ISO/TR 10809-1:2009

Cast irons - Part 1: Materials and properties for design

The purpose of ISO/TR 10809-1:2009 is to assist the designer and engineer in understanding the family of cast iron materials and to utilize them with a more complete knowledge of their potential, among the wide range of other engineering materials and fabrication methods now available. A considerable amount of the data provided is metallurgical, but it is usually the metallurgical aspects of the cast irons that create misunderstandings when these materials are specified. This is because metallurgy is not one of the scientific disciplines taught to engineering students. Thus, such students often have a lack of knowledge regarding the fundamentals underpinning the material properties of cast irons. ISO/TR 10809-1:2009 suggests what can be achieved, what cannot be achieved and why, if and when cast irons are specified. It is not designed to be a textbook of metallurgy. It is intended to help people to choose the correct material for the right reasons and also to help to obviate the specification or expectation of unrealistic additional requirements, which are unlikely to be met and which can be detrimental to the intended application.

Fontes — Partie 1: Matériaux et propriétés pour la conception

General Information

• Status: Withdrawn
• Publication Date: 15-Oct-2009
• ICS: 77.080.10 - Irons
• Technical Committee: ISO/TC 25 - Cast irons and pig irons
• Drafting Committee: ISO/TC 25/WG 16 - Materials and properties for design
• Current Stage: 9599 - Withdrawal of International Standard
• Start Date: 23-Feb-2023
• Completion Date: 13-Dec-2025

Relations

• Revised: ISO/TR 10809-1:2023 - Cast irons - Part 1: Materials and properties for design
• Effective Date: 17-Jul-2021

Standards Content (Sample)

TECHNICAL ISO/TR
REPORT 10809-1
First edition
2009-11-01
Cast irons —
Part 1:
Materials and properties for design
Fontes —
Partie 1: Matériaux et propriétés pour la conception

Reference number
©
ISO 2009
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ii © ISO 2009 – All rights reserved

Contents Page
Foreword .v
Introduction.vi
1 Scope.1
2 Why use cast irons as an engineering material?.1
2.1 Why use grey cast iron?.1
2.2 Why use spheroidal graphite cast iron?.2
2.3 Why use compacted cast iron? .2
2.4 Why use malleable cast iron? .2
2.5 Why use ausferritic cast iron? .2
2.6 Why use abrasion-resistant cast iron? .2
2.7 Why use austenitic cast iron?.3
3 Commentary.3
3.1 Recent changes in standardization .3
3.2 General metallurgy of the cast irons .5
3.3 Section sensitivity and its effects on material properties.6
3.4 Understanding hardness .8
3.5 Heat treatment .8
3.6 Welding.9
4 ISO 185 Grey cast irons .9
4.1 Overview.9
4.2 Effect of structure on properties .12
4.3 Metal composition and carbon equivalent.12
4.4 Graphite form, distribution and size.13
4.5 Section sensitivity.13
4.6 Effect of alloying elements.15
4.7 Heat treatment .15
4.8 Choosing the grade.16
5 ISO 1083 Spheroidal graphite cast irons .16
5.1 Overview.16
5.2 Effect of structure on properties .17
5.3 Metal composition and carbon equivalent.17
5.4 Graphite form and size.18
5.5 Section sensitivity in spheroidal graphite cast iron .18
5.6 Effect of alloying elements.20
5.7 Matrix structure and resultant properties .20
5.8 Spheroidal graphite cast iron with high silicon content .21
5.9 Special case of impact-resistant grades.22
5.10 Heat treatment .22
5.11 Relationship between ferritic spheroidal graphite cast iron and ferritic steel.23
6 ISO 16112 Compacted (vermicular) graphite cast irons.25
6.1 Overview.25
6.2 Why use compacted graphite cast iron? .26
6.3 Effect of structure on properties .27
6.4 Metal composition and carbon equivalent.27
6.5 Graphite form and size.28
6.6 Section sensitivity in compacted graphite cast iron .28
6.7 Matrix structure and the resultant properties.29
6.8 Heat treatment .29
6.9 Choosing the grade.29
7 ISO 5922 Malleable cast irons .29
7.1 Overview.29
7.2 Metal composition and carbon equivalent.32
7.3 Heat treatment.32
7.4 Graphite form and size.34
7.5 Mechanical property requirements and the influence of structure.34
7.6 Impact properties.35
7.7 Section sensitivity .35
7.8 Choosing the grade .35
8 ISO 17804 Ausferrite spheroidal cast irons .36
8.1 Overview.36
8.2 Heat treatment process.38
8.3 Effects of alloying elements .40
8.4 Graphite form and size.40
8.5 Matrix structure and the resultant properties.41
8.6 Section sensitivity .41
8.7 Special case of the impact grade.41
8.8 Special case of the abrasion-resistant grades .41
8.9 Machinability .41
8.10 Choosing the grade .42
9 ISO 21988 Abrasion-resistant cast irons.42
9.1 Overview.42
9.2 Effects of structure on properties.44
9.3 Chemical composition .45
9.4 Unalloyed and low-alloy cast irons.45
9.5 Nickel-chromium cast iron.45
9.6 High-chromium cast iron .45
9.7 Influence of chemical composition on properties and performance .45
9.8 Section sensitivity .46
9.9 Heat treatment.47
9.10 Choosing the material grade .48
10 ISO 2892 Austenitic cast irons .49
10.1 Overview.49
10.2 Effect of structure on properties.50
10.3 Chemical composition and its effect .51
10.4 Effect of composition on carbon equivalent.52
10.5 Graphite form, distribution and size.52
10.6 Heat treatment.52
10.7 Choosing the material grade .53
Annex A (informative) Glossary of terms related to cast iron International Standards.54
Bibliography .56

iv © ISO 2009 – All rights reserved

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
In exceptional circumstances, when a technical committee has collected data of a different kind from that
which is normally published as an International Standard (“state of the art”, for example), it may decide by a
simple majority vote of its participating members to publish a Technical Report. A Technical Report is entirely
informative in nature and does not have to be reviewed until the data it provides are considered to be no
longer valid or useful.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO/TR 10809-1 was prepared by Technical Committee ISO/TC 25, Cast irons and pig irons.
ISO/TR 10809 consists of the following parts, under the general title Cast irons:
⎯ Part 1: Materials and properties for design
⎯ Part 2: Welding
Introduction
Worldwide cast iron production is in excess of 60 000 000 tonnes per annum. It is manufactured in a wide
range of alloys and has applications in all sectors of world production and manufacture. Its use spans many
industries, including automotive, oil, mining, etc.
The technology of cast irons is not widely taught or understood around the globe. This part of ISO/TR 10809 is
intended to provide information about cast iron materials so that users and designers are better able to
understand cast iron as a design material in its own right and correctly specify cast iron for suitable
applications.
vi © ISO 2009 – All rights reserved

TECHNICAL REPORT ISO/TR 10809-1:2009(E)

Cast irons —
Part 1:
Materials and properties for design
1 Scope
The purpose of this part of ISO/TR 10809 is to assist the designer and engineer in understanding the family of
cast iron materials and to utilize them with a more complete knowledge of their potential, among the wide
range of other engineering materials and fabrication methods now available. A considerable amount of the
data provided are metallurgical, but it is usually the metallurgical aspects of the cast irons that create
misunderstandings when these materials are specified. This is because metallurgy is not one of the scientific
disciplines taught to engineering students. Thus, such students often have a lack of knowledge regarding the
fundamentals underpinning the material properties of cast irons. This part of ISO/TR 10809 suggests what can
be achieved, what cannot be achieved and why, if and when cast irons are specified. It is not designed to be a
textbook of metallurgy. It is intended to help people to choose the correct material for the right reasons and
also to help to obviate the specification or expectation of unrealistic additional requirements, which are unlikely
to be met and which can be detrimental to the intended application.
2 Why use cast irons as an engineering material?
The first questions that the designer and engineer will probably ask are:
⎯ Can I use a cast iron?
⎯ Should I use a cast iron?
⎯ Which type and grade are applicable?
⎯ What are the advantages?
The following sub-clauses give general information on the cast iron types currently standardized in
International Standards.
2.1 Why use grey cast iron?
Grey cast iron provides the largest worldwide tonnage of all cast irons produced, mainly because of its wide
range of uses within general engineering, its ease of machining, and its cost advantage. The material has the
highest thermal conductivity among the range of cast irons, which is why it is used in applications where this
property is important. Typical examples are automotive parts such as brake drums, discs, clutch plates, and
cylinder blocks and heads. Grey cast iron lacks ductility, but for parts where requirements for ductility and
impact strength are low or unimportant, a huge range of applications can be found. These include, for
example, the manufacture of machine tools such as lathe beds, where slideways can easily be surface
hardened and the “self-lubricating” properties of the material are advantageous. This highly versatile material
should be considered for a potential application unless there are ductility issues, or the design requires
ultimate strengths in excess of 300 N/mm .
2.2 Why use spheroidal graphite cast iron?
Spheroidal graphite cast iron has the benefit of ductility as well as strength, which is why it is often considered
to be a material superior to grey cast iron. Its main disadvantage in this respect is that it does not have the
thermal conductivity provided by grey cast iron and is not normally used where this property is important. A
large number of grades of spheroidal graphite cast iron are available to the designer, based on the fact that as
tensile strength increases, ductility decreases. Thus the designer has the opportunity to utilize different
combinations of tensile/ductility properties, depending upon the application. The lower-strength grades with
high ductility also have good impact properties and, for this reason, spheroidal graphite cast iron is
increasingly being used to produce cast parts to replace steel fabrications. Large tonnages of spheroidal
graphite cast iron are used to produce centrifugally cast pipe for water and sometimes gas transportation, but
the majority is used in general engineering applications where its considerably higher tensile properties
compared with grey cast iron are of advantage.
2.3 Why use compacted cast iron?
Compacted graphite cast irons have applications as components which require additional strength, stiffness,
and ductility over and above that offered by grey cast iron. Typical applications include cylinder blocks and
heads, brake drums and brake discs, pump housings, hydraulic components, and cylinder liners. The benefits
of the material are that it provides higher tensile strengths and some ductility in conjunction with thermal
conductivity properties similar to those found in grey cast irons.
2.4 Why use malleable cast iron?
There are two different types of malleable cast iron, blackheart and whiteheart. The blackheart grades have
properties similar to the spheroidal graphite cast irons and the materials have traditionally been considered
interchangeable in most general engineering applications. The main advantage of blackheart malleable iron,
compared with spheroidal graphite cast iron, is that it is easier to machine, because of the different metal
composition. The whiteheart malleable grades are still used to produce traditional thin section castings,
particularly fittings such as hinges and locks. Now, however, their uses are more usually confined to the
production of thin section castings where the heat treatment process involved can be adjusted to completely
decarburize the material. This is of considerable advantage to designers; it allows malleable whiteheart
castings to be welded to steels as part of a fabrication process, because the whiteheart material possesses
properties that are not dissimilar to the steel to which it is welded.
2.5 Why use ausferritic cast iron?
The austempering heat treatment carried out on a normal spheroidal graphite cast iron enhances its
properties to produce a range of grades with exceptionally high tensile strengths. The highest tensile strength
grade also has a high hardness that allows it to be used in abrasion-resisting applications, the most common
one being as digger teeth on earth-moving equipment. As with all spheroidal graphite cast iron materials,
increases in tensile strength and hardness are accompanied by decreases in ductility. This allows for a wide
range of properties that can be exploited, provided that their combination is applicable to the component
design. Tensile strengths up to 1 400 N/mm , hardness greater than 400 HBW, and tensile elongation up to
10 % are possible (although not all three simultaneously in the same grade of material). These mechanical
properties also generate a high fatigue strength that is useful in gears and other components for use in a
rotating/bending application.
2.6 Why use abrasion-resistant cast iron?
The abrasion-resisting cast irons are a range of hard and tough materials that compete with other alloys such
as manganese steel, mainly in the mining and extraction industries, in wear-resistant applications such as
slurry pumps and in more generalized applications such as in the operation of shot-cleaning plants. Thus they
are rightly considered to be a consumable item where the rate of wear, or operational life, is important in the
decision-making process regarding the choice of material. Generally speaking, they tend to be less expensive
and easier to manufacture than the abrasion-resisting steels with which they are usually compared. They
perform well in a variety of applications and should not be casually dismissed as the material of choice in any
application that requires abrasion resistance. The effectiveness of any abrasion-resisting material is highly
2 © ISO 2009 – All rights reserved

dependent upon the materials which it is in contact with and the circumstances under which it performs. For
example, slight changes in the composition of an ore in an extraction application, and even its water content,
can significantly influence the wear rate. The 13 grades of abrasion-resisting irons specified in ISO 21988
offer a wide choice of alloys for matching the material against the intended application.
2.7 Why use austenitic cast iron?
The austenitic cast irons (sometimes called Ni-resists) are a range of materials that provide corrosion
resistance, heat resistance or a combination of both. Austenitic cast irons are often compared with stainless
steels when a design is being considered. One specific application for which the austenitic cast iron grades
are considered is where the component to be produced needs to be non-magnetizable and other properties
are of secondary importance. Both flake graphite and spheroidal graphite iron grades are produced: the
spheroidal graphite iron grades exhibit superior tensile properties to those of the flake graphite grades. These
materials vary widely in their metal composition in order to meet a broad range of applications; in general, the
most arduous applications are met by those grades containing the highest nickel content. The 12 grades of
austenitic cast iron cover the spectrum of applications where highly alloyed materials are required in order to
meet arduous conditions in service.
3 Commentary
Cast irons have particular and peculiar metallurgical and other properties which are unique to the material and
which give it specific valuable attributes that make it a useful material in certain applications.
3.1 Recent changes in standardization
ISO/TC 25 is the International Technical Committee responsible for the development of International
Standards for cast irons. Since 1998, when it was reactivated after a dormancy of 14 years, ISO/TC 25 has
been working through a programme of creation, revision, assessment and publication of cast iron material and
related standards. These International Standards include annexes of additional information about material
properties, which are not requirements of the standards, but which provide helpful technical and application
information to designers and engineers.
The International Standards that have been reviewed, created, published or retained in their current form are
shown in Table 1.
Table 1 — International Standards for cast iron materials and microstructure
Scope Standard number
Grey cast irons ISO 185
Spheroidal graphite cast irons ISO 1083
Compacted (vermicular) graphite cast irons ISO 16112
Malleable cast irons ISO 5922
Ausferritic spheroidal graphite cast irons ISO 17804
Abrasion-resistant cast irons ISO 21988
Austenitic cast irons ISO 2892
Designation of microstructure of cast irons – visual analysis ISO 945-1

The seven International Standards for cast iron materials (see Table 1) encompass a huge international
tonnage. In 1999, reported world production reached 49,3 million tonnes/annum, and this figure had increased
to 61,6 million tonnes/annum by 2006 (the last available statistics). The trend is continuing for cast irons
utilized in the manufacture of a wide range of different components ranging in mass from a few grams to more
than 100 tonnes.
The International Standards for cast irons detail the properties of seven individual types of cast iron material
which together specify 84 different grades. It is recommended that these standards and the associated
annexes of supporting information be carefully consulted, in order to allow the most appropriate material to be
chosen for the application. Table 2 provides a short résumé of properties that will lead the user to the relevant
International Standard. It also compares one cast iron material type with another, but does not compare the
cast irons with other materials. For example, if a cast iron with high strength and ductility were required then
an examination of ISO 1083 or ISO 17804 would be beneficial. The individual grades within these two
International Standards can then be consulted to find the most appropriate one and to determine whether the
other, unspecified properties in the annexes are beneficial or detrimental to the application.
Table 2 — General properties for the range of International Standards for cast iron
ISO 16112 ISO 17804 ISO 21988
ISO 185 ISO 1083 ISO 5922 ISO 2892
Property Compacted Ausferritic Abrasion-
Grey Spheroidal Malleable Austenitic
(vermicular) spheroidal resistant
Tensile strength √√ √√√√ √√√ √√√√ √√√√√ 0 √√√
Proof strength √ √√√√ √√ √√√ √√√√√ 0 √√√
Elongation √ √√√√√ √ √√√ √√√ 0 √√√
Impact resistance √ √√√ √ √√√ √√ √√√ √√√
Low-temperature
√√ √√√ √√ √√√ √√ √ √√√
properties
Thermal conductivity √√√√√ √√√ √√√√ √√√ √√√ √ √√√
Thermal expansion √√ √√ √√ √√ √√ √ √√√√
Abrasion resistance √√ √√ √√ √ √√√ √√√√√ √√
Corrosion resistance √√ √√ √√ √√ √√ √√√√√ √√√√√
Heat resistance √√√ √√ √√ √√ √√ √ √√√√
Machinability √√√√√ √√√ √√√ √√√ √√ √ √√√
Weldability √√ √√√ √√ √√√ √ 0 √√
0 Not applicable
√ Low
√√ Average
√√√ High
√√√√ Very high
√√√√√ Highest
Ausferritic spheroidal graphite cast irons should only be welded prior to austempering.
NOTE ISO 5922 JMB grades = √√√, JMW grades = √√√√, JMW-S grade = √√√√√.

Table 3 provides data on typical applications (the list is not exhaustive). Table 3 should also help the designer
and engineer to select the most appropriate International Standard, and ultimately the choice of the grade
within it.
4 © ISO 2009 – All rights reserved

Table 3 — Typical mechanical property ranges and applications for cast irons

2 2
Minimum tensile strength range 100 N/mm to 350 N/mm , elongation < 1 %
ISO 185
Wide range of general engineering parts: pumps, valves, compressor bodies, machine tools,
Grey
cylinder blocks, brake drums and discs, clutch plates, press tools, street furniture.
2 2
Minimum tensile strength range 350 N/mm to 900 N/mm , elongation range 2 % to 22 %
ISO 1083
Wide range of general engineering parts requiring higher strength, elongation, and fatigue
Spheroidal
properties than grey cast iron: crankshafts, valves, pumps, steering knuckles, suspension
components, axle boxes.
2 2
Minimum tensile strength range 300 N/mm to 500 N/mm , elongation range 0,5 % to 2 %
ISO 16112
Compacted
Components requiring good thermal conductivity in conjunction with higher strength than grey cast
(vermicular)
iron: ingot moulds, cylinder blocks, brake drums and discs, cylinder liners, hydraulic parts.
2 2
Minimum tensile strength range 800 N/mm to 1 400 N/mm , elongation range 2 % to 11 %
ISO 17804
Castings requiring very high strengths with good elongation, fatigue, and abrasion resistance
Ausferritic
properties: gears and cams, crankshafts, differentials, digger teeth, wear shoes, track guides.
2 2
Minimum tensile strength range 270 N/mm to 800 N/mm , elongation range 1 % to 16 %
ISO 5922
Wide range of general engineering parts requiring higher strength, elongation, and fatigue
Malleable
resistance with some grades weldable: pipe fittings, suspension components, gear cases, universal
joints.
2 2
Minimum tensile strength range 140 N/mm to 440 N/mm , elongation range 1 % to 25 %
ISO 2892
Parts requiring corrosion and heat resistance, some grades being non-magnetizable: pumps,
Austenitic
manifolds, gas turbine housings, turbochargers, refrigeration components, compressors.
Minimum hardness range 340 HBW to 630 HBW
ISO 21988
Abrasion-
Castings requiring high abrasion and impact resistance: rock crushers, grinding balls, digger teeth,
resistant
shot-cleaning wear-plates, pumps and valves carrying abrasive liquids.

There is often a communication difficulty between casting producers and the engineers and designers
employed by their customers over the understanding of the cast iron material properties beyond those of the
normative requirements of the specific International Standard. This can lead to confusion, a good example of
which is the phenomenon of section sensitivity in grey cast irons, where, depending on the section thickness,
the mechanical properties in the casting may be either lower or higher than those in separately cast test
pieces. Even experienced engineers are sometimes unfamiliar with the properties of the cast irons, leading to
either an underestimation of the true potential of the material or unrealistic expectations of it.
The cast irons have a complex metallurgy and a wide range of different material properties or specific property
requirements can be obtained through the correct choice of material.
3.2 General metallurgy of the cast irons
The glossary of terms relating to International Standards for cast irons (see Annex A) explains the meaning of
the metallurgical terms given below.
The plain carbon steels are iron-carbon alloys where the carbon content dictates the main properties and
other elements are generally at too low a level to be of major significance. At 0 % carbon content, the material
is soft pure iron, or ferrite. As the carbon content is increased, increasing amounts of pearlite are formed,
which is harder and stronger, such that at about 0,9 % carbon content the structure is fully pearlitic. This range
of carbon content is where the majority of plain carbon steels exist. Raising the carbon content results in the
formation of iron carbide in increasing amounts (sometimes called cementite), which is hard and brittle. Above
about 1,7 % carbon content, the material is called white cast iron and comprises a mixture of pearlite and iron
carbide.
It is this structure (a mixture of pearlite and iron carbide) that forms the basis of the manufacture of the
abrasion-resistant cast irons and malleable cast irons, although refinements to metal composition and the use
of heat treatment are required to meet the specified requirements of their respective International Standards.
The International Standards for the other cast irons require the majority of the carbon content to be present in
the form of graphite, and this is achieved by the addition of silicon, which promotes the formation of graphite
instead of carbide. Grey cast irons contain flake (lamellar) graphite, which is the normal graphite form that
occurs during solidification. Spheroidal and compacted graphite cast irons are produced by deliberate
modification of the solidification mechanism, usually by an addition of magnesium. In the case of the austenitic
cast irons, high levels of other elements are also added to produce the required material properties. Ausferritic
cast irons are both alloyed and subjected to heat treatment, in order to meet the requirements of the
appropriate International Standard. Heat treatments are applied to all of these materials, either as part of the
production route, or to enhance properties, or to obtain stress relief in complex components.
Summarizing, therefore, there are seven material types each broadly described as follows.
Grey cast iron — cast iron with a flake graphite form, usually in a pearlitic matrix except for the very lowest
grades where ferrite is present. The material does not normally require heat treatment, unless stress relief is
applied to ensure dimensional stability.
Spheroidal graphite cast iron — cast iron with the solidification mode modified to produce graphite in
spheroids as opposed to flakes. The grades range from those containing fully ferritic to fully pearlitic matrices
including a recently developed high silicon grade. Heat treatment is sometimes used to produce the ferritic
grades, particularly those requiring high impact values at low temperature. The highest-strength grade can be
produced by an oil quench and temper heat treatment. Stress relief can be applied if necessary.
Compacted (vermicular) graphite cast iron — cast iron with the solidification mode modified to produce
stubby, or compacted graphite flakes, usually with a small percentage of spheroidal graphite present. The
grades range from those containing mainly ferritic to fully pearlitic matrices. The material is not normally heat
treated unless stress relief is required.
Malleable cast iron — two types of cast iron called separately blackheart and whiteheart. They are
deliberately produced with a low silicon level to produce iron carbide and are then heat treated to break down
the carbide and form graphite, as ragged spheroids usually known as temper carbon nodules. The grades
range from fully ferritic to fully pearlitic. The material can be oil quenched and tempered to produce the
highest grade.
Ausferritic cast iron — spheroidal graphite cast iron deliberately subjected to an austempering heat
treatment that enhances material properties, producing an ausferritic matrix containing graphite spheroids. It
sometimes requires special alloying to ensure structural uniformity of the matrix in thick sections. It rarely
requires further heat treatment following production.
Abrasion-resistant cast iron — cast iron, usually with a martensitic matrix, resulting from heat treatment,
that contains complex carbides to provide good abrasion resistance.
Austenitic cast iron — cast iron with an austenitic matrix that is stable down to sub-zero temperatures. It
contains grades with either graphite flakes or spheroids, and is highly alloyed and used in special-purpose
applications. It can be stress relieved and stabilized for high-temperature applications.
3.3 Section sensitivity and its effects on material properties
Section sensitivity is one of the most important phenomena to be understood with regard to cast iron material
properties.
Most engineers expect that the same properties will be obtained in both the castings and the test pieces
poured with them. This is largely the case with steels and many other alloys, but is not the case with cast irons,
for reasons related to the section sensitivity.
The expression “section sensitivity” is used to explain the relationship between the results from the separately
cast test piece used to confirm the tensile properties of cast iron materials and the tensile properties in the
casting. These properties usually differ. This is a very important aspect of design with cast iron materials and
is related to the effects produced on material structure, resulting from different speeds of solidification in
varying casting sections.
6 © ISO 2009 – All rights reserved

In thin section castings the solidification will be rapid, whereas in thick sections solidification will be slow. Thus,
depending on the section thickness, there will be differences in the graphite form and size, and also possibly
in the matrix. These effects result in differing mechanical properties within the various casting sections. In
ISO 185, for grey cast irons, where the effects of section sensitivity are most pronounced, a separately cast
test piece of uniform dimensions is used to determine the precise mechanical properties of the material and
the properties in the casting can be obtained empirically to ratify design strengths. Much research has been
conducted to derive data on the properties in different sections and this research has resulted in the collection
of data such as that detailed in ISO 185:2005, Table 1, an extract from which is shown in Table 4.
Table 4 — Extract from Table 1 of ISO 185:2005 relating to section sensitivity
Relevant wall thickness
Tensile strength Tensile strength
mm
(mandatory values in (anticipated values
Material
separately cast samples) in castings)
over up to and including
designation
2 2
N/mm N/mm
minimum minimum
2,5 5 180
5 10 155
10 20 130
ISO 185/JL/150 150
20 40 110
40 80 95
80 150 80
150 300 —
5 10 250
10 20 225
20 40 195
ISO 185/JL/250 250
40 80 170
80 150 155
150 300 —
10 20 315
20 40 280
ISO 185/JL/350 350
40 80 250
80 150 225
150 300 —
Section sensitivity of whiteheart and weldable blackheart malleable cast irons is affected by the
decarburization process (see 6.3 and 6.7).
Section sensitivity is less pronounced in the compacted graphite cast irons, even less pronounced in the
range of cast irons containing graphite spheroids, and least pronounced in the grades of blackheart malleable
cast irons and the abrasion-resistant cast irons. In the International Standards for compacted graphite cast
irons, spheroidal graphite cast irons, and ausferritic spheroidal graphite cast irons, separately cast test pieces
are also required, but with the option of utilizing a cast-on test piece. This arrangement more closely replicates
the properties of the wall thickness to which it is attached, provided that the correct test piece is used. Tables
in the various International Standards for cast iron dictate the required mechanical properties, depending upon
the relevant wall thickness.
The terminology “relevant wall thickness” was deliberately chosen for inclusion in the International Standards
concerned, so that the manufacturer and the producer can agree on the section of the casting where the cast-
on sample, from which the test piece is taken, is placed. The relevant wall thickness would normally be
construed to be the wall thickness that is the most important for the purposes of design; this is often the most
highly stressed area. Where precision is required in the determination of material properties, the International
Standards allow for the option of cutting samples from the casting at an agreed location. Obviously this
destroys the casting and is invariably carried out according to agreed routine sampling plans, or as initial
validation during first-off sampling.
3.4 Understanding hardness
National standards do not always specify hardness, although informative data are sometimes provided for the
various grades. Customers, on the other hand, commonly specify hardness ranges for the materials that are
required. ISO 185 contains special hardness-only grades which are normative and which do not require
tensile strength validation. Therefore, it is now possible to specify castings according to a mandatory hardness
grade, but they might also be produced according to a tensile strength grade where, in addition, the customer
demands a hardness range to be met.
It is important to make clear that the section-sensitivity phenomenon affects hardness. For example, the
graphite in graphitic materials is coarser in thick sections than in thin sections and the matrix may also be
affected by the different cooling rates; thus thick section
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