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Hot work moldย steel is an alloy tool steel specifically designed for molds used in the thermal deformation processing of metals. These applications include hot forging molds, hot extrusion molds, die-casting molds, and hot heading molds. Due to the severe working conditionsโcharacterized by prolonged exposure to high temperatures and high pressureโhot work die steel must possess high strength, hardness, and thermal stability. Essential properties include high thermal strength, thermal fatigue resistance, toughness, and wear resistance.
Hot work tool steel is an essential material in industrial manufacturing, particularly in applications demanding high strength and resistance to thermal fatigue.
High-Temperature Strength and Hardness:ย Hot work tool steel retains a hardness of 40-50 HRC (Rockwell Hardness Scale C) even at temperatures as high as 500-700ยฐC, ensuring that the tools maintain excellent mechanical properties during thermal processing.
Good Toughness:ย This steel exhibits an impact toughness value of approximately 20-30 J/cmยฒ, meaning it can absorb significant energy without fracturing. This makes it particularly suitable for forging applications that involve high impact loads.
Superior Thermal Fatigue Resistance:ย With an optimized alloy composition, including elements like Chromium (Cr) and Molybdenum (Mo), this steel can withstand over 1,000 thermal cycles without developing noticeable cracks, significantly extending the tool’s service life.
Stable Heat Resistance:ย By incorporating stable alloying elements such as Vanadium (V), these steels maintain a stable microstructure and performance even when repeatedly heated to around 600ยฐC.
Excellent Hardenability:ย Hot work tool steel can undergo deep quenching treatments, achieving uniform hardness throughout the material, such as hardening to the core of a 100mm diameter round bar.
Moderate Thermal Conductivity:ย With a thermal conductivity of about 28-32 W/mยทK, this steel allows for rapid and even heating and cooling, reducing the risk of localized overheating.
Good Machinability:ย Modern refining processes like Electroslag Remelting (ESR) ensure high material purity, making this steel easier to machine compared to cold work tool steel, despite its high hardness.
Extended Service Life:ย For example, aluminum alloy die-casting molds made from H13 hot work tool steel can achieve a lifespan of over 100,000 casting cycles, whereas traditional mold materials might fail after less than half that number.
Increased Production Efficiency:ย Due to the durability of these molds, downtime caused by mold issues is minimized. In the automotive industry, for instance, forging dies made from high-quality hot work tool steel can produce tens of thousands of parts without needing replacement or maintenance.
Cost Reduction:ย Although the initial cost of high-quality hot work tool steel may be 20-30% higher, the extended service life and reduced maintenance needs can lower the per-part tooling cost by up to 50% over the long term.
Enhanced Product Quality:ย The excellent thermal conductivity and stable mechanical properties ensure high dimensional accuracy and surface quality of the products. For instance, in aerospace component production, using high-performance hot work tool steel can result in forgings with superior surface finish and dimensional precision.
High-Temperature Strength and Toughness
Hot work die steel must withstand significant impact forces during operation, especially in hot forging molds. These molds experience frequent and intense impact, requiring materials with exceptional strength and toughness to prevent cracking. For instance, a typical hot forging mold might endure impacts of up to 5000 MPa, necessitating materials that can maintain structural integrity under such stress.
Wear Resistance
In addition to the friction and wear from deforming billets, hot work molds are subject to high-temperature oxidation and abrasion from iron oxide scales. This dual exposure requires steel with high hardness and anti-adhesive properties. A wear rate below 0.05 mmยณ/Nm under specific testing conditions indicates excellent wear resistance, ensuring prolonged mold life.
Thermal Stability
Thermal stability refers to the steel’s ability to retain its mechanical properties at high temperatures. Hot work molds often operate at surface temperatures between 400ยฐC and 700ยฐC. Steel that maintains its structure and performance within this range is crucial to avoid plastic deformation and failure. For example, steel grades that retain over 80% of their strength at 600ยฐC are preferred for high-stress applications.
Thermal Fatigue
Resistance Hot work molds undergo repeated heating and cooling cycles, causing significant thermal stress. This can lead to the formation of network-like cracks on the mold surface, known as thermal fatigue. High thermal fatigue resistance is critical to prevent premature mold failure. Studies have shown that steel with a thermal fatigue crack length less than 10 mm after 1000 cycles at 600ยฐC demonstrates superior performance in maintaining mold integrity.
Hardenability
Hot work molds are typically large, requiring uniform mechanical properties throughout the mold’s cross-section. High hardenability ensures that the entire mold achieves the desired hardness and strength. Steel with a hardenability depth greater than 25 mm in standard testing ensures that even the core of thick molds attains optimal properties.
Thermal Conductivity
Effective heat dissipation is essential to prevent overheating, which can degrade the mold’s mechanical properties. Good thermal conductivity helps reduce mold surface temperatures and minimize internal temperature gradients. For instance, steel with thermal conductivity above 30 W/mยทK at operating temperatures can significantly enhance mold performance.
Forming and Processing Properties
To meet manufacturing and forming requirements, hot work die steel must offer excellent machinability and formability. Steels with a machinability rating above 60% compared to standard references ensure efficient mold production without compromising quality.
Hot work die steel is indispensable in several high-demand industries due to its exceptional properties that withstand extreme operating conditions. Here are some key application areas:
Forging Dies:ย Used in the production of critical components like crankshafts, connecting rods, and gears. The high toughness and thermal stability of hot work die steel ensure that these components can be manufactured to meet precise specifications while maintaining durability under intense mechanical stress.
Die-Casting Molds:ย Essential for casting engine blocks, transmission housings, and other intricate parts that require high precision and excellent surface finish. The superior wear resistance and heat tolerance of hot work die steel extend the lifespan of these molds, reducing maintenance costs and downtime.
Precision Forging:ย Utilized in manufacturing high-strength, lightweight components such as turbine blades and structural parts. The high hardenability and thermal fatigue resistance of hot work die steel ensure consistent performance in the demanding conditions of aerospace applications, where reliability and safety are paramount.
Extrusion Dies:ย Employed in producing complex profiles for aircraft frames and other structural elements. The excellent thermal conductivity and resistance to thermal cycling of hot work die steel enhance the efficiency and quality of the extrusion process.
Hot Extrusion Molds:ย Used for creating high-strength steel components for buildings and infrastructure projects. The toughness and wear resistance of hot work die steel make it ideal for molds that must endure the repetitive stress of extrusion processes.
Forging Molds for Heavy Machinery:ย Critical in manufacturing parts for construction equipment, such as bulldozers, cranes, and excavators. The high strength and impact resistance of hot work die steel ensure these molds can produce components that withstand heavy loads and harsh operating environments.
Hot Forging Dies:ย Essential for producing high-performance tools and dies used in various manufacturing processes. The superior thermal stability and hardness of hot work die steel ensure that these tools maintain their precision and effectiveness over extended periods of use.
Press Forging Dies:ย Utilized in creating large, complex parts with high accuracy. The excellent thermal fatigue resistance of hot work die steel prevents premature failure, ensuring long-term productivity and cost-efficiency.
Molds for Turbine Components:ย Used in the production of parts for power generation equipment, including gas and steam turbines. The high-temperature strength and durability of hot work die steel are crucial for ensuring that these molds can operate effectively in the extreme conditions of energy production.
| Hot-Work Mold Steel | ||||||||||||
| NO. | Grade | Chemical Composition (Mass Fraction) /% | ||||||||||
| C | Si | Mn | P | S | Cr | W | Mo | V | Al | Others | ||
| โค | ||||||||||||
| 1 | 5CrMnMo | 0.50~
0.60 |
0.25~
0.60 |
1.20~
1.60 |
0.030 | 0.030 | 0.60~
0.90 |
0.15~
0.30 |
Ni
1.40~ 1.80 |
|||
| 2 | 5CrNiMo | 0.50~
0.60 |
โค0.40 | 0.50~
0.80 |
0.030 | 0.030 | 0.50~
0.80 |
0.15~
0.30 |
||||
| 3 | 3Cr2W8V | 0.30~
0.40 |
โค0.40 | โค0.40 | 0.030 | 0.030 | 2.20~
2.70 |
7.50~
9.00 |
0.20~
0.50 |
|||
| 4 | 5Cr4Mo3SiMnVAI | 0.47~
0.57 |
0.80~
1.10 |
0.80~
1.10 |
0.030 | 0.030 | 3.80~
4.30 |
2.80~
3.40 |
0.80~
1.20 |
0.30~
0.70 |
||
| 5 | 3Cr3Mo3W2V | 0.32~
0.42 |
0.60~
0.90 |
โค0.65 | 0.030 | 0.030 | 2.80~
3.30 |
1.20
1.80 |
2.50~
3.00 |
0.80~
1.20 |
||
| 6 | 5Cr4W5Mo2V | 0.40~
0.50 |
โค0.40 | โค0.40 | 0.030 | 0.030 | 3.40~
4.40 |
4.50~
5.30 |
1.50~
2.10 |
0.70~
1.10 |
||
| 7 | 8Cr3 | 0.75~
0.85 |
โค0.40 | โค0.40 | 0.030 | 0.030 | 3.20~
3.80 |
|||||
| 8 | 4CrMnSiMoV | 0.35~j
0.45 |
0.80~
1.10 |
0.80~
1.10 |
0.030 | 0.030 | 1.30~
1.50 |
0.40~
0.60 |
0.20~
0.40 |
|||
| 9 | 4Cr3Mo3Siy | 0.35~
0.45 |
0.80~
1.20 |
0.25~
0.70 |
0.030 | 0.030 | 3.00~
3.75 |
2.00~
3.00 |
0.25~
0.75 |
|||
| 10 | 4Cr5MoSiV | 0.33~
0.43 |
0.80~
1.20 |
0.20~
0.50 |
0.030 | 0.030 | 4.75~
5.50 |
1.10~
1.60 |
0.30~
0.60 |
|||
| 11 | 4Cr5MoSiV1 | 0.32~
0.45 |
0.80~
1.20 |
0.20~
0.50 |
0.030 | 0.030 | 4.75~
5.50 |
1.10~
1.75 |
0.80~
1.20 |
|||
| 12 | 4Cr5W2VSi | 0.32~
0.42 |
0.80~
1.20 |
โค0.40 | 0.030 | 0.030 | 4.50~
5.50 |
1.60~
2.40 |
0.60~
1.00 |
|||
| Hot-Work Mold Steel | |||||
| NO. | GB | ISO | ASTM | JIS | DIN |
| 1 | 5CrNiMo | 4957 (40CrNiMo) | L6 | SKT4 | 1.2713 (40CrNiMo86) |
| 2 | 3Cr2W8V | X40CrWMoV5-1 | H12 | SKD6 | 1.2581 (X30WCrV9-3) |
| 3 | 4Cr3Mo3SiV | H10 | |||
| 4 | 4Cr5MoSiV | 4957 (X37CrMoV5-1) | H11 | SKD61 | 1.2344 (X40CrMoV5-1) |
| 5 | 4Cr5MoSiV1 | 4957 (X37CrMoV5-1) | H13 | SKD61 | 1.2344 (X40CrMoV5-1) |
