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Q & A
Q Since the mechanical properties of gray iron castings are directly related to the chemistry, is there a method to reliably predict their 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 ?
Background: Since the early 1950s, iron foundries have been using the McElwee-Schneidewind equation to predict the tensile strength of gray iron castings. However, the correlation between the actual and predicted tensile strength was not consistent, especially at the lower tensile strengths. AFS Research in 1992 concluded that: tensile strength is primarily related to graphite flake length; flake length is related to carbon equivalent, cooling rate and percent of alloying elements; and some alloying elements have a negative affect on pearlite pearl·ite
1. A mixture of ferrite and cementite forming distinct layers or bands in slowly cooled carbon steels.
2. Variant of perlite.
Noun 1. fineness and strength. This research produced a tensile strength equation that closely predicts the actual casting properties.
Recommendation: The new formula for predicting the tensile strength of gray iron is:
UTS (Universal Timesharing System) Amdahl's version of Unix System V. Release 4.0 is POSIX compliant. (ksi) = No. 1 x No. 2
where No.1 = 101.1193 - 20.3283 x [%total carbon + %silicon (Si)/4 + %phosphorous phos·pho·rous
Of, relating to, or containing phosphorus, especially with a valence of 3 or a valence lower than that of a comparable phosphoric compound. (P)/2] + 4.3887/cast bar radius;
No. 2 = 1.000 [+ or -] the following factors for alloying elements:
+ 0.1371 x %Si;
-0.0021 x [%manganese-1.7%sulfur(S)];
-0.3132 x %S;
+0.3562 x %chromium;
+ 0.0282 x %nickel;
+0.1107 x %copper;
+0.6297 x %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. ;
-5.2985 x %titanium;
-0.2305 x %tin.
The equation can be computerized and is useful for most fully pearlitic irons. Because the predicted and actual values are on parallel lines with this equation, even if they don't exactly coincide, a constant difference should be a useful indicator of iron consistency.
For additional information, see "Cast Facts: New Formula Equates Tensile Strength of Gray Iron, "modern casting, October 1992, p. 35; and "Composition, Section Size and Microstructural Effects on the Tensile Properties of Pearlitic Gray Cast Iron," AFS Research Report No. 5, Sept. 1991.
Q Is there a nondestructive non·de·struc·tive
Of, relating to, or being a process that does not result in damage to the material under investigation or testing.
non test available to evaluate the graphite structure in a 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. While most varieties of cast iron are brittle, ductile iron is much more ductile, as the name implies. casting?
Background: The current procedures for evaluating graphite nodularity verify a heat of metal prior to pouring but do not qualify a casting. With the industry moving toward more in-mold treatment, there is an increased need for a nondestructive testing method that can be used to verify casting graphite structure and correlate that to casting properties.
An AFS Research Project reported in the 1980 AFS Transactions examined the use of ultrasonic testing to measure the graphite structure and predict principal mechanical properties. According to this report, resonant frequency resonant frequency,
n the specific frequency at which an object vibrates. or ultrasonic velocity measurements can be used to predict the effect of small changes in graphite form on the tensile strength, offset yield strength and other properties of ductile iron castings of known similar matrix structure containing up to 70% non-nodular graphite. To make similar predictions where matrix structure also varies, measurement of eddy current, coercive force or hardness must be used in conjunction with either resonant frequency or ultrasonic velocity.
Recommendations: While the basic test is described above, considerable qualification is required. Although users of this technology have indicated that matrix variations do not influence the test results as significantly as variations in graphite structure, the influence is sufficient to require the use of standard test castings for each part number that is being produced. If the matrix is known to have 100% ferrite fer·rite
1. Any of a group of nonmetallic, ceramiclike, usually ferromagnetic compounds of ferric oxide with other oxides, especially such a compound characterized by extremely high electrical resistivity and used in computer memory or 100% pearlite, then the two nondestructive tests--ultrasonic velocity or resonant frequency--can be used without supplementing the testing. However, if carbides are present, the test results will be altered undesirably. Also, if the ferrite (or the pearlite) is in the structure as a result of heat treatment, the readings will not be the same as 100% ferrite (or 100% pearlite) produced as-cast.