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BASIC METALLURGY AND TECHNICAL INFORMATION FOR SERIES 4000

Model 4000 is made of cast iron (ASTM A126 Class B, standard grey iron). Model 4000D is made of ductile iron (ASTM 536, grade 65-45-12).  Model 4001 is made of stainless steel (ASTM A351 CF8M).

	Minimum Tensile Strength	Minimum Yield Point	Minimum Elongation
Grey Iron A126 Class B	31,000 psi	--	0.1%
Ductile Iron A536 Grade 65-45-12	65,000 psi	45,000 psi	12%
Carbon Steel A216 WCB	70,000 psi	30,000 psi	22%
304 Stainless Steel A-351 CF8	70,000 psi	28,000 psi	35%
316 Stainless Steel A-351 CF8M	70,000 psi	30,000 psi	30%

100% pure iron is never used as a cast metal because it is too soft and weak. When carbon is added, hardness and strength appear. When approximately 0.3% carbon is added, the resulting alloy is steel. Steel is a strong but difficult ferrous metal to manufacture from a production standpoint. Adding more carbon (up to about 2%) creates even more production problems. These "semi-steels" are seldom used.

When more carbon is added (between 2% and 3%), white iron is formed. White iron is true cast iron and is easy to produce. The problem with white iron is that it is very brittle because the carbon exists as iron carbide instead of pure carbon. Iron carbide (Fe3C) is a hard and brittle compound sometimes referred to as cementite. If white iron is subjected to a lengthy heat treatment, the Fe3C decomposes into iron and nodules of graphite. The end product is malleable iron.

When approximately 3.5% carbon is added, Fe3C exceeds its solubility in solid iron (the Fe3C is fully absorbed in the iron until there is no room left. The excess Fe3C is dispersed as graphite flakes). The result is grey iron. Grey iron (standard cast iron) delivers only moderate strength with almost no elongation because the excess Fe3C flakes act as stress raisers (they make cast iron easy to crack). Since grey iron is so economical to produce, its use has been widespread for centuries.

Cast Iron with spheroidal graphite (ductile iron) was first produced in 1948. Its chemical composition and percent of carbon is about the same as grey iron. The transformation to ductile iron occurs when molten grey iron is treated with magnesium. The insertion of magnesium into the pouring ladle (the process is called inoculation) transforms the Fe3C flakes into spheroids. These spheroids strengthen the metal by acting as crack arresters instead of crack assistors. Ductile iron is sometimes referred to as spheroidal or nodular iron.

65-45-12 ductile iron is named for its physical properties (65,000 psi tensile strength, 45,000 psi yield, 12% elongation). Ductile iron chemically can be manufactured as Ferritic or Pearlitic. In Ferritic mixes, the graphite spheroids are in a matrix of pure iron. in Pearlitic mixes, the graphite spheroids are in a matrix of pure iron and cementite (Fe3C). The most common grade of ductile is Pearlitic-Ferritic, a combination of the two. American Valve's 4000D uses a predominately Ferritic mix (9:1) to take advantage of its high impact resistance and added tensile strength (80,000 psi).

Except where API 800-degree F fire safe standards are required for petrochemical refineries, ductile iron is generally preferable to a carbon steel because WCB has a tendency to flake, whereas ductile iron powders when subjected to liquid erosion.  Ductile iron also possesses 50% higher yield strength properties and is more cost effective.  Ductile iron castings have a maximum temperature rating of 650 degrees F.  Traditional glass reinforced PTFE seats begin to deform at 360 degrees F.

	Grey Iron	65-45-12 Ductile Iron	WCB	CF8	CF8M
Carbon % (max)	3.5	3.5	0.3	0.08	0.08
Manganese %	0.5	0.1	1.0	1.5	1.5
Phosphorous %	0.1	0.03	0.04	0.04	0.04
Sulfur %	0.1	0.005	0.05	0.04	0.04
Nickel %	0.02	0	0.5	8.0	9.0
Chromium %	0.05	0.025	0.04	18-21	18-21
Molybdenum %	0.05	0.002	0.25	-	2-3
Silicon %	2.1	3.2	0.3	2	2
Magnesium %	0.005	0.025	-	-	-

ASTM A536-70 (MIL SPEC D-4512) requires each casting to be marked by its foundry heat number. Each heat is chemically tested prior to magnesium inoculation and also afterwards. Chemical certification by heat number is available upon request. Standard cast steel (carbon steel) uses the symbol WCB and is defined under ASTM A-216. It contains a maximum of 0.3% carbon. Stainless steel (ASTM A-351) has carbon levels even lower than WCB (0.08% maximum) making its production more costly. 304 Stainless Steel (CF8) adds 8% nickel, about 20% chromium, and a little more silicon. 316 stainless steel (CF8M) adds 2-3% molybdenum to the above. The addition of chromium, nickel, and molybdenum enhances corrosion resistance, allowing CF8M to be utilized in a wide variety of chemical, petrochemical, and corrosive environments.

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