4Cr5MoSiV1 is a hot-work tool steel grade under the Chinese standard GB/T 1299. It is a widely used chromium-molybdenum-vanadium (Cr-Mo-V) hot work tool steel, commonly known internationally by designations such as H13 (AISI/ASTM), SKD61 (JIS), 1.2344(DIN), and X40CrMoV5-1 (ISO/EN/DIN). This steel grade has excellent strength and toughness, good hot workability, and resistance to thermal fatigue.

1. Chemical Composition (GB/ T 1299—2000)

C	Si	Mn	Cr	Mo	V	P	S
0.32-0.45	0.80-1.20	0.20-0.50	4.75-5.50	1.10-1.75	0.80-1.20	≤0.030	≤0.030

2. Physical Properties of 4Cr5MoSiV1

2.1 Critical Point Temperatures

Critical Point	Ac1	Ac3	Ar1	Ar3	Ms	Mf
Temperature /°C	860	915	775	875	340	215

2.2 Linear Expansion Coefficient

Temperature/°C	20 ~ 100	20 ~ 200	20 ~ 300	20 ~ 400	20 ~ 500	20 ~ 600	20 ~ 700
Linear Expansion Coefficient α/×10⁻⁶℃⁻¹	9.1	10.3	11.5	12.2	12.8	13.2	13.5

2.3 Thermal Conductivity

Temperature/°C	250	650
Thermal Conductivity λ/[W/(m·K)]	32.2	28.8

2.4 Density and Elastic Modulus

Density/(g/cm³)	Elastic Modulus E/MPa
7.8	210 000

3. Hot Forging Process Specification of 4Cr5MoSiV1

Item	Heating Temperature/°C	Initial Forging Temperature/°C	Final Forging Temperature/°C	Cooling Method
Steel Ingot	1140 ~ 1180	1100 ~ 1150	850 ~ 900	Slow Cooling (Sand or Pit Cooling)
Steel Billet	1120 ~ 1150	1050 ~ 1100	850 ~ 900	Slow Cooling (Sand or Pit Cooling)

4. Heat Treatment of 4Cr5MoSiV1

4.1 Preheating

Preheating Treatment Process Specification for 4Cr5MoSiV1 Steel

Pre-heat Treatment Plan	Process Parameters
Post-forging Annealing Process	Heating temperature: 860 ~ 890°C, hold for 3 ~ 4h, cool to below 500°C then air cool. Hardness after annealing ≤229HBW, microstructure is globular pearlite + small amount of carbides.
Stress Relief Annealing	Heating temperature: 730 ~ 760°C, hold for 3 ~ 4h, furnace cool.

Hardness and Microstructure of 4Cr5MoSiV1 Steel Before and After Annealing

	Before Annealing	After Annealing	Microstructure (Before Annealing)	Microstructure (After Annealing)
Indentation Diameter/mm	≈2.75	≥3.9	Sorbite or Martensite	Globular pearlite + small amount of carbides
HBW	≈500	≤241

4.2 Quenching

Quenching Process Specification for 4Cr5MoSiV1 Steel

Quenching Temperature/°C	Cooling	Hardness HRC
1020 ~ 1080	Quenching Coolant	Quenching Coolant Temperature/°C
	Oil or Air	20 ~ 60

Relationship between Quenching Temperature, Hardness, and Grain Size for 4Cr5MoSiV1 Steel

Quenching Temperature/°C	930	950	980	1000	1020	1040	1060	1080	1100
Hardness HRC	50.3	52	53.5	54.8	56.3	57.8	58.2	59.1	59.1
Grain Size/Grade	—	11.2	11.1	11.1	11.1	11	10	8	7

3. Tempering

Tempering Process Specification for 4Cr5MoSiV1 Steel

Purpose	Tempering Temperature/°C	Equipment	Cooling	Tempering Hardness HRC
Relieve stress, reduce hardness	560 ~ 580¹	Molten salt bath or air furnace	Air cool	47 ~ 49

Note: Usually tempered twice. The second tempering temperature is 20°C lower than the first.

Relationship between Tempering Temperature and Hardness for 4Cr5MoSiV1 Steel

Tempering Temperature /°C	Hardness HRC	Tempering Temperature /°C	Hardness HRC
100	59.0	500	57.5
200	57.0	550	53.5
300	54.5	600	49.5
400	54.5	650	40.0
450	57.5	700	30.0

4. Surface Strengthening Treatment Process Specifications for 4Cr5MoSiV1 Steel

Process	Temperature/°C	Time/h	Medium	Diffusion Layer
				Depth/mm	Microhardness HV
Nitriding	560	2	50% KNO₃ + 50% NaNO₃ (mass fraction)	0.04 – 0.07	640 – 690
Nitriding	580	8	Natural Gas + Ammonia	0.25	835 – 860
Nitriding	530 – 550	12 – 20	Ammonia decomposition rate α is 30% – 60%	0.12 – 0.20	550 – 760

5. Mechanical Properties

4Cr5MoSiV1 (H13) steel is an air-hardening hot-work tool steel. It has good toughness and high strength. Because it can be hardened in air, the quenching deformation and residual stress are small, and the tendency for surface oxidation is also small. It can produce a secondary hardening phenomenon, has good thermal stability, and can resist the erosion of molten aluminum alloy. At a working temperature below 650°C, it has high ductility, impact toughness, oxidation resistance, thermal fatigue resistance, as well as high creep strength and tensile strength.

5.1 Longitudinal Mechanical Properties at Room Temperature

Tempering Temperature/°C	After Quenching	200	400	500	520	550	580	600	650	700
Hardness HRC	56	54	54	55.5	54	52.5	49	45.5	33	28
Tensile Strength Rm/MPa	—	—	2040	2100	2080	1980	1780	1650	1180	—
Reduction of Area Z (%)	—	—	40	34	40	48	53	54	55	—
Elongation A (%)	—	—	11	11	11.5	12	12.5	14	18	—
Impact Toughness ak/(J/cm²)	—	—	40	32	35	50	60	70	100	—

Note: 1020°C oil quenching, tempered 2 times.

5.2 Fatigue Performance of 4Cr5MoSiV1 Steel

Test Temperature/°C	Room Temperature	540
σ₋₁/MPa	730	510
σ₋₁ₖ/MPa	670	370

5.3 Longitudinal Impact Toughness of 4Cr5MoSiV1 Steel Bar¹

Tempering Temperature/°C	Hardness2 HRC	Charpy V-notch impact absorption energy/J at the following test temperatures
		-73°C	21°C	260°C	540°C	595°C
524	54	7	14	27	31	—
565	52	7	14	30	34	343
607	47	8	24	41	45	43
615	43	9.5	24	52	60	57

1. Air-cooled from 1010°C, and secondary tempered, tempered twice at each specified temperature.
2. Room temperature.
3. 565°C.

5.4 Longitudinal Tensile Properties of 4Cr5MoSiV1 Steel Bar¹

Room Temp. Hardness HRC	Test Temperature/°C	Tensile Strength Rm/MPa	Lower Yield Strength Rm/MPa	Elongation after Fracture A (%)	Reduction of Area Z (%)
522	425	1620	1240	13.7	50.6
	540	1305	1000	13.9	54
	595	1020	825	17.5	65.4
	650	450	340	28.9	88.9
483	425	1400	1150	15	59.9
	540	1160	960	17.1	62.4
	595	940	750	18	68.5
	650	455	350	33.6	89
444	425	1200	1005	17	64.1
	540	995	820	20.6	70
	595	827	690	22.6	74
	650	450	350	28.4	87

1. Quenched at 1010°C (1850°F) in oil, then tempered to the specified hardness.
2. Tempered at 527°C for 2 × 2 hours.
3. Tempered at 575°C for 2 × 2 hours.
4. Tempered at 605°C for 2 × 2 hours.

6. Applications

4Cr5MoSiV1 steel is widely used in the manufacture of hot extrusion dies and mandrels, hammer forging dies, forging press dies, precision forging dies, and die-casting molds for aluminum, copper, magnesium, and their alloys.