4Cr5MoSiV is a Chinese national standard grade, equivalent to AISI H11 in the United States. Compared with 4Cr5MoSiV1(AISI H13/DIN 1.2343), the vanadium content in the composition of 4Cr5MoSiV is lower. 4Cr5MoSiV1 generally has higher hot strength and hardness, and is more widely used, but 4Cr5MoSiV is still favored for high-speed hammer forging dies due to its excellent thermal fatigue resistance.

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

C	Si	Mn	Cr	Mo	V	P	S
0.33 – 0.43%	0.80 – 1.20%	0.20 – 0.50%	4.75 – 5.50%	1.10 – 1.60%	0.30 – 0.60%	≤0.030%	≤0.030%

2. Physical Properties of 4Cr5MoSiV

2.1 Critical Temperatures

Critical Point	Ac₁	Ac₃	Ar₁	Ar₃	Ms	Mf
Temperature (approx.) / °C	853	912	720	773	310	103

2.2 Coefficient of Linear Expansion

Temperature / °C	20 ~ 100	20 ~ 200	20 ~ 300	20 ~ 400	20 ~ 500	20 ~ 600	20 ~ 700
Coeff. of Linear Expansion α / 10⁻⁶ °C⁻¹	10.0	10.9	11.4	12.2	12.8	13.3	13.6

2.3 Thermal Conductivity

Temperature / °C	100	200	300	400	500	600	700
Thermal Conductivity λ / [W/(m·K)]	25.9	27.6	28.4	28.0	27.6	26.7	25.9

2.4 Modulus of Elasticity

Temperature / °C	20	100	200	300	400	500
Modulus of Elasticity E / MPa	227,000	221,000	216,000	208,000	200,000	192,000

2.5 Density and Specific Heat Capacity

Density / (g/cm³)	Specific Heat Capacity cₚ (20°C) / [J/(kg·K)]
7.69	459.8

3. Hot Forging Process Specification for 4Cr5MoSiV Steel

Item	Heating Temperature / °C	Initial Forging Temperature / °C	Final Forging Temperature / °C	Cooling Method
Steel Ingot	1140 ~ 1180	1100 ~ 1150	≥900	Sand cooling or pit cooling
Steel Billet	1120 ~ 1150	1070 ~ 1100	850 ~ 900	Sand cooling or pit cooling

4. Heat Treatment of 4Cr5MoSiV

4.1 Preheating

Preliminary Heat Treatment Plan	Process Parameters
Post-forging Annealing	Heating temperature 860 ~ 890°C, hold for 2 ~ 4h; furnace cool to below 500°C then air cool. Hardness after annealing ≤229HBW.
Stress Relief Annealing	Heating temperature 730 ~ 760°C, hold for 3 ~ 4h, furnace cool or air cool.

4.2 Quenching

① Recommended Quenching Process Specification

Quenching Temperature / °C	Quenching Medium	Quenching Medium Temperature / °C	Subsequent Step	Hardness HRC
1000 ~ 1030	Oil or Air	20 ~ 60	Cool to oil temperature	53 ~ 55

② Relationship between Quenching Temperature and Hardness

Quenching Temperature / °C	950	975	1000	1025	1050	1075	1100
Hardness HRC	51	53	54.5	56	58	58.5	57.5

4.3 Tempering

① Recommended Tempering Process Specification

Purpose of Tempering	Temperature / °C	Equipment	Cooling	Number of Tempers	Hardness HRC
Eliminate stress and reduce hardness	530 ~ 580	Molten salt bath furnace or air furnace	Air cool	2	47 ~ 49

Note: The second tempering temperature is usually 20 ~ 30°C lower than the first.

② Mechanical Properties after Tempering at Different Temperatures

Tempering Temperature / °C	500	550	600	650
Hardness HRC	57	54.5	46.5	37
aᴋ / (J/cm²)	20	45	60	66

Note: 1000°C air cool, 580°C temper.

4.4 Recommended Surface Strengthening Treatment Process Specification

Process	Temperature / °C	Time / h	Medium	Layer Thickness / mm	Surface Hardness HV
Nitriding	560	2	KNO₃ 50% + NaNO₃ 50% (Mass Fraction)	0.04	640 ~ 690
Nitriding	580	8	Natural Gas + Ammonia	0.25 ~ 0.30	830 ~ 860
Nitriding	540	12 ~ 20	Ammonia decomposition rate 30% ~ 60%	0.15 ~ 0.20	550 ~ 750

5. Mechanical Properties

4Cr5MoSiV (H11) steel is an air-cooling hardening type hot-work tool steel. It has good toughness, and after heat treatment strengthening, its strength can reach over 2070 MPa. Because it can be hardened in air, quenching deformation and residual stress are small, and the tendency for surface oxidation is also small. It can produce a secondary hardening phenomenon and can achieve optimal performance when tempered above 510°C. After high-temperature tempering, most of the internal stress can be eliminated. It has good thermal stability and can resist the erosion of molten aluminum alloy. 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 High-Temperature Mechanical Properties

Test Temperature / °C	Rₘ / MPa	Rₑₗ / MPa	A (%)	Z (%)
300	1504	1311	12.0	39.1
600	895	794	21.9	72.9
650	471	402	33.1	85.5
700	226	179	55.0	94.5

5.2 High-Temperature Hardness

Test Temperature / °C	300	450	600	650	700	750
Hardness HV	491.5	448.5	384.0	302.5	227.5	178.5

Note: Original hardness of the specimen 49~50HRC.

5.3 High-Temperature Impact Toughness

Test Temperature / °C	300	600	650	700
Impact Absorption Energy K / J	28.8	31.0	36.5	70.0

5.4 Thermal Fatigue Performance

	Grade
20 ~ 650°C repeated 1000 times	8.2
20 ~ 750°C repeated 1000 times	14.6

5.5 Thermal Wear Resistance

4Cr5MoSiV Steel Thermal Wear Resistance (I)

Rotations/times	300	600	900	1200	1500	2500
Weight Loss / mg	0.67	0.80	1.4	1.63	1.97	2.62

Note: Test temperature 800 ~ 850°C, pressure 784 ~ 882N, specimen hardness 49 ~ 50HRC.

Table 5-89 4Cr5MoSiV Steel Thermal Wear Resistance (II)

Rotations/times	100	200	300	400	500	600	700	1000
Weight Loss / mg	0.77	1.67	2.50	3.47	4.33	4.90	5.60	7.40

Note: Test temperature 910 ~ 950°C, pressure 1784 ~ 1813N, specimen hardness 49 ~ 50HRC.

5.6 Tempering Resistance

Temperature / °C	500 (Secondary Hardening Peak Temperature)	560	615	600	653
Hardness HRC	55.0 (Highest Secondary Hardening Hardness)	49.0	42.0	36.0	35.0

Note: Specimen quenched in oil at 1020°C, hardness 59~60HRC.

5.7 Thermal Corrosion Resistance

Test Temperature and Time	620°C × 4h	680°C × 4h
Weight Loss / (g/dm²)	4.4188	16.4

5.8) Fatigue Limit

Test Temperature / °C	Room Temp	300	400	450	500
σ-1 / MPa	880	680	640	630	610
σ-1k / MPa	570	440	430	—	420

5.9 Thermal Stability of 4Cr5MoSiV Steel at 620°C

Holding Time / h	2	4	6	8	11.5	14.5	17.5	21
Hardness HRC	39.4	38.4	36.9	35.1	34.4	33.2	32.6	32.3

Note: Original hardness of the specimen was 49.9 HRC.

6. Applications

4Cr5MoSiV (H11) steel is commonly used for manufacturing die-casting molds for aluminum castings, hot extrusion dies, tools and core rods for piercing, press forging dies, plastic molds, etc. Additionally, due to its good medium-temperature strength, it is also used for manufacturing structural components for aircraft, rockets, and parts for steam turbines and gas turbines.