Nickel boundaries

A finite-element thermal-stress model of continuous casting mold is conducted to predict deformation of copper plates and its change with different cooling structure. The results show that deformation behavior of copper plates is mainly governed by cooling structure and thermal-mechanical conditions, deformation amount is related to structure geometry, and a small deformation mutation occurs in cooper-nickel boundary due to different properties. The maximum deformation of hot surface centricities of wide face locate at 100 mm below meniscus and that of narrow face locate at meniscus and terminal of water slots and sigiiiiicant curvature fluctuations on both sides of copper-nickel boundary. The maximum deformation of centricities is increased up to 0.05 mm with thickness increment 5 mm of copper plates, and maximum deformations are only depressed 0.01 mm and 0.02 mm with increments of 1 mm nickel layer thickness and 2 mm water slot depth respectively. 

The effect of thickness of mold copper plates on deformation of hot surface centricities is shown in Figure 3. The maximum occurs in position 100 mm below meniscus in wide face, while two peaks appear in narrow face including not only below meniscus, but also at copper-nickel boundary. The deformation is increased with thickness of copper plates and greater thickness leads to significant increment. The maximum deformations are promoted 0.03 mm and 0.06 mm in wide face and 0.03 mm and 0.05 mm in narrow face when thickness of copper plates is increased from 30 mm to 35 mm and from 45 mm to 50 mm, reqtectively. The high profile curvature in meniscus and near water slot terminals reveals that primary cooling and heat flux have greater impact on deformation of copper plates. However, property difference of copper and nickel has little effeet on deformation, and a small protrusion appears at copper-nickel boundary with thin eopper plates and oiily becomes apparent with thickness of 45 mm or more. 

The nickel layer is too thin to affect deformation significantly, and almost no impact on wide face. The maximum decline of 0.01 mm with thickness increment 1 mm appears in narrow face adjacent to copper-nickel boundary. 

Fig. 5. Metastable Fe—Ni—Cr "temary"-pliase diagram where C content is 0.1 wt % and for alloys cooled rapidly from 1000°C showing the locations of austenitic, duplex, ferritic, and martensitic stainless steels with respect to the metastable-phase boundaries. For carbon contents higher than 0.1 wt %, martensite lines occur at lower ahoy contents (43). A is duplex stainless steel, eg. Type 329, 327 B, ferritic stainless steels, eg. Type 446 C, 5 ferrite + martensite D, martensitic stainless steels, eg. Type 410 E, ferrite + martensite F, ferrite + pearlite G, high nickel ahoys, eg, ahoy 800 H,...

Yttrium, on the otlrer hand, which has a larger cation radius than Cr +, appears to affect the grain boundary cation diffusion and not the volume diffusion of Ni +. The effects of the addition of small amounts of yttrium to nickel is to decrease dre rate of tire low temperamre grain-boundary dominated oxidation kinetics. 

Another type of nickel alloy with which problems of intergranular corrosion may be encountered is that based on Ni-Cr-Mo containing about 15% Cr and 15% Mo. In this type of alloy the nature of the grain boundary precipitation responsible for the phenomenon is more complex than in Ni-Cr-Fe alloys, and the precipitates that may form during unfavourable heat treatment are not confined to carbides but include at least one inter-metallic phase in addition. The phenomenon has been extensively studied in recent years . The grain boundary precipitates responsible are molybdenum-rich M C carbide and non-stoichiometric intermetallic ix... 

As with alloys of other metals, nickel alloys may suffer stress-corrosion cracking in certain corrosive environments, although the number of alloy environment combinations in which nickel alloys have been reported to undergo cracking is relatively small. In addition, intergranular attack due to grain boundary precipitates may be intensified by tensile stress in the metal in certain environments and develop into cracking. Table 4.28 lists the major circumstances in which stress corrosion or stress-assisted corrosion of nickel and its alloys have been recorded in service and also shows the preventive and remedial measures that have been adopted, usually with success, in each case. 

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