Section 3 Spheroidal or nodular graphite iron castings

3.1 Scope

3.1.1 This Section gives the specific requirements for spheroidal or nodular graphite iron castings.

3.1.2 These requirements are generally applicable to castings intended for use at ambient temperatures. Additional requirements will be necessary when the castings are intended for service at either low or elevated temperatures. Impact test requirements are given for low temperature service in Ch 7, 3.4 Mechanical tests 3.4.2.

3.2 Heat treatment

3.2.1 The special qualities with 350 N/mm² and 400 N/mm² nominal tensile strength and impact test are to undergo a ferritising heat treatment, see Ch 7, 3.4 Mechanical tests 3.4.2.

3.3 Test material

3.3.1 The test samples are to be as detailed in Table 7.3.1 Type A (U-type) test samples, Table 7.3.2 Type B (Double U-type) test samples or Table 7.3.3 Type C (Y-type) test samples. The dimensions of the test specimens and testing procedures used are to be in accordance with Ch 2 Testing Procedures for Metallic Materials. Test samples of other dimensions may be specially required for some castings and these are to be agreed with the Surveyor.

Table 7.3.1 Type A (U-type) test samples

Dimension	Standard sample, mm	Alternative samples when specially required, mm
u	25	12	50	75
v	55	40	90	125
x	40	30	60	65
y	100	80	150	165
Z	To suit testing machine Approximately 5
R _s	To suit testing machine Approximately 5

Table 7.3.2 Type B (Double U-type) test samples

Dimension	Standard sample, mm
u	25
v	90
x	40
y	100
Z	To suit testing machine
R _s	Approximately 5

Table 7.3.3 Type C (Y-type) test samples

Dimension	Standard sample, mm	Alternative samples when specially required, mm
u	25	12	50	75
v	55	40	100	125
x	40	25	50	65
y	140	135	150	175
Z	To suit testing machine
Minimum thickness of mould surrounding test sample	40	40	80	80

3.3.2 The test samples may be either gated to the casting or separately cast.

3.3.3 Where separately cast test samples are used, they are to be taken towards the end of pouring of the castings.

3.4 Mechanical tests

3.4.1 The tensile strength and elongation are to be determined and are to comply with the requirements of Table 7.3.4 Mechanical properties for acceptance purposes: spheroidal or nodular graphite iron castings. Minimum values for the 0,2 per cent proof stress are also included in this Table but are to be determined only if included in the specification. Typical ranges of hardness values are also given in Table 7.3.4 Mechanical properties for acceptance purposes: spheroidal or nodular graphite iron castings and are intended for information purposes.

3.4.2 Impact tests may be required for some applications in which case the selection of the grade is to be confined to those listed in Table 7.3.5 Mechanical properties: special qualities. These castings are to be given a ferritising heat treatment. The mechanical test results are to comply with Table 7.3.5 Mechanical properties: special qualities.

3.4.3 Castings may be supplied to any specified minimum tensile strength selected within the general limits detailed in Table 7.3.4 Mechanical properties for acceptance purposes: spheroidal or nodular graphite iron castings and Table 7.3.5 Mechanical properties: special qualities but subject to any additional requirements of the relevant Rules.

Table 7.3.4 Mechanical properties for acceptance purposes: spheroidal or nodular graphite iron castings

Specified minimum tensile strength N/mm²	0,2% proof stress (see Note) N/mm² minimum	Elongation on 5,65% minimum	Typical hardness value HB (see Ch 7, 3.4 Mechanical tests 3.4.1)	Typical structure of matrix (see Ch 7, 3.5 Metallographic examination 3.5.2)
370	230	17	120 – 180	Ferrite
400	250	12	140 – 200	Ferrite
500	320	7	170 – 240	Ferrite/pearlite
600	370	3	190 – 270	Pearlite/ferrite
700	420	2	230 – 300	Pearlite
800	480	2	250 – 350	Pearlite or tempered structure
Note Proof stresses need only be determined if specifically requested.

Table 7.3.5 Mechanical properties: special qualities

Specified minimum tensile strength N/mm²	0,2% proof stress minimum (See Note 1) N/mm²	Elongation on 5,65 minimum% (See Note 2)	Typical hardness value	Charpy V-notch impact tests
Specified minimum tensile strength N/mm²	0,2% proof stress minimum (See Note 1) N/mm²	Elongation on 5,65 minimum% (See Note 2)	Typical hardness value	Test temperature °C (See Note 3)	Average energy J minimum (See Note 4)
350	220	22	110 – 170	20	17 (14)
				–40	12 (10)
400	250	18	140 – 200	20	14 (11)
				–20	12 (10)
Note 1. Proof stresses need only be determined if specifically requested. Note 2. In the case of integrally cast samples, the acceptable elongation may be taken as 2 percentage points less. Note 3. Tests need only be made at either of the temperatures listed, as appropriate. Note 4. The average value measured on three Charpy V-notch specimens. One of the three values may be below the specified minimum average value, but not less than the value shown in brackets. Note 5. Typical structure of the matrix is ferrite.

3.5 Metallographic examination

3.5.1 Samples for metallographic examination are to be prepared for spheroidal or nodular graphite iron castings. These samples are to be representative of each ladle used and may conveniently be taken from the tensile test specimens. Alternative arrangements for the provision of these samples may, however, be adopted subject to the concurrence of the Surveyor. They are, however, to be taken towards the end of the pour.

3.5.2 Examination of the samples is to show that at least 90 per cent of the graphite is in a dispersed spheroidal or nodular form. Details of typical matrix structures are given in Table 7.3.4 Mechanical properties for acceptance purposes: spheroidal or nodular graphite iron castings and are intended for information purposes.