How Does Vacuum Degassing Refining Improve Material 1.2379?

Alloying Elements And Carbides of Material 1.2379

The typical composition of material 1.2379 includes about 1.50%–1.60% carbon, 11.0%–12.0% chromium, 0.60%–0.80% molybdenum, and 0.90%–1.10% vanadium. After solidification and heat treatment, these alloying elements form many high-hardness carbides, such as M₇C₃ and MC. These carbides give the material excellent wear resistance.

Inclusions And Cracks

Based on the structure of 1.2379 tool steel, it is a ledeburitic high-carbon and high-chromium tool steel with many large carbides. If the steel contains many non-metallic inclusions, such as oxides, sulfides, and nitrides, or has high levels of hydrogen, oxygen, and nitrogen, these defects can become starting points for fatigue cracks. Cracks can easily start at the interface between the inclusions and the matrix, especially in high-stress areas such as blanking edges and cold-heading die cavities. This can lead to edge chipping, peeling, fatigue fracture, or grinding cracks.

VD Vacuum Degassing Refining Of Material 1.2379

Vacuum degassing is an important secondary refining process. Its basic principle is to place molten steel in a vacuum environment, which greatly reduces the gas pressure above the molten steel. According to Henry’s law, the partial pressure of gases dissolved in the molten steel also falls. Hydrogen, oxygen, nitrogen, and other gases that were dissolved in the molten steel then leave the steel naturally and are removed by the vacuum system. At the same time, argon stirring or electromagnetic stirring makes the molten steel circulate. This helps deoxidation products and inclusions collide, gather, and float upward, resulting in deep cleaning.

Process Position Of The VD Method

For high-carbon and high-chromium cold-work tool steels such as material 1.2379, the commonly used vacuum degassing method is VD. In this method, the molten steel is treated under vacuum inside the ladle. It is mainly used to remove hydrogen and oxygen and to remove non-metallic inclusions. This process is usually carried out after primary melting in an electric arc furnace or induction furnace and refining in an LF furnace. Its main functions can be divided into three parts:

Deep Degassing of 1.2379 Tool Steel

In a vacuum environment, the partial pressure of gases in the molten steel is greatly reduced. Hydrogen, oxygen, and nitrogen dissolved in the molten steel leave the steel naturally and are removed.

• Lower Hydrogen Content: The hydrogen content can be controlled below about 2 ppm, greatly reducing the risk of white spots and hydrogen cracks in large-section tool steel.
• Lower Oxygen Content: The oxygen content can be reduced from 30–50 ppm with a conventional process to 15 ppm or even lower. This directly reduces the sources of brittle oxide inclusions such as Al₂O₃ and SiO₂.
• Control Nitrogen Content: This prevents the formation of large, hard, and brittle nitride inclusions such as TiN and AlN while keeping small and useful carbonitrides.

Inclusion Removal of 1.2379 Steel

Vacuum treatment is often used together with argon stirring or electromagnetic stirring. The strong but controlled flow of molten steel makes small deoxidation products and outside inclusions collide, gather, grow, and float into the slag layer for removal. Compared with simply leaving the molten steel still, vacuum degassing is much more effective at removing inclusions. It also provides good cleaning results for small inclusions below 20 μm.

Uniform Composition And Temperature

During vacuum treatment, the molten steel is fully stirred. This makes the distribution of alloying elements and temperature more uniform and reduces large-scale segregation and local changes in composition. For high-carbon and high-chromium steel such as 1.2379, uniform composition means more even carbide distribution, more stable deformation during later heat treatment, and more consistent performance in every part of the die.

Cleanliness And Service Life Of 1.2379 Steel

Fatigue Life of Material 1.2379

For 1.2379 material, non-metallic inclusions are the main starting points for fatigue cracks. Reducing the number and size of inclusions is similar to reducing the “internal notches” in the steel. Under alternating loads, fatigue cracks in 1.2379 tool steel take much longer to start, and the fatigue limit increases. For cold-heading dies, stamping dies, and other applications that receive repeated impact, this means a longer service life.

Impact Toughness And Resistance To Edge Chipping

steel 1.2379 with high cleanliness has better impact toughness. When a growing crack reaches an inclusion, it can change direction or grow faster. In clean steel, the crack growth path is more uniform and uses more energy. In a die, this improves the resistance of the cutting edge to chipping and reduces the risk of early edge damage or pieces breaking away.

Polishing Performance And Mirror Surface Retention

For precision dies made from material 1.2379 that require high surface quality, inclusions may come loose during polishing and form small holes or pits. They may also become starting points for sticking or scratching during die use. After vacuum degassing, 1.2379 has a lower inclusion rating, fewer surface defects after polishing, and a longer-lasting mirror surface. It is especially suitable for high-finish stamping and precision blanking applications.

Grinding Cracks And Heat Treatment Cracking

High hydrogen content is one of the main causes of grinding cracks and quench cracking. Vacuum degassing reduces hydrogen to a very low level, greatly reducing the cracking sensitivity of 1.2379 during grinding or heat treatment. Fewer inclusions also reduce local stress concentration during grinding and provide a wider grinding process range.

Dimensional Stability of Material 1.2379

Steel with high cleanliness has fewer internal defects and a more even distribution of residual stress. Its dimensions change less during long-term use and temperature changes. For precision dies made from material 1.2379, this means more stable fitting accuracy and a longer accuracy retention life.

How To Confirm The Cleanliness Of Material 1.2379

• Melting Process Route: Check whether the production process uses “electric arc furnace/EAF + LF refining + VD/vacuum degassing” or even “electroslag remelting/ESR.” Electroslag remelting normally provides higher cleanliness, but it also costs more.
• Inclusion Rating: An inclusion rating based on standards such as DIN 50602 or ISO 4967 can be requested. This may include the K method or A, B, C, and D inclusion ratings. A lower value means higher cleanliness.
• Ultrasonic Testing Results: Steel with a dense internal structure and no clear defects normally has better cleanliness and uniformity. For steel 1.2379, the EAF + LF + VD production route can reach the D/d grade. Further ESR electroslag remelting can reach the E/e grade.

Value Of Vacuum Degassing For DIN 1.2379

The value of vacuum degassing refining for material 1.2379 is much more than having “slightly fewer impurities.” Through degassing, inclusion removal, and uniform treatment, it reduces fatigue crack starting points, lowers the risk of hydrogen cracking, and improves carbide distribution from the beginning. This allows DIN 1.2379 steel to move from “qualified composition” to “long service life and high reliability.”