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Type of graphite Total carbon, % Resistance to scuffing(a) Sleeve wear, mm/1000 h (in./1000 h) Ring wear (gap increase), mm/1000 h (in./1000 h) 2 100% type D 3.10−3.40 1.11 0.075 (0.003) 0.050 (0.002) 4 Type A, size 4 to 6, some type B 3.25−3.50 1.30 0.050 (0.002) 0.685 (0.027) 5 Type A, size 3 to 4, some type C 4.00 1.45 0.090 (0.0035) 2.15 (0.085) (a) See Table 17 Effect of Graphite Structure. It was concluded from the above tests that graphite produces a surface-roughening effect, which accounts for both the greater scuff resistance and the higher ring wear as the size and quantity of graphite are increased. In testing type D graphite sleeves with the rougher finish previously mentioned, improved scuff resistance was also obtained, but at the expense of greater ring wear, apparently from cutting. The larger quantity of graphite in test 5 leaves less load-carrying metal surface, and greater normal wear on the sleeve is the logical result. The relatively high sleeve wear in test 2 was probably caused by slight scuffing, which gave high wear values for some sleeves tested, presumably because of the low safety margin of scuff resistance in this type of iron. Surprisingly, this mild scuffing did not seem to affect the chromium-plated rings, which apparently wore less severely in the presence of fine graphite. The plain gray iron oil-control rings, however, wore more in test 2 than in test 4. The principal effect of graphite on wear resistance is the elimination of scuffing, and when graphite is present in greater quantity and size than required for this purpose, it will reduce resistance to normal wear unnecessarily. Effect of Matrix Microstructure. Gray iron is used for wear resistance in both the as-cast and hardened conditions. To show the effects of some of the matrix variations on wear resistance, comparable engine wear tests were made on seven types of gray iron cylinders, all of which apparently wore in a normal manner. These data are summarized in Tables 21 and 22 . Table 21 Effect of matrix microstructure on resistance of gray iron to normal wear Rate of wear 2 3.08 0.68 2.34 0.45 0.56 0.22 ... 0.110 0.033 3 3.43 0.73 2.28 0.44 0.09 ... 1.29 0.143 0.068 Type A fine graphite(c) 1 3.38 0.61 1.99 0.45 0.59 ... 1.63 ... ... 2 3.28 0.70 2.46 0.24 0.27 ... 0.94 0.23 0.068 3(b) 3.35 0.70 2.20 0.35 0.12 ... 1.15 0.12 0.09 4 3.28 0.67 2.08 ... ... ... 0.40 0.125 0.067 5 3.12 0.35 2.67 0.38 0.27 0.11 1.23 0.176 0.047 Type A coarse graphite(d) 1 4.00 0.77 1.54 ... 1.39 0.42 ... 0.056 0.023 (a) Corresponds to test 2 in Table 17 . (b) Typical composition. (c) Corresponds to tests 3 and 4 in Table 17 . (d) Corresponds to test 5 in Table 17 Surface finish effects were determined by running similar tests on cylinder sleeves with honed finishes of 0.75 and 2.3 µm (30 and 90 µin.) rms. In each, the sleeves were made from type D graphite iron, hardened, and tempered at 205 °C (400 °F). The coarser finish gave about 20% greater scuff resistance; however, this effect was lost if the finish became finer under normal operating conditions. The loss of scuff resistance by the smoothing effect of normal wear may account for some of the failures that occur in certain applications after break-in has apparently been successful. Other important factors affecting scuff resistance are the material and finish of the mating part and the type of lubricant used. Resistance to Normal Wear The scuff resistance described above should not be used as a basis for selecting a material that must resist normal wear. Resistance to normal wear, like resistance to scuffing, is affected by both graphite form and matrix microstructure (and possibly by the composition of the iron), but in a different manner. Some of the same sleeve materials involved in the scuff tests were operated under conditions that produced normal wear with very little evidence of scuffing. Tests were run for approximately 1000 h using chromium-plated compression rings on the pistons. All sleeves were hardened and tempered at 205 °C (400 °F). Results are given in Table 20 . Each of the three sleeve materials performed best when different types of wear were considered: the material in No. 2 test gave the lowest ring wear; in No. 4, the lowest sleeve wear; and in No. 5, the greatest resistance to scuffing. Thus, the choice of optimum sleeve material is a compromise. Table 20 Effect of type of graphite on wear resistance Test No.(a) Type of graphite Total carbon, % Resistance to scuffing(a) Sleeve wear, mm/1000 h (in./1000 h) Ring wear (gap increase), mm/1000 h (in./1000 h) 2 100% type D 3.10−3.40 1.11 0.075 (0.003) 0.050 (0.002) 4 Type A, size 4 to 6, some type B 3.25−3.50 1.30 0.050 (0.002) 0.685 (0.027) 5 Type A, size 3 to 4, some type C 4.00 1.45 0.090 (0.0035) 2.15 (0.085) (a) See Table 17 Effect of Graphite Structure. It was concluded from the above tests that graphite produces a surface-roughening effect, which accounts for both the greater scuff resistance and the higher ring wear as the size and quantity of graphite are increased. In testing type D graphite sleeves with the rougher finish previously mentioned, improved scuff resistance was also obtained, but at the expense of greater ring wear, apparently from cutting. The larger quantity of graphite in test 5 leaves less load-carrying metal surface, and greater normal wear on the sleeve is the logical result. The relatively high sleeve wear in test 2 was probably caused by slight scuffing, which gave high wear values for some sleeves tested, presumably because of the low safety margin of scuff resistance in this type of iron. Surprisingly, this mild scuffing did not seem to affect the chromium-plated rings, which apparently wore less severely in the presence of fine graphite. The plain gray iron oil-control rings, however, wore more in test 2 than in test 4. The principal effect of graphite on wear resistance is the elimination of scuffing, and when graphite is present in greater quantity and size than required for this purpose, it will reduce resistance to normal wear unnecessarily. Effect of Matrix Microstructure. Gray iron is used for wear resistance in both the as-cast and hardened conditions. To show the effects of some of the matrix variations on wear resistance, comparable engine wear tests were made on seven types of gray iron cylinders, all of which apparently wore in a normal manner. These data are summarized in Tables 21 and 22 . Table 21 Effect of matrix microstructure on resistance of gray iron to normal wear Rate of wear ASM Handbook,Volume 1 Gray Iron 01 Sep 2005 Copyright ASM International. All Rights Reserved. Page 53 Iron(a) No. of tests Type and size of graphite Matrix mm/1000 h in./1000 h A 28 A, size 3 to 4 Lamellar pearlite 0.14 0.0057 B 19 A, size 4 Lamellar pearlite plus phosphide 0.03 0.0012 C 4 A, size 5 to 6 Fine lamellar pearlite 0.022 0.0009 D 6 A, size 7 to 8 Very fine lamellar pearlite plus undetermined constituent 0.025 0.00097 E 30 A, size 5 to 6 Same as iron D 0.016 0.00062 F 3 A, size 3 to 4 Lamellar pearlite plus ferrite 0.050 0.002 G 2 Not shown Martensite 0.012 0.00048 (a) Compositions are given in Table 22 . Table 22 Compositions of irons reported in Table 21 Iron Composition, % TC Mn Si Cr Mo P S Others A 3.00−3.30 0.90−1.10 1.15−1.35 ... ... 0.20 max 0.12 max 0.80−1.10 Cu B 3.40 max 0.90 max 1.50 max ... ... 0.35−0.50 0.13 max ... C 2.85−3.30 1.00 max 1.25−1.75 0.30−0.40 0.25−0.35 0.20 max 0.12 max 1.00−1.50 Ni D 2.80−3.10 0.80 max 4.6−5.0 1.90−2.20 ... 0.20 max 0.12 max ... E 3.10−3.40 0.80−1.00 3.30−3.70 1.20−1.50 ... 0.40 max 0.12 max ... F 3.30−3.40 0.90−1.10 1.75−2.00 ... 0.40−0.50 0.20 max 0.12 max ... G 3.00−3.20 0.90−1.10 1.15−1.35 ... ... 0.20 max 0.12 max ... By present standards, hardening is the process that can produce the most significant
