Grey Cast Iron Magnetic Properties

Gray Iron Comparison				Microstructure（Volume Fractions）（％）
China（GB/T 9439)	ISO 185	ASTM A48/A48M	EN 1561	Matrix Structure
HT100 (HT10-26)	100	No.20 F11401	EN-GJL-100	Pearlite: 30-70％, coarse flakes; Ferrite: 30-70％; Binary Phosphorus Eutectic: ＜7％
HT150 (HT15-33)	150	No.25A F11701	EN-GJL-150	Pearlite: 40-90％, medium coarse flakes; Ferrite: 10-60％; Binary Phosphorus Eutectic:＜7％
HT200 (HT20-40)	200	No.30A F12101	EN-GJL-200	Pearlite: ＞95％, medium flakes; Ferrite＜5％; Binary Phosphorus Eutectic＜4％
HT250 (HT25-47)	250	No.35A F12401 No.40A F12801	EN-GJL-250	Pearlite: ＞98％ medium thin flakes; Binary Phosphorus Eutectic:＜2％
HT300   (HT30-54)	300	No.45A F13301	EN-GJL-300	Pearlite: ＞98％ medium thin flakes; Binary Phosphorus Eutectic:＜2％
HT350   (HT35-61)	350	No.50A F13501	EN-GJL-350	Pearlite: ＞98％ medium thin flakes; Binary Phosphorus Eutectic:＜1％

 

The magnetic properties of gray cast iron vary widely, from low permeability and high coercive force to high permeability and low coercive force. These changes mainly depend on the mictrostructure of gray cast iron. Adding alloying elements to obtain the required magnetic properties is achieved by changing the structure of gray cast iron.

Ferrite has high magnetic permeability and low hysteresis loss; pearlite is just the opposite, it has low magnetic permeability and large hysteresis loss. Pearlite is formed into ferrite by annealing heat treatment, which can increase the magnetic permeability by four times. Enlarging ferrite grains can reduce hysteresis loss. The presence of cementite will reduce the magnetic flux density, permeability and remanence, while increasing the permeability and hysteresis loss. The presence of coarse graphite will reduce the remanence. The change from A-type graphite (a flake-shaped graphite that is uniformly distributed without a direction) to a D-type graphite (a finely curled graphite with a non-directional distribution between dendrites) can significantly increase the magnetic induction and coercive force.

Before reaching the non-magnetic critical temperature, the temperature rise significantly increases the magnetic permeability of gray cast iron. The Curie point of pure iron is the α-γ transition temperature of 770°C. When the mass percentage of silicon is 5%, the Curie point will reach 730°C. The Curie point temperature of cementite without silicon is 205-220°C.

The matrix structure of commonly used grades of gray cast iron is mainly pearlite, and their maximum permeability is between 309-400 μH/m.

 

Magnetic Properties of Grey Cast Iron
Code of Grey Iron	Chemical Composition (%)
	C	Si	Mn	S	P	Ni	Cr
A	3.12	2.22	0.67	0.067	0.13	＜0.03	0.04
B	3.30	2.04	0.52	0.065	1.03	0.34	0.25
C	3.34	0.83 - 0.91	0.20 - 0.33	0.021 - 0.038	0.025 - 0.048	0.04	＜0.02
Magnetic Properties		A		B		C
		Pearlite	Ferrite	Pearlite	Ferrite	Pearlite	Ferrite
Carbide Carbon w(%)		0.70	0.06	0.77	0.11	0.88	/
Remanence / T		0.413	0.435	0.492	0.439	0.5215	0.6185
Coercive Force / A•m-1		557	199	716	279	637	199
Hysteresis Loss / J•m-3•Hz-1 (B=1T)		2696	-696	2729	1193	2645	938
Magnetic Field Strength / kA•m-1 (B=1T)		15.9	-5.9	8.7	8.0	6.2	4.4
Max. Magnetic Permeability / μH•m-1		396	1960	353	955	400	1703
Magnetic Field Strength when Max. Magnetic Permeability / A•m-1		637	199	1035	318	1114	239
Resistivity / μΩ•m		0.73	0.71	0.77	0.75	0.42	0.37

 

Here in the following are the mechanical properties of grey cast iron:

Mechanical Properties of Gray Cast Iron
Item according to DIN EN 1561	Measure	Unit	EN-GJL-150	EN-GJL-200	EN-GJL-250	EN-GJL-300	EN-GJL-350
			EN-JL 1020	EN-JL 1030	EN-JL 1040	EN-JL 1050	EN-JL 1060
Tensile Strength	Rm	MPA	150-250	200-300	250-350	300-400	350-450
0.1% Yield Strength	Rp0,1	MPA	98-165	130-195	165-228	195-260	228-285
Elongation Strength	A	%	0,3 – 0,8	0,3 – 0,8	0,3 – 0,8	0,3 – 0,8	0,3 – 0,8
Compressive Strength	σdB	MPa	600	720	840	960	1080
0,1% Compressive Strength	σd0,1	MPa	195	260	325	390	455
Flexural Strength	σbB	MPa	250	290	340	390	490
Schuifspanning	σaB	MPa	170	230	290	345	400
Shear Stress	TtB	MPa	170	230	290	345	400
Modules of elasticity	E	GPa	78 – 103	88 – 113	103 – 118	108 – 137	123 – 143
Poisson number	v	–	0,26	0,26	0,26	0,26	0,26
Brinell hardness		HB	160 – 190	180 – 220	190 – 230	200 – 240	210 – 250
Ductility	σbW	MPa	70	90	120	140	145
Tension and pressure change	σzdW	MPa	40	50	60	75	85
Breaking Strength	Klc	N/mm3/2	320	400	480	560	650
Density		g/cm3	7,10	7,15	7,20	7,25	7,30