9Cr18Mo and 102Cr17Mo are the same type of steel. 9Cr18Mo is the old designation used in the Chinese national standard GB/T 1220-1992. 102Cr17Mo is the new designation adopted in the revised Chinese national standards GB/T 1220-2007 and GB/T 20878-2007.

9Cr18Mo(102Cr17Mo) is a high-carbon, high-chromium martensitic stainless steel, developed from the 95Cr18 (9Cr18) grade through the addition of molybdenum (Mo). Consequently, it exhibits superior hardness, wear resistance, high-temperature strength, tempering resistance, and corrosion resistance compared to 95Cr18 (9Cr18) steel. This steel also possesses good high-temperature dimensional stability, making it suitable for manufacturing plastic molds, bearings, surgical instruments, and measuring tools that operate under high loads, high wear, and corrosive conditions. As a ledeburitic steel, it is prone to the formation of non-uniform carbide segregation, which can adversely affect the service life of components. Therefore, it is imperative to control the processing parameters and select an appropriate processing ratio during hot working.

1. Compostion(GB/T 20878-2007)

C	Cr	Mo	Ni	Si (≤)	Mn (≤)	P (≤)	S (≤)
0.95 – 1.10	16.00 – 18.00	0.40 – 0.70	-0.6	0.8	0.8	0.04	0.03

Equivalent Grades and Compositions

Standard	Steel Grade	C	Cr	Mo	Ni	Si (≤)	Mn (≤)	P (≤)	S (≤)
Japan JIS	SUS440	0.95 – 1.20	16.00 – 18.00	≤(0.75)	-0.6	1	1	0.04	0.03
USA ASTM	440C / S4400C	0.95 – 1.20	16.0 – 18.0	≤0.75	—	1	1	0.04	0.03
International ISO	X105CrMo17	0.95 – 1.20	16.0 – 18.0	0.40 – 0.80	—	1	1	0.04	0.015
Europe EN	X105CrMo17 / 1.4125	0.95 – 1.20	16.0 – 18.0	0.40 – 0.80	—	1	1	0.04	0.015

2. Critical Points of 9Cr18Mo(102Cr17Mo)

• Ac₁​≈815∼865℃: This is the lower critical temperature upon heating. It represents the temperature range at which austenite begins to form from the ferrite-carbide matrix.
• Ar₁​≈665∼765℃: This is the lower critical temperature upon cooling. It represents the temperature range where the transformation of austenite to ferrite or pearlite is completed.
• Ms​≈145℃: This is the Martensite start temperature. It is the temperature at which the transformation of austenite to martensite begins during rapid cooling (quenching).

3. Hot Froging Process of 9Cr18Mo(102Cr17Mo)

Item	Heating Temperature/°C	Initial Forging Temp./°C	Final Forging Temp./°C	Cooling Method
Steel Ingot	1130 ~ 1150	1080 ~ 1100	850 ~ 900	Sand Cooling
Steel Billet	1100 ~ 1120	1050 ~ 1080	850 ~ 900	Sand Cooling

Special attention should be paid to the hot working process of 9Cr18Mo (102Cr17Mo)steel. It is recommended to use a cold-charged furnace for heating, and the heating rate should not be too fast, especially below 700°C. At the same time, the final forging temperature should be controlled at a higher level, and strict attention should be paid to the cooling conditions.

4. Heat Treatment of 9Cr18Mo(102Cr17Mo)

The processes for preliminary heat treatment are as follows:

• Recrystallization Annealing: Heat to a temperature of 730∼750°C, followed by air cooling.
• Annealing: Heat to a temperature of 850∼870°C and soak for 4 to 6 hours. Subsequently, furnace cool to below 600°C, followed by air cooling. The hardness after annealing should be ≤255HBW.

• Quenching: Heat to a temperature of 1050∼1100∘C, followed by an oil quench. The as-quenched hardness should be ≥58HRC.
• Tempering: Heat to a temperature of 160∼180∘C and soak for 3 to 5 hours. The final hardness after tempering should be ≥58HRC.

The effect of quenching temperature and cold treatment on hardness

Quenching Temperature (°C)	1020	1040	1060	1080	1100
Hardness after Conventional Quenching (HRC)	58.5	58	61.5	61	61
Hardness after Cold Treatment (HRC)	60	60.5	62	63	64

Relationship between hardness and tempering temperature

	Tempering Temperature (°C)	Untempered	100	200	300	400	500	600	700
950°C Air Cooling	Hardness (HRC) / Quenching	50	47	48	48	47	47	38	25
1000°C Air Cooling		56	51.5	52	50	49	49	40.5	27
1050°C Air Cooling		58	56	56	53	52	52	43	29
1100°C Air Cooling		60.5	57	58	56	54	55	47	32

5. Mechanical Properties

Influence of Quenching Temperature and Cryogenic Treatment on Mechanical Properties

Quenching Temperature /°C	Not Cryogenically Treated		After -75°C Cryogenic Treatment (held for 1h)
	σbb/MPa	aK / J・cm⁻²	σbb/MPa	aK / J・cm⁻²
1020	3250	30	30	30
1040	3000	37	37	11
1060	3500	40	40	6
1080	2750	25	25	3
1100	2500	3	3	2.5

6. Corrosion Resistance

Corrosion Resistance of 102Cr17Mo (9Cr18Mo) Steel

Heat Treatment Process	Hardness HRC	Medium Conditions			Corrosion Rate /g·(m²·h)⁻¹
		Medium	Mass Fraction (%)	Temperature/°C
1050°C Oil Quenching	61	Sulfuric Acid	2	Boiling	575.6
		Sulfuric Acid	5		1003.9
		Nitric Acid	40		1.15
1050°C Oil Quenching, 150°C Tempering for 1h	60	Sulfuric Acid	2		502
		Sulfuric Acid	5		968.3
		Nitric Acid	40		1.04