1.2379 Steel - The Electroslag Remelting (ESR) Principle

Position Of ESR In The Tool Steel Production Process

Electroslag remelting is a secondary refining process. Its purpose is to remelt and deeply purify steel ingots made by conventional melting. The complete high-end tool steel production chain for DIN 1.2379 steel is: electric arc furnace primary melting → ladle furnace refining → vacuum degassing → electroslag remelting secondary refining → forging or rolling → heat treatment. ESR does not replace primary melting. It adds a finishing process after primary melting.

ESR Sensitivity Of 1.2379 Steel

The chemical composition of material 1.2379 makes it very sensitive to its microstructure. The combination of 1.40-1.60% carbon and 11.0-13.0% chromium gives it very high wear resistance. However, this same combination also makes large and uneven carbides very easy to form during solidification. This sensitivity is the main reason for including ESR in the production route.

Slag Resistance Heating Principle Of 1.2379 Steel

ESR Heat Source Mechanism

For 1.2379 material, the most basic technical feature of ESR is that its heat comes from electrical resistance heating in the slag, also called Joule heat, rather than from an electric arc discharge. This principle defines the main difference between ESR and an electric arc furnace. The heat source of an electric arc furnace is the arc produced by gas ionization and discharge, while the heat source of ESR is the electrical resistance of the slag. The slag is both the heating element and the refining medium.

Power Circuit And Heat Distribution

The consumable electrode, slag, molten metal pool, ESR ingot, and water-cooled base box form a complete power circuit with the transformer through short power cables. When current flows through the circuit, the high electrical resistance of the slag produces a large amount of heat in the slag pool according to Joule’s law. This heats the slag to a temperature far above the melting point of the consumable electrode.

Working Process And Parts of ESR

4 Parts

• Consumable Electrode: During steel 1.2379 remelting, steel produced by conventional melting is cast or forged into a rod-shaped consumable electrode. The electrode is gradually consumed during remelting.
• Slag: The slag is a calcium fluoride-based material with high electrical resistance and high basicity. It provides both heating and refining. After melting starts, the slag temperature must quickly reach 1580 to 1680 degrees Celsius.
• Water-Cooled Mold: The water-cooled mold is a copper water-cooled container. It forces the molten steel to cool and solidify in one direction.
• Power Supply System: The power supply system includes a transformer and short power cables. It supplies the high current needed for remelting.

4 Working Process

1. Put The Consumable Electrode Into The Slag: Put the end of the consumable electrode into the high-temperature slag inside the water-cooled mold.
2. Apply Power To Produce Resistance Heat: Apply power to produce resistance heat and raise the slag pool temperature far above the melting point of the consumable electrode.
3. Electrode Melting And Droplet Passage Through The Slag Layer: The end of the consumable electrode melts layer by layer at high temperature. It forms a liquid metal film that gathers into droplets. Under gravity, the droplets pass through the slag pool and fully contact the slag. During this process, refining reactions such as desulfurization and the removal of non-metallic inclusions take place.
4. Water-Cooled Crystallization And Directional Solidification: The clean metal droplets enter the molten metal pool. Under the forced cooling of the water-cooled mold, the metal solidifies in sequence from bottom to top. A thin slag skin forms between the ingot and the mold wall. It slows radial cooling and improves the surface quality of the finished ingot. Ingots produced by ESR have a solidified structure with less segregation.

Carbide Defects From Conventional Melting Of Material 1.2379

Carbide Problems In Conventional Electric Arc Melting

In large-section applications, 1.2379 steel produced by conventional electric arc melting has large and unevenly distributed carbides. During solidification, carbon and chromium become enriched and segregated in the liquid phase. They form local carbon-rich and chromium-rich areas at the dendrite boundaries. After cooling, large and angular primary Cr₇C₃ carbides form. They can reach 8 to 18 micrometers in size and gather in clusters along the dendrite network instead of being evenly distributed in the matrix.

Effect Of Carbide Defects On Mold Life

Under repeated compressive and tensile loads, the interface between the carbides and the matrix becomes the first place for cracks to start. The sharp corners of angular carbides can produce a stress concentration factor of 3 to 4 compared with the nominal stress. Once a crack starts, it grows mainly along the banded carbide layers. This can finally cause the mold to break along a plane parallel to the carbide bands. The material certificate may show that all chemical composition values meet the requirements, but the metallographic examination can show a completely different result. This failure mode is not an inherent property of the material grade. It is a result of the production route.

Improvement Mechanisms Of ESR In DIN 1.2379

Solidification Process Control

ESR controls the solidification process of the steel ingot. It removes defective as-cast structures at the ingot stage before downstream processing such as forging and rolling. This provides a more uniform raw material for later hot working.

Carbide Refinement And Uniform Distribution

In a protective-atmosphere ESR system, precise control of the solidification conditions greatly refines the angular Cr₇C₃ carbide clusters and makes their distribution much more uniform. Magnetically controlled ESR technology uses an external magnetic field to further refine the grain and carbide sizes.

Improved Cleanliness

ESR-grade 1.2379 material has better material cleanliness and higher tensile and compressive strength. It is suitable for precision mold applications that require higher cleanliness and strength. 1.2379 ESR steel is clean and has no risk of quench cracking.

Protective-Atmosphere ESR

In a protective-atmosphere ESR system, the protective atmosphere prevents air from polluting the slag and molten steel. High-chromium steels such as DIN 1.2379 steel are especially sensitive to this process. In conventional ESR exposed to air, chromium can be oxidized during remelting. A protective atmosphere can effectively reduce this loss.

Advantages Of 1.2379 Material ESR

Cleanliness And Structural Density Of 1.2379 Steel

After material 1.2379 undergoes ESR, non-metallic inclusions are deeply removed and the material reaches a higher level of cleanliness. ESR ingots are free from center shrinkage cavities and serious composition segregation. The tendency for axial crystallization and segregation is greatly reduced. Better structural density and uniformity directly improve plasticity during hot working.

1.2379 Steel Properties

For steel 1.2379, tensile strength and compressive strength are greatly improved. This makes ESR material the preferred choice for applications that require higher cleanliness, high tensile strength, and high compressive strength.

Wear Resistance And Edge Retention

1.2379 steel ESR has high resistance to abrasive wear and adhesive wear, as well as excellent edge retention. It is suitable for bending tools, plastic molds, machine knives, cold shear blades, cold extrusion tools, thread rolling dies, deep-drawing tools, punching tools, and milling cutters.

ESR Value Of 1.2379 Steel

Core Logic Of Electroslag Remelting

Electroslag remelting is a secondary refining technology that uses slag resistance heat as the heat source, a consumable electrode as the raw material, and a water-cooled mold as the mold. Its core logic can be summarized as deep refining by high-temperature slag plus directional solidification by water cooling. The slag is both the heating element and the refining medium. The water-cooled mold ensures that the steel ingot solidifies in one direction from bottom to top, producing a dense as-cast structure with very little segregation.

ESR Value Of DIN 1.2379 Steel

• Optimization Of Carbide Shape And Distribution: The 8 to 18 micrometer angular Cr₇C₃ clusters are removed, and the carbides become finer and more evenly distributed.
• Improvement Of Material Cleanliness: Deep desulfurization and inclusion removal are completed. The material reaches the SEP 1921 E/e inspection standard, and the risk of quench cracking is removed.
• Improvement Of Structural Density And Uniformity: Segregation and shrinkage cavities are removed, producing a dense structure with a clear axial crystallization tendency.

These three levels of improvement finally provide higher tensile and compressive strength, longer mold life, and more stable performance in service. They allow ESR-grade 1.2379 to meet the needs of high-end precision mold applications that require very high material cleanliness, strength, and structural uniformity.