Materials of Construction - Meehanite®
October 02, 2001

Introduction Types General Engineering Types Wear Resisting Types         Austempered Ductile Iron Types Heat Resisting Types Corrosion Resisting Types Properties

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Introduction

Meehanite® is the registered trademark of a family of cast ferrous materials manufactured under rigid metallurgical control so that their properties meet established engineering specifications.   The dense, fine grain structure of Meehanite® metal which assures casting solidity and uniform physical properties regardless of mass or section is achieved by the use of well established Meehanite® control procedures.

This process involves a number of patented features seeking to control and produce the desired graphite distribution and the desired matrix structure in the casting.  It depends primarily on the establishment of a melt of desired degree of undercooling and the controlled nucleation of this melt, usually by means of alkaline earth silicide additions.  It requires very careful selection of raw materials, meticulous process controls and a very thorough knowledge of the foundry behavior of cast iron.

The Meehanite® process involves the use of standard procedures in all phases of casting manufacture including gating and risering techniques, sand control testing methods and many specialized molding procedures.

Types

Meehanite® metal types have been divided into a number of broad type classifications based on use.  These categories relate to the end use of the casting and are further subdivided on the basis of metallurgical structure and property values.

1.    General Engineering
2.    Wear Resisting
3.    Heat Resisting
4.    Corrosion Resisting

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General Engineering Types

This Meehanite® metal series is classified into flake graphite metals designated by the prefix G and nodular graphite metals designated by the prefix S.

The flake graphite (G types) are subdivided according to the tensile strength.  Tensile strength is given in minimum values, but G type metals can be produced to any specific minimum value either exactly corresponding to any specific type or to values that may fall exactly in between designated types.

Nodular graphite S types are also subdivided according to tensile strength.

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Wear Resisting Types (Almanite®)

This series produced primarily for wear resistance having specific mechanical properties is broadly classified according to metallurgical structure which, in turn, determines the wear resistance.  These materials may contain free carbon as graphite or as carbides or both.  Those containing carbides as the major properties of carbon are white irons.  Subdivisions within this type are:

    Type W 1 - carbidic, pearlitic matirx
    Type W 2 - carbidic, martensitic matrix
    Type W 4 - carbidic, austenitic matrix
    Type WS - nodular graphite, bainitic matrix
    Type WSH - nodular graphite, austenitic matrix

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Austempered Ductile Iron (ADI) Types

This series offers a unique combination of high strength properties and excellent machinability.  It differs from all unalloyed or lightly alloyed common carbon steels and cast irons in that its microstructure does not contain any hard and brittle iron carbide.  The basic components of Meehanite ADI types are ferritic, retained austenitic and nodular graphite.  The classification is based on median hardness value:

    Type K295
    Type K325
    Type K405

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Heat Resisting Types

While even the General Engineering irons have some good heat resisting properties, the heat resisting type of Meehanite® are specifically produced to meet a wide range of high temperature servce conditions.  Sub-division is based on the type of application but is characterized by structure.

    Type HR - carbidic/pearlitic (scale and creep resistance)
    Type HS - nodular graphite, ferritic (temperature up to 981°C (1800°F) (maximum resistance to scaling)
    Type HSV - nodular graphite, ferritic/pearlitic (high mechanical heat strength)
    Type HE - flake graphite, pearlitic (heat shock) (thermal   shock resistance)

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Corrosion Resisting Types

This series is sub-divided very broadly according to structure but composition may be varied considerably to suit exact conditions of service.   The austenitic nickel types CR and CRS may be modified to meet all standard specifications for this type of material.

    Type CC - flake graphite
    Type CR - flake graphite, nickel/austenitic
    Type CRS - nodular graphite, nickel/austenitic
    Type CHS - nodular graphite, ferritic

For mildly corrosive conditions, Type CC is an all-around inexpensive general engineering material.  For more corrosive conditions, Type CR and CRS should be used.  These two types are austenitic nickel-bearing irons corresponding to ASTM Specification A436 and A439.  Type CC has excellent corrosion resistance to 100% sulphuric acid at temperatures up to 121°C (250°F).  Corrosion increases with increasing temperature and decreasing acid concentration.  Type CR and CRS resist corrosion by cold dilute sulphuric acid.  Type CHS is a higher strength material recommended for use in acidic conditions at high temperatures.

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Properties

Meehanite® materials are used in converter parts, acid piping, and specialty parts in acid systems (i.e. thimbles).  Typical properties of the various type of Meehanite materials specifically used in sulphuric acid plants are given in the following table.

	HS	GE	HR	CS/CHS
Tensile Strength	414/690 N/mm² 60,000/100,000 psi	207 N/mm² (min) 30,000 psi (min)	276 N/mm² (min) 40,000 psi (min)	414/690 N/mm² 60,000/100,000 psi
Yield Strength	310/517 N/mm² 45,000/75,000	-	-	310/517 N/mm² 45,000/75,000 psi
Compressive Stength	-	816 N/mm² 120,000 psi	1,122 N/mm² 165,000 psi	-
Brinell Hardness (nominal)	200	170	300	200
Elongation	2-10%			2-10%
Description	HS compares very favourably from a strength standpoint with any heat resisting metal and is recommended for applications at temperatures up to 981°C (1800°F) under both conditions of cyclic and continuous heating without thermal shock.   Compositional adjustments are made to suit the exact service conditions.  It machines easily and provides maximum resistance to scaling and growth.	This material is available as an alternative and superior material for all applications replacing ordinary grey cast iron.  It is manufactured under the same strict control as the other Meehanite types and therefore offers the benefits of structural uniformity and soundness.  It permits higher machining feeds and speeds because of the uniformity and complete absence of hard spots, corners and edges.	HR is a strong, dense iron of high rigidity and excellent resistance to scaling undermost conditions.  Type HR is non-growing for temperatures up to 734°C (1350°F).  It posses good load carrying ability.	Corrosion resistant type with higher strength and good shock resistance.   Compositional adjustments are made to suit exact service conditions.   Recommended for use for components subjected to concentrated sulphuric acid or oleum.

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