Documents

01 - Properties and Selection Irons Steels and High Performance Alloys.docx

Categories
Published
of 2
All materials on our website are shared by users. If you have any questions about copyright issues, please report us to resolve them. We are always happy to assist you.
Related Documents
Share
Description
Fig. 7 Mechanical properties of class 30 and class 50 gray iron as a function of section size. Composition of the class 30 iron: 3.40% C, 2.38% Si, 0.71% Mn, 0.423% P, and 0.152% S; for the class 50 iron: 2.96% C, 1.63% Si, 1.05% Mn, 0.67% Mo, 0.114% P, and 0.072% S. Source: Ref 4 The hazards involved in pouring a given class of gray iron in a plate section thinner than recommended are discovered when the casting is machined. Typical losses as a result of specifying too h
Transcript
    Fig. 7 Mechanical properties of class 30 and class 50 gray iron as a function of section size. Composition of the class 30 iron: 3.40% C, 2.38% Si, 0.71% Mn, 0.423% P, and 0.152% S; for the class 50 iron: 2.96% C, 1.63% Si, 1.05% Mn, 0.67% Mo, 0.114% P, and 0.072% S. Source: Ref 4 The hazards involved in pouring a given class of gray iron in a plate section thinner than recommended are di s covered when the casting is machined. Typical losses as a result of specifying too high a strength for a prevailing section of 9.5 mm C   3   8   in.) are given below Crejections were for hard spots that made it impossible to machine the castings by normalmethods): class   Rejections, % 35 Negllglble   45 25      55 80-100   In marginal applicat i on s ,  a higher class of iron may sometimes be used if the casting is cooled slowly Cin effect, increasing the section thickness) by judicious placement of flow-offs and risers. An example is the successful productio n of a 25 mm C1 in.) diam single-throw crankshaft for an air compressor. This shaft was hard at the extreme ends when poured in class 50 iron. The difficulty was corrected by flowing metal through each end into flow-off risers tha t adequately balanced the cooling rate at the ends with the cooling rate at the center. In sum, the selection of a suitable grade of gray iron for a specific casting necessarily requires an evaluation of the size and shape of the cas t i ng   as related to its cooling rate, or volumelarea ratio. For a majority of part s ,   this evaluat i on   need be no more than a determination of whether or not the VIA ratio of the casting exceeds the minimum VIA ratio i ndicated  for the grade considered. Reference cited in this section   4. R.A. Flinn and R.W. Kraft, I mprov e d   Test Bars for Standard and Ductile Grades of Cast Iron, Trans. AFS,   Vol 58, 1950, p 153-167 Test Bar Properties   Mechanical property values obtained from test bars are sometimes the only available guides to the mechanical propertie s of the metal in production cas t i ng s .   When test bars and castings are poured from metal of the same chem i cal  history, correlations can be drawn between the thermal history of the casting and that of the test bar. The strength of the test bar gives a relative strength of the casting, corrected for the cooling rate of the various section th i ckness .   T hrough   car e fu l analysis of the critical sections of a casting, accurate predictions of mechanical behavior can be ach i e ved.   Usual Tests. T en s i on   and transverse tests on bars that are cast specifically for such tests are the most common method s used for evaluating the strength of gray ir o n.  Yield strength, elongation, and reduction of area are seldom determined for gray iron in standard tension te s t s .   T h e transverse test measures strength in bending and has the additional advantage that a deflection value may be obtain ed readily. Minimum specification values are given in Table 5. Data can usually be obtained faster from the transverse t es t than from the tension test because machining of the specimen is unnece ss ary .   The surface condition of the bar will affec t the transverse test but not the tension test made on a machined specimen. Conversely, the presence of coarse graphite in the center of the bar, which can occur in an iron that is very section sensitive, will affect the tension test but not th e transverse t e s t.   Table 5 Transverse breaking loads of gray irons tested per ASTM A 438   ASTM class (a)   Approxlmate tenslle strength   Corrected transverse breaking load Ca)   A bar (b)   B bar (c)   C bar Cd)   Mpa   ksl   kg   lb   kg   lb   kg   lb 20 138 20 408 900 816 1800 2720 6,000   25 172 25 465 1025 907 2000 3080 6,800   30 207 30 522 1150 998 2200 3450 7,600  

Unc Shuffle

Jul 23, 2017

Revenue Management

Jul 23, 2017
Search
Tags
Related Search
We Need Your Support
Thank you for visiting our website and your interest in our free products and services. We are nonprofit website to share and download documents. To the running of this website, we need your help to support us.

Thanks to everyone for your continued support.

No, Thanks