Volume 13 - Corrosion Part 7 pot

Fig. 74 Embrittlement of 4140 steel by various liquid metals below their melting point and their effects on normalized true fracture strength and reduction of area as a function of homologous temperature T H· T and T m are the test and melting temperatures of the liquid metal. Source: Ref 108 Although SMIE of metals has not been mentioned or recognized as an embrittlement phenomenon in industrial processes, many instances of loss in ductility, strength, and brittle fracture of metals and alloys have been reported for electroplated metals and coatings or inclusions of low-melting metals below their T m (Ref 109). Delayed failure of cadmium-plated high-strength steel has been observed below the T m of cadmium (Ref 110, 111). Accordingly, cadmium-plated steel bolts, despite their excellent resistance to corrosion, are not recommended for use above 230 °C (450 °F). Notched tensile specimens of various steels are embrittled by solid cadmium. Solid cadmium, silver, and gold embrittle titanium. Leaded steels are embrittled by solid lead, with considerable loss in ductility below the T m of lead; this phenomenon accounts for numerouselevated-temperature failures of leaded steels, such as radial cracking of gear teeth during induction-hardening heat treatment, fracture of steel shafts during straightening at elevated temperature, and heat treatment failure of jet- engine compressor disks. Liquid and solid cadmium metal environments, as well as cadmium dissolved in inert nonembrittling coolant liquid, serve to embrittle the Zircaloy-2 nuclear fuel cladding tubes used in nuclear reactors (Ref 112). Inconel vacuum seals are cracked by solid indium. These reports of brittle failure clearly indicate the importance of SMIE in industrial processes. Solid metal induced embrittlement was first recognized and investigated in the mid-1960s and early 1970s by studying the delayed failure of steels and titanium in a solid-cadmium environment (Ref 113, 114, 115). Results of these studies are shown in Fig. 75 and 76. A systematic investigation of SMIE of steel by a number of solid-metal embrittling species (Fig. 74) found that solid metal as an external environment can cause embrittlement and for steels represents a generalized phenomenon of embrittlement. Fig. 75 Crack depth as a function of exposure time to solid cadmium environment for various titanium alloys at three stress levels. STA, solution treated and aged; ST, solution treated; VAC STA, vacuum solution treated and aged; β A, β-annealed; A, annealed; MA, mill annealed. Source: Ref 111 Fig. 76 Crack morphology for Ti-6Al- 4V (solution treated and aged). (a) Typical specimen with multiple cracks in the indented area. (b) Fracture surface of (a) showing the depth of cadmium- induced cracking. (c) Cross section showing mixed intergranular cracking and cleavage in cadmium- induced crack. Etched with Kroll's reagent. (d) TEM fractograph (two-stage replica) of similar area showing intergra nular cracking and cleavage. Courtesy of D.A. Meyn Solid metal induced embrittlement can also occur when the embrittling solid is an internal environment, that is, present in the solid as an inclusion (Ref 108). It has been clearly demonstrated that internally leaded steel is embrittled below the T m of the lead inclusion of steel (Ref 108). Brittle fracture in LME and SMIE is of significant scientific interest because the embrittling species are in the vicinity of or at the tip of the crack and are not transported by dislocations or by slip due to plastic deformation into the solid, as is hydrogen in the hydrogen embrittlement of steels. Also, embrittling species are less likely to be influenced by the effects of grain-boundary impurities, such as antimony, phosphorus, and tin, which cause significant effects on the severity of hydrogen and temper embrittlement of metals. Investigations of SMIE and LME, therefore, can be interpreted less ambiguously than similar effects in other environments, such as hydrogen and temper embrittlement of metals. Thus, solid-liquid environmental effects provide a unique opportunity to study embrittlement mechanisms in a simple and direct manner under controlled conditions. It is conceivable that a common mechanism may underlie solid, liquid, and gas phase induced embrittlement. The interactions at the solid/environment interface and the transport of the embrittling species to the crack tip may characterize a specific embrittlement phenomenon. A study of SMIE and LME may provide insights into the mechanisms of hydrogen and temper embrittlement. It is apparent that the phenomenon of SMIE is of both industrial and scientific importance. A review of the investigations of the occurrence and mechanisms of SMIE follows. Characteristics of SMIE To date, SMIE has been observed only in those couples in which LME occurs, suggesting that LME is a prerequisite for the occurrence of SMIE. Solid metal induced embrittlement may occur in the absence of LME if a brittle crack cannot be initiated at the T m of the embrittler. A recent compilation of SMIE couples is given in Tables 6 and 7, which show that all solid-metal embrittlers are also known to cause LME. Table 6 Occurrence of SMIE in steels Onset of embrittlement Base metal Embrittler (melting point) °C °F Test type (b) Specimen type (c) 1041 Pb (327 °C, or 621 °F) 288 550 ST S 1041 leaded Pb 204 399 ST S 1095 ln (156 °C, or 313 °F) 100 212 ST S Sn (232 °C, or 450 °F) 204 399 ST N 3340 Pb 316 601 ST N 4130 Cd (321 °C, or 610 °F) 300 572 DF N Cd 300 572 DF N 4140 Pb 204 399 ST S Pb-Bi (NA) (a) Below solidus ST S Pb-Zn (NA) Below solidus ST S Zn (419 °C, or 786 °F) 254 489 DF N Sn 218 424 DF N Cd 188 370 DF N Pb 160 320 DF N ln Room temperature DF N Pb-Sn-Bi (NA) Below solidus ST S ln 80 176 DF S Sn 204 399 ST S Sn-Bi (NA) Below solidus ST S Sn-Sb (NA) Below solidus ST S ln 110 230 DF S ln 93 199 DF S ln-Sn (118 °C, or 244 °F) 93 199 DF S Sn 204 399 ST S ln 121 250 ST S Pb-4Sn (NA) 204 399 ST S Pb-Sn (NA) 204 399 ST S Pb-Sb (NA) 204 399 ST S 4145 Pb 288 550 ST S 4145 leaded Pb 204 399 ST S Cd 260 500 DF N Cd 300 572 DF N Cd 38 100 DF S 4340 Zn 400 752 DF N 4340M Cd 38 100 DF S 8620 Pb 288 550 ST S 8620 leaded Pb 204 399 ST S A-4 Pb 288 550 ST S A-4 leaded Pb 204 399 ST S D6ac Cd 149 300 DF N Courtesy of Dr. A. Druschitz (a) NA, data not available. (b) ST, standard tensile test; DF, delayed-failure tensile test. (c) S, smooth specimen; N, notched specimen. Table 7 Occurrence of SMIE in nonferrous alloys All test specimens were smooth type. Onset of embrittlement Base metal Embrittler (melting point) °C °F Test type (a) Cd (321 °C, or 610 °F) 38 100 DF Ti-6Al-4V Cd 149 300 BE Cd 38 100 DF Ti-8Al-1Mo-1V Cd 149 300 BE Ti-3Al-14V-11Cr Cd 149 300 BE Cd 149 300 BE Ag (961 °C, or 1762 °F) 204-232 399-450 BE Ti-6Al-6V-2Sn Au (1053 °C, or 1927 °F) 204-232 399-450 BE Cu-Bi (b) Hg (-39 °C, or -38 °F) -84 -119 ST Cu-Bi (c) Hg -87 -125 ST Cu-3Sn (c) Hg -48 -54 ST Cu-1Zn (c) Hg -46 -51 ST Tin bronze Pb (327 °C or 621 °F) 200 392 IM Zinc Hg -51 -60 ST Inconel ln (156 °C, or 313 °F) Room temperature RE Zircaloy-2 Cd 300 572 ST Courtesy of Dr. A Druschitz (a) DF, delayed-failure tensile test; BE, bend test; ST, standard tensile test; IM, impact tensile test; RE, residual stress test. (b) Heat treated to uniformly distribute solutes. (c) Heat treated to segregate solutes to grain boundaries. Solid metal induced embrittlement and liquid-metal embrittlement are strikingly similar phenomena. The prerequisites for SMIE are the same as those for LME: intimate contact between the solid and the embrittler, the presence of tensile stress, crack nucleation at the soli/embrittler interface from a barrier (such as a grain boundary), and the presence of embrittling species at the propagating crack tip. Also, metallurgical factors that increase brittleness in metals, such as grain size, strain rate, increases in yield strength, solute strengthening, and the presence of notches or stress raisers, all appear to increase embrittlement. The susceptibility to SMIE is stress and temperature sensitive and does not occur below a specific threshold value. Embrittlement by delayed failure is also observed for both LME and SMIE (Table 8). Table 8 Delayed failure in SMIE and LME systems Base metal Liquid Solid Type A behavior: delayed failure observed 4140 steel Li Cd 4340 steel Cd ln 4140 steel ln Cd 4140 steel . . . Pb 4140 steel . . . Sn 4140 steel . . . ln 4140 steel . . . Zn 2024 Al Hg . . . 2424 Al Hg-3Zn . . . 7075 Al Hg-3Zn . . . 5083 Al Hg-3Zn . . . Al-4Cu Hg-3Zn . . . Cu-2Be Hg . . . Cu-2Be Hg . . . Type B behavior: delayed failure not observed Zn Hg . . . Cd Hg . . . Cd Hg + ln . . . Ag Hg + ln . . . Al Hg . . . Courtesy of Dr. A. Druschitz Some differences also exist. Multiple cracks are formed in SMIE; in LME, a single crack usually propagates to failure. The fracture in SMIE is propagation controlled. However, crack propagation rates are at least two to three orders of magnitude slower than in LME. Brittle intergranular fracture changes to ductile shear because of the inability of the embrittler to keep up with the propagating crack tip. Incubation periods have been reported, indicating that the crack nucleation process may not be the same as in LME (Ref 116, 117, 118). Nucleation and propagation are two separate stages of fracture in SMIE. These differences may arise because of the rate of reaction or interactions at the metal/embrittler interface and because the transport properties of solid- and liquid-metal embrittlers are of significantly different magnitudes. It has been suggested that reductions in the cohesive strength of atomic bonds at the tip are responsible for both SMIE and LME (Ref 109, 116, 117, 119, 120). However, transport of the embrittler is the rate-controlling factor in SMIE. Another possibility is that stress-assisted penetration of the embrittler in the grain boundaries initiates cracking, but surface self-diffusion of the embrittling species similar to that proposed for LME controls crack propagation. Investigations of SMIE The first investigations of delayed failure were reported in cadmium-, zinc-, and indium-plated tensile specimens of 4340, 4130, 4140, and 18% Ni maraging steel in the temperature range of 200 to 300 °C (390 to 570 °F), as shown in Fig. 77 and 78. The results indicated that 4340 was the most susceptible and that 18% Ni maraging steel was the least susceptible alloy to cadmium embrittlement. The activation energy for steel-cadmium embrittlement was 39 kcal/mol (Fig. 79), which corresponded to diffusion of cadmium in the grain boundary. A thin plated layer of nickel or copper has been reported to act as a barrier to the embrittler and to prevent SMIE of steel (Ref 110). Solid indium is reported to embrittle steels (Ref 117, 118), and an incubation period exists for crack nucleation. Fig. 77 Embrittlement behavior of cadmium- plated 4340 steel. Specimens were tested in delayed failure at 300 °C (570 °F) and unplated steel in air at 300 °C (570 °F). Source: Ref 110 Fig. 78 Embrittlement behavior of cadmium-plated 4340 steel. Specimens were teste d in delayed failure at temperatures ranging from 360 to 230 °C (680 to 445 °F). Source: Ref 110 [...]... calculated vapor-transport times at the embrittler-melting temperatures Embrittler Vapor pressure Time, s Pa torr Zn 20 1.5 × 1 0-1 5 × 1 0-3 Cd 10 7. 5 × 1 0-2 1 × 1 0-2 Hg(a) 0.3 2.25 × 1 0-3 3 × 1 0-1 Sb 4 × 1 0-4 3.0 × 1 0-6 3 × 102 K 1 × 1 0-4 7. 5 × 1 0 -7 1 × 103 Na 2 × 1 0-5 1.5 × 1 0 -7 5 × 103 Ti 4 × 1 0-6 3.0 × 1 0-8 3 × 104 Pb 5 × 1 0 -7 3 .75 × 1 0-9 2 × 105 Bi 2 × 1 0-8 1.5 × 1 0-1 0 5 × 106 Li 2 × 1 0-8 1.5 × 1 0-1 0 5 ×... S.P Clough, and L.A Heldt, Metall, Trans A, Vol 7A, 1 976 , p 1241; Metall Trans A, 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 Vol 6A, 1 975 , p 1 479 A.J Forty, Physical Metallurgy of Stress Corrosion Fracture, T.N Rhodin, Ed., Interscience, 1959, p 99 K Sieradzki and R.C Newman, Philos Mag A, Vol 51 (No 1), 1985, p 95 I.-H Lin and R.M Thomson, J Mater Res., Vol 1 (No... 2,611 3.6 2 ,76 5 3 .7 Tin free steel 889 1.2 945 1.3 Tin mill products all other 58 0.1 66 0.1 hot rolled 12,952 17. 7 13, 133 17. 8 cold rolled 13, 574 18.6 13, 664 18.5 hot dipped 6,850 9.4 6,100 8.3 electrolytic 6 97 0.9 659 0.9 all other metallic coated 1,122 1.5 1,109 1.5 electrical 413 0.6 490 0 .7 hot rolled 586 0.8 650 0.9 cold rolled 876 1.2 1,002 1.3 Total steel mil products 73 ,043 100.0 73 ,73 9 100.0... equipment 1,215 1 .7 1,339 1.8 Cans and closures 3044 4.2 3268 4.4 Barrels, drums, and shipping pails 465 0.6 5 07 0 .7 All other 580 0.8 577 0.8 Total 4,089 5.6 4,352 5.9 2 67 0.4 242 0.3 Agricultural Containers, packaging and shipping materials Ordnance and other military Export (reporting companies only) 494 0 .7 428 0.6 Nonclassified shipments 7, 7 67 10.6 7, 8 07 10.6 Total shipments 73 ,043 100.0 73 ,73 9 100.0... 1963, p 2 47 A.J McEvily and P.A Bond, J Electrochem Soc., Vol 112, 1965, p 141 E.N Pugh, in Stress Corrosion Cracking and Hydrogen Embrittlement of Iron Based Alloys, National Association of Corrosion Engineers, 1 977 , p 37 J.A Beavers, I.C Rosenberg, and E.N Pugh, in Proceedings of the 1 972 Tri-Service Conference on Corrosion, MCIC -7 3-1 9, Metals and Ceramics Information Center, 1 972 , p 57 T.R Pinchback,... maintenance 7, 900 10.8 7, 522 10.2 Contractors' products 3,330 4.6 2,631 3.6 Total 11,230 15.4 10,153 13. 8 Vehicles, parts, etc 12,689 17. 3 12, 571 17. 1 Independent forgers 261 0.4 311 0.4 Total 12,950 17. 7 12,882 17. 5 280 0.4 3 47 0.4 Automotive Rail transportation Freight cars, passenger cars, and locomotives Rails and all other 78 1 1.0 1,091 1.5 Total 1,061 1.4 1,438 1.9 Shipbuilding and marine equipment 3 37. .. Corrosion, Vol 29, 1 973 , p 19 2-1 96 112 W.T Grubb, Cadmium Metal Embrittlement of Zircaloy, Nature, Vol 265, 1 977 , p 3 6-3 7 113 Y Iwata, Y Asayama, and A Sakamoto, Delayed Failure of Cadmium Plated Steels at Elevated Temperature, J Jpn Inst Met., Vol 31, 19 67, p 73 (in Japanese) 114 D.N Fager and W.F Spurr, Solid Cadmium Embrittlement in Steel Alloys, Corrosion, Vol 27, 1 971 , p 72 115 D.N Fager and W... Embrittlement of Titanium Alloys, Corrosion, Vol 26, 1 970 , p 409 116 P Gordon, Metal Induced Embrittlement of Metals An Evaluation of Embrittler Transport Mechanisms, Metall Trans A, Vol 9, 1 978 , p 26 7- 2 72 1 17 P Gordon and H.H An, The Mechanisms of Crack Initiation and Crack Propagation in Metal-Induced Embrittlement of Metals, Metall Trans A, Vol 13A, 1982, p 45 7- 4 72 118 A Druschitz and P Gordon, Solid... 1,329 1.8 1,184 1.6 reinforcing 4,326 5.9 4,432 6.0 cold finished 1,255 1 .7 1,484 2.0 60 0.1 61 0.1 standard 855 1.1 74 3 1.0 oil country goods 1,299 1.8 1,406 1.9 line 77 5 1.1 77 5 1.0 mechanical 812 1.1 940 1.3 pressure 87 0.1 89 0.1 structural 219 0.3 270 0.4 stainless 49 0.1 52 0.1 drawn 874 1.2 963 1.3 nails and staples 170 0.2 1 47 0.2 Bars Tool steel Pipe and tubing Wire barbed and twisted 38 0.1 52... Organization, 1 971 J.C Scully, Corros Sci., Vol 15, 1 975 , p 2 07 D.A Vermilyea, J Electrochem Soc., Vol 119, 1 972 , p 405 D.A Vermilyea, Stress Corrosion Cracking and Hydrogen Embrittlement of Iron Based Alloys, National Association of Corrosion Engineers, 1 977 , p 208 R.W Staehle, in The Theory of Stress Corrosion Cracking in Alloys, North Atlantic Treaty Organization, 1 971 , p 233 R.W Staehle, Stress Corrosion . 19 27 °F) 20 4-2 32 39 9-4 50 BE Cu-Bi (b) Hg (-3 9 °C, or -3 8 °F) -8 4 -1 19 ST Cu-Bi (c) Hg -8 7 -1 25 ST Cu-3Sn (c) Hg -4 8 -5 4 ST Cu-1Zn (c) Hg -4 6 -5 1 ST Tin bronze Pb (3 27 °C. 10 -1 5 × 10 -3 Cd 10 7. 5 × 10 -2 1 × 10 -2 Hg (a) 0.3 2.25 × 10 -3 3 × 10 -1 Sb 4 × 10 -4 3.0 × 10 -6 3 × 10 2 K 1 × 10 -4 7. 5 × 10 -7 1 × 10 3 Na 2 × 10 -5 1.5 × 10 -7 . DF Ti-6Al-4V Cd 149 300 BE Cd 38 100 DF Ti-8Al-1Mo-1V Cd 149 300 BE Ti-3Al-14V-11Cr Cd 149 300 BE Cd 149 300 BE Ag (961 °C, or 176 2 °F) 20 4-2 32 39 9-4 50 BE Ti-6Al-6V-2Sn