Malleable cast irons – Flake (grey), cast irons
Malleable cast irons – Cast iron is the name given to those ferrous metals containing more than 1.7% carbon.Since the maximum amount of carbon which can be held in solid solution as austenite ( phase) is 1.7%, there will be excess carbon in all cast irons. This can be either taken up by the iron as cementite (combined carbon) or precipitated out as free carbon in the form of graphite flakes (uncombined carbon).

Slow cooling results in coarse gains of ferrite and large flakes of graphite.

More rapid cooling results in both ferrite and pearlite being present together with finer and more uniformly dispersed flakes of graphite. This results in a stronger, tougher and harder cast iron.

Rapid cooling results in very fine flake graphite dispersed throughout a matrix of pearlite. This results in a further increase in strength and hardness.

It is the grey appearance of the freshly fractured surface of cast iron, resulting from the flake graphite, that gives ferritic and pearlitic cast irons the name grey cast irons.

Very rapid cooling and a reduction in silicon content results in all the carbon remaining combined as pearlite and cementite. Since no grey carbon is visible in the fractured surface, such cast iron is referred to as white cast iron. It is too hard and brittle to be of immediate use, but white iron castings are used as a basis for the malleable cast irons.

As well as iron and carbon the following elements are also present in cast irons:

Silicon This softens the cast iron by promoting the formation of uncombined carbon (graphite) at the expense of combined carbon (cementite). The silicon content is increased in small castings, which tend to cool rapidly, to promote the formation of ferrite and pearlite, and prevent the formation of excess cementite.

Phosphorus This is a residual impurity from the extraction process. Its presence causes embrittlement and hardness. However, its presence is desirable in complex, decorative castings, where strength and shock resistance is relatively unimportant, as it increases the fluidity of molten iron.

Sulphur This is also a residual impurity. It stabilizes the cementite and prevents the formation of flake graphite, thus hardening the iron. The presence of iron sulphide (FeS) causes embrittlement.

Manganese This is added in small quantities to neutralize the effects of the sulphur. It also refines the grain of the cast iron and so increases its strength. Since excess manganese stabilizes the cementite and promotes hardness, the manganese content must be balanced with the silicon content.

A typical composition for a grey cast iron could be as follows

Carbon 3.3%
Silicon 1.5%
Manganese 0.75%
Sulphur 0.05%
Phosphorus 0.5%
Iron remainder

BS EN 1561: 1997 Grey cast irons

BS EN 1561 specifies the requirements of seven grades of grey cast iron. Unlike earlier standards it does not specify the composition or its processing in the foundry. BS EN 1561 specifies the properties, test conditions and quality control of the castings. How these are attained are left to the foundry in consultation with the customer. In addition the customer may specify or require:

(a) a mutually agreed chemical composition;
(b) casting tolerances, machining locations;
(c) test bars and/or test certificates;
(d) whether testing and inspection is to be carried out in the presence of the customer’s representative;
(e) any other requirement such as hardness tests and their locations, non-destructive tests, and quality assurance.

The main properties of grey cast irons as specified in BS EN 1561 are given in the table on page 576. Note that for grey cast iron, hardness is not related to tensile strength but varies with casting section thickness and materials composition.

Tensile strength of grey cast irons

Material designation		Relevant wall thicknessa (mm)		Tensile strength  mandatory values (N/mm2)		Tensile strength  anticipated values in castinge (N/mm2)
Symbol	Number	Over	Up to and including	In separately cast sample	In cast-on sample (min.)	(min.)
EN-GJL-100	EN-JL1010	5f	40	100 to 200g	–	–
EN-GJL-150	EN-JL1020	2.5f 5 10 20 40 80 150	5 10 20 40 80 150 300	150 to 250g	– – – 120 110 100 90e	180 155 130 110 95 80 –
EN-GJL-200	EN-JL1030	2.5f 5 10 20 40 80 150	5 10 20 40 80 150 300	200 to 300g	– – – 170 150 140 130e	230 205 180 155 130 115 –
EN-GJL-250	EN-JL1040	5f 10 20 40 80 150	10 20 40 80 150 300	250 to 350g	– – 210 190 170 160e	250 225 195 170 155 –
EN-GJL-300	EN-JL1050	10f 20 40 80 150	20 40 80 150 300	300 to 400g	– 250 220 210 190e	270 240 210 195 –
EN-GJL-350	EN-JL1060	10f 20 40 80 150	20 40 80 150 300	350 to 450g	– 290 260 230 210e	315 280 250 225 –

^aIf a cast-on sample is to be used the relevant wall thickness of the casting shall be agreed upon by the time of acceptance of the order.

^bIf by the time of acceptance of the order proving of the tensile strength has been agreed, the type of the sample is also to be stated on the order.

If there is lack of agreement the type of sample is left to the discretion of the manufacturer.

^cFor the purpose of acceptance the tensile strength of a given grade shall be between its nominal value n (position 5 of the material symbol) and (n + 100) N/mm².

^dThis column gives guidance to the likely variation in tensile strength for different casting wall thicknesses when a casting of simple shape and uniform wall thickness is cast in a given grey cast iron material. For castings of non-uniform wall thickness or castings containing cored holes, the table values are only an approximate guide to the likely tensile strength in different sections, and casting design should be based on the measured tensile strength in critical parts of the casting.

^eThese values are guideline values. They are not mandatory.

^fThis value is included as the lower limit of the relevant wall thickness range.

^gThe values relate to samples with an as-cast casting diameter of 30 mm, this corresponds to a relevant wall thickness of 15 mm.

Note:

1. 1 N/mm² is equivalent to 1 MPa.
2. For high damping capacity and thermal conductivity, EN-GJL-100 (EN-JL1010) is the most suitable material.
3. The material designation is in accordance with EN 1560.
4. The figures given in bold indicate the minimum tensile strength to which the symbol of the grade is related.

Brinell hardness of castings of grey cast iron, mandatory and anticipated values at the agreed test position

Material designation		Relevant wall thickness (mm)		Brinell hardnessa,b (HB30)
Symbol	Number	Over including	Up to and	min.	max.
EN-GJL-HB155	EN-JL2010	40c 20 10 5 2.5	80 40 20 10 5	– – – – –	155 160 170 185 210
EN-GJL-HB175	EN-JL2020	40c 20 10 5 2.5	80 40 20 10 5	100 110 125 140 170	175 185 205 225 260
EN-GJL-HB195	EN-JL2030	40c 20 10 5 4	80 40 20 10 5	120 135 150 170 190	195 210 230 260 275
EN-GJL-HB215	EN-JL2040	40c 20 10 5	80 40 20 10	145 160 180 200	215 235 255 275
EN-GJL-HB235	EN-JL2050	40c 20 10	80 40 20	165 180 200	235 255 275
EN-GJL-HB255	EN-JL2060	40c 20	80 40	185 200	255 275

^aFor each grade, Brinell hardness decreases with increasing wall thickness.

^bBy agreement between the manufacturer and the purchaser a narrower hardness range may be adopted at the agreed position on the casting, provided that this is not less than 40 Brinell hardness units. An example of such a circumstance could be castings for long series production.

^cReference relevant wall thickness for the grade.

Note:

1. Information on the relationship between Brinell hardness and tensile strength is indicated in Figure B.1 and the relationship between Brinell hardness and relevant wall thickness in Figure C.2 of Annexes B and C, respectively (see: BS EN 1561).
2. The material designation is in accordance with EN 1560.
3. The figures given in bold indicate the minimum and maximum Brinell hardness, to which the symbol of the grade is related and the corresponding reference relevant wall thickness range limits.

Malleable cast irons

BS EN 1562: 1997

BS EN 1562 specifies the requirements of malleable cast irons. The type of cast iron is indicated by the symbol thus:

EN-GJMW whiteheart malleable cast iron

EN-GJMB blackheart malleable cast iron

This initial letter is followed by a two-figure code designating the minimum tensile strength in MPa of a 12 mm diameter test piece. The test result is divided by ten to give the code. Finally, there are two figures representing the minimum elongation percentage on the specified gauge length.

Thus a complete designation of a malleable cast iron could be EN-GJMW-350-4 this is a whiteheart malleable cast iron with a minimum tensile strength of 350 N/mm2 on a 12 mm diameter test piece, and a minimum elongation of 4%.

As for grey irons, the specification is not concerned with the composition of the iron. The composition and manufacturing processes are left to the discretion of the foundry in consultation with the customer.

The melt and the castings made from it will have satisfied the requirements of BS 6681 providing the test results and general quality of the castings meet the specifications laid down therein.

Whiteheart process
White iron castings are heated in contact with an oxidizing medium at about 1000°C for 70–100 h, depending upon the mass and the thickness of the castings. The carbon is drawn out of the castings and oxidized, leaving the castings with a ferritic structure at the surface and a pearlitic structure near the centre of the casting. There will be some residual rosettes of free graphite. Whiteheart castings behave more like steel castings but have the advantage of a much lower melting point and greater fluidity at the time of casting.

Applications: Wheel hubs, bicycle and motor cycle frame fittings; gas, water, and steam pipe fittings.

Blackheart process
White iron castings are heated out of contact with air at 850–950°C for 50–170 h, depending upon the mass and the thickness of the castings. Cementite breaks down into small rosettes of free graphite dispersed throughout a matrix of ferrite. This results in an increase in malleability, ductility, tensile strength and toughness.

Applications: Wheel hubs, brake drums, conduit fittings, control levers and pedals.

Pearlitic process
This is similar to the blackheart process but is accompanied by rapid cooling. This prevents the formation of ferrite and flake graphite and instead, results in some rosettes of graphite dispersed throughout a matrix of pearlite. This results in castings which are harder, tougher and with a higher tensile strength, but with reduced malleability and ductility.

Applications: Gears, couplings, camshafts, axle housings, differential housings and components.

Mechanical properties of whiteheart malleable cast irons

Material designation		Nominal diameter of test piece d (mm)	Tensile strength Rm (N/mm2) min.	Elongation A3.4 (%) min.	0.2% proof stress Rp0.2 (N/mm2) min.	Brinell hardness (for information only) HB max.
Symbol	Number
EN-GJMW-350-4	EN-JM1010	6 9 12 15	270 310 350 360	10 5 4 3	– – – –	230
EN-GJMW-360-12b	EN-JM1020b	6 9 12 15	280 320 360 370	16 15 12 7	–a 170 190 200	200
EN-GJMW-400-5	EN-JM1030	6 9 12 15	300 360 400 420	12 8 5 4	–a 200 220 230	220
EN-GJMW-450-7	EN-JM1040	6 9 12 15	330 400 450 480	12 10 7 4	–a 230 260 280	220
EN-GJMW-550-4	EN-JM1050	6 9 12 15	– 490 550 570	– 5 4 3	–a 310 340 350	250

^aDue to the difficulty in determining the proof stress of small test pieces, the values and the methodof measurement shall be agreed between the manufacturer and the purchaser at the time of acceptance of the order.

^bMaterial most suitable for welding.

Note:

1. 1 N/mm² is equivalent to 1 MPa.
2. The material designation is in accordance with EN 1560.
3. The figures given in bold indicate the minimum tensile strength and minimum elongation A_3.4to which the symbol of the grade is related, and the preferred nominal diameter of the test piece and the corresponding minimum 0.2% proof stress.

Mechanical properties of blackheart malleable cast irons

Material Designation		Nominal diameter of test piecea d (mm)	Tensile strength Rm (N/mm2) min.	Elongation A3.4 (%) min.	0.2% proof stress Rp0.2 (N/mm2) min.	Brinell hardness (for information only) HB
Symbol	Number
EN-GJMB-300-6b	EN-JM1110b	12 or 15	300	6	–	150 maximum
EN-GJMB-350-10	EN-JM1130	12 or 15	350	10	200	150 maximum
EN-GJMB-450-6	EN-JM1140	12 or 15	450	6	270	150 to 200
EN-GJMB-500-5	EN-JM1150	12 or 15	500	5	300	165 to 215
EN-GJMB-550-4	EN-JM1160	12 or 15	550	4	340	180 to 230
EN-GJMB-600-3	EN-JM1170	12 or 15	600	3	390	195 to 245
EN-GJMB-650-2	EN-JM1180	12 or 15	650	2	430	210 to 260
EN-GJMB-700-2	EN-JM1190	12 or 15	700	2	530	240 to 290
EN-GJMB-800-1	EN-JM1200	12 or 15	800	1	600	270 to 320

^aWhere a 6 mm diameter test piece is representative of the relevant wall thickness of a casting, this size of the test piece may be used byagreement between the manufacturer and the purchaser at the time of acceptance of the order. The minimum properties given in this table shall apply.

^bMaterial intended particularly for applications in which pressure tightness is more important than a high degree of strength and ductility.

Note:

1. 1 N/mm² is equivalent to 1 MPa.
2. The material designation is in accordance with EN 1560.
3. The figures given in bold are related to the minimum tensile strength and minimum elongation A_3.4 of the grade.