AISI H13 Tool Steel Ι DIN 1.2344 Ι SKD61

H13 steel is a main hot working tool steel with balanced performance and wide application as per ASTM A681 standard.

As one of the internationally recognized general-purpose hot working die steels, H13 steel has achieved a good balance between high temperature strength, toughness, and thermal fatigue resistance. With good processing and versatility, it has become one of the preferred materials for manufacturing aluminum alloy die-casting dies, hot forging dies, hot extrusion dies, and other dies that withstand high temperature, high stress, and thermal cycle loads.

H13 steel can fully exert its potential and significantly extend the life of the die through reasonable heat treatment and surface treatment.

CHEMICAL COMPOSITION：H13 & EQUIVALENT GRADE

Standard	Grade	C	Si	Mn	P	S	Cr	Mo	V
ASTM A681	H13	0.32-0.45	0.8-1.2	0.20-0.50	0.03	0.03	4.75-5.50	1.1-1.75	0.8-1.2
DIN ISO 4957	1.2344	0.37-0.42	0.9-1.2	0.3-0.5	0.03	0.03	4.8-5.5	1.2-1.5	0.9-1.1
GB/T 1299	4Cr5MoSiV1	0.32-0.42	0.8-1.2	0.2-0.5	0.03	0.03	4.75-5.5	1.1-1.75	0.8-1.2
JIS G4404	SKD61	0.35-0.42	0.8-1.2	0.25-0.5	0.03	0.03	4.8-5.5	1-1.5	0.8-1.15

H13 Core Element Characteristics

Carbon (C): 0.32-0.45% – Provides basic hardness and wear resistance.
Chromium (Cr): 4.75-5.50% – Mainly provides hardenability, high temperature strength, oxidation resistance and corrosion resistance.
Molybdenum (Mo): 1.10-1.75% – Significantly improves hardenability, high temperature strength, resistance to temper softening (secondary hardening) and wear resistance.
Vanadium (V): 0.80-1.20% – Forms fine and hard carbides, greatly improves wear resistance, refines grains and contributes to secondary hardening.
Silicon (Si): 0.80-1.20% – Improves strength, oxidation resistance and resistance to temper softening.
Manganese (Mn): 0.20-0.50% – Improves hardenability and solid solution strengthening.

H13 steel Core Features:

Excellent high temperature strength and hardness: It can maintain high hardness and strength at high temperatures (usually up to about 600°C), which is the key performance of hot working die steel.
Good toughness and thermal fatigue resistance: It can withstand the stress generated by repeated heating and cooling (thermal cycle) and resist the generation and expansion of cracks (such as cracking). This is the main reason why H13 steel is widely used in die casting, forging and other occasions with repeated thermal shock.
Good wear resistance: Vanadium and chromium carbides provide good resistance to wear, especially at high temperatures.
Good hardenability: Due to the high content of chromium and molybdenum, molds with larger cross-sections can also obtain uniform hardness and performance.
Good thermal conductivity: It is conducive to the transfer of heat during the working process of the mold and reduces thermal stress.
Good resistance to temper softening (thermal stability): Working for a long time at high temperature, the hardness decreases slowly and the service life is long.
Good comprehensive processing performance: It has good machinability in the annealed state; the heat treatment process is relatively mature and stable; polishing, nitriding and other surface treatments can be performed.
Moderate corrosion resistance: Chromium content provides better atmospheric corrosion and oxidation resistance than carbon tool steel and low alloy steel, but not as good as stainless steel.

H13 STEEL PHYSICAL PROPERTY

Temperature	20°C	400°C	1110°C
Density，g/cm3	7.8	7.7	7.6
Modulus of elasticity，N/mm2	210000	180000	140000
Coefficient of thermal expansion，per °C from 20°C	—	12.6 x 10^–6	13.2 x 10^–6
Thermal conductivity，W/m °C	25	29	30
Melting point	1427°C
Specific Gravity	7.75
Machinability	65-70% of a 1% carbon steel

H13 STEEL FORGING

The forging of H13 steel is a crucial step in its manufacturing process, aiming to obtain a dense internal structure, uniform component distribution, reasonable streamline distribution and the required preliminary shape, laying the foundation for subsequent heat treatment and finishing. Due to the high alloy content of H13 steel (especially Cr, Mo, V), relatively poor thermal conductivity and sensitivity to overheating, its forging process needs to be strictly controlled.

Forging process	Temperature range	Operation requirements
Preheating temperature	650-750°C	Extremely important! H13 steel has poor thermal conductivity and must be preheated slowly and fully to avoid cracking due to excessive thermal stress.
Initial Forging Temperature	1050-1150°C	It is strictly forbidden to exceed 1200°C, otherwise it will lead to coarse grains, overheating or even overburning, which will seriously damage the material properties.
Final Forging Temperature	850-900°C	The final forging temperature must be strictly controlled, generally not less than 850°C - 900°C. Below this temperature, the plasticity of the steel drops sharply, the deformation resistance increases greatly, and continued forging is prone to cracks, and the formed work hardening structure is difficult to completely eliminate in subsequent annealing. Forging in the blue brittle zone (about 200-400°C) is absolutely prohibited.
Cooling After Forging	Furnace cooling/sand cooling	This is one of the most problematic links in H13 forging. After slow cooling, annealing must be carried out immediately.

H13 STEEL HEAT TREATMENT

The heat treatment of H13 steel is the core link that determines its final performance. It needs to be precisely controlled to achieve its excellent high temperature strength, toughness, thermal fatigue resistance and wear resistance. The main process includes preliminary heat treatment (annealing) and final heat treatment (quenching + tempering), and surface strengthening treatment can also be performed according to needs.

Preliminary Heat Treatment: Spheroidizing Annealing

Annealing purpose:
1.Eliminate residual stress and uneven structure after forging or rolling.
2.Obtain uniform and fine spherical pearlite structure, reduce hardness (180-220 HB), and facilitate processing.
3.Provide an ideal organizational foundation for subsequent quenching.
Annealing process:
1.Heating temperature: 840-870°C (slowly increase temperature to avoid thermal stress).
2.Housing time: 2-4 hours (depending on the size of the workpiece, to ensure through burning).
3.Cooling method:
–Slow cooling method: furnace cooling at a rate of ≤30°C/hour to below 500°C and air cooling out of the furnace.
–Isothermal method (more commonly used):After heating to 840-870°C and keeping warm, quickly cool to 720-760°C (avoid carbide precipitation). Keep warm at isothermal temperature for 4-6 hours to fully spheroidize the carbides.Furnace cooling to 500°C and air cooling.
4.Structure after annealing: evenly distributed fine spherical carbides (Cr, Mo, V carbides) and ferrite matrix.

Final Heat Treatment: Quenching + Tempering
H13 Quenching (Austenitizing)
Key Process Parameters:

Preheating: must be preheated in stages (600-650°C + 800-850°C) to avoid thermal stress and cracking (due to poor thermal conductivity of H13).
Austenitizing temperature: 1020-1050°C (most commonly used range).
Temperature selection principle:
-1020-1030°C: focus on high toughness (such as hot forging dies with large impact loads).
-1040-1050°C: focus on high hardness and wear resistance (such as die casting dies).
It is strictly forbidden to exceed 1100°C (grain coarsening, toughness drops sharply).
Insulation time: calculated according to effective thickness (1.2-1.5 minutes/mm), avoid overburning or decarburization.
Cooling method:
–Gas quenching (recommended): vacuum high-pressure gas quenching (nitrogen or argon), small deformation, good surface quality (hardness 55-58 HRC).
-Oil quenching: traditional method, low cost, but high risk of deformation and cracking (need to be tempered in time).

H13 Tempering
Purpose of Tempering:

Eliminate quenching stress and improve toughness.
Improve high temperature hardness and thermal stability through secondary hardening (precipitation of Mo and V carbides).
It is necessary to temper 2~3 times (because the residual austenite is transformed into untempered martensite after the first tempering).

Tempering Process Key Points:

Temperature range: 540-650°C (select according to target hardness):

Tempering temperature (°C)	Typical hardness (HRC)	Applicable scenarios
540-560°C	50-52	High wear resistance requirements (before surface treatment)
580-600°C	48-50	Best comprehensive performance (die casting mold/hot forging mold)
620-650°C	44-46	High toughness requirements (such as impact forging mold)

Holding time: 2-4 hours each time (workpiece through burning).
Cooling: After each tempering, air cool to room temperature before the next one.
Secondary hardening peak: Appears at about 550°C tempering (due to Mo₂C/V₄C₃ carbide dispersion precipitation).

H13 Steel Key Properties after Heat Treatment

Hardness:44-52 HRC (depending on tempering temperature)
Tensile strength:1500-2000 MPa
Impact toughness:15-30 J/cm² (Charpy V-notch)
High temperature strength:≥1000 MPa at 600°C
Thermal fatigue resistance:Excellent (due to high toughness and thermal conductivity)

Surface Strengthening Treatment (Optional)
To improve wear resistance, molten metal corrosion resistance and seizure resistance, the following are often performed:

Nitriding/nitrocarburizing:
-Surface hardness can reach 1000-1200 HV (equivalent to more than 70 HRC).
-Deepness of nitriding layer: 0.1-0.3 mm (gas nitriding or ion nitriding).
PVD/CVD coating:
-TiN, CrN, TiAlN and other coatings significantly reduce the friction coefficient and resist aluminum liquid adhesion (preferred for die casting molds).

Note: Surface treatment must be performed after final tempering (to avoid high temperature affecting the coating/nitriding layer).

H13 STEEL MAIN APPLICATION AREAS

Die casting mold: This is the main application area of H13 steel, especially for key components such as core, cavity, slider, ejector pin, etc. of aluminum alloy, magnesium alloy, zinc alloy die casting mold. It has good resistance to erosion and thermal fatigue of molten metal.
Hot forging mold: used for forging hammer forging die, press forging die, forging press die (such as connecting rod, crankshaft, gear forging die, etc.), bearing impact load and high temperature.
Hot extrusion die: used for extrusion cylinder, extrusion rod, extrusion die (die pad, die core, die sleeve) of metals such as aluminum, copper, brass, and steel.
Plastic mold: H13 is also a common choice for high-performance plastic molds (such as engineering plastics, injection molds containing abrasive fillers) that require high wear resistance, high polishing and good corrosion resistance.
Other hot working tools: such as hot shear blades, hot rolling rollers (auxiliary rollers), copper alloy gravity casting molds, etc.