The Nickel-Chromium-Molybdenum Alloys

Hastelloy alloy C-2000 is a trademark of Haynes International. It is one of the nickel-chromium-molybdenum alloys. The chemical composition is shown in Table 15.14. 

The nickel-chromium-molybdenum alloys also show higher resistance to uncontaminated HCl. For example, alloys C-276, 625, and C-22 show very good resistance to dilute HCl at elevated temperatures and to a wide range of HCl concentrations at ambient temperature. The... 

Nickel-chromium-molybdenum alloys are used in reactor vessels in the production of acetic acid. These alloys are cost-effective compared to Ni-Cr stainless steels and have good resistance to oxidizing corrosive media Ni-Mo alloys have good resistance to reducing media. Molybdenum together with the chromium stabilizes the passive film in the presence of chlorides and is particularly effective in increasing resistance to pitting and crevice corrosion. 

Figure 6.5 illustrates how the presence of an oxidizing agent affects the observed polarization behavior of a metal. It shows the polarization curves of a nickel-chromium-molybdenum alloy in sulfuric acid, with and without ferric sulfate added... 

Nickel-copper and nickel-chromium-molybdenum alloys are the nickel-base alloys that are t5fpically used in seawater. The nickel-copper alloys have good corrosion resistance in high velocity seawater, but do exhibit localized corrosion in quiescent seawater [79]. Alloy 625, a nickel-chromium-molybdenum alloy, is susceptible to crevice corrosion in both quiescent and flow conditions [97-700]. Other nickel-chromium-molybdenum alloys, such as Alloys C-276, C-22, 59 and 686 have increased seawater crevice corrosion resistance as compared to Alloy 625 [97,98],... 

Nickel-chromium-molybdenum alloys offer excellent corrosion resistance and good mechanical properties over a wide range of enviromnents and temperatures. CW2M, ffie cast version of Hastelloy C, is the workhorse of the group. Castings should not be called "Hastelloy." The properties of the different Hastelloy alloys vary widely in specific applications. Disaster can result from use of the wrong grade. 

The stainless steels (types 303, 316, and 316LVM) as well as the cobalt-nickel-chromium-molybdenum alloy MP35N are protected from corrosion by a thin passivation layer that develops when exposed to atmospheric oxygen and which forms a barrier to further reaction. In the case of stainless steel, this layer consists of iron oxides, iron hydroxides, and chromium oxides. These metals inject charge by reversible oxidation and reduction of the passivation layers. A possible problem with these metals is that if the electrode potential becomes too positive... 

Alloying elements such as nickel, chromium, molybdenum, and copper, which may be introduced with scrap, can increase the hardenability, although only slightly, because the concentrations are ordinarily low. However, the heat-treating characteristics may change, and for appHcations in which ductihty is important, as in low carbon steels for deep drawing, the increased hardness and lower ductiHty imparted by these elements may be harmful. 

Low-carbon, low-alloy steels are in widespread use for fabrication-welded and forged-pressure vessels. The carbon content of these steels is usually below 0.2%, and the alloying elements that do not exceed 12% are nickel, chromium, molybdenum, vanadium, boron and copper. The principal applications of these steels are given in Table 3.8. 

Steel is essentially iron with a small amount of carbon. Additional elements are present in small quantities. Contaminants such as sulfur and phosphorus are tolerated at varying levels, depending on the use to which the steel is to be put. Since they are present in the raw material from which the steel is made it is not economic to remove them. Alloying elements such as manganese, silicon, nickel, chromium, molybdenum and vanadium are present at specified levels to improve physical properties such as toughness or corrosion resistance. 

The trade name Hastelloy covers a range of nickel, chromium, molybdenum, iron alloys that were developed for corrosion resistance to strong mineral acids, particularly HC1. The corrosion resistance, and use, of the two main grades, Hastelloy B (65 per cent Ni, 28 per cent Mo, 6 per cent Fe) and Hastelloy C (54 per cent Ni, 17 per cent Mo, 15 per cent Cr, 5 per cent Fe), are discussed in papers by Weisert (1952a,b). 

Normally a steel is considered in tins category if it has a yield strength of 160,000 psi or more. The first of these steels to be produced was a chromium-molybdenum alloy steel, shortly followed by a stronger chromium-nickel-moly bdenum grade. 

Most modern industrial materials are designed to be passive i.e., covered by an adherent, chemically inert, and pore-free oxide that is highly insoluble in aqueous solutions and hence dissolves at an extremely slow rate. Examples would be modern stainless steels, nickel-chromium-molybdenum, and titanium alloys. The concept of passivity is often defined by reference to the polarization curve for metals and alloys in aggressive acidic solutions, Fig. 22. This curve defines the potential regions within which the alloy would be expected to corrode actively or passively. 

The trade name Hastelloy covers a range of nickel, chromium, molybdenum iron alloys that were developed for corrosion resistance to strong mineral acids. 

INMETCO s High Temperature Metals Recovery process reclaims the nickel, chromium, iron, molybdenum and cobalt fi om the secondary wastes indicated above and produces a remelt alloy in cast pig form, weighing 25-30 pounds. The remelt alloy is shipped to most of the stainless steel manufacturers in the United States, as well as certain other international companies, for use as raw material feedstock in the production of more stainless steel. As an ISO 9002 certified facility, INMETCO, a fully permitted facility, is the only High Temperature Metals Recovery facility in North America dedicated to the recovery of nickel, chromium, iron and molybdenum from both hazardous and non-hazardous wastes. 

Elements, which usually originate from alloyed steel scrap and non-ferrous metals in the steel charge, of the type which can be added to steels as alloying elements. They include nickel, chromium, molybdenum, copper, niobium and vanadium. Residual elements... 

Put] Putman, J.W., Grant, N.J., Bloom, D.S., a Phase in Chromium-Molybdenum Alloys with Iron or Nickel in Symposium on the Nature, Occurrence, and Effects of Sigma Phase , American Society for Testing Materials, Philadelphia, PA, 61-68 (1950) (Morphology, Phase Diagram, Experimental, 6)... 

Metals are used in the cardiovascular area including heart valves, heart pacemaker leads, and heart pacemaker cases. These metals include titanium, titanium aUojrs, cobalt-chromium alloys, and cobalt-nickel alloys. Metals used for aneurism clips include cobalt-chromium-molybdenum alloys, cobalt-nickel-chromium-molybdenum allojfs, and, previously, stainless steels were used. Metal seeds are used for fractionated hyperthermia treatment of prostate disease, and corrosion analysis showed the alloy, PdCo may be suitable for the seed implants [52],... 

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