STEEL

CASTINGS
HANDBOOK

Supplement 8
High Alloy Data Sheets
Corrosion Series

Steel Founders' Society of America

Chemical composition - %
Description C Mn Si P S Cr Ni Mo Fe
min. 11.5 3.5 0.4
Type CA6NM is an iron-chromium- max. 0.060 1.00 1.00 0.040 0.030 14.0 4.5 1.0 bal
nickel-molybdenum alloy that is
hardenable by heat treatment. It is Physical properties
similar in general corrosion resistance to Modulus of elasticity, psi x 106 29.0
type CA15, but the addition of nickel and Density, lb/in3 0.278
molybdenum to the CA6NM composition Sp. Heat, Btu/lb.oF, at 70 oF 0.11
improves its resistance to attack by sea Electrical resistivity, 6.m, at 70 oF 0.78
water. Although the tensile strength Melting point, approximate oF 2750
properties of CA6NM are comparable to Magnetic permeability Ferromagnetic
those of CA15, the impact strength is
about twice as high, as is the resistance Thermal conductivity Mean coefficient of
to damage from cavitation effects. Btu/(ft.h. oF) Linear thermal expansion
Heavy sections and complex structures  in./(in. oF)
are cast in CA6NM with less difficulty ______________________ _______________________
than experienced with the CA15 alloy,
and for cast-weld construction, or where At 212 oF 14.5 70 - 212 oF 6.0
field welding is involved, type CA6NM At 1000 oF 16.7 70 - 1000 oF 7.0
offers the advantage of not requiring a
preheat. A major application of the alloy
has been in large hydraulic turbine Mechanical properties
runners for power generation. at room temperature
Representative Minimum tensile
The alloy normally is used in the tensile properties & toughness
normalized and tempered condition in air cooled from requirements
which the microstructure is essentially >1900 oF ASTM A743,
100 percent martensite. CA6NM can temper at 1100- A757
contain appreciable amounts of retained 1150 oF
austenite because this structure provides _______________ ______________
the optimum combination of strength,
ductility, hardness, and toughness. Tensile strength, ksi 120.0 110.0
Variations in heat treatment can be Yield strength, 0.2% offset, ksi 100.0 80.0
selected to enhance one or more of Elongation, in 2in., % 24 15
these properties. Improved corrosion Reduction of area, % 60 35
resistance, particularly resistance to Brinell hardness (HBW) 268 -
sulfide stress corrosion, can be obtained Charpy V-notch, @ -100 oF, ft.lbs - 20/12
with a lower carbon as in grade CA6NM (A757)A
Class B (ASTM A487). A lower carbon Toughness and impact properties
content, as in grade CA6NM Class B,
permits heat treating to a lower Impact, Charpy V-notch - see Fig.1
maximum hardness (and strength) which Fracture toughness, Kic - see Fig.2
results in improved corrosion resistance,
particularly resistance to sulfide stress At elevated temperatures
corrosion cracking.
Short time elevated temperature properties - see Fig.3
Castings of type CA6NM alloy have good
machining and welding properties if Creep rupture properties - see Table 1 and Figs. 4 - 6
proper techniques are employed. The ______________________
alloy is magnetic and has a coefficient of A
thermal expansion slightly less than that 20 ft.lb average on three specimens, 15 ft.lb minimum allowed on one
of carbon steel. Thermal conductivity is specimen only
about 45 percent less than carbon steel but almost 60 percent greater than the CF alloy types. Electrical
resistivity is about five times that of carbon steel.

Heat Treatment

The alloy is hardened by heating between 1900 and 1950°F (1038 to 1066°C) followed by cooling in either
air or oil. After the castings have cooled below the martensite finish temperature, which varies with the
compositional balance, they should be tempered as soon as possible. Depending on strength requirements,
the alloy is tempered at 600°F (316°C) or more commonly in the range of 1100 to 1150°F (593 to 621°C).
Tempering in the vicinity of 900°F (482°C) should be avoided because lower toughness will result. Some re-
austenitization may occur if tempering temperatures above 1200°F (649°C) are employed, and upon cooling,
the microstructure may contain untempered martensite. Double tempers are employed to achieve hardness
values below 22 HRC for castings intended for wet H2S environments. A typical double temper heat treatment
would consist of a 1250°F (677°C) temper followed by a 1125°F (607°C) temper.

Highest strength and hardness are obtained by tempering at 600°F (316°C); however, impact strength is
reduced by 50 percent and ductility is reduced to about 12 percent. Holding times for austenitizing and
tempering will vary with the thickness of casting sections involved, but should be sufficiently long to heat all
sections to a uniform temperature throughout.

Applications

The following lists of consuming industries, cast parts, and corrosive materials are useful as examples of
typical applications where type CA6NM alloy has been employed successfully; they are not comprehensive,
nor are they intended as guides to alloy selection for specific end uses.

Industries Chemical, Marine, Oilfield, Petroleum Refining, Pollution Control, Power Plant.

Castings Casings, compressor impellers, diaphragms, diffusers, discharge spacers, Francis runners,
hydraulic turbine parts, impulse wheels, packing housings, propellers, pump impellers, suction spacers, valve
bodies and parts.

Corrosives Boiler feed water [250°F (115°C)], sea water, steam, sulfur, water to 400°F (204°C).

NOTE: Corrosion rate data obtained in carefully controlled laboratory tests using chemically pure reagents
are helpful in screening alloys for further consideration, but the difference between such tests and commercial
operation should not be overlooked. Concentration, temperature, pressure, contamination, and velocity of
corrosives all influence the rate of attack, as do surface finish and casting design. Reference should be made
to the extensive alphabetical lists of corrodents published by many alloy foundries and to corrosion data
surveys published by the NACE to determine whether type CA6NM is suitable for the particular corrosive
involved, and the designer should provide the foundry with as much pertinent information as possible on
operating conditions before reaching a definite decision to use this alloy.

The mechanical and physical property data presented in tabular and graphical form are representative for alloy
CA6NM. These data are neither average nor minimum values, and should not be used for either specification
or design purposes. Specification and/or design information may be obtained from appropriate technical
associations such as ASTM, ASME, API, NACE, and SAE.

Design Considerations

Section thicknesses from 3/16 inch up can be cast satisfactorily in CA6NM alloy. Somewhat lighter sections
are feasible depending on casting design and pattern equipment. Complex designs involving light and heavy
sections are successfully made in this alloy, but drastic changes in section should be avoided as far as
possible. This applies to the casting as cast; i.e., including finish allowance of 1/8 inch or more on surfaces
to be machined. Normally used patternmakers' shrinkage allowance for this alloy is 1/4 inch per foot.
Fabricating Considerations

Dimensional tolerances for rough castings are influenced by the quality of pattern equipment provided. In
general, overall dimensions and locations of cored holes can be held to 1/16 inch per foot.

Welding Welds in light sections and in unstressed areas can be made without preheating. Welding in the
heat treated condition is generally preferred. For welding very heavy sections or highly stressed regions,
castings may require preheating in the range of 212 to 350°F (100 to 176°C) and should be maintained at 300
to 500°F (176 to 260°C) during welding as a guideline. After welding, cool to at least 212°F (100°C) or below
the martensite finish temperature prior to re-tempering at 1100 to 1150°F (593 to 621°C). Cooling through
the range of 1100 to 950°F (593 to 266°C) should be as rapid as possible to avoid loss in toughness.

Welding procedure utilizing SMAW technique is described in this section.

Machining Most machining operations can be performed satisfactorily on castings of CA6NM alloy. The
work-hardening rate of this grade is much lower than the iron-chromium-nickel types, but it is advisable in all
cases that the tool be kept continually entering into the metal. Slow feeds, deep cuts, and powerful, rigid
machines are necessary for best results. Work should be firmly mounted and supported, and tool mountings
should provide maximum stiffness. Both high speed steel and carbide tools may be used successfully. Chips
are stringy but not abrasive. Chip curlers are recommended for carbide tools.

Good lubrication and cooling are essential. The low thermal conductivity of the alloy makes it most important
to have the cutting fluid flood both the tool and the work.

Information on the procedures for specific machining operations is contained in SFSA Steel Casings
Handbook, 6th Edition, Chapter 26.

Casting designations, specifications, and corresponding wrought alloy

Cast ASTM: A743 (CA6NM), A757 (E3N), A487 (CA6NM), A352 (CA6NM).

Wrought A-182, Grade F6NM.

[Air cooled from above 1900°F (1038°C);Tempered at 1100-1150°F (593-621°C)]

Rupture strength, ksi

800 427 54.5 41.0

850 454 39.0 29.0

900 482 28.0 20.0

950 510 19.7 14.3

1000 538 14.2 10.1

Creep strength, ksi

o o
F C 0.1%/1000 hrs. 0.01%/1000 hrs.

800 427 41.0 31.0

850 454 29.6 22.5

900 482 22.0 16.3

950 510 16.0 11.8

1000 538 11.8 --

B
"The Elevated Temperature Properties of Alloy CA6NM", G.V. Smith, CAST METALS FOR
STRUCTURAL AND PRESSURE CONTAINMENT APPLICATIONS, ASME 1979.