Printer Friendly
The Free Library
22,741,889 articles and books

Welding ductile iron to steel: a new welding process will allow ductile iron castings to be welded to steel, making fabrications using both metals a reality.



When welded, ductile iron Ductile iron, also called ductile cast iron or nodular cast iron, is a type of cast iron invented in 1943 by Keith Millis[1]. While most varieties of cast iron are brittle, ductile iron is much more ductile, as the name implies.  is liquefied in the welded area and may solidify so·lid·i·fy  
v. so·lid·i·fied, so·lid·i·fy·ing, so·lid·i·fies

v.tr.
1. To make solid, compact, or hard.

2. To make strong or united.

v.intr.
 with a carbidic structure in the fusion zone that limits the toughness of the weldment weld·ment  
n.
A unit composed of an assemblage of pieces welded together.

Noun 1. weldment - an assembly of parts welded together
assembly - a group of machine parts that fit together to form a self-contained unit
. Avoiding the formation of this carbidic zone is a difficult task.

This article presents the results of an attempt to improve the mechanical properties of gas metal arc welded ductile iron and steel components in order to enlarge the range of applications for such fabrications. And, as will be seen, significant improvements in properties have been made for welding welding, process for joining separate pieces of metal in a continuous metallic bond. Cold-pressure welding is accomplished by the application of high pressure at room temperature; forge welding (forging) is done by means of hammering, with the addition of heat.  ferritic and pearlitic ductile iron to mild steel.

Just In Time

The history of metal joining can be traced to the year 3000 B.C., but its development really accelerated in the late 19th century. The discovery of a process in which an electric arc is used to melt the edges of two pieces of metal and join them together allowed the rapid growth of arc welding. That process has evolved to become the prevalent welding technique for ferrous ferrous (fĕr`əs), iron in the +2 valence state.


Containing or having to do with iron. The difference between ferrous and ferric is the number of valence electrons they contain (ferrous contains two and ferric contains three), which
 alloys.

While welding steels has been rapidly and successfully introduced in all industrial sectors, the difficulty of welding cast irons was recognized early. Because of its high carbon content, molten iron tends to solidify with a carbidic structure. This limits the ductility ductility, ability of a metal to plastically deform without breaking or fracturing, with the cohesion between the molecules remaining sufficient to hold them together (see adhesion and cohesion). Ductility is important in wire drawing and sheet stamping.  and toughness of the weld, which has restricted the use of cast iron parts in many fabrications that could have taken advantage of the casting process and its properties. Ductile irons with properties competing with those of steel would find many new applications if it could be welded without becoming brittle. Processes for welding ductile irons have been developed in the past, but improving the quality would enlarge the range of applications, specifically in the heavy vehicle industry.

The Road to Weldsville

To ease the road toward an improved bond between ductile iron and steel, researchers employed welding procedures that used existing equipment and could be easily introduced in industrial manufacturing processes (i.e. with an acceptable level of productivity). All laboratory and application welding tests were performed with industrial equipment and commercially available consumables (Table 1). A multi-pass approach was selected to minimize the interactions between the base materials and the heat involved during the welding process.

In order to achieve optimal results, it was necessary to use a shielding gas Shielding gases are inert or semi-inert gases that are commonly used in several welding processes, most notably gas metal arc welding and gas tungsten arc welding. Their purpose is to protect the weld area from atmospheric gases, such as oxygen, nitrogen, carbon dioxide, and water  containing both argon argon (är`gŏn) [Gr.,=inert], gaseous chemical element; symbol Ar; at. no. 18; at. wt. 39.948; m.p. −189.2°C;; b.p. −185.7°C;; density 1.784 grams per liter at STP; valence 0.  and helium in combination with small amounts of some oxidizing components.

The welding procedures included pre-welding heat treatments from 300-320C (572-608F) and post-welding cooling followed by heating to 600-620C (1,112-1,148F) maintained for two hours. In order to identify the heat treatment parameters, test plates were instrumented with thermocouples to monitor the temperature profiles obtained as a function of the welding parameters.

The initial welding tests consisted of joining 0.59-in. (15-mm) thick ductile iron plates (ferritic or pearlitic) to low carbon steel; the typical chemical compositions of the materials are listed in Table 2. The test coupon assembly had a gap of 0.08-0.12 in. (2-3 mm), supported by a ceramic/copper backing, and each plate had a bevel angle any angle other than one of 90°.

See also: Bevel
 of 30 degrees (Fig. 1).

[FIGURE 1 OMITTED]

The welded specimens were characterized by metallographic met·al·log·ra·phy  
n.
The study of the structure of metals and alloys, especially by optical and electron microscopy and x-ray diffraction.



met
 examination, hardness and microhardness measurements, and impact, tensile and bending tests. Impact resistance was measured in different locations of the weldments, as well as in the parent metals. Tensile properties were measured in both transverse To cross from side to side.  and longitudinal directions with respect to the weld (Fig. 2).

[FIGURE 2 OMITTED]

A typical macrostructure The notion of macrostructure has been used in several disciplines in order to distinguish large-scale, or 'global' structures, from small-scale, or 'local' structures, that is, microstructures.  and microhardness profile of a welded steel-to-ferritic ductile iron joint was obtained during the initial trials (Fig. 3). The microhardness profile showed a smooth transition between the steel and the weld, but a high hardness P peak occurred in the transition zone between the weld and the ductile iron. A narrow, typical fusion zone arose at the steel-weld interface. A fusion zone containing carbides carbides (kar´bīdz),
n 1. in chemistry, carbon binary compounds with strong electron-releasing properties.
2. mixtures of carbon with at least one heavy metal. E.g.
 was present on the ductile iron side, resulting in high hardness in the vicinity of the fusion line. The adjacent heat affected zone (HAZ HAZ Heat Affected Zone
HAZ Hazardous Cargo
HAZ Hazard/Hazardous
HAZ HAWK Assignment Zone
) also displayed a multi-phase pearlite/ferrite/cementite structure (Fig. 4). Such a mixed structure usually shows low impact resistance (less than 5 J at room temperature) and tensile elongation elongation, in astronomy, the angular distance between two points in the sky as measured from a third point. The elongation of a planet is usually measured as the angular distance from the sun to the planet as measured from the earth.  (0.5%). The goal then was to minimize the extent of the HAZ and fusion zone to achieve properties approaching those of the parent ductile iron. Changes in the welding procedures allowed the reduction of the thickness of the embrittling layer to less than 0.01 in. (0.3 mm), and small graphite nodules Nodules
A small mass of tissue in the form of a protuberance or a knot that is solid and can be detected by touch.

Mentioned in: Leprosy
 developed in the HAZ/fusion zone (Fig. 5). Micro-hardness measurements (VHN VHN Vickers Hardness Number
VHN Virtual Health Network (UK)
VHN Virtual Home Network
 100 g) in the HAZ/fusion zone ranged between 200 and 250 VHN, which was significantly lower than the 600 VHN peak.

[FIGURES 3-5 OMITTED]

Testing the Process

The improved specimens were submitted to Charpy impact (Table 3) and bending tests. The range of the impact resistance values exceeded past data for similar ductile iron and steel materials.

Material used in Test F4, which tested the effect of test temperature on impact resistance, also was submitted to low temperature Charpy impact test The Charpy impact test is a standardized high strain-rate test which determines the amount of energy absorbed by a material during fracture. This absorbed energy is a measure of a given material's toughness and acts as a tool to study brittle-ductile transition.  (Table 4). The parent ductile ductile /duc·tile/ (duk´til) susceptible of being drawn out without breaking.

duc·tile
adj.
Easily molded or shaped.



ductile

susceptible of being drawn out without breaking.
 iron's HAZ/ fusion zone and the welding material had a ductile/brittle transition temperature lower than -4F (-20C), while the steel HAZ was embrittled at low temperature.

Bending tests were carried out on welded specimens by hammering on the extremities ex·trem·i·ty  
n. pl. ex·trem·i·ties
1. The outermost or farthest point or portion.

2. The greatest or utmost degree: the extremity of despair.

3.
a.
 of the ductile iron and steel sections in order to locate the maximum stress in the weld region. Cracking occurred in the parent ductile iron, but the weld remained intact (Fig. 6).

[FIGURE 6 OMITTED]

The conditions used for welding ferritic ductile iron were adapted to pearlitic irons. Some of the pearlitic ductile iron plates were low in magnesium content (Table 2), with a resulting structure consisting in a mixture of nodular nodular

marked with, or resembling, nodules.


nodular dermatofibrosis
see dermatofibrosis.

nodular episcleritis
see nodular fasciitis (below).

nodular fasciitis
a firm painless nodular swelling, 0.
 and vermicular vermicular /ver·mic·u·lar/ (ver-mik´u-ler) wormlike in shape or appearance.

ver·mic·u·lar
adj.
1. Having the shape or motion of a worm.

2. Caused by or relating to worms.
 graphite particles in a pearlitic matrix. As a result, the typical tensile properties of these iron plates were those of a compacted graphite iron (UTS (Universal Timesharing System) Amdahl's version of Unix System V. Release 4.0 is POSIX compliant.  of 430-550 MPa and elongation of 1-2%). Nevertheless, the properties measured in the HAZ and fusion zone should have been comparable to those of welded pearlitic ductile irons, since the vermicular graphite particles dissolved faster than the nodular ones during welding because of their large specific surface area.

As for ferritic iron, its thickness was in the 0.004-0.01-in. (0.1-0.3-mm) range. It was followed by an HAZ containing fine pearlite pearl·ite  
n.
1. A mixture of ferrite and cementite forming distinct layers or bands in slowly cooled carbon steels.

2. Variant of perlite.

Noun 1.
 and tempered martensite mar·ten·site  
n.
A solid solution of iron and up to one percent of carbon, the chief constituent of hardened carbon tool steels.



[After Adolf Martens (1850-1914), German metallurgist.
.

The typical microhardness measured in the HAZ/ fusion zone was higher than that of the ductile iron (represented by P1-P5 in Table 6) but did not reach values typical of a mostly carbidic structure. The hardness values of the HAZ/fusion zone reported in this study after annealing annealing (ənēl`ĭng), process in which glass, metals, and other materials are treated to render them less brittle and more workable.  in the 1,112-1,202F (600-650C) range are lower than those found in the past for welds submitted to a similar heat treatment.

Will It Hold?

The properties of the welds (specimens P6, P7 and P8) were verified by impact and tensile tests at room temperature. The location and identification of specimens P1-P8 are shown in Fig. 2.

Charpy V-notch impact energy was measured in the weld metal and the ductile iron HAZ/fusion zone (Table 6). The welding rod used in past tests was Ni-61, which most probably explained the difference seen in the properties of the weld metal zones. The results obtained in the HAZ/fusion zone with the new welding procedures were clearly superior to those reported in the past.

A few tensile tests were carried out in the transverse direction of the weld. However, the results were strongly influenced by the tensile properties of the iron plates, which were those of compacted graphite iron rather than those of ductile iron (lower ductility and strength). This made them non-representative of the mechanical strength of the weld. This was confirmed by the fact that some samples failed in the cast iron section of the bar away from the weld.

Tensile tests were run on longitudinal specimens, including the following regions: the iron (No. 9), the HAZ (No. 10) and the fusion zone (No. 11). Results are presented in Table 7. As previously discussed, the poor nodularity of the graphite particles caused the samples machined in the iron to be the weakest. Those including the HAZ and fusion zone, however, exhibited tensile properties close to those of pearlitic ductile irons. In these samples, the vermicular graphite particles were dissolved rapidly, and graphite re-precipitated in a more nodular shape.

The new welding procedure reduced the thickness of the carbidic fusion zone from 0.024 in. (0.6 mm) to less than 0.01 in. (0.3 mm), and the technique was found applicable to both ferritic and pearlitic ductile irons. The toughness and tensile properties of the resulting welds significantly improved upon earlier attempts to join the metals.

For More Information

"Specifying Steel Castings Steel casting is a manufacturing process in which molten metal is poured into a mold, allowed to solidify within the mold, and then the mold is broken and the solid piece is taken out.  Keeping Alloy Composition in Mind," J.D. Carpenter and B.R. Hanquist, Engineered Casting Solutions, Fall 2001, p. 41.

"Designing With Ductile Iron to Achieve Strength and Economy," Ductile iron Marketing Group, Engineered Casting Solutions, Winter 1999, p. 47.

M. Gagne and S. Leclerc, Rio Tinto Rio Tinto may refer to:
  • Rio Tinto (Paraíba), in Paraíba State, Brazil.
  • Río Tinto (river), a river in Spain.
  • Rio Tinto Group, a multinational mining company.
  • Rio Tinto (Gondomar), a civil parish in the municipality of Gondomar, Portugal.
 Iron and Titanium Inc., Montreal S Montreal (mŏn'trēôl`), Fr. Montréal (môNrāäl`), city (1991 pop. 1,017,666), S Que., Canada, on Montreal island, surrounded by St. Lawrence River and Rivière des Prairies. . Helgee, N. Stenbacka and J. Tani, Linde Gas, Stockholm, Sweden
Table 1. Welding Equipment, Parameters and Consumables

Welding Equipment   ESAB Auto 500
Welding Operation   Mechanized
Deposition Rates    Root pass: 7.7 kg/hour, multi-pass:
                    8.6 kg/hour
Shielding Gas       Linde Gas MISON 2 He
Filler Material     Ni-rod metal 44
Wire Diameter       1.2 mm

Table 2. Typical Chemical Composition of Test Materials

Element   Ferritic Ductile    Pearlitic Ductile   Mild Steel
                Iron                Iron

   C          3.3-3.4%            3.6-3.7%          0.08%
   S            0.01%              0.008%           0.022%
  Si            2.4%              2.4-2.5%          0.24%
   P           0.017%               0.01%           0.015%
  Mn            0.16%               0.15%          0.5-0.6%
  Cr           0.027%               0.03%           0.12%
  Ni           0.025%               0.06%         0.08-0.13%
  Cu           0.058%               0.70%         0.19-0.25%
  Mg           0.035%          0.025-0.035% *         --

* Vermicular graphite found in plates with lower magnesium content.

Table 3. Impact Test Results at 20C

Position       Test F1   Test F2   Test F3   Test F4   Past Data

Weld Metal     63/101     89-91     64-73      45         60
Fusion Zone     12-18     16-20     14-18     11-20      8, 11
HAZ             16-18      NA       14-16      --       11, 12
Ductile Iron     12        12        12        14         --
Steel            --        --        --        65         --
Steel HAZ        --        --        --        50         --

Table 4. Effect of Test Temperature on Impact
Resistance (Test F4)

Region                      +20C          -20C

Ductile Iron                13.6          12.2
D.I. HAZ/Fusion Zone        13.2          11.3
Weld                        41.3          30.5
Steel HAZ                   50.2           19

Table 5. Microhardness of HAZ/Fusion Areas in
Pearlitic Ductile Iron * (in VHN 100g)

Test Number             Ductile Iron   HAZ/Fusion

P1                          314           322
P2                          300           322
P3                          268           297
P4                          323           366
P5                          277           336
Past Tests                   --         420-500

* Stress relieved at 600-650C.

Table 6. Results of Impact Tests for Pearlitic Ductile Iron

Notch Position    P6      P7     P8 *    Past Results

Weld             24-38   16-27   12-16        11
HAZ/Fusion        8-9     5-7      7         3-4

* High Manganese welding rod

Table 7. Tensile Properties of Longitudinal Specimens

Sample                    P6                       P7

Position           9      10       11       9      10       11
Description      Iron     HAZ    Fusion   Iron     HAZ    Fusion
YS (MPa)          344     358     363      444     450     450
UTS (MPa)         430     555     550      577     721     710
Elongation (%)    1.9     7.7     8.4      0.8     5.7      6

Sample                    P8

Position           9      10       11
Description      Iron     HAZ    Fusion
YS (MPa)          442     453     447
UTS (MPa)         540     583     714
Elongation (%)    1.8     1.7     5.7
COPYRIGHT 2007 American Foundry Society, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2007, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company.

 Reader Opinion

Title:

Comment:



 

Article Details
Printer friendly Cite/link Email Feedback
Author:Tani, J.
Publication:Modern Casting
Date:Jun 1, 2007
Words:1902
Previous Article:2007 Casting Competition: Smith Foundry claimed the 2007 Casting of the Year prize with is austempered ductile iron seed boot, one example of the...
Next Article:Casting shipments to slow: a review of the first quarter indicates a minimal decline in 2007 following growth in 2006.
Topics:



Related Articles
International meeting updates technology, stresses need to reach casting specifiers.
Converting steel weldments to ductile iron castings.
In this case, be a follower.
GM to invest more than $120 million in casting operations at Saginaw, defiance facilities.
Keeping with policy to end in-house metalcasting, ford to stop casting production in Cleveland.
U.S. Pipe to build first new ductile plant in more than 55 years.
Bahr Bros. Manufacturing buys green sand metalcaster.
Thresher Industries looks for new Midwestern plant site, opens office for Asian operations.
Hoyt lecture: reexamination of engineering education is due.

Terms of use | Copyright © 2014 Farlex, Inc. | Feedback | For webmasters