A. The basic engineering alloys had numbers ranging from 200-900. All the even numbered alloys were solid solution alloys (hardenable only by cold work)

NICKEL 200/201 series

Alloy 400 series (400/R405)

Alloy 600 series (600/601/625/686)

Alloy 800 series (800/800H/800HT/802/803/825)

 

All of the odd numbers were the age-hardenable equivalents;

NICKEL series (301)

Alloy 500 series (K500)

Alloy 700 series (X750/718)

Alloy 900 series (903/907/909)

Over the years, a large number of proprietary alloys have been developed, which has resulted in a wide variety of classification. 
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2. Can Alloy 400 be magnetic?

A. Although this is a fully austenitic material, alloy 400 can still become magnetic, especially after cold work. The reason relates to the Curie temperature associated with the nickel-copper chemistry relationship.

Alloy K500 will remain totally non-magnetic at room temperature, since its Curie point for magnetic/non-magnetic response occurs at -100F(-73C) to -150F(-101C).

Alloy 400, depending upon its copper-nickel chemistry relationship could range from 30 to 70 F, and therefore could show a weak magnetic response. This could be further emphasized by cold work. If the magnetic structure is immersed in boiling water, all magnetic sensitivity will disappear. 
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3. Are nickel-base alloys subject to stress corrosion cracking?

A. As far as chloride stress corrosion cracking (SCC) is concerned, the high nickel contents of these materials make them immune to this particular form of stress corrosion.

However, the nickel base alloys are sensitive to other forms of environmental stress corrosion cracking.

Alloy 400 mercury; chromic acid; hydrofluoric acid vapors

Alloy 600 fused caustic

200/201 mercury; molten metals

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4. What alloys should be considered to overcome polythionic acid cracking?

A. Alloys 825 and alloy 801 are materials that resist this form of attack.

5. Can the nickel base alloys handle chlorine?

A. Yes, when it is dry chlorine. In fact, alloys 200/201 and alloys 600 offer the best resistance to high temperature chlorine atmospheres.

However, when environment involves wet chlorine and chlorine condensates, nickel base can be aggressively attacked. Those alloys with the highest molybdenum contents e.g. Alloy 625 and alloy C276 provide limited service in bleach plant washer service. Hastelloy alloy B, with 29% molybdenum, offers the best of the nickel-base alloys for handling wet chlorine environments.

General rule of thumb: Titanium for wet chlorine service; Nickel base alloys for dry chlorine service. 
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6. What is the difference between alloys 800, 800H and 800HT?

A. These alloys have the same chemistry, but by varying the aluminum and titanium ranges and controlling the carbon levels, different sets of properties can be realized.

Incoloy alloy 800 was approved by the ASME Boiler and Pressure Vessel committee in 1963. The alloy contained 0.15% aluminum and 0.60% titanium.

Two additional grades were developed as Grade I and Grade II, which were differentiated by final annealing practices of 1800F(982C) and 2100F(1149C), respectively. This created approved materials for service up to 1100F(593C) and 1500F(816C), respectively.

Grade I was renamed alloy 800H.

By controlling carbon levels in the range of 0.05-0.10% carbon, the Grade II material realizes grain sizes of 5 or greater, thereby improving stress rupture strengths.

With greater restriction of carbon (.06-0.10%) and aluminum and titanium combined (0.85-1.20%), higher maximum allowable stresses were recognized by the ASME Codes and a new alloy, alloy 800HT, was created. 
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7. What is the difference between mill annealed and solution annealed material?

A. They are both standard annealing practices, which place materials into their "soft" conditions.

The mill anneal is conducted at a lower temperature than the solution anneal e.g. 1950F(1066C) versus 2150F(1177C).

However, the solution anneal is high enough to redissolve all carbides and intermetallic phases and take them into solution while a mill anneal allows redistribution of carbides by diffusion. Also, holding for longer times at the higher temperatures can result in large grain and grain growth. 
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8. What is the difference between Nickel 200 and Nickel 201?