SKD6 Tool Steel

SKD6 Tool Steel Product Introduction

SKD6 tool steel is an air-hardening hot work mould steel conforming to the Japanese Industrial Standard (JIS G 4404) and is classified as a high alloy tool steel. Its chemical composition is based on balanced ratios and it has high hardenability, which can be achieved by air cooling, reducing the risk of heat treatment distortion.
Through specific heat treatments (e.g. preheating at 790°C, austenitising at 1000-1020°C followed by air cooling and tempering at 520-550°C), SKD6 can be optimised to a fine-grained martensitic organisation, with an increased hardness of 50-55 HRC, and a combination of high-temperature strength and toughness ( The tensile strength is 1000-1500 MPa and the yield strength is 800-1000 MPa.) The essence of the design is the use of chromium-molybdenum carbides to enhance heat and thermal fatigue resistance, maintaining dimensional stability at 400-500°C, while vanadium is used to refine the grain to improve wear resistance.

SKD6 Tool Steel Types and Options

The table below shows the size range, surface condition and tolerance details for SKD6 Mould Steel:

Shape	Pocess	Size range	Surface	Tolerance
Flat Bar	Hot Rolled	Thickness: 10-400mm Width: 200-800mm Length: 3000-5800mm	Black; Sandblasted	Thickness :0-+2MM Width:0-+5MM/0-+10MM
	Hot Forged	Thickness: 50-500mm Width: 50-1500mm Length: 3000-5800mm	Black	Thickness:+2-+5MM Width:0-+5MM/0-+10MM
			Turned/Machined/Milled/Bright	Thickness :0-+2MM Width:0-+5MM/0-+10MM
Round Bar	Hot Rolled	Diameter:10-65mm Length:3000-5800mm	Black	0-+2MM
			Turned/Machined	0-+2MM
	Hot Forged	Diameter:70-700mm Length:3000-5800mm	Grinded	0-+5MM/+2-+5MM
			Turned/Machined/Milled/Bright	0-+2MM

SKD6 Tool Steel Customized Options

1. Customized chemical composition: GB, DIN, ASTM, JIS and other standard grades can be produced. Chemical composition can be customized individually.
2. Customized specifications: round steel (diameter), plate (thickness, width) can be customized production.
3. Specialized packaging for long term storage or extreme transportation conditions: includes spraying black paint all around, wrapping plastic film, spraying anti-rust oil, and shipping in wooden crates.
4. Customized production based on samples or technical agreements.
5. SKD6 Tool Steel Electroslag Remelting (ESR): premium option with higher purity and isotropic properties for critical applications.

SKD6 Tool Steel Chemical Composition

Standard/Steel Grade		Chemical Composition(%)
		C	Si	Mn	Cr	Mo	V
ASTM	H11	0.33~0.43	0.80~1.20	0.20~0.50	4.75~5.50	1.10~1.60	0.30~0.60
DIN/W-Nr.	X38CrMoV5-1/1.2343	0.36~0.42	0.90~1.20	0.30~0.50	4.80~5.80	1.10~1.40	0.25~0.50
JIS	SKD6	0.32~0.42	0.80~1.20	≤0.50	4.50~5.50	1.00~1.50	0.30~0.50

SKD6 Tool Steel Heat Treatment Process

1.Annealing

Purpose: to eliminate internal stresses generated during forging or rolling, reduce hardness, improve cutting performance, and prepare for subsequent processing and heat treatment.
Process parameters:
Heating temperature: 800-850 ℃, holding time 2-4 hours, with the furnace cooling to below 500 ℃, and then air-cooled.

2.Quenching

Purpose: to make the tool steel to obtain martensitic organization, improve hardness and wear resistance.
Process parameters:
Heating temperature: 1000-1050 ℃ (commonly used 1020-1040 ℃), holding time according to the size of the workpiece to determine, generally 30-60 minutes.
Cooling: oil cooling or air cooling (for small size or simple shape of the workpiece), large workpieces can be graded quenching (in the 260-300 ℃ salt bath cooling for a period of time and then air-cooled), in order to reduce the quenching stress, to prevent deformation and cracking.

3.Tempering

Purpose: to eliminate quenching stress, adjust the hardness and toughness, stable organization and size.
Process parameters:
low-temperature tempering: 150-250 ℃, insulation 2-3 hours, air-cooled, tempered hardness of 58-62HRC, for molds requiring high hardness and wear resistance.
Medium temperature tempering: 300-500 ℃, insulation 2-3 hours, air-cooled, tempered hardness of 50-58HRC, can improve the toughness, suitable for molds subject to impact load.
High-temperature tempering: 500 ℃ or more, insulation 2-3 hours, air-cooled, tempered hardness 45-50HRC, mainly for the need for higher toughness of the occasion.

4.Precautions

Heating process should control the rate of heating to avoid too rapid a rise in temperature leading to workpiece surface oxidation and decarburization. Protective atmosphere heating can be used or placed in the furnace charcoal and other anti-decarburization agent.
When quenching and cooling, choose the appropriate cooling medium and cooling method according to the shape and size of the workpiece to ensure the quenching effect while reducing the risk of deformation and cracking.
Tempering must be sufficient to ensure the elimination of internal stresses to avoid mold failure due to stress release during use. For large molds or workpieces with complex shapes, multiple tempering can be used.

SKD6 Tool Steel Quality Inspection

1.Surface Condition Inspection

FCS factory has a very strict quality inspection team, we will carefully check the surface condition of each piece of tool steel to ensure that the steel surface is free from cracks, folds, knots, oxidized skin, pitting, scratches and other defects.

2.Chemical Composition Testing

To verify whether the content of alloying elements meets the standard requirements and to safeguard the basis of the mechanical properties of the material. We will let the staff use full-spectrum direct reading spectrometer to analyze multiple elements at the same time. Sampling needs to remove the surface oxidation layer, using a block specimen to stimulate the test.

3.Dimension and Tolerance Inspection

FCS factory will use professional measuring tools to inspect the dimensions and tolerances of the steel to ensure compliance with the customer's contract requirements. Corresponding gauges will be selected according to the dimensional accuracy requirements, including tape measure, high-precision vernier calipers (0.02mm), micrometers (0.001mm), and special inspection gauges. Inspection items cover: diameter, thickness, width, length, hole diameter, chamfering dimensions, etc., to ensure that the tolerances and dimensions meet the contract requirements.

4.Hardness test

Our FCS factory will use professional hardness tester to test the hardness of steel to ensure that it meets the customer's contract requirements.

5.Ultrasonic Testing

Ultrasonic Testing Standard (UT Test Standard) is: Sep 1921-84 Class3 D/d,E/e.
FCS factory uses ultrasonic testing equipment to detect macro defects inside the material (such as cracks, shrinkage holes, inclusions, white spots, etc.), and every piece of round steel and plate will be examined by a second flaw detection test before shipment to ensure that the quality is qualified before shipment.

6.Microstructure Inspection

(1) Metallographic Analysis

FCS factory will use metallographic analysis instrument to detect the microstructure state after heat treatment, including carbide distribution, martensite morphology, residual austenite content, etc.

 (2) Grain size rating

FCS factory will use the comparative method to determine the austenite grain size by comparing the microstructure of the specimen with the standard rating chart, to ensure that it meets the customer's requirements.

SKD6 Tool Steel Technical Specifications

Property	Value	Test Method
Hardness (Annealed)	≤229 HBS	ASTM E10
Density	7.8 g/cm³	ASTM B311
Melting Range	1371-1427°C	DSC Analysis
Thermal Conductivity	24.3 W/m·K	ASTM E1461
Specific Heat Capacity	460 J/kg·K	ASTM E1269
Coefficient of Thermal Expansion	10.8 × 10⁻⁶/°C (20-600°C)	ASTM E228
Young's Modulus	210 GPa	ASTM E111
Tensile Strength (Hardened)	1200-1590 MPa	ASTM E8
Compressive Strength	1800-2200 MPa	ASTM E9
Charpy Impact Toughness	15-25 J (48-52 HRC)	ASTM E23
Relative Machinability	65-75% (with AISI 1212 as 100%)	Standard Shop Test

SKD6 Tool Steel Product Applications

Main application scenarios

Forging dies and tools

Hot forging operations benefit from SKD6's excellent resistance to mechanical and thermal fatigue. The steel's toughness prevents premature cracking while maintaining wear resistance at forging temperatures. When an aerospace component supplier used our SKD6 forging dies, tool life was increased by 35% and the dimensional consistency of the forged parts improved, leading directly to improved manufacturing efficiencies and lower cost per part.

HOT SHEAR BLADES

SKD6 combines high hardness, wear resistance and toughness, making it ideal for hot shear blades used in steel mills and metal fabricators. These blades maintain cutting edge integrity at high temperatures for clean cuts and extended maintenance intervals. One steel fabricator reduced blade replacement frequency by 45% with our SKD6 hot shear blades.

Plastic moulds for high temperature resins

For injection moulding of high temperature engineering plastics (PPS, PEI, PEEK), SKD6 offers excellent wear resistance and polishability. Its thermal properties ensure efficient heat transfer and stable cooling, producing high-quality moulded parts with reduced cycle times. One manufacturer of electronic components reported improved surface finish quality and 25% faster cycle times after upgrading to our SKD6 moulds.

Industry-specific applications

1. Automotive industry: transmission component dies, engine block dies, suspension component forging dies
2. Aerospace: turbine blade forging tools, structural component extrusion dies, high-strength fastener tools
3. Electronics industry: heat sink extrusion dies, connector dies, semiconductor packaging tools
4. Construction industry: aluminium window frame extrusion dies, structural steel forging tools
5. Consumer Goods: durable component dies, appliance component tooling
6. Military / Defence: precision component tooling for critical applications requiring Military / Defence: precision component tooling for critical applications requiring reliability
7. Medical Equipment: surgical instrument tooling, implant component tooling requiring high accuracy

SKD6 Tool Steel Competitive Advantage Comparison

Characteristics	FCS Factory's SKD6 Tool Steel	Standard Hot Work Tool Steel	High-end Competitive Tool Steel
Heat Resistance	Maintains hardness up to 595°C	Softens above 550°C	Maintains hardness up to 580°C
Heat Fatigue Resistance	Excellent resistance to heat cracking	Moderate resistance to heat cracking	Good resistance to heat cracking
Wear Resistance	Excellent wear resistance at high temperatures	Good at room temperature, decreases with increasing temperature	Very good wear resistance across all temperature ranges
Impact Toughness	15-25 J	8-15 J	12-20 J
Machinability	65-75% (relative to 1212 steel)	60-70%	50-65%
Polishability	Excellent	Good	Very good
Nitriding Response	Significant increase in surface hardness	Good response	Very good response
Technical Support	Comprehensive application consulting	Basic technical data	Standard technical support

SKD6 Tool Steel Customer Success Stories

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SKD6 Tool Steel Pricing Structure Information

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SKD6 Tool Steel Frequently Asked Questions

Q: How does SKD6 compare to standard H13 tool steel?
A: SKD6 is a Japanese grade (JIS) that is roughly equivalent to AISI H13, but our SKD6 has tighter chemical composition control, optimised machining and tighter quality control within the H13 specification, resulting in superior performance characteristics, particularly in terms of thermal fatigue resistance and toughness.

Q: Can SKD6 be welded and repaired?
A: Yes, SKD6 can be successfully welded using the proper procedures; we recommend preheating to 315-370°C, using compatible filler materials, maintaining interlayer temperatures, and post-weld heat treatment. Our technical support team can provide detailed welding procedures for your specific application.

Q: How does section size affect the performance of SKD6?
A: SKD6 maintains good hardenability up to a cross-section size of approximately 150mm. Larger cross sections may result in progressively lower core hardness. For critical applications in tools and moulds with large cross sections, we recommend SKD6-SD (Special Deep Hardening variant) or consider a high end electroslag remelting / vacuum arc remelting grade to enhance full cross section hardness.

Q: How should SKD6 be stored prior to use?
A: It should be stored in a dry, temperature-controlled environment to prevent corrosion. Light oil should be applied for long term storage. Large sections should be properly supported to prevent warping. If corrosion occurs, it should be thoroughly removed prior to heat treatment.