use of this test is restricted as follows: 
(1) This test is used for base metal in the thickness 
range of 1/4 in (6 mm) to 1/2 in (13 mm). A variation of 
this test, called the mini-varestraint test, is used for base 
metal in the thickness range of 1/8 in (3 mm) to 1/4 in 
(6 mm); 
(2) Specialized equipment for testing (see Figure 
10.5.1) and specimen examination is required; 
(3) Welding usually is done by the mechanized gas 
tungsten arc welding (GTAW) process to minimize vari- 
ables in the welding parameter and testing results; and 
(4) Specimens are tested under laboratory conditions. 
Shop floor or field examination of specimens may not be 
practical. 
10.5.1.3 The following information shall be furnished: 
(1) Weld procedure (process and parameters); 
(2) Number of specimens to be tested; 
(3) Orientation of specimens relative to the rolling 
direction of the base metal, if known; 
(4) Base-metal chemical composition; 
(5) Base-metal thickness; 
(6) Desired weld bead surface geometry (weld bead 
profile); 
(7) Specimen surface finish; 
(8) Value of augmented tangential strain (see 10.5.5.4); 
(9) Magnification to be used in examination for cracks; 
and 
(10) The rate of loading of the specimen during the 
test (if applicable). 
10.5.2 Summary of Method 
10.5.2.1 The test is conducted by depositing a weld on 
a cantilevered specimen beginning at one end of the 
specimen (Figure 10.5.1). When the weld progresses 
along the centerline of the specimen to a predetermined 
point (A), the specimen is bent to conform to a curved 
die (B) as the arc continues to a location (C) near the end 
of the specimen. A series of decreasing radius dies is 
used to provide various magnitudes of strain, i.e., aug- 
mented tangential strain, to the solidifying weld in a cor- 
responding series of test specimens. The strain that 
results in solidification cracking is an index of the crack 
susceptibility of the base metal. 
10.5.2.2 After cooling, the surface of the weld is 
examined for the presence of cracks. Examination is 
done at a magnification of 40X to 80X, and the length 
and location of each crack is noted and recorded. The 
specimen may be sectioned and polished for a more 
accurate determination of the presence of cracks. 
10.5.2.3 A smaller scale test, called the mini- 
varestraint test, is used to study the hot-crack suscepti- 
bility of expensive base metals or more common base 
metals in sheet thicknesses. This test utilizes a smaller 
test specimen [1 in (25 mm) wide × 6 in (152 mm) long] 
and correspondingly smaller test equipment. The mini- 
varestraint test may not be practical for thicker material 
since its testing apparatus may not have the loading 
capacity to bend the thicker material. 
10.5.3 Significance. The varestraint test is used for the 
analytic investigation of the hot-crack sensitivity of weld 
deposits, the effect of specific alloying elements on this 
sensitivity and the basic mechanisms of hot cracking. 
This test combines a direct correlation with actual fabri- 
cation behavior, reproducibility of results, an ability to 
differentiate between small differences in test and weld- 
ing variables, and uses relatively small test plates. 
10.5.4 Definitions and Symbols. Unless otherwise noted, 
the following designations are used: 
A = point of arc progression at which bending force 
is applied 
B = a series of decreasing radius die blocks 
C = location of termination of test weld 
e = augmented tangential strain (%) 
T = specimen thickness 
R = die block radius 
10.5.5 Apparatus 
10.5.5.1 The equipment required for conducting the 
varestraint test clamps one end of the flat specimen and 
provides a method for bending the specimen around a 
fixed curved die during welding. This concept is illus- 
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AWS B4.0:2007 CLAUSE 10. WELDABILITY TESTING 
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trated in Figure 10.5.1. Curved dies having different 
radius are used while conducting a series of tests. Each 
specimen of the series is bent around a die having a 
smaller radius than the die used with the previous speci- 
men. The tests are continued until the die radius is small 
enough to cause cracking. 
10.5.5.2 Localized bending in the vicinity of the mol- 
ten weld puddle is avoided by using auxiliary bending 
plates to force the test specimen to conform to the die 
contour. These plates are clamped into the edges of the 
specimen and are bent along with the specimen. The 
plates are made from rolled steel; their size is 1/2 in 
(13 mm) thick by 2 in (50 mm) wide by 12 in (305 mm) 
long. These auxiliary plates are illustrated in Figure 
10.5.2. Auxiliary plates used with the mini-varestraint 
test are 1/4 in (6 mm) thick. 
10.5.5.3 The bending force may be applied either 
hydraulically or pneumatically. The design of the equip- 
ment and method for bending depends on the individual 
equipment builder. 
10.5.5.4 The augmented tangential strain for given 
radius of curvature of the die block can be calculated 
from the following formula: 
where 
e = augmented tangential strain (%), 
T = specimen thickness, and 
R = die block radius. 
The typical range of augmented tangential strain is 0% to 
4%. The required die radius for a given value of aug- 
mented tangential strain can be calculated using the same 
equation. 
10.5.5.5 Die block radii for the mini-varestraint test 
are calculated in the same manner as for the varestraint 
test. The overall size of the mini-varestraint die block 
may be smaller as the test specimen is smaller. 
10.5.6 Specimens. The varestraint test specimens are 
rough sawed and machined to size. The specimen size is 
2 in (50 mm) wide by 12 in (305 mm) long. The speci- 
men size thickness is 1/4 in (6 mm) or 1/2 in (13 mm) 
The mini-varestraint specimen is 1 in (25 mm) wide by 
6 in (152 mm) long. Typical mini-varestraint specimen 
thicknesses are in the range of 1/8 in (3 mm) to 1/4 in 
(6 mm). The specimen surface on which the test weld 
will be produced should be machined in the longitudinal 
direction to a finish no rougher than 125 microinches 
(3 micrometers) R 
a 
unless it is desired to simulate a sur- 
face condition used in service. 
e 
T 
2 R T + ( ) 
--------------------- = 
10.5.7 Procedure 
10.5.7.1 The varestraint specimen is clamped in the 
test fixture. Auxiliary bending plates, when needed to 
facilitate bending, are clamped in the fixture with the 
specimen. The removable die block of the desired radius 
is fastened in the position shown in Figure 10.5.1. The 
arc is initiated on the centerline of the specimen, approx- 
imately 2 in (50 mm) from the specimen’s unclamped 
end. The bending force (F) is suddenly applied as the 
center of the arc passes Point A, which is near the point 
of tangency between the curved surface of the die block 
and the fixed end of the specimen. The specimen and 
auxiliary bending plates are bent downward until the 
specimen conforms to the radius of curvature of the top 
surface of the die block. The rate of arc travel is constant 
from its point of initiation to its point of termination in 
the runoff area at location C. 
10.5.7.2 The bending load and the shielding gas flow 
(if used) are maintained for five minutes after termina- 
tion of the weld pass. The specimen then is removed 
from the fixture for examination. 
10.5.7.3 The following test parameters shall be 
maintained: 
(1) Number of Specimens. A minimum of three speci- 
mens shall be tested under the same conditions at each 
selected or required value of augmented tangential strain. 
(2) Specimen Orientation. The specimen shall be 
taken from the base metal so that the 12 in (305 mm) 
dimension is parallel to the final direction of rolling or 
major working unless the specimen used is a casting or if 
service conditions in which a different orientation of roll- 
ing direction are to be simulated. 
(3) Weld Geometry. The weld puddle geometry is 
kept constant when using the maximum crack length cri- 
terion [see 10.5.8.3(2)] for screening of materials. 
10.5.8 Report 
10.5.8.1 The as-welded surface near Point A is exam- 
ined for visual evidence of cracks at a magnification of 
40X, 60X, or 80X. The locations of any HAZ or fusion- 
zone cracks are shown schematically in Figure 10.5.3. 
The length of each crack shall be measured to the nearest 
0.001 in (0.025 mm) with a low-power microscope (40X, 
60X, or 80X) containing a calibrated reticle in the eye- 
piece. The test results that are reported shall include the 
following: 
(1) The base-metal type, composition, thickness, and 
condition; 
(2) The percent augmented tangential strain; 
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CLAUSE 10. WELDABILITY TESTING AWS B4.0:2007 
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(3) The total crack length of the three specimens 
tested under the same conditions that were found on the 
as-welded surface at the specified magnification (40X, 
60X, or 80X) and the location of the cracks (weld metal 
or HAZ); 
(4) The maximum crack length of each of the three 
specimens tested under the same conditions that were 
found on the as-welded surface at the specified magnifi- 
cation (40X, 60X, or 80X) and the location of the cracks 
(weld metal or HAZ); 
(5) Weld procedure (process and parameters); 
(6) Rate of loading of the specimen during the test (if 
available). 
10.5.8.2 The following criteria can be used to evaluate 
the test results: 
(1) Cracking Threshold. The cracking threshold is 
the minimum augmented tangential strain required to 
cause cracking in a particular base metal with a given set 
of welding variables. This criterion provides a quantita- 
tive method for comparing welding procedures. 
(2) Maximum Crack Length. The maximum crack 
length that is measured in a given specimen can be used 
as a quantitative index for preliminary screening of base 
metal, filler metal, or both, at comparable levels of 
augmented tangential strain, provided constant puddle 
geometry is maintained. This criterion is useful when 
searching for metals with low crack sensitivity. 
(3) Total Combined Crack Length. The total com- 
bined crack length is obtained by adding the lengths of 
cracks found in the weld metal and in the HAZ of each 
specimen. The total combined crack length produced in 
the weld metal and HAZ will give the best quantitative 
index of the hot-crack sensitivity of the weld metal and 
HAZ, respectively, for a given welding procedure. This 
criterion also may be used to examine the effects of 
welding procedure changes. 
10.5.8.3 Test data should be recorded on a Test 
Results Sheet similar to Figure 10.5.4. 
10.5.9 Commentary 
10.5.9.1 The technology of the varestraint test is un- 
dergoing further refinement. The test specimen size and 
geometry, test apparatus, interpretation of results, and 
understanding of the effect of test variables on cracking 
susceptibility are being examined in detail. Two 
articles 
5, 6 
describing these investigations are included in 
the Bibliography of this document. The classical aspects 
of the varestraint test have been presented herein. 
10.5.9.2 The rate of loading can affect test results and 
use of certain rates of loading may result in scatter in test 
results.