AISI H13 open-die forgings

What is AISI H13 tool steel?

AISI H13 is a chromium–molybdenum–vanadium hot work tool steel, air hardening, with nominally 5 % chromium, 1.4 % molybdenum and 1 % vanadium. It is the most widely used hot work tool steel in the world, and it is the default material for aluminium high-pressure die casting dies, aluminium extrusion tooling and hot forging dies.

It holds that position on balance rather than on any single property. The 5 % chromium and the molybdenum give H13 hot strength, so it keeps its hardness while the die face sits at 500–600 °C. Vanadium forms fine carbides that resist hot wear and washout. Carbon is held near 0.40 %, low for a tool steel, which leaves enough toughness for a die face that takes molten aluminium and then a water-based release agent spray, hundreds of times an hour. That cycle is what produces heat checking, the crazed surface cracking that ends most die lives, and nothing else at comparable cost resists it as well.

Because H13 through-hardens in air, it also works well in cold-work and general tooling roles where section thickness would defeat an oil-hardening grade. In that role it offers better hardenability and wear resistance than a quenched-and-tempered alloy steel such as AISI 4140.

Where forging comes in

H13 is almost never used as-cast. Ingot cast H13 contains centreline porosity, coarse primary carbides and alloy segregation, all of which become crack initiation sites in a die. Open-die forging closes that porosity, breaks up and redistributes the carbides, and refines the grain. Jiangyin Jiangnan Metal forges every H13 order to a minimum reduction ratio of 4:1, and to 6:1 or higher where the buyer specifies premium die casting quality. The forging ratio is recorded on the mill certificate.

H13 equivalent grades and standards

H13 appears under a different designation in almost every national standard. The nominal chemistry is the same and the grades are interchangeable in most applications, but the composition windows differ slightly between standards. On critical tooling, state which standard the certificate must reference.

NADCA #207, Special Quality Die Steel & Heat Treatment Acceptance Criteria for Die Casting Dies, is not an alternative chemistry. It sits on top of H13 chemistry and sets minimum requirements for melt practice, annealed microstructure, microcleanliness, ultrasonic soundness and transverse Charpy V-notch toughness. A NADCA Grade B H13 must average 8 ft·lb (10.8 J) on the Charpy with no individual reading below 6 ft·lb (8.1 J).

H13 chemical composition

The composition below is the ASTM A681 window for H13, which Jiangyin Jiangnan Metal works to unless the order calls out a different standard. Both ladle and product analysis are reported on the mill certificate against the heat number.

Source: ASTM A681 Standard Specification for Tool Steels Alloy; cross-checked against EN ISO 4957 for 1.2344. For premium die casting quality, Jiangyin Jiangnan Metal restricts P and S well below the standard maxima and reports the actual values.

H13 physical and mechanical properties

Physical properties

Indicative values for a hardened and double-tempered condition around 45 HRC. Thermal conductivity in particular varies with melt practice and tempering; treat these as design guidance, not acceptance values.

Strength against hardness

H13 is specified by hardness, not by tensile strength, and the tensile figures below follow from the hardness rather than being ordered independently. Use them for design calculation only.

Converted from hardness per ASTM A370 conversion practice. A tensile test on the actual heat can be run and certified on request; it is not a substitute for the hardness acceptance in ASTM A681.

H13 forged shapes and size range

Jiangyin Jiangnan Metal forges H13 to the shape closest to the finished tool, which cuts the buyer's machining time and scrap. The ranges below are the standard envelope; enquire for anything outside them.

Maximum single piece weight is approximately 30 tonnes. Pieces are supplied black forged, shot blasted, rough machined with 3–6 mm stock per surface, or finish machined to drawing. There is no minimum tonnage. A single die block is an acceptable order.

Delivery condition

• Forged and annealed. The standard condition, 235 HBW maximum, ready for your own machining and heat treatment.
• Forged, annealed and rough machined. Turned, milled or gun-drilled with an agreed stock allowance.
• Hardened and tempered to 44–52 HRC. Quenched and double tempered in-house, hardness survey certified.
• ESR or premium ESR. Remelted stock for die casting and high-cycle tooling.

How Jiangnan Metal forges H13

The route below is what the mill certificate documents for a standard H13 order. Every stage removes a defect that would otherwise end up in the buyer's die.

1. Melt and remeltElectric arc furnace plus ladle refining and vacuum degassing for standard H13. For premium tooling the ingot is electroslag remelted, which lowers sulphur and oxide inclusions and tightens carbide size and distribution.
2. Homogenise and upsetThe ingot is soaked, then upset and drawn out to break the as-cast dendritic structure. This is the step that determines whether banding will show up later under the microscope.
3. Open-die forge to 4:1 minimumForged on hydraulic presses with manipulators, cross-forged so that properties are as close to isotropic as the section allows. Premium die casting quality is forged to 6:1 or higher. The achieved ratio is recorded.
4. Post-forge annealSlow-cooled spheroidise anneal to 235 HBW maximum, giving a uniform spheroidised carbide structure that machines predictably and responds evenly to the buyer's hardening cycle.
5. Rough machine and de-scaleTurning, milling or blasting removes decarburised skin. Decarburisation left on a die surface becomes a soft, crack-prone layer in service.
6. Ultrasonic test and inspect100 % volumetric UT to SEP 1921 or ASTM A388, plus hardness survey, dimensional check and chemistry verification on the finished piece.
7. Certify and packEN 10204 3.1 certificate issued against the heat number, then rust-preventive coating, VCI wrap and seaworthy crating or steel pallet.

H13 heat treatment route

H13 will not perform at its rated toughness unless the quench is fast enough and the temper is done twice. The route below follows ASTM A681 practice with the NADCA #207 quench-rate requirement, and it is the cycle Jiangyin Jiangnan Metal runs when heat treatment is ordered with the forging.

1. PreheatHeat at no more than 222 °C/h (400 °F/h) to 620–680 °C and equalise, then raise to 815–870 °C and equalise. Use both stages on complex or thick tools to limit distortion; simple tools need only the second stage.
2. AustenitiseHeat rapidly from preheat to 1000–1030 °C (1830–1890 °F). Use the low end for maximum toughness, the high end for maximum hardness and thermal fatigue resistance. Soak 30–90 minutes.
3. QuenchStill air, forced air, pressurised gas or warm oil. Sections to 127 mm generally through-harden in still air; above that, accelerate the cooling. NADCA practice requires at least 28 °C/min (50 °F/min) to below 538 °C. No other variable in the cycle affects impact toughness as much as the quench rate. For oil, quench to about 480 °C then air cool to 50–65 °C.
4. Temper twiceTemper immediately, before the part reaches room temperature and cracks. 540–620 °C, one hour per 25 mm of thickness with two hours minimum, air cool to ambient between tempers. Two tempers are mandatory: the first converts retained austenite to fresh martensite, the second tempers it. The second temper must sit at least 25 °C above the secondary hardening peak near 510 °C.
5. Stress relieve after finishingA third temper 15–25 °C below the final tempering temperature, run after all finish machining, grinding and EDM, relieves machining stress. On EDM surfaces, grind or polish off the recast white layer first. It is untempered and it cracks.
6. Anneal before any re-hardeningHeat at no more than 222 °C/h to 857–885 °C, hold one hour per 25 mm and two hours minimum, then furnace cool at no more than 28 °C/h to 538 °C, then cool freely. Resulting hardness: 235 HBW maximum.

Surface treatments

Gas or plasma nitriding to 0.10–0.30 mm gives a 1000–1100 HV case for extrusion dies and ejector pins, but a nitrided case is brittle and should not be used on die casting surfaces exposed to severe thermal shock. Nitriding must always follow the final temper, and the nitriding temperature must stay below the tempering temperature or the core will soften.

H13 compared with H11, 1.2367 and H21

Choosing among the 5 % chromium hot work grades comes down to one trade-off. Vanadium and molybdenum buy hot strength and wear resistance, and they cost toughness. Pick the leanest grade that survives the service temperature.

Most buyers start at H13. Go down to H11 if the tool is cracking rather than wearing. Go up to 1.2367 if the insert is thick and the thermal load is severe enough that H13 softens. H21 earns its extra cost only when the metal being formed is copper or brass. Jiangyin Jiangnan Metal forges all five grades on the same line; see tool steel forgings.

What H13 forgings are used for

High-pressure die casting

Die blocks, cavity and core inserts, slides, shot sleeves, plungers, sprue bushings, ejector pins and runner blocks for aluminium, magnesium and zinc casting. Die casting accounts for more H13 tonnage than any other application, and it is where the ESR and NADCA #207 requirements come from.

Aluminium extrusion tooling

Flat and porthole dies, backers, bolsters, die rings and holders, containers and liners, stems, dummy blocks and mandrels. Extrusion tooling usually runs at the higher end of the hardness range and is typically nitrided.

Hot forging and press tooling

Forging die blocks and inserts, trimming dies, hot shear blades, upsetter dies, bolt and nut header dies, piercing punches and hot gripper dies.

Plastics and general tooling

Mould cavities and cores where wear resistance matters more than polish, barrels and screws for plastics processing, shrink rings, wear parts, profiling rolls and cold heading die casings.

Quality, testing and documentation

Jiangyin Jiangnan Metal issues an EN 10204 3.1 mill test certificate with every H13 shipment, signed by the works inspection department and traceable to the heat number stencilled on the piece. The certificate covers the following as standard.

For die casting tooling, specify NADCA #207 Grade B, Premium or Superior on the purchase order. One line on the order calls up the melt practice, annealed microstructure limits, microcleanliness limits, UT class and minimum transverse Charpy value together, and takes most of the ambiguity out of an H13 enquiry.

How to order H13 forgings

Send the five items below and Jiangyin Jiangnan Metal will come back with price, weight and lead time, normally within one working day.

1. Grade and standard. H13, or the designation on your drawing (1.2344, SKD61, 4Cr5MoSiV1), and which standard the certificate must reference.
2. Shape and dimensions. A drawing, a sketch, or finished dimensions plus the machining allowance you want left on.
3. Quantity. Pieces, or annual usage if you are qualifying a supplier.
4. Delivery condition. Black forged, rough machined or finish machined; annealed, or hardened and tempered to a stated hardness.
5. Quality level. Standard, ESR, or NADCA #207 Grade B / Premium / Superior, plus any extra testing.

Shipping terms: FOB Shanghai, Ningbo or Zhangjiagang as standard; CIF, CFR and DDP are available. Payment by T/T or irrevocable L/C at sight. Single pieces are accepted. There is no minimum order tonnage.

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Glossary of terms on this page

Open-die forging

Forging between flat or simply shaped dies that do not fully enclose the workpiece, allowing very large sections and high reduction ratios. Also called free forging or smith forging.

Reduction ratio

Original cross-sectional area divided by the final area. Higher ratios mean more work put into closing porosity and refining structure; 4:1 is the practical minimum for H13 tooling.

ESR

Electroslag remelting. The ingot is progressively remelted through a molten slag layer, which removes sulphur and oxide inclusions and gives a sounder, more homogeneous ingot.

Heat checking

Thermal fatigue cracking of a die face, appearing as a crazed network of fine cracks after repeated heating and cooling. The usual end of a die casting die's life.

Secondary hardening

A rise in hardness on tempering near 500–520 °C, caused by precipitation of fine molybdenum and vanadium carbides. It is why H13 keeps its hardness at working temperature.

EN 10204 3.1

A mill test certificate issued by the manufacturer's own inspection department, independent of the production department, reporting results of tests on the actual product supplied.

HBW / HRC

Brinell hardness with a tungsten carbide ball, used for annealed material; Rockwell C, used for hardened material.

About the manufacturer

Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory located at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China. The works sits in the Yangtze River delta, within two hours of the ports of Shanghai, Ningbo and Zhangjiagang. It forges carbon steel, alloy steel, tool and die steel, stainless steel and nickel alloys into bars, blocks, seamless rolled rings, sleeves, discs, shafts and flanges, and supplies die casting, extrusion, hot forging, oil and gas, power generation and general engineering customers worldwide.

Related grades and forged shapes

Other hot work and tool steel grades

• All tool and die steel forgings
• AISI 4140, 42CrMo4 and SCM440 for die holders and bolsters
• 18CrNiMo7-6 and 17CrNiMo6, carburising grades for gear and drive components
• AISI 8630 and AISI 4130

H13 in other forged forms

• Forged and seamless rolled rings
• All forged products by shape
• Stainless steel forgings · Nickel alloy forgings