Factors Affecting Ductile Iron's Impact, Tensile Strength.At Giddings & Lewis Castings, elemental elemental emanating from or pertaining to elements. elemental diet see elemental diet. additions to 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. were studied for their effects on casting strength and real-world application. Consistent results when casting high-impact-resistant ductile iron are always important, especially considering the need to ensure final component performance during end-use. For example, in the automotive industry The automotive industry is the industry involved in the design, development, manufacture, marketing, and sale of motor vehicles. In 2006, more than 69 million motor vehicles, including cars and commercial vehicles were produced worldwide. , it is essential to be confident that a given cast component will stand up to actual conditions, like the impact from a succession of potholes on a cold, wintry win·try also win·ter·y adj. win·tri·er also win·ter·i·er, win·tri·est also win·ter·i·est 1. Belonging to or characteristic of winter; cold. 2. day. The primary problem for foundries is identifying where sources for potential failure (fracture) may lie and correcting them before a casting "hits the street." For Giddings & Lewis Castings (G&L), a 140-employee 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. and gray iron foundry in Menominee, Michigan, at issue were the impact, tensile tensile, adj having a degree of elasticity; having the ability to be extended or stretched. and yield strength, and 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. of 1600-5000 lb low-temperature impact-resistant ductile iron castings it was producing. G&L was looking to better characterize how its elemental additions to the molten ductile iron were affecting the final casting's mechanical properties. This article focuses on a study performed at the foundry during which a range of element additions were made during casting. From the results, foundries may determine a new alloying method for their impact-resistant ductile iron to ensure component performance in application. Casting Testing G&L was casting ductile iron grade GGG GGG German Goo Girls (pornography website) GGG Giggle (email, USENET, chat slang) GGG Gadolinium Gallium Garnet GGG Gimme Gimme Gimme (TV show) 40.3. The mechanical requirements it was looking to achieve were: * impact strength at -4F (-20C) using an impact specimen per DIN 50115, U-notch, 10 ft-lb average with a minimum individual value of 8 ft-lb; * tensile strength tensile strength Ratio of the maximum load a material can support without fracture when being stretched to the original area of a cross section of the material. When stresses less than the tensile strength are removed, a material completely or partially returns to its : 58 ksi mm.; * yieldstrength:36.25ksi at 0.2% offset min.; * elongation: 18% min. For the study, the foundry cast Y-block test castings in the mold with the production casting, and subjected these test castings to the same full anneal To take the brittleness out of metal, plastic or certain carbon composites. Performed in the preparation of new products or in their restoration, annealing is accomplished via a heat treating process. heat treatment. Chemical analysis was performed on the test castings to determine the concentration of carbon (C), silicon (Si), manganese manganese (măng`gənēs, măn`–) [Lat.,=magnet], metallic chemical element; symbol Mn; at. no. 25; at. wt. 54.938; m.p. about 1,244°C;; b.p. about 1,962°C;; sp. gr. 7.2 to 7. (Mn), phosphorus phosphorus (fŏs`fərəs) [Gr.,=light-bearing], nonmetallic chemical element; symbol P; at. no. 15; at. wt. 30.97376; m.p. 44.1°C;; b.p. about 280°C;; sp. gr. 1.82 at 20°C;; valence −3, +3, or +5. (P), sulfur (S), nickel nickel, metallic chemical element; symbol Ni; at. no. 28; at. wt. 58.69; m.p. about 1,453°C;; b.p. about 2,732°C;; sp. gr. 8.902 at 25°C;; valence 0, +1, +2, +3, or +4. (Ni), chromium chromium (krō`mēəm) [Gr.,=color], metallic chemical element; symbol Cr; at. no. 24; at. wt. 51.996; m.p. about 1,857°C;; b.p. 2,672°C;; sp. gr. about 7.2 at 20°C;; valence +2, +3, +6. (Cr), molybdenum molybdenum (məlĭb`dənəm) [Gr.,=leadlike], metallic chemical element; symbol Mo; at. no. 42; at. wt. 95.94; m.p. about 2,617°C;; b.p. about 4,612°C;; sp. gr. 10.22 at 20°C;; valence +2, +3, +4, +5, or +6. (Mo), copper (Cu) and magnesium magnesium (măgnē`zēəm, –zhəm), metallic chemical element; symbol Mg; at. no. 12; at. wt. 24.305; m.p. about 648.8°C;; b.p. about 1,090°C;; sp. gr. 1.738 at 20°C;; valence +2. (Mg). Preliminary testing revealed that impact sample machining influenced the impact results. At first, little difference existed between impact strength determined on samples with Charpy V notch notch (noch) incisure; an indentation on the edge of a bone or other organ. aortic notch dicrotic n. cardiac notch 1. (ASTM ASTM abbr. American Society for Testing and Materials ) and the key hole PIN 50115 U-notch. However, major differences between the machining techniques used to form the notch were identified. When the notch was broached, an estimated 30% of the impact bars failed the impact requirements. When the notch was ground, more than 90% of the bars passed the impact requirements. Statistical Analysis The data collected from the mechanical testing, impact testing and chemical analysis of the 83 Y-blocks were studied statistically to determine if a correlation could be established between composition and the required critical properties. It has been demonstrated that Si will adversely affect low-temperature-impact strength. In this investigation, Si in the range of 1.74-2.61% had a 0.21 correlation factor The ratio of a ground dose rate reading to a reading taken at approximately the same time at survey height over the same point on the ground. with the measured impact strength. For reference purposes, a correlation factor of 1.0 would be considered a perfect match and a correlation factor of 1.0 would be considered a completely random match. Any factor above 0.5 would be considered a better than acceptable correlation. The 0.21 correlation factor between Si and the impact data was considered reasonably acceptable and representative of its known effect. Personnel at G&L, however, thought that a Si level greater than 2.2% exceeded the amount that could be added, considering all the Si sources. Consequently, a correlation between the Si content and the Al content was determined. As the Al content increased for the first 40 sets of data, the Si content increased. From this correlation, it was determined that a non-uniform inoculant in·oc·u·lant n. See inoculum. distribution was occurring. When steps were taken to counteract this effect, the correlation between the Si and the Al was more random. This corrective cor·rec·tive adj. Counteracting or modifying what is malfunctioning, undesirable, or injurious. n. An agent that corrects. corrective, n measure was taken during the production of the Y-blocks in the last 43 sets of data. Consideration of all 83 sets of data shows that a definite relationship still existed between the Si and Al, but that the relationship was more random. Nothing in the multiple regression Multiple regression The estimated relationship between a dependent variable and more than one explanatory variable. analysis was found to correlate well with elongation. The highest correlation factor with elongation was 0.16 when the effect of all eight elements was considered. The highest correlation in this investigation occurred when the effect of C, Si and Ni was considered on ultimate tensile strength (0.695) and on yield strength (0.673). There was a low correlation between the predicted elongation and the actual elongation when considering the effects of C, Si and Ni. Comparison of C, Si and Ni with impact strength resulted in a relatively strong correlation factor of 0.34. Comparison of C, Mg, Si, Cu, Ni, Cr, Mo and Al resulted in the highest correlation factor with impact strength of 0.44. Further analysis revealed a strong correlation factor of 0.38 between impact strength and Si, Cu, Ni and Al. An additional comparison was made to evaluate the impact strength data using a pass/fail mechanism. The data was compared based on whether the average impact strength was above or below 8, 9 and 10 ft-lb. Molybdenum was the only element that had averages that were significant and statistically different using all three criteria. Figure 1 shows how the Mo affected the percent of the readings that passed using the 8, 9 and 10 ft-lb criteria and the effect it had on the average impact value. It is possible that Mo was acting only as a tracing element--the actual cause for this relationship has yet to be found. However, 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 evaluations of the structures from impact bars have shown a significant correlation with the occurrence of intercellular intercellular /in·ter·cel·lu·lar/ (-sel´u-lar) between or among cells. in·ter·cel·lu·lar adj. Located among or between cells. 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. and low impact strength. Microporosity is associated with these carbides and it is a strong possibility that the occurrence of intercellular carbides and the Mo content are related. Metallographic Analysis Four ductile iron Y-blocks were subjected to routine chemical analysis, mechanical testing and low-temperature -4F (-20C) impact testing. Two of the Y-blocks, Samples 1 and 2, represented ladles that had been inoculated with foundry grade ferrosilicon fer·ro·sil·i·con n. An alloy of iron and silicon used in the production of carbon steel. , the standard process at G&L. The other two Y-blocks, Samples 3 and 4, were inoculated with a cerium-bearing (Ce) inoculant. During testing, the Y-blocks inoculated with Ce displayed higher impact strengths than the Y-blocks inoculated via standard procedure. A comparison of the composition, mechanical properties and the impact strengths of the Y-blocks is in Table 1. Additional information indicated that Samples 1 and 2 were from one heat and that Samples 3 and 4 were from a second heat. The chemical analysis and mechanical properties that are indicated in Table 1 confirmed this relationship. Impact bars representing the Y-blocks were arbitrarily selected for metallographic analysis. The fractured surfaces displayed a white-specked appearance. The two Y-blocks from the normal process, Samples 1 and 2, had more specks than the other two Y-blocks inoculated with Ce (Fig. 2a). The selected impact bars were cut to provide cross sections. The four samples were prepared for metallographic examination at magnifications up to 560X to compare the microstructures. Unetched, all four samples exhibited acceptable nodularity rated as 95% ASTM Types 1 and II graphite graphite (grăf`īt), an allotropic form of carbon, known also as plumbago and black lead. It is dark gray or black, crystalline (often in the form of slippery scales), greasy, and soft, with a metallic luster. . Nodule nodule: see concretion. nodule In geology, a rounded mineral concretion that is distinct from, and may be separated from, the formation in which it occurs. count was estimated as 50/sq mm for Samples 1 and 2 and 70/sq mm for the Ce-treated Y-blocks. Minor duplex (communications) duplex - Used to describe a communications channel that can carry signals in both directions, in contrast to a simplex channel which only ever carries a signal in one direction. graphite nodule size was observed for all four Y-blocks. Representative graphite structures can be seen in Figs. 2b and 2d. The etched etch v. etched, etch·ing, etch·es v.tr. 1. a. To cut into the surface of (glass, for example) by the action of acid. b. structures revealed that all four Y-blocks had spheroidized intercellular carbides in a predominantly ferritic matrix. A significant difference in the quantity of spheroidized carbides existed between the two groups. The Ce-treated Y-blocks (Samples 3 and 4) had less carbides than the normally treated Y-blocks. Figures 2b-e compare the etched microstructures and microporosity associated with the carbides. Conclusions Based on the statistical analysis, it was concluded that two major factors had negatively influenced the impact strength of the ductile iron Y-blocks. The first of these factors was a nonuniform distribution of the in-the-mold inoculant. Apparently, the first metal through the gating system received an extra amount of inoculant. A Y-block placed off the mold cavity, where the initial metal entering the cavity would fill it, was compared to a Y-block placed off the cavity at the top of the mold, which would fill last. Presumably pre·sum·a·ble adj. That can be presumed or taken for granted; reasonable as a supposition: presumable causes of the disaster. , the last metal was a more homogenous homogenous - homogeneous mixture of all the metal entering the cavity. The Y-block containing the initial metal had more Si and Al than the Y-block filled with the last metal. The influence of Mo was the second major factor. The microporosity from intercellular carbides, which can result from Mo (and probably other carbide-forming elements), also negatively influenced the impact strength. A multiple regression analysis revealed that none of the elements monitored in this investigation had a meaningful correlation with elongation. However, relatively good correlation was found when the C, Si and Ni considered together were compared to ultimate tensile strength, yield strength and impact strength. The regression formulae for all of the comparisons are shown in Table 2. Based on the results of the metallographic analysis, it was concluded that the difference in impact strength between Y-blocks cast without Ce and those cast with it was the consequence of a difference in the amount of intercellular spheroidized carbides. Cerium cerium (sēr`ēəm) [from the asteroid Ceres], metallic chemical element; symbol Ce; at. no. 58; at. wt. 140.12; m.p. 799°C;; b.p. 3,426°C;; sp. gr. 6.77 at 25°C;; valence +3 or +4. in ductile iron is known to reduce the effects of tramp elements. In this instance, the Ce in the inoculant effectively reduced the intercellular segregation segregation: see apartheid; integration. of tramp elements and reduced the formation of intercellular carbides. These carbides can reduce both fatigue and impact strength. Reducing the occurrence of these carbides can, as shown, improve the impact strength. This article was adapted from a paper (00-52) presented at the 2000 AFS A distributed file system for large, widely dispersed Unix and Windows networks from Transarc Corporation, now part of IBM. It is noted for its ease of administration and expandability and stems from Carnegie-Mellon's Andrew File System. AFS - Andrew File System Casting Congress and is available from the AFS Library at 800/537-4237.
Chemical Analysis and Mechanical
Properties of the Four Sample Groups
Element (%) Sample 1 Sample 2 Sample 3 Sample 4
C 3.75 3.71 3.79 3.75
Mn 0.19 0.19 0.15 0.15
P 0.009 0.009 0.007 0.008
S 0.008 0.007 0.010 0.007
Si 2.09 2.02 1.98 1.95
Cu 0.09 0.09 0.07 0.07
Ni 0.65 0.64 0.63 0.62
Cr 0.034 0.034 0.032 0.033
Mo 0.011 0.011 0.007 0.007
Al 0.011 0.011 0.009 0.009
Mg 0.06 0.06 0.05 0.049
Properties
Impact Strength
at -4F (-20C) (ft-lb) 9, 10, 9 10, 9, 10 12, 11, 12 12, 12, 12
Tensile Strength (ksi) 59.7 59.1 58.2 58.1
Yield Strength, 0.2%
Offset (ksi) 40.9 40.7 39.7 39.5
Elongation (%) 21 22 22 22
Regression Formulae for Correlation of
Elements Tested to Impact (ft-lb), Yield
(ksi) and Ultimate (ksi) Strength and
Elongation (%)
Dependent
Variable Constant C Mn P S Si
Impact: -2.557 3.237
12.359 -18.737
9.434 -22.445
9.848 -54.569
16.988 -3.663
11.714
11.852
14.586
11.127
10.886
7.784
3.836 3.659 -3.735
14.425 -3.925
-8.003 3.962
-2.805 4.627 -4.060
14.288 -2.135
17.449 1.381 -6.691 -4.059
-6.947 4.384
15.790 -3.706
Yield: 28.532 -2.827 11.305
Ultimate: 43.594 -1.145 10.391
Elongation: 27.478 -4.037
-4.391 6.966
-5.506 9.753 13.671 -3.281
27.904 -8.628
5.982 5.930 -3.447
1.099 5.368
27.508 -3.274
2.141 6.482 -3.824
15.588
19.183
16.773
22.289
19.583
16.536
25.371 -3.492
17.994 -3.865
16.028 203.240
15.728 13.357
-4.074 6.058
Dependent
Variable Cu Ni Cr Mo Al Mg
Impact:
-33.248
-3.730
-137.875
-233.023
-108.603
26.743
4.831
4,349
5.577
-3.578 -72.886 -141.319 -22.438
9.872 -4.579 1.637 -124.943 -12.612
3.998 -243.827 -21.443
12.954 3.554 -235.583
Yield: 1.288
Ultimate: 0.789
Elongation: 6.488 -4.513 183.891
-4.988 124.235 -46.571
2.534 5.080 -227.886 365.320 -26.525
-11.887 -3.088 -261.718 377.138 -35.255
-4.109
-4.023
44.685
-75.382
145.770
-11.330
-2.450
19.083
Dependent
Variable Correlation
Impact: 0.029
0.094
0.001
0.007
0.209
0.195
0.018
0.061
0.142
0.216
0.024
0.247
0.279
0.088
0.338
0.192
0.441
0.284
0.381
Yield: 0.673
Ultimate: 0.695
Elongation: 0.094
0.105
0.158
0.075
0.088
0.040
0.083
0.081
0.017
0.030
0.015
0.011
0.002
0.017
0.050
0.000
0.015
0.013
0.027
[Graph omitted] |
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