DU

PL

EX

Duplex

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Introduction

Principles of centrifugal castingsWhen it comes to metal forming,casting metal can be one of the sim-plest, most cost-effective routes to anear net shape manufactured good.Centrifugal casting in particular hasthe capability of utilizing these de-sirable benefits during the produc-tion of cylindrical stainless steelproducts.

Centrifugal casting is a processwhere molten metal is funneledinto a rotating mold (commonly700 to 1300 rpm). The rotation ofthe die creates centrifugal forcewhich thrusts the metal towards themold wall.

Centrifugal casting can be performedhorizontally or vertically. The aspectratio of the part to be cast is what de-termines which of these two tech-niques are used. When the diameterof the desired part is large in com-parison to the overall-length (ringshaped), vertical casting is mostcommonly used. Likewise, when thelength is larger compared to the di-ameter (tube shaped), horizontalcasting setups are used.

Benefits

Process ControlSignificant cost savings can be a re-sult of process control.At Spuncast raw materials purchasedare received and the chemistry eval-uated. The chemistries are acquiredthrough one of three methods: au-diting pieces from various locationsin that lot on the spectrometer, thepurchased scrap comes with a certi-fied chemistry, or a 100lb sample ofmaterial is melted down and achemistry slug evaluated. Thisknown/averaged chemistry createsthe necessary control needed whenworking with low carbon alloys(such as Duplex). Charge sequenceand temperature control also play a

large role in controlling processvariables. Charge sequence can con-trol the amount of elemental recov-ery, as well as the cycle time of eachmelt. Temperature control allowsthe melter opportunity to avoid su-perheating the melt, ultimately af-fecting the chemistry, and tap thefurnace with the exact amount oftemperative increase needed to pourthe casting above but close to itsliquidus temperature. Another way

temperature control plays a key roleis during the casting solidificationprocess. Centrifugal casting pro-motes directional grain growth dur-ing solidification, as shown in thepictures below.

Secondary RefiningThe centrifugal forces promote met-al cleanliness by forcing the non-metallic’s (less dense) to the innerdiameter of the casting. As solidifi-cation takes place, the inner surfaceacts as a riser feeding the outer di-ameter with the metal it needs toproduce a solid, dense casting. Theless dense materials (the dirt, dross,or slag) that were forced to the boreof the casting can now be subse-quently machined off. Since the useof gating and risers are eliminated,the productions of these castingshave an extremely high castingyield.

Shapes and SizesCentrifugal casting is most appropri-ate when producing relatively sim-ple cylindrical shaped parts. The listthat follows shows the size rangesand limitations for the productionof parts using this unique castingprocess.

Centrifugally cast duplex stainless steel

Discussion of benefits

Shawn Martin, Greg Mooren, Alan Holtz, Spuncast, Inc, USA

Figure 1: Cross-Section of a Horizontal Die with a Line Designating its Axis of Rotation.

Figure 2: Casting cross-section macro-etched with HydrogenPeroxide and Muriatic Acid, displaying direction solidificationand grain growth from the outer diameter to the innerdiameter.

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Utilizing a vertical casting orienta-tion, more complex shapes are quitepossible by the use of either chemi-cally bonded sand inserts or invest-ment (lost-wax) shell inserts.

Advantage and LimitationCentrifugal castings can be morecost effective than forgings andhave properties that surpass those ofmost other casting processes. Thiscentrifugally cast dense structurecreates castings with a longer life.These parts also can withstandgreater loads and impacts withoutfracturing.

Several wrought material gradeshave recently been introduced thataccomplish cost saving by loweringthe amount of Ni, but none of thesewere designed for castability (specif-ically centrifugal casting).

‘SCLean’

SCLean - Spuncast’s Cast Grade ofLean Duplex

Table 4: SCLean - Nominal Chemistry

As stated earlier, maximizing me-chanical properties while minimiz-ing the use of expensive raw materi-als was the primary objective. Onewithout the other (mechanicalproperties / lower cost per kg) is ofno use.

Size Limits: [1]

Diameter: Up to 3 m (10 feet)

Length: 15 m (50 feet)

Wall Thickness: 2.5 mm to 125 mm (0.1 - 5.0 in)

OD Tolerance: as fine as 2.5 mm (0.1 in)

ID Tolerance: can be 3.8 mm (0.15 in)

Figure 3: Size Limitations for Centrifugal Casting

Forged Roll

(Billet)

Sand

Casting

Centrifugal

Casting

� Wrought Material Properties

�Low Tooling Costs

�Low Manufacturing Costs

�Improved Proprieties

�Secondary Refining (denser)

�Directional Solidification

� High material cost

�Double Energy Costs

�Significant amount of Machining.

�Strength Limitations

�Micro-porosity

�Inherent Inclusions

� Shape and Size

Forged Roll

(Billet)

Sand

Casting

Centrifugal

Casting

� Wrought Material Properties

�Low Tooling Costs

�Low Manufacturing Costs

�Improved Proprieties

�Secondary Refining (denser)

�Directional Solidification

� High material cost

�Double Energy Costs

�Significant amount of Machining.

�Strength Limitations

�Micro-porosity

�Inherent Inclusions

� Shape and Size

Table 1: Above is a list of advantages and limitations to ac-knowledge when selecting a form of product manufacturing.

Decanter Centrifuges

Solids Discharge Main Effluent

Duplex Stainless SteelDuplex Stainless Steel

Figure 5: On-Ship Hydraulic Accumulators - Energy storage basin in which hydraulic fluids are heldunder pressure by a peripheral source.

On-ship Hydraulic Accumulators

Duplex Stainless SteelProperty Comparison

Mechanical Property Comparison:Wrought vs. Centrifugally Cast

The primary U.S specification forcast duplex stainless steels is ASTMA890. There are eight grades withinthis specification. To date there isno accepted specification for a castlean duplex. The following data is acomparison of achievable cast prop-erties to wrought specifications forduplex grades 4A and 1B. Thesetwo were selected because they bothhave an abundance of history anddata available. There are other du-plex grade properties available, butthe information is fairly limited.

Grade 4A 2205 - J92205

Grade 1B2550 - J92205

UTS UTS

(MPa) (ksi)

Yield

(MPa)

Yield

(ksi)

Elongation

(%)

Spuncast Avg. 802.5 116.4 557.1 80.8 32.7

Wrought Spec.

(S32205) 760 110 550 80 15

UTS UTS

(MPa) (ksi)

Yield

(MPa)

Yield

(ksi)

Elongation

(%)

Spuncast Avg. 731 106 534 77.4 28.4

Wrought Spec.

(S32550) 621 90 450 65.3 25.0

y

C Mn Si P S Cr Ni Mo

0.025 4.2 0.68 0.02 0.005 22.25 1.5 0.49

W Cu Nb V Al Zr N

0.013 1 0.06 0.05 0.005 0.007 0.19

UTS UTSTest Sample (MPa) (ksi)

Yield

(MPa)

Yield

(ksi)

Elongatio

n (%)

Furnace /

HT

1 - 7489 639 92.71 483 70.01 32.31 1120oC WQ

2 - 7490 632 91.71 476 69.06 39.20 1120oC WQ

3 - 7496 628 91.12 470 68.17 34.56 1120oC WQ

4 - 7497 623 90.35 486 70.45 32.13 1120oC WQ

Average 630 91 479 69 34.6

Stress-Stain Diagram

Figure 4: Decanter Centrifuges - Separating solids from liquids plays a key role in countless indus-trial, food and waste treatment processes.

Two samples of centrifugally cast Duplex Stainless Steel parts:

Table 2: Mechanical property summary for 70 cast andheat treated tensile bars (1120°C Water Quench)

Table 3: Mechanical property summary for 16 cast andheat treated Tensile bars (1120°C Water Quench)

Table 5: Mechanical property breakdown for tensilebars cut from the heat treated castings (1120°F WaterQuench)

Figure 6: Stress-Strain curve recorded from one of theSCLean tensile bars pulled (Sample 1-7497).

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Duplex

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The previously shown mechanicalproperties were made at the follow-ing price:

SCLean = $1.67 / Kg (based on$44.31/Kg Ni - LME)

For reference: That same week hadthe following prices:

CD4MCuN = $ 3.88 / KgDuplex4A = $ 4.54 / Kg

ConclusionCentrifugal castings use directionalsolidification and pressure from thecentrifugal force to create castingswith a denser more sound structureexhibiting superior physical proper-ties to that of statically poured cast-ings.

It has been made clear that centrifu-gal casting is a versatile process withbenefits in the areas of mechanicalproperties and overall process cost-effectiveness. The utilization ofthis process can be beneficial whenproducing a variety of products.One particular example shown wasthe specific development of SCLeanas a “castable” lean duplex.

About the authorsShawn Martin Academic Education & Degrees:

Bachelors of Science - Material Science & Engineering,

Michigan Technological University

Current Position:

Metallurgist,

Spuncast, Inc, Watertown, WI USA

Greg Mooren Academic Education & Degrees:

Bachelors of Science - Material Science & Engineering,

Michigan Technological University

Current Position:

Metallurgist, Spuncast, Inc, Watertown, WI USA

Alan Holtz Academic Education & Degrees:

Bachelor of Arts - History,

University of Pennsylvania

Bachelor of Science - Metallurgical Engineering,

University of Missouri - Rolla

Current Position: Vice President - Sales & Engineering,

Spuncast, Inc, Watertown, WI USA

Reference(s)Centrifugal Casting. (2007) In efunda, engineering fundamentals.

Retrieved 13:08, July 2nd. 2007, from ”http://www.efunda.com/processes/metal_process-

ing/centri_casting.efm

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