SKD61 Tool Steel Composition, Equivalents, and Heat Treatment
SKD61 is a chromium-molybdenum-vanadium hot work die steel defined under the Japanese Industrial Standard JIS G4404. It is one of the most widely specified hot work grades globally, and buyers sourcing across Japanese, American, European, and Chinese supply chains often need to confirm how SKD61 lines up against ASTM, DIN, ISO, and GB equivalents before placing an order, since a mismatch in equivalent grade assumptions is a common source of specification disputes in bulk purchasing.
Chemical Composition (JIS G4404-2006, weight %)
| Element | Range | Function |
|---|---|---|
| Carbon (C) | 0.32 – 0.42% | Base hardness and strength |
| Silicon (Si) | ≤ 1.00% | Deoxidation, improves oxidation resistance |
| Manganese (Mn) | ≤ 0.50% | Hardenability |
| Chromium (Cr) | 4.50 – 5.50% | Hardenability and wear resistance |
| Molybdenum (Mo) | 1.20 – 1.60% | High-temperature strength, resistance to softening |
| Vanadium (V) | 0.80 – 1.20% | Fine grain structure, improved toughness and wear resistance |
Exact ranges can vary slightly by mill and by which standard revision a supplier certifies against, which is why buyers working with multiple mills should always request the mill test certificate rather than relying on nominal composition alone.
SKD61 Equivalent Grades
| Standard | Designation | Notes |
|---|---|---|
| Japan (JIS G4404) | SKD61 | Reference grade |
| USA (ASTM/AISI) | H13 | Closest match, minor Mn/V tolerance differences |
| Germany (DIN/EN) | 1.2344 / X40CrMoV5-1 | Widely used European equivalent |
| ISO | 35CrMoV5 | International reference designation |
| China (GB/T 1299) | 4Cr5MoSiV1 | Common domestic equivalent, verify Si content when cross-certifying |
These grades are close but not always metallurgically identical. Vanadium and manganese content in particular can shift toughness and wear resistance slightly between an H13 heat and an SKD61 heat, so when a project specification calls out one standard and the available stock is certified to another, it is worth confirming the actual mill certificate rather than assuming a one-to-one substitution. The designations this grade family carries across standards, and how closely each one matches, are compared in the H13 equivalent grades reference.
SKD61 is a hot-work grade, and the cold-work grade it is most often measured against is SKD11. The two are compared in SKD11 vs SKD61.
Key Characteristics
SKD61 is selected for hot work tooling because it holds up under repeated thermal cycling rather than failing from a single overload. Good hardenability means it reaches consistent hardness through the cross-section even in larger die blocks, which matters for tool life in thick-section forging and extrusion dies. High wear resistance comes from the fine, uniformly distributed carbides formed by the vanadium and chromium content, giving the steel good resistance to abrasive wear during forming. Because hot work tooling is heated and cooled thousands of times per production run, resistance to thermal fatigue and hot cracking is often the property that actually determines service life, more so than raw hardness. The molybdenum content gives SKD61 good resistance to softening at elevated temperatures, so dies retain their working hardness through extended production runs instead of tempering back during use. The same fine carbide structure that gives wear resistance also supports good toughness, which is what prevents chipping and cracking under repeated mechanical shock.
SKD61 requires careful control during heat treatment. Decarburization at the surface or overheating during austenitizing are the two most common causes of premature die failure in the field, and both are avoidable with correct furnace atmosphere control and temperature monitoring.
Heat Treatment Parameters
| Stage | Parameter |
|---|---|
| Hot working/forging | 1100°C down to 900°C |
| Preheating | Approximately 790°C |
| Austenitizing | 1000°C (salt bath) or 1010°C (controlled atmosphere), hold 5-15 minutes |
| Quenching | Air cooling, sufficient given SKD61’s hardenability |
| Tempering | Approximately 550°C, targeting ≥60 HRC before service tempering back to working hardness |
Because SKD61 is air-hardening, distortion risk during quenching is lower than oil-hardening grades, which is one reason it is preferred for larger die blocks where dimensional stability after heat treatment matters. Strict adherence to these parameters, and to the furnace atmosphere control needed to avoid decarburization, is what separates a die that reaches its expected service life from one that fails early from an avoidable heat treatment defect.
Applications
SKD61’s combination of thermal fatigue resistance, hot hardness retention, and toughness makes it the standard choice for tooling that faces repeated heating and cooling cycles under load. Typical applications include dies for hot extrusion of aluminum and other non-ferrous metals, die casting dies for aluminum alloys where resistance to thermal fatigue and erosion from molten metal is critical, forging dies, bolt heading dies, hot shearing blades, mandrels, and punches. In each of these, the failure mode SKD61 is chosen to resist is heat checking and softening from cyclical thermal load, not just static wear.