Typical uses. Simple, highly stressed castings of uniformDensity. 1.83 g/cm (0.066 lb/in. ) at 20 pdf

Typical uses. Simple, highly stressed castings of uniform
cross section. High in cost. Intricate castings subject to
microporosity and cracking due to shrinkage. Not
readily welded. Sometimes used in the artificially aged
condition (T5 temper) but usually in the solution-heat
treated and artificially aged condition (T6 temper) to
develop properties fully
Mechanical Properties
Tensile properties. T6 temper: tensile strength, 310 MPa
(45 ksi); yield strength, 195 MPa (28 ksi); elongation in
50 mm (2 in.), 10%
Fatigue properties. At least equal to those of the Mg-Al-Zn
alloys
Mass Characteristics
Density. 1.83 g/cm
3
(0.066 lb/in.
3
) at 20 °C (68 °F)
Thermal Properties
Liquidus temperature. 635 °C (1175 °F)
Solidus temperature. 530 °C (985 °F)
Coefficient of linear thermal expansion. 27.0 μm/m · K (15.0
μin./in. · °F) at 20 to 200 °C (68 to 390 °F)
Fabrication Characteristics
Weldability. Not readily weldable. Addition of Th or rare
earths decreases porosity and improves weldability.
Casting temperature. Sand castings, 705 to 815 °C (1300 to
1500 °F)
Tin and Tin Alloys
Revised by William B. Hampshire, Tin Research Institute, Inc.

Introduction
TIN was one of the first metals known to man. Throughout ancient history, various cultures recognized the virtues of tin
in coatings, alloys, and compounds, and the use of the metal increased with advancing technology. Today, tin is an
important metal in industry even though the annual tonnage used is much smaller than those of many other metals. One
reason for the small tonnage is that, in most applications, only very small amounts of tin are used at a time.
Tin Production and Consumption
Tin is produced from both primary and secondary sources. Secondary tin is produced from recycled materials (see the
article "Recycling of Nonferrous Alloys" in this Volume). Figure 1 shows the consumption of primary and secondary tin
in the United States during recent years. Figure 2 shows 1988 data for the relative consumption of tin in the United States
by application.

Fig. 1 U.S. consumption of primary and secondary tin in recent years

Fig. 2 Relative consumption of tin in the United States by application. 1988 data. Source: U.S. Bureau of Mines

Primary Production. Tin ore generally is centered in areas far distant from centers of consumption. The leading tin-
producing countries (excluding the USSR and China) are, in descending order, Brazil, Indonesia, Malaysia, Thailand,
Bolivia, and Australia (1988 totals). These countries supply over 85% of total world production.
Cassiterite, a naturally occurring oxide of tin, is by far the most economically important tin mineral. The bulk of the
world's tin ore is obtained from low-grade placer deposits of cassiterite derived from primary ore bodies or from veins
associated with granites or rocks of granitic composition.
Primary ore deposits can contain very low percentages of tin (0.01%, for example), and thus large amounts of soil or rock
must be worked to provide recoverable amounts of tin minerals. Unlike ores of other metals, cassiterite is very resistant to
chemical and mechanical weathering, but extended erosion of primary lodes by air and water has resulted in deposition of
the ore as eluvial and alluvial deposits.
Underground lode deposits of tin ores are worked by sinking shafts and driving adits, and the rock is broken from the
working face by drilling and blasting. Cassiterite is recovered from eluvial and alluvial deposits by dredging, gravel
pumping, and hydraulicking. In open-pit mining, a much less widely employed mining method, mechanical and manual

methods are used to move tin-bearing materials. After ball mill concentration of the ore, a final culling is provided at
dressing stations.
The final concentrates, which contain 70 to 77% tin, are then sent to the smelter, where they are mixed with anthracite
and limestone. This charge is heated in a reverberatory furnace to about 1400 °C (2550 °F) to reduce the tin oxide to
impure tin metal, which is again heated in huge cast iron melting pots to refine the metal. Steam or compressed air is
introduced into the molten metal, and this treatment, plus addition of controlled amounts of other elements that combine
with the impurities, results in tin of high purity (99.75 to 99.85%). This high-purity tin often is treated again by liquating
or electrolytic refining, which provides tin with a purity level approaching 99.99%.
After the tin is refined, it is cast into ingots weighing 12 to 25 kg (26 to 56 lb) or bars in weights of 1 kg (2 lb) and
upwards. Tin normally is sold by brand name, and the choice of brand is determined largely by the amounts of impurities
that can be tolerated in each end product. High-purity brands of tin may contain small amounts of lead, antimony, copper,
arsenic, iron, bismuth, nickel, cobalt, and silver. Total impurities in commercially pure tin rarely exceed 0.25%.

Tin in Coatings
Tinplate. The largest single application of tin worldwide is in the manufacture of tinplate (steel sheet coated with tin),
which accounts for about 40% of total world tin consumption. Since 1940, the traditional hot dip method of making
tinplate has been largely replaced by electrodeposition of tin on continuous strips of rolled steel. Electrolytic tinplate can
be produced with either equal or unequal amounts of tin on the two surfaces of the steel base metal. Nominal coating
thicknesses for equally coated tinplate range from 0.38 to 1.5 μm (15 to 60 μin.) on each surface. The thicker coating on
tinplate with unequal coatings (differential tinplate) rarely exceeds 2.0 μm (80 μin.). Tinplate is produced in thicknesses
from 0.15 to 0.60 mm (0.006 to 0.024 in.).
Over 90% of world production of tinplate is used for containers (tin cans). Traditional tinplate cans are made of three
pieces of tin-coated steel: two ends and a body with a soldered side seam. Innovations in can manufacture have produced
two-piece cans made by drawing and ironing. Tinplate cans find their most important use in the packaging of food
products, beer, and soft drinks, but they are also used for holding paint, motor oil, disinfectants, detergents, and polishes.
Other applications of tinplate include signs, filters, batteries, toys, and gaskets, and containers for pharmaceuticals,
cosmetics, fuels, tobacco, and numerous other commodities.
Electroplating accounts for one of the major uses of tin and tin chemicals. Tin is used in anodes, and tin chemicals are
used in formulating various electrolytes and for coating a variety of substrates. Tin electroplating can be performed in
either acid or alkaline solutions. Sodium or potassium stannates form the bases of alkaline tinplating electrolytes that are

very efficient and capable of producing high-quality deposits. Advantages of these alkaline stannate baths are that they
are not corrosive to steel and that they do not require additional agents. Acid electrotinning solutions operate at higher
current densities and higher plating rates and require additions of organic compounds.
A number of alloy coatings can be electroplated from mixed stannate-cyanide baths, including coatings of tin-zinc and
tin-cadmium alloys and a wide range of tin-copper alloys (bronzes). The bronzes range in tin content from 7 to 98%. Red
bronze deposits contain up to 20% tin; high-tin bronzes, called speculum, usually contain about 40% tin.
Tin-nickel and tin-lead electrodeposits are plated from acid electrolytes and are important coatings for printed circuits and
electronic components. Tin-cobalt plate is used in applications requiring an attractive finish and good corrosion
resistance.
Two ternary alloy electrodeposits are used by industry. These are the copper-tin-lead for bearing surfaces and the copper-
tin-zinc alloy for coatings in certain electronic applications.
Hot Dip Coatings. Coating steel with lead-tin alloys produces a material called terneplate (see the article "Lead and
Lead Alloys" in this Volume). Terneplate is easily formed and easily soldered. It is used as a roofing and weather-sealing
material and in the construction of automotive gasoline tanks, signs, radiator header tanks, brackets, chassis and covers
for electronic equipment, and sheathing for cable and pipe.
Hot dip tin coatings are used both on wire for component leads and on food-handling and food-processing equipment. In
addition, hot dip tin coatings are used to provide the bonding layer for the babbitting of bearing shells.
Pure Tin
Commercial tin is considered to be pure when it contains a minimum of 99.8% Sn. Of the various types of commercially
pure tin, about 80 to 90% is a high-purity commercial tin known as Grade A tin as specified in ASTM B 339. According
to this specification, Grade A tin must have a minimum tin purity of 99.85% Sn and maximum residual impurities of
0.04% Sb, 0.05% As, 0.030% Bi, 0.001% Cd, 0.04% Cu, 0.015% Fe, 0.05% Pb, 0.01% S, 0.005% Zn, and 0.01% (Ni +
Co). Other specifications for commercially pure tin include:
• U.S. government specification QQT-371, Grade A (99.75% Sn)
• British specification BS 3252, Grade T (99.8% Sn)
• German specification DIN 1704, Grade A2 (99.75% Sn)
Table 1 summarizes selected physical, thermal, electrical, and optical properties of pure tin. Further information is
contained in the article "Properties of Pure Metals" in this Volume. General applications of Grade A tin include tinplate
foil, collapsible tubes, block tin products, and pewter.
Table 1 Physical, thermal, electrical, and optical properties of commercially pure tin

Property Value
Physical properties
Atomic number 50
Atomic weight 118.69
Crystal structure α phase or β phase
Density, g/cm
3
(lb/in.
3
)
α phase at 1 °C (33.8 °F) 5.765 (0.2083)
β phase at 20 °C (68 °F) 7.168 (0.2590)
Liquid surface tension at 400-800 °C (750-1470 °F), mN/m 700-0.17 × T + (25 + 0.015 × T)
(a)


Hardness, HB
At 20 °C (68 °F) 3.9
At 60 °C (140 °F) 3.0
At 100 °C (212 °F)
2.3
Modulus of elasticity, GPa (10
6
psi)
Cast (coarse grain) 41.6 (6.03)
Self-annealed (fine grain) 44.3 (6.43)
Poisson's ratio 0.33
Volume change on freezing, % 2.8%
Volume change on phase transformation, % ~27%
Thermal properties

Melting point, °C ( °F) 231.9 (449.4)
Boiling point, °C ( °F) 2270 (4118)
Phase transformation temperature on cooling (β phase to α phase), °C (°F)

13.2 (55.8)
Latent heat of fusion, J/g (Btu/lb) 59.5 (25.6)
Latent heat of phase transformation, J/g (Btu/lb) 17.6 (7.57)
Latent heat of vaporization, kJ/g (Btu/lb) 2.4 (1.03 × 10
3
)
Specific heat, J/kg · K (Btu/lb · °F)
α phase at 10 °C (50 °F) 205 (49 × 10
-3
)
β phase at 25 °C (77 °F) 222 (53 × 10
-3
)
Linear coefficient of thermal expansion, 10
-6
/K
α phase at - 100 °C (-150 °F) 18.1
α phase at -50 °C (-60 °F) 19.2
β phase at 100 °C (212 °F) 23.8
β phase at 150 °C (300 °F) 26.7
Thermal conductivity, W/m · K
βphase at 100 °C (212 °F) 60.7
β phase at 200 °C (390 °F) 56.5
Electrical properties
Electrical conductivity (volumetric) at 20 °C (68 °F) 15.6% IACS
Electrical resistivity, μΩ· m

At 0 °C (32 °F) 0.110
At 100 °C (212 °F) 0.155
At 200 °C (390 °F) 0.200
Optical properties (546.1 nm wavelength)
Reflectance index
Film, 42-200 nm thick 0.70
Bulk solid 0.80
Refractive index
Film, 42-200 nm thick 2.4
Bulk solid 1.0
Absorptive index
Film, 42-200 nm thick 1.9
Bulk solid 4.2

(a)

T, temperature in degrees Kelvin

Mechanical Properties. Typical tensile properties of commercially pure tin are given in Table 2. Hardness and
elasticity values are given in Table 1.
Table 2 Tensile properties of commercially pure tin
Temperature

Yield strength

°C °F MPa

ksi
Elongation

in 25 mm

(1 in.), %
Reduction in area, %

Strained at 0.2 mm/m · min (0.0002 in/in. · min)
-200

-328

36.2 5.25 6 6
-160

-256

90.3 13.10

15 10
-120

-184

87.6 12.71

60 97
-80 -112

38.9 5.64 89 100
-40 -40 20.1 2.92 86 100
0 32 12.5 1.81 64 100

23 73 11.0 1.60 57 100
Strained at 0.4 mm/m · min (0.0004 in./in. · min)
15 59 14.5 2.10 75 . . .
50 122 12.4 1.80 85 . . .
100 212 11.0 1.60 55 . . .
150 302 7.6 1.10 55 . . .
200 392 4.5 0.65 45 . . .
Note: It is uncertain if the inconsistencies among these data are due to differences in purity or the difference in straining rate.

Creep Characteristics. Like lead, tin is subject to creep deformation and rupture even at room temperature.
Consequently, tensile strength may not be an important design criterion because creep rupture can occur at stresses even
below the yield strengths in Table 2. For example, one series of tests on a commercially pure tin resulted in the following
creep characteristics at room temperature:

Initial stress
MPa

psi
Time,

days
Extension,

%
1.083

157.0 551 3.5
1.351

196.0 551 7

2.256

327.1 173
*
101
2.772

402.1 79
*
132
3.227

468.1 21
*
119
4.214

611.2 4.6 105
7.069

1025.2

0.5
*
78

Fatigue Strength. Rotating-cantilever fatigue tests on a commercially pure tin resulted in fatigue strength levels of 2.9
MPa (430 psi) for 10
7
cycles at 15 °C (59 °F) and 2.6 MPa (380 psi) for 10

8
cycles at 100 °C (212 °F). Because creep
deformation of tin occurs at room temperature, fatigue strengths may be influenced by creep-fatigue interaction and thus
may depend on the frequency and/or waveform of stress cycling.
Impact Strength. Charpy V-notch tests on commercially pure tin at various temperatures resulted in the following
impact strengths:

Temperature

Charpy V-notch

impact energy
°C °F J ft · lbf
-80 -112 3.7 2.75
-60 -76 11.5 8.5
-15 5 28.5 21.0
0 32 44.1 32.5
150 302 22.7 16.75
190 374 20.3 15.0
215 419 2.7 2.0

Specific Damping Capacity. Tests on bars vibrating at audio frequencies in the free-free mode produced these results:

Temperature

Logarithmic decrement
°C °F Polycrystalline

Single crystals

25 77 0.022 0.0010
50 122 0.045 0.0013
75 167 0.060 0.0015
100 212 0.054 0.0018
125 257 0.045 0.0024
150 302 0.060 0.0032

Chemical Properties and Corrosion Behavior. Tin reacts with both strong acids and strong alkalies, but it is
relatively resistant to near-neutral solutions. Oxygen greatly accelerates corrosion in aqueous solutions. In general, with
mineral acids the rate of attack increases with the temperature and concentration. Dilute solutions of weak alkalies have
little effect on tin, but strong alkalies are corrosive even in cold dilute solutions. Salts with an acid reaction at tack tin in
the presence of oxidizers or air. Tin resists demineralized waters but is slightly attacked near the water line by hard tap
waters. The corrosion resistance of tin in specific environments is summarized in Table 3. Additional information on the
corrosion of tin is given in Corrosion, Volume 13 of ASM Handbook, formerly 9th Edition Metals Handbook.
Table 3 Resistance of tin to specific corroding agents

Corrosive agent Resistance Remarks
Acid, acetic Slight attack Increased by air
Acid, butyric Resistant . . .
Acid, citric Moderate attack

At water line
Acids, fatty Moderate attack

. . .
Acid, hydrochloric Severe attack In presence of air

Acid, hydrofluoric Severe attack In presence of air

Acid, lactic Moderate attack

Increased by air
Acid, nitric Severe attack . . .
Acid, oxalic Moderate attack

(a)

Acid, phosphoric Resistant . . .
Acid, salts Severe attack Air present
Acid, sulfuric Severe attack
(b)

Acid, tartaric Slight attack . . .
Air Resistant . . .
Ammonia Resistant . . .
Bromine Severe attack . . .
Carbon tetrachloride

Resistant . . .
Chlorine Severe attack . . .
Iodine Severe attack . . .
Milk Resistant . . .
Motor fuel Resistant . . .
Petroleum products Resistant . . .
Potassium hydroxide

Severe attack Increased by air
Sodium carbonate Slight attack . . .
Sodium hydroxide Severe attack Increased by air
Water, distilled Resistant . . .

Water, sea Slight attack . . .

(a)

Most corrosive of common organic acids.
(b)

Increased with concentration and in the presence of air

Applications of Unalloyed Tin. There are only a few applications where tin is used unalloyed with other metals.
Unalloyed tin is the most practical lining material for handling-purity water in distillation plants because it is chemically
inert to pure water and will not contaminate the water in any way.
In the manufacture of plate glass, the molten glass is fed from the furnace onto the surface of a molten tin bath, which is
protected from oxidation by an atmosphere that contains nitrogen and some hydrogen. The natural forces of surface
tension and gravity within the bath ordinarily produce plate glass about 6 mm (
1
8
in.) thick, but the thickness of the glass
can be varied by adjusting the speed at which the molten glass is drawn from the float bath and the temperature of the tin.
With this process, glass ribbons are formed with flat and parallel surfaces. The surfaces of the glass are so smooth that
surface polishing is not required.
Powder Applications. Much of the supply of tin powders is used in making sintered bronze or sintered iron parts.
However, tin powders are also increasingly employed in making paste solders and creams used in the plumbing and
electronic manufacturing industries. Tin and tin alloy powders find minor uses in sprayed coatings for food-handling
equipment, metallizing of nonconductors, and bearing repairs. Tin particles can also be used in food can lacquers to
decrease the dissolution of iron and any exposed lead-base solder by the food product.
Additions of 2% tin powder and 3% copper powder aid the sintering of iron compacts. The tin provides a low-melting-
point phase, which in turn provides diffusion paths for the iron. Iron-tin-copper compacts sintered at 950 °C (1740 °F)
have mechanical properties comparable to those of iron-copper powder metallurgy parts containing 7 to 10% Cu sintered
at 1150 °C (2100 °F). In addition, closer control of finished dimensions is afforded by the iron-tin-copper mixture, and

this control results in improved quality and cost effectiveness.
Sintered compacts made from mixtures of iron and tin-lead solder powders are suitable for certain low-stress engineering
applications. Warm compressing of these compacts (at 450 °C, or 840 °F) provides cohesion of the iron solder mixtures
but does not recrystallize the iron powder; therefore, any work hardening obtained during compaction is retained.
Different properties can be obtained in the pressed-and-sintered compacts by varying the pressing conditions and the
relative amounts of the iron and solder powders.


Tin in Chemicals
The manufacture of inorganic and organic chemicals containing tin constitutes one of the major uses of metallic tin. The
use of tin compounds has grown so rapidly over the past quarter century that the tin chemicals industry has been
transformed from one based mainly on recovered secondary tin to one that consumes significant amounts of primary ingot
tin.
Tin chemicals are used for such widely diversified applications as electrolyte solutions for depositing tin and its alloys;
pigments and opacifiers for ceramics and glazes; catalysts and stabilizers for plastics; pesticides, fungicides, and
antifouling agents in agricultural products, paints, and adhesives; and corrosion-inhibiting additives for lubricating oils.
Solders
Solders account for the largest use of tin in the United States (Fig. 2). Tin is an important constituent in solders because it
wets and adheres to many common base metals at temperatures considerably below their melting points. Tin is alloyed
with lead to produce solders with melting points lower than those of either tin or lead (see the article "Lead and Lead
Alloys" in this Volume). Small amounts of various metals, notably antimony and silver, are added to tin-lead solders to
increase their strength. These solders can be used for joints subjected to high or even subzero service temperatures.
Solder compositions and the applications of joining by soldering are many and varied (Table 4). Commercially pure tin is
used for soldering side seams of cans for special food products and aerosol sprays. The electronics and electrical
industries employ solders containing 40 to 70% Sn that provide strong and reliable joints under a variety of environmental
conditions. High-tin solders are used for joining parts of electrical apparatuses because their electrical conductivity is
higher than that of high-lead solders. High-tin solders are also used where lead may be a hazard, for example, in contact
with food-stuffs or in potable-water plumbing applications.
Table 4 Applications, specifications, and nominal compositions of selected tin-base solder materials
Specifications Liquidus

temperature

Solidus
temperature

Common
name
ASTM

Government

British

German
Nominal
composition,
%
°C °F °C °F
Typical
applications
Commercially
pure tin
B 339,
Grade
A
QQ-T-371,
Grade A
BS
3252,
Grade

T
DIN
1704,
Grade A2
(a)
. . . . . . . . . . . . Soldering
sideseams of cans
for foods or
aerosols
Antimonial-tin
solder
B 32,
Grade
S65
. . . . . . . . . 95 Sn, 5 Sb 240 464 234 452 Soldering of
electrical
equipment, joints
in copper tubing,
and cooling coils
for refrigerators.
Resistant to SO
2

Tin-silver
solder
B 32,
Grade
Sn95
. . . . . . . . . 95 Sn, 5 Ag 245 473 221 430 Soldering of
components for

electrical and
high-temperature
service
Tin-silver
eutectic alloy
B 32,
Grade
Sn96
QQ-S-571,
Grade Sn96
. . . . . . 96 Sn, 3.5
Ag
221 430 221 430 Popular choice
with properties
similar to those of
ASTM B 32,
Grade Sn95
Soft solder
(70-30 solder)
B 32,
Grade
Sn70
QQ-S-571,
Grade Sn70
. . . . . . 70 Sn, 30 Pb 192 378 183 361 Joining and
coating of metals
Eutectic solder
(63-37 soft
solder)
B 32,

Grade
Sn63
QQ-S-571,
Grade Sn63
. . . DIN
1707, LSn
63Pb
63 Sn, 37 Pb 183 361 183 361 Lowest-melting
(eutectic) solder
for electronics
Soft solder
(60-40 solder)
B 32,
Grade
Sn60
QQ-S-571,
Grade Sn60
BS 219,
Grade
K
DIN
1707, LSn
60Pb(Sb)
60 Sn, 40 Pb 190 374 183 361 Solder for
electronic and
electrical work,
especially mass
soldering of
printed circuits

(a)

See the section "Pure Tin" in this article for minimum tin contents.

General-purpose solders (50Sn-50Pb and 40Sn-60Pb) are used for light engineering applications, plumbing, and sheet
metal work. Lower-tin solders (20 to 35% Sn, balance Pb) are used in joining cable and in the production of automobile
radiators and heat exchangers. Some solders are used to fill crevices at seams and welds in automotive bodies, thereby
providing smooth joints and contours.
Tin-zinc solders are used to join aluminum. Tin-antimony and tin-silver solders are employed in applications requiring
joints with high creep resistance, and in applications requiring a lead-free solder composition, such as potable-water
plumbing. Also, tin solders that contain 5% Sb (or 5% Ag) are suitable for use at higher temperatures than are the tin-lead
solders. Further information on solders is provided in Ref 1 and in Welding, Brazing, and Soldering, Volume 6 of the
ASM Handbook.
Impurities in solders can affect wetting properties, flow within the joint, melting temperature of the solder, strength
capabilities of joints, and oxidation characteristics of the solder alloys. The most common impurity elements and their
principal levels and effects are discussed below.
Aluminum. Traces of aluminum in a tin-lead solder bath can seriously affect soldering qualities. More than 0.005% Al
can cause grittiness, lack of adhesion, and surface oxidation of the solder alloy. A deterioration in the surface brightness
of a molten bath sometimes is an indication of the presence of aluminum.
Antimony is slightly detrimental to wetting properties, but it can be used as an intentional additional for strengthening.
As an impurity, antimony tends to reduce the effective spread of a solder alloy. High-lead solder specifications usually
require a maximum limit of 0.5% Sb. The general rule is that antimony should not exceed 6% of the tin content, although
in some applications this rule can be invalid. In various high-lead solders (such as Sn40B, Sn30B, Sn35B, Sn25B, and
Sn20B in ASTM B 32), the presence of antimony is used to ensure that a transformation from βtin to α tin does not take
place. Such a transformation would result in a volume change and a drastic loss in solder strength.
Arsenic. A progressive deterioration in the quality of the solder is observed with increases in arsenic content. As little as
0.005% As induces some dewetting, and dewetting becomes more severe as the percentage of arsenic is increased to
0.02%. Arsenic levels should be kept within this range. At the maximum allowable level of 0.03%, arsenic can cause
dewetting problems when soldering brass.
Bismuth. Low levels of bismuth in the solder alloy generally do not cause any difficulties, although some discoloration

of soldered surfaces occurs at levels above 0.5%.
Cadmium. A progressive decrease in wetting capability occurs with additions of cadmium to tin-lead solders. While
there is no significant change in the molten appearance, small amounts of cadmium can increase the risk of bridging and
icicle formation in printed circuits. For this reason, and for health reasons, cadmium levels should be kept to a minimum.
Copper. Although copper levels above about 0.25% can cause grittiness of solder, for the most part, the role of copper as
a solder contaminant appears to be variable and related to the particular product. A molten tin-lead solder bath is capable
of dissolving copper at a high rate, and the level of copper in the bath can easily reach 0.3%. Copper in liquid solder does
not appear to have any deleterious effect upon the wetting rate or joint formation. Excess copper settles to the bottom of a
solder bath as an intermetallic compound sludge. New solder alloy allows a maximum copper content of 0.08%.
Iron and nickel are not naturally present in solder alloy. The presence of iron-tin compounds in tin-lead solders can be
identified as a grittiness. Generally, iron is limited to a maximum of 0.02% in new solder. There are no specification
limits for nickel, but levels as low as 0.02% can produce some reduction in wetting characteristics. Iron levels above
about 0.1% cause grittiness of solder.
Phosphorous and Sulfur. Phosphorous at a level of 0.01% is capable or producing dewetting and some grittiness. At
higher levels, surface oxidation occurs, and some identifiable problems such as grittiness and dewetting become readily
discernible. Sulfur causes grittiness in solders at a very low level and should be held to 0.001%. Discrete particles of tin-
sulfide can be formed. Both of these elements are detrimental to good soldering.
Zinc. The ASTM new solder alloy specification states that zinc content must be kept to a maximum of 0.005% in tin-lead
solders. At this maximum limit, even with new solders in a molten bath, some surface oxidation can be observed, and
oxide skins may form, encouraging icicles and bridging. Up to 0.01% Zn has been identified as the cause of dewetting on
copper surfaces. Excessive zinc causes oxidation of solder to be more noticeable.
The combined effects of the above impurity elements can be significant. Excessive contamination in solder baths or
dip pots generally can be identified through surface oxidation, changes in the product quality, and the appearance of
grittiness or frostiness in joints made in this bath. A general sluggishness of the solder also may indicate excessive
impurities. In addition to analysis, experience with solder bath operation is helpful in determining the point at which the
material should be renewed for good solder joint production. The ASTM solder specifications, which specify maximum
allowable impurity concentrations, are useful when purchasing solder for general use (Table 5). In particular applications,
specific contaminants or a combination of elements may be detrimental to a particular soldered product. On occasion,
determining a revised or limited specification for solder materials is required.
Table 5 Impurity limits in ASTM specifications for the tin-base solders listed in Table 4

Impurity limits, %
(a)
Common name Nominal
composition,
%
Sb Ag Al As Bi Cd Cu Fe Pb S Zn Other

Commercially pure
tin (ASTM B 339,
Grade A)
99.85 Sn min 0.04

. . . . . . 0.05

0.015

0.001

0.04

0.015

0.05

0.01

0.005

(b)

Antimonial-tin
solder
95 Sn, 5 Sb 4.5-
5.5
0.015

0.005

0.05

0.15 0.03 0.08

0.04 0.2 . . . 0.005

. . .
Tin-silver solder 95 Sn, 5 Ag 0.12

4.4-
4.8
0.005

0.01

0.15 0.005

0.08

0.02 0.10

. . . 0.005

. . .
Tin-silver eutectic
alloy
96 Sn, 3.5 Ag 0.12

3.4-
3.8
0.005

0.01

0.15 0.005

0.08

0.02 0.10

. . . 0.005

. . .
70-30 solder 70 Sn, 30 Pb 0.50

0.015

0.005

0.03

0.25 0.001

0.08

0.02 30
nom

. . . 0.005

. . .
Eutectic solder (63-
37 solder)
63 Sn, 37 Pb 0.50

0.015

0.005

0.03

0.25 0.001

0.08

0.02 37
nom

. . . 0.005

. . .
60-40 solder 60 Sn, 40 Pb 0.50

0.015

0.005

0.03

0.25 0.001

0.08

0.02 40
nom

. . . 0.005

. . .

(a)

Maximum unless a range or nominal (nom) is specified.
(b)

Ni + Co, 0.01% max

Impurities of a metallic and nonmetallic nature can be found in raw materials and in the scrap solder that is sometimes
used by reclaimers. Reclaimed solder is used in many industrial applications where impurities may not be detrimental.
However, correct selection of solder grade is important for economical production. Manufacturing problems can result
from inappropriate solder selection, from the use of solder baths for longer periods than contamination build-up will
tolerate, or from processing methods that rapidly contaminate a solder bath. Determination of suitable specifications, of

allowable impurities in new materials, and of allowable impurities in the solder bath through its deterioration to the point
at which it is discarded should be included in any soldering quality control program.
Electrical and mechanical property data for selected tin-base solders are given in Table 6. The effects of elevated
temperatures on the tensile strength and elongation of 60-40 solder are listed in Table 7.
Table 6 Electrical and mechanical properties of selected tin-base solders
Antimonial-tin solder (95Sn-5Sb)
Tensile properties. Cast: typical tensile strength, 40.7 MPa (5.9 ksi); elongation in 100 mm (4 in.), 38%. Soldered copper joint: typical
tensile strength, 97.9 MPa (14.2 ksi)
Shear strength. Cast, 41.4 MPa (6.0 ksi). Soldered copper joint, 76.5 MPa (11.1 ksi)
Impact strength. Cast (Izod test), 27 J (20 ft · lbf)
Electrical conductivity. Volumetric, 11.9% IACS at 20 °C (68 °F)
Electrical resistivity. 145 nΩ · m at 25 °C (77 °F)
Tin-silver solder (95Sn-5Ag)
Tensile properties. Sheet, 1.02 mm (0.040 in.) thick, aged 14 days at room temperature: typical tensile strength, 31.7 MPa (4.6 ksi); yield
strength, 24.8 MPa (3.6 ksi); elongation in 50 mm (2 in.), 49%. Soldered copper joint: typical tensile strength, 96.5 MPa (14 ksi)
Shear strength. Soldered copper joint, 73.1 MPa (10.6 ksi)
Electrical conductivity. Volumetric, 16.6% IACS at 20 °C (68 °F)
Electrical resistivity. 104 nΩ · m at 0 °C (32 °F)
Temperature coefficient of electrical resistivity. 0-100 °C (32-212 °F), 42.3 pΩ · m/K
70-30 soft solder (70Sn-30Pb)
Tensile properties. Cast: typical tensile strength, 46.9 MPa (6.8 ksi)
Hardness. 12 HB
Electrical conductivity. Volumetric, 11.8% IACS
Electrical resistivity. 146 nΩ · m
Eutectic solder (63Sn-37Pb)
Tensile properties. Cast: typical tensile strength, 51.7 MPa (7.5 ksi); elongation in 100 mm (4 in.), 32%. Soldered copper joint: typical
tensile strength, 200 MPa (2g ksi)
Shear strength. Cast, 42.7 MPa (6.2 ksi); soldered copper joint, 55.2 MPa (8 ksi)
Hardness. Cast, 14 HB
Impact strength. Cast (Izod test), 20 J (15 ft · lbf)

Creep characteristics. Minimum creep rate: at room temperature and 2.3 MPa (335 psi), 0.1 mm/m (100 μin./in.) per day; at 80 °C (176
°F) and 467 MPa (68 psi), 0.1 mm/m (100 μin./in.) per day
Dynamic viscosity. 1.33 mPa · s (0.0133 poise) at 280 °C (536 °F)
Liquid surface tension. 0.490 N/m at 280 °C (536 °F)
Electrical conductivity. Volumetric, 11.9% IACS
Electrical resistivity. 145 nΩ · m
60-40 soft solder (60Sn-40Pb)
Tensile properties. Bulk solder at room temperature (measurements depend greatly on conditions of casting and testing): mean tensile
strength, 52.5 MPa (7.61 ksi); elongation, 30-60%.
Shear strength. Mean, 37.1 MPa (5.38 ksi) (depends greatly on conditions of casting and testing)
Hardness. 16 HV (depends on casting conditions)
Elastic modulus. Tension (bulk solder), 30.0 GPa (4.35 × 10
6
psi)
Creep-rupture characteristics. Limiting creep stress, 2.2-3.0 MPa (320-430 psi) for a strain rate of 10
-4
m/m per day at room temperature.
Rupture life: 1000 h under stress of 4.5 MPa (650 psi) at 26 °C (79 °F); 1000 h under stress of 1.4 MPa (200 psi) at 80 °C (176 °F)
Dynamic liquid viscosity. Estimated, 2.0 mPa · s (0.020 poise) at the liquidus temperature
Liquid surface tension. Estimated: 468 mN/m at 330 °C (626 °F), 461 mN/m at 430 °C (806 °F)
Electrical conductivity. Volumetric, 11.5% IACS
Electrical resistivity. 149.9 nΩ · m
Thermoelectric potential. Same as pure tin when measured against copper
Temperature of superconductivity. 7.05 K. Critical field, 83.2 mT at 1.3 K

Table 7 Effect of temperature on properties of 60-40 solder cast at 300 °C (570 °F) in steel molds (specimens
not machined)
Temperature

Tensile strength

°C °F MPa ksi
Elongation,

%
Cast in 150 °C (300 °F) molds
19 66 56.4 8.18 60
(a)

50 122 45.4 6.58 80
(a)

75 167 41.7 6.05 90
(a)

100 212 30.9 4.48 110
(a)

125 257 19.3 2.80 180
(a)

150 302 12.4 1.80 180
(a)

Cast in 200 °C (390 °F) molds
0 32 59 8.6 50
(b)

-40 -40 76 11.0 50
(b)

-80 -112

97 14.1 55
(b)

-120

-184

119 17.3 30
(b)

-160

-256

112 16.2 10
(b)

-200

-328

109 15.8 5
(b)


(a)

In 22.5 mm (0.89 in.).
(b)

In 25.4 mm (1.00 in.)

When measuring the tensile properties of bulk solder, the results depend greatly on the casting and testing conditions. For
example, eutectic and near-eutectic 60-40 solder compositions were examined for superplasticity. It was found that the
strain rate sensitivity m has a value of about 0.4 at a strain rate of 10
-4
m/m · s, increasing to a relative maximum of about
0.5 at a strain rate of 10
-3
mm/m · 2, then decreasing to a value near 0.2 at a strain rate of 10
-1
m/m · s.
Thermal Properties. Solidus and liquidus points of various solder compositions are given in Table 4 and in the article
"Lead and Lead Alloys" in this Volume. Other thermal properties include:

Solder Linear thermal expansion

at 15-110 °C
(60-230 °F), 10
-6
/K
Thermal conductivity at

0-180 °C (32-355 °F),
W/m · K
70Sn-30Pb

21.6 . . .
63Sn-37Pb

24.7 50
60Sn-40Pb

24 . . .

The 60-40 solder has a specific heat of 176 J/kg · K (0.042 Btu/lb · °F) and an estimated heat of fusion of 37 J/g (16
Btu/lb).

Reference cited in this section
1.

R.J. Klein Wassink, Soldering in Electronics, 2nd ed., Electrochemical Publications, 1989


Pewter
Pewter is a tin-base white metal containing antimony and copper. Originally, pewter was defined as an alloy of tin and
lead, but to avoid toxicity and dullness of finish, lead is excluded from modern pewter. These modern compositions
contain 1 to 8% Sb and 0.25 to 3.0% Cu. Pewter casting alloys usually are lower in copper than pewters used for spinning
hollowware and thus have greater fluidity at casting temperatures.
Modern pewter consists of a cored solid solution of antimony in tin within which are distributed fine crystals of
(Cu
6
Sn
5
) phase. Pewter is malleable and ductile, and it is easily spun or formed into intricate designs and shapes. Pewter
parts do not require annealing during fabrication. Much of the costume jewelry produced today is made of pewter alloys
centrifugally cast in rubber or silicone molds. Typical pewter products include coffee and tea services, trays, steins, mugs,

candy dishes, jewelry, bowls, plates, vases, candlesticks, compotes, decanters, and cordial cups.
Chemical Composition. Although a wide range of compositions has been called pewter, the usual modern alloys
contain 90 to 95% Sn and 1 to 3% Cu, with the balance consisting of antimony. Some pewterlike materials are sand cast
or spun aluminum alloys, which are traditionally not considered to be pewter. Although some pewter contains lead as an
alloying constituent, a considerable portion of lead is undesirable for applications in which the material may be in contact
with food or beverages. In addition, lead may impart a dullness to the ware.
Composition limits of modern pewter are shown in Table 8.
Table 8 Chemical composition limits for modern pewter
Composition, % Specification

Sn Sb Cu Pb max

As max

Fe max

Zn max

Cd max

ASTM B 560


Type 1
(a)
90-93

6-8 0.25-2.0

0.05 0.05 0.015 0.005 . . .

Type 2
(b)
90-93

5-7.5 1.5-3.0 0.05 0.05 0.015 0.005 . . .
Type 3
(c)
95-98

1.0-3.0

1.0-2.0 0.05 0.05 0.015 0.005 . . .
5-7 1.0-2.5 0.5 . . . . . . . . . 0.05 BS 5140 bal
3-5 1.0-2.5 0.5 . . . . . . . . . 0.05
1-3 1-2 0.5 . . . . . . . . . . . . DIN 17810 bal
3.1-7.0

1-2 0.5 . . . . . . . . . . . .

(a)

Casting alloy, nominal composition 92Sn-7.5Sb-0.5Cu.
(b)

Sheet alloy, nominal composition 91Sn-7Sb-2Cu.
(c)

Special-purpose alloy

Physical Properties. Typical tensile properties and hardnesses of pewter are given in Table 9. The effect of processing

variables on the mechanical properties of pewter is covered in Table 10. In addition to those properties given in Table 9,
pewter has:
• An elastic modulus of 53 GPa (7.7 × 10
6
psi)
• A density of 7.28 g/cm
3
(0.263 lb/in.
3
)
• A liquidus temperature of 295 °C (563 °F)
• A solidus temperature of 244 °C (471 °F)
Table 9 Typical mechanical properties of pewter
Section thickness

Tensile strength

Form and condition
mm in. MPa ksi
Elongation in

50 mm (2 in.), %

Hardness,

HB
Chill cast
(a)
19.05 0.750 . . . . . . . . . 23.8
Sheet, annealed 1 h at 205 °C (400 °F), air cooled

6.12 0.241 59 8.6 40 9.5
Sheet, cold rolled, 32% reduction 6.12 0.241 52 7.6 50 8.0

(a)

Modulus of elasticity, 53 GPa (7.7 × 10
6
psi)

Table 10 Effect of processing variables on the mechanical properties of pewter sheet and on the amount of
earing during drawing
Properties are mean values of three determinations each on 1 mm (0.04 in.) thick sheets of Sn-6Sb-2Cu alloy that were cold rolled
from 25 mm (1.00 in.) thick cast stabs.
Tensile strength at angle to rolling
direction of
0° 55° 90°
Elongation, % at
angle to
rolling direction
of
Processing Delay
between
processing
and testing
MPa

ksi

MPa

ksi MPa

ksi 0° 55° 90°
Hardness,

HV
Earing,

%
12 months 64 9.3

62 9.0 64 9.3 56 49 53 15 10 Cross rolling from
intermediate thickness
24 h 48 7.0

48 7.0 50 7.3 92 136 122 13
4
1
2

Unidirectional rolling, with
heat treatment
(a)
at
intermediate thickness
24 h 68 9.9

69 10.0

73 10.6

47 36 17 20
2
1
2

Source: Ref 2
(a)

About 150-200 °C (302-392 °F).

Chemical Properties and Corrosion Resistance. Pewter tarnishes in soft water, with the production of a visible
film of interference-tint thickness. It does not tarnish in hard water, but localized attack can occur at the water line and
sometimes elsewhere if a chalky deposit is formed from the water. Pewter is attacked by dilute hydrochloric and citric
acids in the presence of air.
Fabrication Characteristics. Pewter has good solderability. Casting temperatures of pewter range from 315 to 330 °C
(600 to 625 °F).
Pewter can be formed by rolling, hammering, spinning, or drawing. The earing of pewter sheet can be reduced by an
intermediate cross-rolling operation or heat treatment; rolling can then be continued down to final thickness.

Reference cited in this section
2.

R. Duckett and P.A. Ainsworth, Sheet Met. Ind., Vol 50 (No. 7), 1973, p 412


Bearing Alloys
The primary consideration in the selection of a bearing alloy is that the material must have a low coefficient of friction.
Bearing alloys also must maintain a balance between softness and strength. Aluminum-tin bearing alloys, for example,

provide an excellent compromise between the requirement for high fatigue strength and the need for good surface
properties such as softness, seizure resistance, and embeddability. Tin-base bearing alloys are specified in ASTM B 23,
AMS 4800, and U.S. Government specification QQ-M-161.
Compositions. Table 11 lists the chemical compositions of various tin-base bearing alloys specified in ASTM and SAE
standards. Tin has a low coefficient of friction and thus meets the primary requirement of a bearing material. Tin is
structurally a weak metal; therefore, when it is used in bearing applications it is alloyed with copper and antimony for
increased hardness, tensile strength, and fatigue resistance. Normally, the quantity of lead in these alloys, called tin-base
babbitts, is limited to 0.35 to 0.5% to avoid formation of the tin-lead eutectic, which would significantly reduce strength
properties at operating temperatures.
Table 11 Compositions of tin-base bearing alloys
Nominal composition, % Designation
Sn
(a)


Sb Pb
max
(b)

Cu Fe
max
As
max
Bi
max
Zn
max
Al
max
Total

other
max
ASTM B 23 alloys
Alloy 1 91.0

4.5 0.35 4.5 0.08 0.10 0.08 0.005 0.005 0.05 Cd
(c)

Alloy 2 89.0

7.5 0.35 3.5 0.08 0.10 0.08 0.005 0.005 0.05 Cd
(c)

Alloy 3 84.0

8.0 0.35 8.0 0.08 0.10 0.08 0.005 0.005 0.05 Cd
(c)

Alloy 11 87.5

6.8 0.50 5.8 0.08 0.10 0.08 0.005 0.005 0.05 Cd
(c)

SAE alloys
SAE 11 86.0

6.0-
7.5
0.50 5.0-
6.5

0.08 0.10 0.08 0.005 0.005 0.20
SAE 12 88.0

7.0-
8.0
0.50 3.0-
4.0
0.08 0.10 0.08 0.005 0.005 0.20
Intermediate lead-tin alloys
Lead-tin babbitt 75 12 9.3-10.7 3 0.08 0.15 . . . . . . . . . . . .
ASTM B 102, Alloy 65 15 17-19 2 0.08 0.15 . . . 0.01 0.01 . . .
(a)
Desired minimum in ASTM alloys; specified minimum in SAE alloys.
(b)
Maximum unless a range is specified.
(c)
Total named elements, 99.80%

The presence of zinc in tin-base bearing metals generally is not favored. Arsenic increases resistance to deformation at all
temperatures; zinc has a similar effect at 38 °C (100 °F), but causes little or no change at room temperature. Zinc has a
marked effect on the microstructures of some of these alloys. Small quantities of aluminum (even less than 1%) will
modify their microstructures. Bismuth is objectionable because, in combination with tin, it forms a eutectic that melts at
137 °C (279 °F). At temperatures above this eutectic, alloy strength is appreciably decreased.
In high-tin alloys, such as ASTM grades 1, 2, and 3, and SAE 11 and 12, lead content is limited to 0.50% or less because
of the deleterious effect of higher percentages on the strength of these alloys at temperatures of 150 °C (300 °F) and
above. Lead and tin form a eutectic that melts at 183 °C (361 °F). At higher temperatures, bearings become fragile as a
result of the formation of a liquid phase within them.
Lead-base bearing alloys, called lead-base babbitts, contain up to 10% Sn and 12 to 18% Sb. In general, these alloys
are inferior in strength to tin-base babbitts, and this must be equated with their lower cost. Segregation of the constituents
of these alloys may provide some difficulties during centrifugal casting of linings. During casting, careful selection of

rotational speed in relation to bearing size is necessary. Additions of cerium, arsenic, or nickel also assist in controlling
segregation of these alloys. Lead-base babbitt alloys are discussed in more detail in the article "Lead and Lead Alloys" in
this Volume.
Intermediate Lead-Tin Babbitt Alloys. In addition to the tin-base and lead-base babbitts, there is a series of
intermediate lead-tin bearing alloys. These alloys have tin and lead contents between 20 and 65%; in addition, they
contain various amounts of antimony and copper. Increasing the tin content of these alloys provides higher hardness and
greater ease of casting. These alloys are less prone to segregation during melting than lead-base babbitts. Cast
intermediate bearing alloys, however, exhibit lower strength values than either tin-base or lead-base babbitts.
Aluminum-tin bearing alloys represent an excellent compromise between the requirement for high fatigue strength
and the need for good surface properties such as softness, seizure resistance, and embeddability. Aluminum-tin bearing
alloys are usually employed in conjunction with hardened-steel or ductile-iron crankshafts, and they allow significantly
higher loading than tin- or lead-base bearing alloys.
Low-tin aluminum-base alloys (5 to 7% Sn) containing small amounts of strengthening elements, such as copper
and nickel, are often used for connecting-rod and thrust bearings in high-duty engines. Strict dimensional tolerances must
be adhered to, and oil contamination should be avoided. Alloys containing 20 to 40% Sn and a balance of aluminum show
excellent resistance to corrosion by products of oil breakdown; they also exhibit good embeddability, particularly in dusty
environments. The higher-tin alloys have adequate strength and better surface properties, which make them useful for
crosshead bearings in high-power marine diesel engines.
Properties of Tin-Base Bearing Alloys. The mechanical properties of selected tin-base bearing alloys are shown in
Tables 12 and 13. The mechanical-property values obtained from massive cast specimens are dependent on temperature.
Also, hardness and compression tests are sensitive to the duration of the load because of the plastic nature of these
materials. Bulk properties may be of some value in initial screening of materials, but they do not accurately predict the
behavior that the material will exhibit when it is in the form of a thin layer bonded to a strong backing, which is the
manner in which the babbitts are normally used. The relationship that exists between bearing life and the thickness of the
babbitt is shown in Fig. 3, which also shows the marked influence of operating temperature.
Table 12 Physical properties and compressive strengths of selected tin-base bearing alloys
Compressive
yield strength
(a)(b)

Compressive
ultimate strength
(a)(c)

At 20 °C

(68 °F)
At 100 °C

(212 °F)
At 20 °C

(68 °F)
At 100 °C

(212 °F)
Hardness, HB
(d)
Solidus
temperature

Liquidus
temperature

Pouring
temperature

Designation Specific

gravity

MPa

ksi MPa

ksi MPa

ksi MPa

ksi At 20 °C

(68 °F)
At 100 °C

(212 °F)
°C °F °C °F °C °F
ASTM B 23, Alloy 1 7.34 30.3 4.40

18.3 2.65

88.6 12.85

47.9 6.95

17.0 8.0 223 433 371 700 440 825
ASTM B 23, Alloy 2 7.39 42.1 6.10

20.7 3.00

102.7

14.90

60.0 8.70

24.5 12.0 241 466 354 669 425 795
ASTM B 23, Alloy 3 7.46 45.5 6.60

21.7 3.15

121.3

17.60

68.3 9.90

27.0 14.5 240 464 422 792 490 915
Lead-tin babbitt from Table II 7.53 38.3 5.55

14.8 2.15

111.4

16.15

47.6 6.9 24
(e)
12 184 363 306 583 . . . . . .
ASTM B 102, Alloy PY1815A (die cast)

7.75 34 5 14 2.1 103 15 46 6.7 23 10 181 358 296 565 . . . . . .

(a)

The compression test specimens were cylinders 38 mm (1
1
2
in.) long and 13 mm (
1
2
in.) in diameter, machined from chill castings 50 mm (2 in.) long and 20 mm (
3
4
in.) in diameter.
(b)

Values for yield point were taken from stress-strain curves at a deformation of 0.125% reduction of gage length.
(c)

Values for ultimate strength were taken as the unit load necessary to produce a deformation of 25% of the length of the specimen.
(d)

Tests were made on the bottom face of parallel machined specimens cast at room temperature in a steel mold 50 mm (2 in.) in diameter by 16 mm (
5
8
in.). deep. The Brinell hardness values listed are the
averages of three impressions on each alloy, using a 10 mm ball and applying a 500 kg load for 30 s.
(e)

Chill cast hardness of 27 HB

Table 13 Mechanical properties of selected tin-base babbitt alloys
See Table 12 for compressive strengths.
Typical tensile
strength
Elastic
modulus
Izod impact
strength
Fatigue
strength
ASTM B 23
alloy
Condition

MPa ksi
Elongation,
%
GPa 10
6
psi J ft · lbf MPa ksi
Chill cast 64 9.3 2
(a)
50 7.3 3.4
(b)
2.5
(b)
26
(c)
3.8
(c)

Alloy 1
Die cast 62 9 2
(a)
. . . . . . . . . . . . . . . . . .
Chill cast 77
(d)
11.2
(d)
18
(e)
. . . . . . . . . . . . 33
(c)
4.8
(c)
Alloy 2
Die cast 87
(f)
12.6
(f)
. . . 52
(g)
7.6
(g)
. . . . . . . . . . . .
(a)
Elongation in 50 mm (2 in.).
(b)

Izod impact energy of 0.9 J (0.7 ft · lbf) at 200 °C (390 °F).
(c)

Fatigue strength for 2 × 10
7
cycles, R.R. Moore-type test.