China Gray Iron Casting Factory

Gray cast iron refers to cast iron with flake graphite. It is called gray cast iron because the fracture surface is dark gray when it breaks.

1.Performance characteristics of Gray Iron Casting

The mechanical properties of gray cast iron are related to the structure of the matrix and the morphology of graphite. The flake graphite in gray cast iron seriously cuts the matrix, which easily causes stress concentration at the sharp corners of graphite, making the tensile strength, plasticity and toughness of gray cast iron far lower than that of steel, but the compressive strength is equivalent to that of steel. It is also the cast iron with the worst mechanical properties among commonly used cast iron parts. At the same time, the matrix structure also has a certain influence on the mechanical properties of gray cast iron. The graphite flakes of ferrite-based gray cast iron are coarse, with the lowest strength and hardness, so it is less used; the graphite flakes of pearlite-based gray cast iron are fine, with higher strength and hardness, and are mainly used to manufacture more important castings; the graphite flakes of ferrite-pearlite-based gray cast iron are slightly coarser than pearlite gray cast iron, and the performance is not as good as pearlite gray cast iron. Therefore, pearlite-based gray cast iron is more commonly used in industry.

Gray cast iron has good casting performance, good vibration damping, good wear resistance, good cutting performance and low notch sensitivity.

Table: Grades and mechanical properties of gray iron castings
Brand	Casting wall thickness	Minimum tensile strength ?b/MPa	Hardness classification	Casting hardness range HBS	Main metallographic structures
HT100	2.5～10	130	H145	≤170	Ferrite
	10～20	100
	20～30	90
	30～50	80
HT150	2.5～10	175	H175	150～200	Ferrite +Pearlite
	10～20	145
	20～30	130
	30～50	120
HT200	2.5～10	220	H195	170～220	Pearlite
	10～20	195
	20～30	170
	30～50	160
HT250	4.0～10	270	H215	190～240	Pearlite
	10～20	240
	20～30	220
	30～50	200
HT300	10～20	290	H235	210～260	100% pearlite (nodular cast iron)
	20～30	250
	30～50	230
HT350	10～20	340	H255	230～280	100% pearlite (nodular cast iron)
	20～30	290
	30～50	260

2、Chemical composition of grey cast iron

National standard chemical composition of grey cast iron (%)
Ingredients Standard	C	S	Mn	P	Si
HT100	3.2~3.8	≤0.15	0.5~0.8	<0.3	2.1~2.7
HT150	3.0~3.7	≤0.12	0.5~0.8	<0.2	1.8~2.4
HT200	3.0~3.6	≤0.12	0.6~1.0	<0.15	1.4~2.2
HT250	2.9~3.5	≤0.12	0.7~1.1	<0.15	1.2~2.0
HT300	2.8~3.4	≤0.12	0.8~1.2	<0.15
HT350	2.7~3.2	≤0.12	0.8~1.4	<0.15

3、Comparison of Chinese and foreign grades of grey cast iron

Serial number	Country	Cast iron grade
1	China		HT350	HT300	HT250	HT200	HT150	HT100
2	Japan		FC350	FC300	FC250	FC200	FC150	FC100
3	United States	NO.60	NO.50	NO.45	NO.35	N0.30	NO.20
4	Former Soviet Union	C440	C435	C430	C425	C420	C415	C410
5	Germany	GG40	GG35	GG30	GG25	GG20	GG15
6	Italy		G35	G30	G25	G20	G15	G10
7	France	FGL400	FGL350	FGL300	FGL250	FGL200	FGL150
8	United Kingdom		350	300	250	200	150	100
9	Poland	Z140	Z135	Z130	Z125	Z120	Z115
10	India	FG400	FG350	FG300	FG260	FG200	FG150
11	Romania	FC400	FC350	FC300	FC250	FC200	FC150
12	Spain		FG35	FG30	FG25	FG20	FG15
13	Belgium	FGG40	FGG35	FGG30	FGG25	FGG20	FGG15	FGG10
14	Australia	T400	T350	T300	T260	T220	T150
15	Sweden	0140	0135	0130	0125	0120	0115	0110
16	Hungary	OV40	OV35	OV30	OV25	OV20	OV15
17	Bulgaria		Vch35	Vch30	Vch25	Vch20	Vch15
18	International Standard (IS0)		350	300	250	200	150	100
19	Pan-American Standard (COPANT)	FG400	FG350	FG300	FG250	FG200	FG150	FG100
20	Taiwan, China			FC300	FC250	FC200	FC150	FC100
21	Netherlands		GG35	GG30	GG25	GG20	GG15
22	Luxembourg	FGG40	FGG35	FGG30	FGG25	FGG20	FGG15
23	Austria		GG35	GG30	GG25	GG20	GG15

4、Application areas of grey cast iron

1) Ferritic gray cast iron, grade HT100, is suitable for unimportant castings with small loads and no special requirements for friction and wear, such as protective covers, covers, oil pans, handwheels, brackets, base plates, heavy hammers, small handles, etc.

2) Ferritic-pearlitic gray cast iron, grade HT150, is suitable for castings with medium loads, such as machine bases, brackets, boxes, tool holders, bed bodies, bearing seats, workbenches, pulleys, end covers, pump bodies, valve bodies, pipelines, flywheels, motor bases, etc.

3) Pearlitic gray cast iron, grade HT250, is suitable for more important castings that bear larger loads and require certain air tightness or corrosion resistance, such as cylinders, gears, machine bases, flywheels, bed bodies, cylinder blocks, cylinder liners, pistons, gear boxes, brake wheels, coupling discs, medium pressure valve bodies, etc.

4) Nodular cast iron, with grades HT300 and HT350, is used for important castings that require high load, wear resistance and high air tightness, such as the bed, base and frame of heavy machine tools, shearing machines, presses and automatic lathes, high-pressure hydraulic parts, piston rings, gears, cams and bushings with large forces, crankshafts, cylinder blocks, cylinder liners and cylinder heads of large engines, etc.

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