DUCTILE IRON DATA FOR DESIGN ENGINEERS

 

 

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SECTION V.  ALLOY DUCTILE IRONS

INTRODUCTION
SILICON-MOLYBDENUM DUCTILE IRONS
Effects of Silicon
Effect of Molybdenum
High Silicon with Molybdenum
Applications
Production Requirements
AUSTENITIC DUCTILE IRONS
Specifications and Recommendations
Mechanical Properties
Elastic Properties
Strength and Elongation
Low Temperature Properties
High Temperature Properties
Thermal Cycling Resistance
Oxidation Resistance
Corrosion Resistance
Wear and Galling
Erosion Resistance
Physical Properties
Thermal Conductivity
Thermal Expansion
Electrical and Magnetic Properties
Production Requirements
Machinability
Heat Treatment
REFERENCES

INTRODUCTION

Three families of alloy Ductile Irons - austenitic (high nickel - Ni - Resist), bainitic and ferritic (high silicon-molybdenus) - have been developed either to provide special properties or to meet the demands of service conditions that are too severe for conventional or austempered Ductile Irons. While conventional and austempered Ductile Irons contain limited percentages of alloying elements primarily to provide the desired microstructure, alloy Ductile Irons contain substantially higher levels of alloy in order to provide improved or special properties. The high silicon levels, combined with molybdenum, give the ferritic Ductile Irons superior mechanical properties at high temperatures and improved resistance to high temperature oxidation. The high nickel content of the austenitic Ductile Irons, in conjunction with chromium in certain grades, provides improved corrosion resistance, superior mechanical properties at both elevated and low temperatures and controlled expansion, magnetic and electrical properties.   Bainitic irons are used where high strength and good wear resistance are obtainable in either the as cast state or heat treated using from 1 - 3% alloy (Ni and Mo).  The bainitic irons are not as widely used as the austenitic or Si-Mo Ductile Irons, so they will not be covered in this chapter.  The reader is encouraged to contact us for more information or consult other publications such as the "Iron Castings Handbook" available through the American Foundrymen's Society.

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SILICON- MOLYBDENUM DUCTILE IRONS

Alloy Ductile Irons containing 4-6% silicon, either alone or combined with up to 2 % molybdenum, were developed to meet the increasing demands for high strength Ductile Irons capable of operating at high temperatures in applications such as exhaust manifolds or turbocharger casings. The primary properties required for such applications are oxidation resistance, structural stability, strength, and resistance to thermal cycling.

These unalloyed grades retain their strength to moderate temperatures (Figures 3.21, 3.22, 3.23), perform well under low to moderate severity thermal cycling (Figure 3.37) and exhibit resistance to growth and oxidation that is superior to that of unalloyed Gray Iron (Table 3. 1).  Ferritic Ductile Irons exhibit less growth at high temperatures due to the stability of the microstructure. Alloying with silicon and molybdenum significantly improves the high temperature performance of ferritic Ductile Irons while maintaining many of the production and cost advantages of conventional Ductile Irons.

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Effect of Silicon

Silicon enhances the performance of Ductile Iron at elevated temperatures by stabilizing the ferritic matrix and forming a silicon-rich surface layer which inhibits oxidation. Stabilization of the ferrite phase reduces high temperature growth in two ways. First, silicon raises the critical temperature at which ferrite transforms to austenite (Figure 5.1). The critical temperature is considered to be the upper limit of the useful temperature range for ferritic Ductile Irons. Above this temperature the expansion and contraction associated with the transformation of ferrite to austenite can cause distortion of the casting and cracking of the surface oxide layer, reducing oxidation resistance. Second, the strong ferritizing tendency of silicon stabilizes the matrix against the formation of carbides and pearlite, thus reducing the growth associated with the decomposition of these phases at high temperature.

The oxidation protection offered by silicon increases with increasing silicon content (Figure 5.2). Silicon levels above 4% are sufficient to prevent any significant weight gain after the formation of an initial oxide layer.

Table 5.1 Effect of silicon and molybdenum on the high temperature tensile and creep rupture strengths of ferritic Ductile Iron.

Material Tensile Strength
ksi(MPa)
Stress Rupture
ksi (MPa)
  800oF
425oC
1000oF
540oC
1200oF
650oC
1000oh @ 1000oF
540oC
Gray Iron 37(255) 25(173) 12(83) 5.9(41)
60-40-18 D.I. 40(276) 25(173) 13(90) 8.3(57)
4% Si D.I. 56(386) 36(248) 13(90) 10(69)
4% Si - 1% Mo D.I. 61(421) 44(304) 19(131) 14(97)
4% Si - 2% Mo D.I. 65(449) 46(317) 20(138) 17(117)

Gray Iron: Unalloyed, stress-relieved. Ductile Irons: Sub-Critically annealed at 1450oF (788oC).

Silicon influences the room temperature mechanical properties of Ductile Iron through solid solution hardening of the ferrite matrix. Figure 5.3 shows that increasing the silicon content increases the yield and tensile strengths and reduces elongation. For silicon levels above 6%, the material may become too brittle for engineering applications requiring any degree of toughness. Thus, the best combination of heat resistance and mechanical properties are provided by silicon contents in the range 4-6%. The solid solution strengthening effect of silicon persists to temperatures as high as 1000oF (540oC) but above that temperature the tensile strength of high-silicon alloys is reduced as well  (Table 5.1). Figures 5.4 and 5.5 illustrate the high temperature creep and stress-rupture strengths obtained in ferritic Ductile Irons containing 4% silicon.

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Effect of Molybdenum

Molybdenum, whose beneficial effect on the creep and stress-rupture properties of steels is well known, also has a similar influence on Ductile Irons. Figures 5.6 and 5.7 show that the addition of 0. 5 % molybdenum to ferritic Ductile Iron produces significant increases in creep and stress rupture strengths, resulting in high temperature properties that are comparable to those of a cast steel containing 0. 2 % carbon and 0. 6 % manganese.

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High Silicon with Molybdenum

The addition of up to 2% molybdenum to 4% silicon Ductile Irons produces significant increases in high temperature tensile strength (Table 5. 1), stress-rupture strength (Tables 5.1 and 5.2 and Figure 5.5) and creep strength (Figure 5.4). Molybdenum additions in the range 0-1% to high-silicon Ductile Irons have been found to be very effective in increasing resistance to thermal fatigue (Table 5.3 and Figure 3.37).

Table 5.2 Effect of silicon and molybdenum on stress-rupture strength of ferritic Ductile Irons.

Type of iron Temperature,
oC
Stress to rupture
MPa (ksi)
100 h 1000 h
2.2% Si 650 40 (5.8) 20 (2.9)
4% Si
4% Si 1% Mo
650
650
28 (4.1)
43 (6.2)
 
4% Si
4% Si 1% Mo
705
705
19 (2.7)
33 (4.8)
12 (1.7)
23 (3.3)
4% Si
4% Si 1% Mo
815
815
7 (1.0)
9 (1.3)
 

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Table 5.3 Influence of silicon and molybdenum on the thermal cycling behaviour of ferritic Ductile Iron.

Type of iron Temperature cycling,
oC
Cycles to failure
2.1% Si 200 - 650 80
3.6% Si
3.6% Si 0.4% Mo
200 - 650
200 - 650
173
375
4.4% Si 0.2% Mo
4.4% Si 0.5% Mo
200 - 650
200 - 650
209
493

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Applications

High silicon-molybdenum Ductile Irons offer the designer and end user a combination of low cost, good high temperature strength, superior resistance to oxidation and growth, and good performance under thermal cycling conditions. As a result these materials have been very cost-effective in applications with service temperatures in the range 1200-1500oF (650-820oC) and where low to moderate severity thermal cycling may occur. Ductile Irons with 4% silicon and 0.6-0.8% molybdenum are presently specified for numerous automotive manifolds and turbocharger casings. High silicon irons containing 1% molybdenum are used for special high temperature exhaust manifolds and heat treating racks.

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Production Requirements

High silicon-molybdenum Ductile Irons can be produced successfully by any competent Ductile Iron foundry that has good process control, provided that the following precautions are taken.

Carbon levels should be kept in the range 2.5-3.4%. Carbon content should be reduced as the silicon level and section size increase.

Silicon may vary from 3.7 to 6% according to the application. Increasing the silicon content improves oxidation resistance and increases strength at low to intermediate temperatures but reduces toughness and machinability.

Molybdenum contents up to 2% may be used. Increasing the molybdenum level enhances high temperature strength and improves machinability but reduces toughness and may segregate to form grain boundary carbides. Other pearlite and carbide stabilizing elements should be kept as low as possible to ensure a carbide-free ferritic matrix.

Normal nodularizing and inoculation practices should be used but pouring temperatures should be higher than for normal Ductile Iron. Increased dross levels require good gating and pouring practices, and increased shrinkage necessitates larger risers. Castings must be shaken out and handled carefully to avoid breakage, and all castings should be heat treated to improve toughness.  Castings are commonly given a subcritical anneal - 4h at 1450oF (790oC) and furnace cooled to 400oF (200oC) - but a full anneal is required if the matrix contains significant quantities of carbides and pearlite. Machinability is similar to normal pearlitic /ferritic Ductile Irons with hardness values in the range 200-230 BHN.

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AUSTENITIC DUCTILE IRONS

A family of austenitic, high alloy Ductile Irons identified by the trade name "Ductile Ni-Resist" have been produced for many years to meet a wide range of applications requiring special chemical, mechanical and physical properties combined with the economy and ease of production of Ductile Iron. Ductile Ni-Resist irons containing 18-36% nickel and up to 6% chromium combine tensile strengths of 55-80 ksi (380-550 MPa) and elongations of 4-40% with the following special properties:

  • corrosion, erosion and wear resistance,
  • good strength, ductility and oxidation resistance at high temperatures,
  • toughness and low temperature stability,
  • controlled thermal expansion,
  • controlled magnetic and electrical properties and
  • good castability and machinability.

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Specifications and Recommendations

Table 5.4 summarizes the ASTM and ASME specifications for Ductile Ni-Resist Irons and lists typical applications for each grade. Section XII contains further information on international specifications for these materials. The applications listed for each grade take advantage of the following general characteristics.

Type D-2, the most commonly used grade, is recommended for service requiring resistance to corrosion, erosion and frictional wear up to temperatures of 1400oF (760oC).

Type D-2B, provides higher resistance to erosion and oxidation than Type D-2 and is also recommended for use with neutral and reducing salts.

Type D-2C, is recommended where resistance to corroision is less severe and high ductility is required.

Type D-2M (2 classes) is recommended for cryogenic applications requiring structural stability and toughness.

Type D-3 exhibits excellent elevated temperature properties and resistance to erosion. It is recommended for applications involving thermal shock and thermal expansion properties similar to ferritic stainless steels.

Type D-3A provides good resistance to galling and wear, and intermediate thermal expansion.

Type D-4 provides resistance to corrosion, erosion and oxidation that is superior to Types D-2 and D-3.

Type D-5 is recommended for applications requiring miniumu thermal expansion.

Type D-5B should be used in aplications requiring minimum thermal stresses, and good mechanical properties and resistance to oxidation at high temperatures.

Type 5-S provides excellent resistance to oxidation when exposed to air at temperatures up to 1800oF (980oC) and is also recommended for applications involving thermal cycling at temperatures up to 1600oF (870oC).

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Table 5.4 ASTM and ASME specifications and typical applications for all types of Ductile Ni-Resist Irons.

Speci
fying
Body
Spec.
No.
Class
or
Grade
Min.
Tensile
psi
Min.
Yield
psi
%
Elonga-
tion
Heat
Treat-
ment
Chemical Analysis
and Hardness

Typical
Applications

 

ASTM

A439-84

    %
T.C.
%
SI
%
Mn
%
P
%
Ni
%
Cr
BHN  
D-2 58,000 30,000 8   Min.
Max.
3.00 1.50
3.00
0.70
1.25
0.08 18.00
22.00
1.75
2.75
139
202
Valve stem bushings, valve and pump bodies
in petroleum, salt water and caustic service, manifolds, turbocharger housings, air compressor parts.
D-2B 58,000 30,000 7   Min.
Max.
3.00 1.50
3.00
0.70
1.25
0.08 18.00
22.00
2.75
4.00
148
211
Turbocharger housings, rolls.
D2-C 58,000 28,000 20   Min.
Max.
2.90 1.00
3.00
1.80
2.40
0.08 21.00
24.00
0.50 121
171
Electrode guide rings, steam turbine
dubbing rings.
D-3 55,000 30,000 6   Min.
Max.
2.60 1.00
2.80
1.00 0.08 28.00
32.00
2.50
3.50
139
202
Turbocharger nozzles and housings,
steam turbine diaphragms, gas
compressor diffusers.
D-3A 55,000 30,000 10   Min.
Max.
2.60 1.00
2.80
1.00 0.08 28.00
32.00
1.00
1.50
131
193
High temperature bearing rings requiring resistance to galling.
D-4 60,000   Min.
Max.
2.60 5.00
6.00
1.00 0.08 28.00
32.00
4.50
5.50
202
273
Diesel engine manifolds, manifold joints.
D-5 55,000 30,000 20   Min.
Max.
2.40 1.00
2.80
1.00 0.08 34.00
36.00
0.10 131
185
Guidance system housings, gas turbine
shroud rings, glass rolls.
D-5B 55,000 30,000 6   Min.
Max.
2.40 1.00
2.80
1.00 0.08 34.00
36.00
2.00
3.00
139
193
Optical system mirrors and parts for dimensional stability, stators for compressors.
D-5S 65,000 30,000 10   Min.
Max.
2.30 4.90
5.50
1.00 0.08 34.00
37.00
1.75
2.25
131
193
Manifolds, turbine housings,
turbochargers where high temperatures
and severe thermal cycling occur.
ASTM

ASME
A571-71
(1976)
SA571
D-2M 65,000 30,000 30 Annealed Min.
Max.
2.20
2.70
1.50
2.50
3.75
4.50
0.08 21.00
24.00
0.20 121
171
Compressors, expanders pumps and
other pressure-containing parts
requiring a stable austenitic matrix
at minus 423F (-234C).

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Mechanical Properties

The room temperature mechanical properties of Ductile Ni-Resist Irons are described in Tables 5.4 and 5.5. The data shown in Table 5.5 are from either 1 inch (25 mm) keel blocks or castings tested in the as-cast condition. Castings should be ordered according to ASTM A439 or other specifications, but for special applications specific properties may be defined in more detail by agreement between the customer and the foundry.

Table 5.5 Typical room termperature mechanical properties of Ductile Ni-Resist Irons.

Typical Mechanical Properties of Ductile Ni-Resist Irons
  Type D-2 Type D-2B Type D-2C Type D-2M* Type D-3 Type D-3A Type D-4 Type D-5 Type D-5B
Tensile Strength, psi 58-60000 58-70000 58-65000 65-75000 55-65000 55-65000 60-7000 55-60000 55-65000
Yield Strength, psi (.2% offset) 30-35000 30-35000 28-35000 30-35000 30-35000 30-65000 --- 30-35000 30-35000
Elongation, % in 2 in. 8-20 7-15 20-40 35-45 6-15 10-20 --- 20-40 6-12
Prop. Limit, psi 16.5-18500 16-19000 12-16000 --- 16-19000 15-19000 12-16000 9.5-11000 10.5-13000
Mod. of Elas. psi x 106 16.5-18.5 16.5-19.0 15.0 17 13.5-14.5 16-18.5 12.0 16-20 16-17.5
Hardness, BHN 140-200 150-210 130-170 120-170 140-200 130-190 170-240 130-180 140-190
Impact, ft.-lb. (Charpy Vee Notch)
Room Temperature
12 10 28 --- 7 14 --- 17 6
Commpressive Yield Strength,
psi (.2% offset)
35-40000 --- --- --- --- --- --- --- ---
Compressive Ultimate Strength, psi 180-200000 --- --- --- --- --- --- --- ---
Fatigue Limit, psi, (106 cycles)
- Smooth bar
- Notched bar
30000
20000
---
---
---
---
---
---
---
---
---
---
---
---
---
---
---
---
*Normalized from 1700oF.

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Elastic Properties

Ductile Ni-Resist Irons have elastic moduli in the range 13-19 x 106 psi (90-130 GPa). These values are significantly lower than those of conventional Ductile Irons and are very similar to Ni-Resist irons with flake graphite. The proportional limit of as-cast Ductile Ni-Resists varies from 10 to 19 ksi (70-130 MPa), reflecting the influence of the austenite matrix and chromium content on initial yielding.

Strength and Elongation

With the exception of Type D-2M, the 0.2% yield strength and tensile strength are similar for all Types because of their common austenitic matrix. Unlike strength, elongation and toughness vary significantly between Types, depending upon the chromium, molybdenum, and silicon contents. In the low-chromium Types D-2C and D-5, as-cast elongations vary from 25 to 40%, with correspondingly good toughness. Types D-2, D-2B, D-3 and D-5B, all containing nominally 2 to 3% chromium, have as-cast elongations the range of 5 to 20% and lower toughness. Due to the stability of the austenite matrix, the mechanical properties of Ductile Ni-Resists are not strongly affected by heat treatments. High temperature treatments to disperse carbides can increase the yield and tensile strengths of Type D-2 by 10-15 ksi (70-105 MPa) while retaining good elongation. Annealing treatments may improve elongation values through the reduction of the carbide content and the spheroidization of any remaining carbides.

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Low Temperature Properties

Ductile Ni-Resist Irons, due to their austenitic matrices, retain their toughness and ductility to very low temperatures (Table 5.6). Type D-2M, with slightly higher nickel and manganese contents to extend the stability of the austenite phase to extremely low temperatures, improves on the already superior low temperature properties demonstrated by the other Types of Ni-Resist. Figure 5.8 shows that the Charpy v-notch impact energy of Type D-2M increases with decreasing temperature, peaking at -275oF (-170oC) and retaining room temperature toughness to temperatures as low as -320oF (-195oC).

Table 5.6 Effect of temperature on impact properties of different types of 
Ductile Ni-Resist (1ft-lbf = 1.3558 J).

Sub-Zero Temperature Impact Properties
Charpy Vee Notch (ft.-lb.)
  Type D-2 Type D-2C Type D-3 Type D-3A Type D-5 Type D-5B
Room Temperature 12.5 28 7 14 17 5.5
0oF 11.5 15 --- 14 15 5.5
-100oF 10 6.5 6.5 13 14 4.5
-320oF 4.5 4 3.5 7.5 11 4

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High Temperature Properties

Table 5.7 summarizes the high temperature mechanical properties of the various Types of Ductile Ni-Resist Irons. Creep data for these materials are shown in Figure 5.9, with those of CF-4 stainless steel included for reference. The addition of 1% molybdenum to Ductile Ni-Resist increases the high temperature creep and rupture strengths of Types D-2, D-3 and D-5B to the extent that their creep and rupture properties are equal or superior to those of cast stainless steels HF and CF-4. Figure 5.10 shows the short-term, tensile properties of type D-2 from room temperature to 1400oF (760oC). It is interesting to note that there is no temperature range in which embrittlement occurs, and that yield strength does not decrease appreciably until temperatures exceed 1200oF (650oC).

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Table 5.7 Elevated temperature properties of Ductile Ni-Resist Irons.

Elevated Temperature Properties of Ductile Ni-Resist Alloys
  Type D-2 Type D-2
with Mo
Type D-2C Type D-3 Type D-3
with Mo
Type D-4 Type D-4
with Mo
Type D-5B Type D-5B
with Mo
Tensile Strength, psi
Room Temp
800
oF
1000
oF
1200
oF
1400
oF

59400
54000
47700
35600
22100

61500
---
37000
38500
24900

62200
52400
42000
28000
17200

58300
---
48000
41700
26500

61000
---
46800
44000
28800

64000
---
60700
48000
21800

60500
---
54500
45500
22300

60800
---
47200
40600
24900

61200
---
48800
46400
31100
Yield Strength, psi
Room Temp.
800
oF
1000
oF
1200
oF
1400
oF

35000
28000
28000
25000
17000

37500
---
29200
25200
17100

34100
26200
23100
24200
16600

39300
---
28400
27400
15200

40000
---
28500
29000
21800

44300
---
41400
34000
18500

43000
---
38400
35500
18600

41000
---
25800
24200
18600

41000
---
28600
29900
24300
Impact Strength
(unnotched Charpy, ft. lbs.)
Room Temp
1000
oF
1100
oF
1200
oF
1350
oF
1500
oF


26
35
29
32
42
35


23*
21*
23*
24*
27*
27*


---
---
---
---
---
---


---
---
---
---
---
---


---
---
---
---
---
---


---
---
---
---
---
---


---
---
---
---
---
---


---
---
---
---
---
---


---
---
---
---
---
---
Stress Rupture (1000 hrs)
1000
oF
1100
oF
1200
oF
1300
oF
1400
oF

28000
(18000)
12000
(8500)
(5500)

---
26000
(15500)
11000
(6000)

21000
(13500)
9000
(6000)
(4000)

---
23500
(15000)
9700
(6000)

---
30500
(18000)
11000
(7000)

---
17000
(9500)
6200
(3000)

---
19000
(11000)
7500
(4000)

---
25000
(15000)
10000
(5500)

---
32000
(18500)
12000
(6500)
Creep Data (.0001%/hr)
1000
oF
1100
oF
1200
oF
1300
oF

23000
(13100)
8000
(4800)

(27000)
16000
(9600)
5600

13000
(9000)
5700
(3400)

---
---
---
---

(29000)
18000
(12000)
7000

---
---
---
---

---
---
---
---

(27000)
(16000)
(9600)
8000

(28000)
17000
(10500)
(6000)
(0.00001%/hr)
1000
oF
1100
oF
1200
oF
1300
oF

9000
(5600)
3400
(2100)

(18000)
11000
(6000)
3600

---
---
---
---

---
---
---
---

(21000)
13000
(8000)
5000

---
---
---
---

---
---
---
---

---
10000
---
5600

(18000)
11000
(6700)
4000
Elongation (%)
Stress Rupture
1000
oF
1100
oF
1200oF
1300
oF


6
---
13
---


---
5.5
---
11.5


14
---
13
---


---
7
---
12.5


---
5
---
16


---
10.5
---
25


---
10
---
21


---
6.5
---
13.5


---
5.5
---
11.5
Short Time Tensile
Room Temp.
800
oF
1000
oF
1200
oF
1400
oF

10.5
12
10.5
10.5
15

8.5
---
1.5
3
14.5

25
23
19
10
13

7.5
---
7.5
7
18

7
---
7
4
13

3.5
---
4
11
30

2.5
---
3.5
8
24.5

7
---
9
6.5
24.5

7.5
---
7.5
6.5
12.5
Footnote: Values in parentheses are extrapolated or interpolated. *Type D-2B no Mo.

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Thermal Cycling Resistance

When cycled to temperatures of 1250oF (675oC) and above, conventional ferritic Ductile Irons and steels pass through a "critical range" in which phase changes produce volume changes resulting in warping, cracking and loss of oxidation resistance. Ductile Ni-Resist Irons, because they are austenitic at all temperatures, do not undergo such phase changes and thus possess superior resistance to high temperature thermal cycling.

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Oxidation Resistance

Table 5.8 compares oxidation data for certain Types of Ductile Ni-Resist with conventional and high-silicon Ductile Irons, conventional Ni-Resist, and type 309 stainless steel. The chromium-containing Ductile Ni-Resists D-2, D-2B, D-3, D-4 and D-5B provide good resistance to oxidation and maintain satisfactory mechanical properties at temperatures as high as 1400oF (760oC). These properties make these grades highly suitable for applications such as furnace parts, exhaust lines and valve guides. For service temperatures exceeding 1300oF (700oC), Types D-2B, D-3, and D-4 are preferable. Type D-5S, with its superior dimensional stability and oxidation resistance, should be used when these properties are required for service temperatures as high as 1600oF (870oC).

Table 5.8 Oxidation resistance of Ductile Ni-Resists, Ni-Resist, conventional and high silicon Ductile Irons and type 209 stainless steel.

Oxidation Resistance
  Inches Penetration Per Year
Test 1 Test 2
Ductile Iron (2.5 Si) .042 .50
Ductile Iron (5.5 Si) .004 .051
Ductile Ni-Resist Type D-2 .042 .175
Ductile Ni-Resist Type D-2C .07 ---
Ductile Ni-Resist Type D-4 .004 0.0
Conventional Ni-Resist Type 2 .098 .30
Type 309 Stainless Steel 0.0 0.0
Test 1 - Furnace atmosphere - air, 4000 hr. at 1300oF.
Test 2 - Furnace atmosphere - air, 600 hr. at 1600o-1700oF, 600 hr.
between 1600o-1700oF,and 800o-900oF, 600 hr. at 800o-900oF.

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Corrosion Resistance

Ductile Ni-Resists and Ni-Resist with flake-type graphite exhibit corrosion resistance which is intermediate between those of unalloyed Ductile Iron and chromium-nickel stainless steels. Table 5.9 summarizes the corrosion resistance of Types D-2 and D-2C Ductile Ni-Resist in a number of corrosive environments. It is generally desirable to have chromium contents in excess of 2% for materials exposed to corrosive media. Therefore, Types D-2, D-2B, D-3, D-4, D-5B and D-5S are recommended for applications where a high level of corrosion resistance is desired. There are exceptions to these general comments and the reader is advised to consult the International Nickel Company bulletin "Engineering Properties and Applications of Ni-Resists and Ductile Ni-Resists," for information on the corrosion behaviour of Ductile Ni-Resist Irons in over 400 environments.

Table 5.9 Corrosion resistance of Ductile Ni-Resist Irons. Types D-2 and D-2C.

Corrosion Resistance of Ni-Resist Austenitic Nickel Irons
Expressed in inches penetration per year (i.p.y.)
Corrosive Media Type D-2C Type D-2
Ammonium chloride solution: 10% NH4CL, pH 5.15, 13 days at 30C (86F), 6.25 ft/min. 0.0280 0.0168
Ammonium sulfate solution: 10% (NH4)2SO4, pH 5.7, 15 days at 30C (86F), 6.25 ft/min. 0.0128 0.011
Ethylene vapors & splash: 38% ethylene glycol, 50% diethylene glycol, 4.5% H2O, 4% Na2SO4,
2.7% NaCl, 0.8% Na2CO3 + trace NaOH, pH 8 to 9, 85 days at 275-300F
0.0023 0.0019*
Fertilizer: commercial "5-10-5", damp, 290 days at atmospheric temp. --- 0.0012
Nickel chloride solution: 15% NiCl2, pH 5.3, 7 days at 30C (86F), 6.25 ft/min. 0.0062 0.0040
Phosphoric acid, 85%, aerated at 30C (86F), Velocity 16 ft. per min., 12 days 0.213 0.235
Raw sodium chloride brine, 300 gpl of chlorides, 2.7 gpl CaO, 0.06 gpl NaOH,
traces of NH3 & H2S, ph 6-6.5, 61 days at 50F, .1 to .2 fps
0.0023 0.0020*
Sea water at 26.6C (80F), Velocity 27 ft per sec, 60 day test 0.039 0.018
Soda & brine: 15.5% NaCl, 9.0% NaOH, 1.0% Na2SO4, 32 days at 180F 0.0028 0.0015
Sodium bisulfate solution: 10% NaHSO4, pH 1.3, 13 days at 30C (86F), 6.25 ft/min. 0.0431 0.0444
Sodium chloride solution: 5% NaCl, pH 5.6, 7 days at 30C (86F), 6.25 ft/min. 0.0028 0.0019
Sodium hydroxide: 50% NaOH + heavy conc. of suspended NaCl, 173 days at 55C (131F), 40 gal/min. 0.0002 0.0002
Sodium hydroxide: 50% NaOH saturated with salt, 67 days at 95C (203F), 40 gal/min. 0.0009 0.0006
Sodium hydroxide: 50% NaOH, 10 days at 260F, 4 days at 70F 0.0048 0.0049
Sodium hydroxide: 30% NaOH + heavy conc. of suspended NaCl, 82 days at 85C (185F) 0.0004 0.0005
Sodium hydroxide: 74% NaOH, 19-3/4 days, at 260F 0.005 0.0056
Sodium sulfate solution: 10% Na2SO4, pH 4.0, 7 days at 30C (86F), 6.25 ft/min. 0.0136 0.0130
Sulfuric acid: 5%, at 30C (86F) aerated, Velocity 14 ft per min., 4 days 0.120 0.104
Synthesis of sodium bicarbonate by Solvay process: 44% solid NaHCO3 slurry plus 200 gpl NH4Cl,
100gpl NH4HCO3, 80 gpl NaCl, 8 gpl NaHCO3, 40 gpl CO2, 64 days at 30C (86F)
0.0009 0.0003
Tap water aerated at 30F, Velocity 16 ft. per min., 28 days 0.0015 0.0023
Vapor above ammonia liquor: 40% NH3, 9% CO2, 51% H2O, 109 days at 85C (185F), low velocity 0.011 0.025
Zinc chloride solution: 20% ZnCl2, pH 5.25, 13 days at 30C (86F), 6.25 ft/min. 0.0125 0.0064
*Contains 1% chromium.

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Wear and Galling

The presence of dispersed graphite, as well as the work-hardening character of Ductile Ni-Resist alloys, provide a high level of resistance to frictional wear and galling. Types D-2, D-2C, D-3A and D-4 offer good wear properties when used with a wide variety of other metals at temperatures from sub-zero to 1500oF (815oC). Tests performed from room temperature to 1000oF (540oC) have shown that Types D-2 and D-2C have lower wear rates than bronze, unalloyed Ductile Iron, and INCONEL 600. The improved wear resistance is attributed to the spheroidal graphite and the formation of a nickel oxide film at higher temperatures. Types D-2B and D-3 provide inferior wear resistance compared to other Ductile Ni-Resists because they contain massive carbides which might abrade a mating material.

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Erosion Resistance

Ductile Ni-Resist castings, particularly those containing higher chromium levels, provide excellent service where resistance to erosion and corrosion are required, such as in the handling of wet steam, salt slurries and relatively high velocity corrosive liquids. Steam turbine components such as diaphragms, shaft seals and control valves are proven examples of the excellent resistance of Types D-2 and D-3 to steam erosion at high temperatures. Resistance to cavitation erosion makes Ductile Ni-Resist suitable for pump impellers and small-boat propellers. Higher-chromium Types D-2B, D-3, and D-4 are recommended when cavitation erosion is severe. Service results show that Type D-2 is superior to straight chromium stainless steels or bronzes in resisting cavitation for applications such as boat propellers and pump impellers.

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Physical Properties

Table 5.10 summarizes the general physical properties of Ductile Ni-Resist Irons.

Table 5.10 Physical properties of Ductile Ni-Resist.

Physical Properties of Ductile Ni-Resist
  Type D-2 Type D-2B Type D-2C Type D-3 Type D-3A Type D-4 Type D-5 Type D-5B
Specific Gravity 7.41 7.45 7.41 7.45 7.45 7.45 7.68 7.72
Density, lb. per cu. in. .268 .27 .268 .27 .27 .27 .278 .279
Melting Point, F 2250 2300 2250 2250 2250 2200 2250 2250
Thermal Expansion 70-400F.,
Millionths per oF
10.4 10.4 10.2 7.0 --- 8.0 --- ---
Thermal Conductivity, Cal./cc/sec/oC .032 --- --- --- --- --- --- ---
Electrical Resistivity, microhms per cc 102 --- --- --- --- --- --- ---
Magnetic Response Non-
magnetic
Slightly
magnetic
Non-
magnetic
Definitely
magnetic
Definitely
magnetic
Slightly
magnetic
Definitely
magnetic
Definitely
magnetic
Magnetic Permeability,
H=300 at room temp.
1.02-1.04 1.04-1.08 1.03 --- --- 1.10 --- ---

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Thermal Conductivity

The thermal conductivities of Type D-2 Ductile Ni-Resist, Ni-Resist, Gray Iron and several steels are listed in Table 5. 11. The spheroidal graphite shape and austenitic matrix are responsible for the relatively low conductivity of Ductile Ni-Resists.

Table 5.11 Thermal conductivity of type D-2 Ductile Ni-Resist, Gray Iron, and steels.

Thermal Conductivity

Material

Cal/cm3/sec/oC
(0 to 100C)
Btu/Hr/Ft2/in/oF
(50 - 200F)
Ductile Ni-Resist Type D-2 0.032 93
Flake Graphite Ni-Resist 0.090-0.095 260-275
Gray Cast Iron 0.108-0.131 313-380
Steel 0.15-0.17 435-495
12% Cr Steel 0.045 130
18% Cr-8% Ni Steel 0.039 113

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Thermal Expansion

Figures 5.11 and 5.12 illustrate the wide range of thermal expansion exhibited by the different Types of Ductile Ni-Resist and the influence of nickel content on the thermal expansion behaviour of Type D-3. High expansion Types D-2 and D-4 are used to match the expansion of materials such as aluminium, copper, bronze and austenitic stainless steels. Type D-3, with different nickel levels, is used to obtain the controlled, intermediate thermal expansion required to match the thermal expansions of a wide variety of steels and cast irons. Types D-5 and D-5B are recommended for applications requiring maximum dimensional stability, such as machine tool parts, glass molds and gas turbine housings.

Electrical and Magnetic Properties

Table 5.12 compares the electrical resistivity of Type D-2 Ductile Ni-Resist with that of Ni-Resist, Gray Iron and various steels. Table 5.13 compares the magnetic permeability of all Types of non-magnetic Ductile Ni-Resist with that of Ni-Resist, Gray Iron, bronzes and a variety of steels. Values for Types D-3, D-3A, D-5 and D-5B are not shown because they are ferromagnetic. The non-magnetic character of Types D-2 and D-2C has been applied in several industrial applications where magnetic permeability must be kept at a minimum in order to prevent excessive heat generation and power loses from eddy currents.

Table 5.12 Electrical resistivity of Ductile Ni-Resist, Ni-Resist, Gray Iron and different steels.

Electrical Resistance

Material

Electrical Resistance

(microhms/cc)
Ductile Ni-Resist Type D-2 102
Flake Graphite Ni-Resist 130-170
Gray Cast Iron 75-100
Plain Medium C Steel 18
12% Cr Steel 57
18% Cr-8% Ni Steel 70

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Table 5.13 Magnetic permeability of different types of Ductile Ni-Resist, Ni-Resist, Gray Iron, various steels and bronzes.

Magnetic Permeability

Material

Permeability

Ductile Ni-Resist Type D-2 1.02-1.04
Ductile Ni-Resist Type D-2B 1.04-1.08
Ductile Ni-Resist Type D-2C 1.03
Ductile Ni-Resist Type D-2M 1.01-1.03
Ductile Ni-Resist Type D-4 1.10
Flake Graphite Ni-Resist 1.03
Gray Cast Iron* 125
Mild Steel* 150
12% Cr Steel Ferromagnetic
10-14% Mn Steel 1.03-1.10
18% Cr-8% Ni Steel <1.001
Bronzes <1.001
*Initial permeability.

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Production Requirements

Special Ductile Iron foundry practices, some of which affect cating design, are required for the production of Ductile Ni-Resist castings. To obtain maximum casting performance and minimum production cost, the design engineer should initiate consultations, at an early stage in the design process, with a Ductile Iron foundry experienced in the production of Ductile Ni-Resist castings.

Machinability

The machinability of Ductile Ni-Resists falls between that of pearlitic Gray Iron with a hardness of about 240 BHN and mild steel when machining practices follow those recommended in the Inco publication A242, "Machining and Grinding Ni-Resist and Ductile Ni-Resist."

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Heat Treatment

Large and complex Ductile Ni-Resist castings should be mold-cooled to 600oF (315oC) before shakeout to relieve stresses. When required, stress-relief should be performed at 1150-1250OF (620-675oC). Annealing, which softens and improves ductility primarily by the decomposition and spheroidization of carbides, should be conducted at 1750-1900oF (960-1035oC) for 1 to 5 hours, depending on section size and the degree of decomposition and spheroidization desired. Annealing should be followed by air cooling or furnace cooling if minimum hardness and maximum elongation are required.

When Ductile Ni-Resist is to be used at temperatures of 900oF (480oC) and above, the casting can be stabilized to minimize growth and warpage by holding at 1600oF (870oC) for two hours, followed by furnace cooling to 1000oF (540oC), followed by air cooling to room temperature. To assure dimensional stability for all Types of Ductile Ni-Resist, the following heat treatment should be performed: hold at 1600oF (870oC) for 2 hours plus 1 hour per inch of section size; furnace cool to 1000oF (540oC); hold for 1 hour per inch of section size, and slowly cool to room temperature. After rough machining, reheat to 850-900oF (450-460oC) and hold for 1 hour per inch of section size to relieve machining stresses. Furnace cool to below 500oF (260oC).

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REFERENCES

S. I. Karsay, Ductile Iron II, Quebec Iron and Titanium Corporation, 1972.

Annual Book of ASTM Standards, Volume 01.02, Ferrous Castings, 1987.

Engineering Properties and Applications of the Ni-Resists and Ductile Ni-Resists, The International Company, New York, NY, 1978.

The Iron Castings Handbook, Iron Castings Society, Inc., 1981.

Metals Handbook, American Society for Metals, Vol. 1, 8th edition, 1961.

E. Soehnchen and O. Bernhofen, "The Thermal Expansion Coefficient of Cast Iron, " Archive fur das Eisenhattenwesen, Vol. 8, 1935.

H. T. Angus, Cast Iron: Physical and Engineering Properties, 2nd ed., Butterworths Inc, 1967.

E. Piwowarsky, Hochwertiges Gusseisen, Springer-Verlag, Berlin, 1942.

G. N. J. Gilbert, Engineering Data on Nodular Cast Irons, British Cast Iron Research Association, 1968.

High Strength Irons, Climax Molybdenum Company, New York.

Ductile Iron, International Nickel Company, New York, NY, 1956.

"Ductile Iron" Alloy Digest Data Sheet, Engineering Alloys Digest, Inc., Upper Montclair, NJ, 1956.

"Ductalloy, " Alloy Digest Data Sheet, Engineering Alloys Digest, Inc., Upper Montclair, NJ, 1956.

B. E. Neimark, et al, "Thermophysical Properties of Cast Irons, " Russian Castings Production, September, 1967.

A Design Engineer's Digest of Ductile Iron, 5th edition, 1983, QIT-Fer et Titane Inc., Montreal, Quebec, Canada.

Ductile Iron, Metals Handbook, American Society for Metals, 9th edition, Vol 15, 1988.

W. Fairhurst and K. Rorhrig "High-silicon Nodular Irons." Foundry Trade journal, March 29, 1979, pp. 657-681.

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