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DIN 1.2379 - Full Production Process Guide

1.2379 steel starts from iron ore and alloy materials up to finished mold steel. It goes through multiple steps: EAF primary melting, LF ladle refining, VD vacuum degassing, ESR electroslag remelting, high-temperature forging, rolling, spheroidizing annealing, stress relief after rough machining, quenching and tempering. Every step has its parameter range and affects the final performance. This article breaks down the full production process of DIN 1.2379.

Table of Content

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DIN 1.2379
1.2379 Material
Material 1.2379
1.2379 Steel
1.2379 Tool Steel

Smelting and Refining of DIN 1.2379

EAF of DIN 1.2379

  • The production of 1.2379 tool steel starts with EAF primary melting. The goal at this stage is to keep main elements within the standard range and supply qualified molten steel for subsequent refining.
  • Raw materials are proportioned according to target composition. Carbon is controlled at 1.40–1.60%, chromium 11.00–13.00%, molybdenum 0.70–1.20%, vanadium 0.50–1.10%. In primary melting, high heat from electrode arc melts scrap steel and alloy materials. Basic composition adjustment is finished, and part of impurities such as phosphorus and sulfur are removed.

Ladle Refining (LF)

The molten steel after primary melting is transferred to the ladle refining furnace. The core task of LF is desulfurization and fine adjustment of chemical composition. By slagging, heating and alloying, the sulfur content in DIN 1.2379 is reduced below 0.030%. Carbon, chromium, molybdenum, vanadium and other elements are fine-tuned to target values. During ladle refining, argon gas is blown from the bottom to stir the liquid steel. It helps inclusions float up and keeps uniform composition and temperature.

Vacuum Degassing (VD)

Molten steel after LF refining goes to the vacuum degassing station. The VD step removes dissolved hydrogen, oxygen and nitrogen in steel under vacuum. LF+VD refining controls oxygen content of 1.2379 steel below 16 ppm and hydrogen content below 2 ppm. Low oxygen means less oxide inclusions. Low hydrogen means lower risk of flake cracking. It greatly reduces internal defect sources of DIN 1.2379.
 

Electroslag Remelting (ESR)

For higher-demand applications, refined ingots need electroslag remelting. ESR remelts the ingot in the form of a consumable electrode. When molten drops pass through the high-temperature slag layer, non-metallic inclusions are absorbed and removed by slag. The sulfur content of DIN 1.2379 steel can be further reduced below 0.015%. ESR controls the solidification process to improve the shape and distribution of carbides. The final material gains better cleanliness and isotropic properties. It can reach SEP 1921 E/e grade in ultrasonic testing.

Hot Rolling / Forging of DIN 1.2379

Heating of 1.2379 Tool Steel

The starting hot working temperature of 1.2379 material is 1050°C, and the finishing temperature shall not be lower than 850°C. This 200°C temperature window balances the hot plasticity and microstructure control of the material. Heating must be slow and uniform to prevent thermal stress cracking caused by large temperature difference between inner and outer parts. Slow cooling is required after forging or rolling to avoid cracks from rapid cooling.

Forging Ratio Control of 1.2379 Material

1.2379 tool steel is repeatedly upset and drawn in multiple directions. The forging ratio is usually required to be above 4:1. It fully breaks the cast carbide network and makes distribution more uniform. The coarse angular carbide clusters of 8–18 μm in cast structure are crushed into fine and evenly distributed particles.

Hot Rolling (2 mm ≤ Diameter or Thickness ≤ 80 mm)

1.2379 tool steel with diameter or thickness ≤80 mm is usually formed by hot rolling. The finishing rolling temperature shall not be lower than 900°C. Deformation amount and finishing rolling temperature must be controlled during rolling to ensure uniform microstructure and good surface quality. The deformation of each pass is 5–12%, and the roll speed of 40–60 r/min is adopted before finished pass and finished pass. Bars or flat steel after hot rolling are slowly cooled.

Forging Forming (Diameter or Thickness ＞ 80 mm)

DIN 1.2379 material with diameter or thickness ＞80 mm usually uses forging for bloom breaking. For sizes from 80 mm to 200 mm, the forging ratio is above 4:1 as required. Repeated multi-direction upsetting and drawing breaks the cast carbide network for even distribution. The deformation of each heating cycle is controlled in a proper range to avoid cracking caused by excessive single deformation. Slow cooling after forging prevents thermal stress cracks.
 

Upsetting and Drawing (Diameter or Thickness ＞ 200 mm)

For DIN 1.2379 with diameter or thickness over 200 mm, Keyspark Steel can carry out the “three upsetting and three drawing” forging process per high-end customer requirements. It means three times of upsetting and three times of drawing. The total forging ratio is much higher than conventional forging and usually reaches 6:1. Repeated upsetting and drawing fully break coarse eutectic carbides inside large steel ingots. It makes carbide distribution more uniform and improves microstructure density. It applies to large precision molds, high-load stamping molds and other applications with strict requirements for material isotropic performance.

Heat Treatment of 1.2379 Steel

Spheroidizing Annealing

Hot-worked DIN 1.2379 steel undergoes spheroidizing annealing, which is the delivery condition of the material. The annealing process: heat to 800–850°C, hold, then slowly cool down to 600°C at a cooling rate of 10°C/h, followed by air cooling. After annealing, the hardness is controlled ≤255 HB. The microstructure is uniform spheroidal pearlite for easy machining. Controlling the cooling rate at 10°C/h is the key to obtain uniform spheroidized microstructure.

Quenching and Tempering

DIN 1.2379 adopts two-stage preheating before quenching: 550–600°C and 800–850°C. It is then austenitized at 1000–1040°C, with air cooling, oil cooling or salt bath cooling as options. Tempering must start right after quenching, at least twice. Low-temperature tempering at 150–200°C achieves hardness ≥61 HRC; high-temperature tempering at 480–540°C gives hardness ≥58 HRC and improves red hardness.

Cryogenic Treatment

For precision molds requiring high dimensional stability, cryogenic treatment at -70 to -80°C can be performed after quenching. Cryogenic treatment promotes the transformation of retained austenite. It increases the hardness of 1.2379 material by 1–3 HRC and improves dimensional stability.

Subsequent Machining Services of 1.2379 Material

Saw Cutting of DIN 1.2379

1.2379 mold steel can be cut to your required length and width. It works for 1.2379 round bar, steel plate and steel block. Keyspark Steel cuts material to fixed lengths following your size list.

Peeling

Peeling service is for DIN 1.2379 round bars. The machine cuts the outer layer of bars. It takes away surface scale, decarburized layer and small defects, to get clean surface.

Turning

We use centerless lathe to finely cut 1.2379 steel. It makes smooth surface and exact diameter. You can use it directly for blanking or rough work.
 

Milling

Milling works for 1.2379 steel plate and steel block. Milling removes scale and decarburized layer. You get flat surface and exact thickness.
 

Grinding

Grinding machine works on surface of 1.2379 die steel. It makes better surface quality and more exact size, with lower surface roughness and nicer look.

FAQ of DIN 1.2379

Q1: Why does DIN 1.2379 need LF+VD refining instead of only EAF primary melting?

A: EAF primary melting can only adjust basic composition and remove part of phosphorus and sulfur. LF+VD refining further reduces sulfur below 0.030%, controls oxygen content below 16 ppm and hydrogen below 2 ppm. Low oxygen cuts oxide inclusions, and low hydrogen lowers the risk of flake cracking. It provides cleaner molten steel for subsequent ESR or direct application.

A: ESR remelts the ingot as a consumable electrode. Non-metallic inclusions are absorbed and removed when molten droplets pass through high-temperature slag. Sulfur content can be further reduced below 0.003%. Meanwhile, ESR controls the solidification process to improve carbide shape and distribution. DIN 1.2379 gets better cleanliness and isotropic properties, and it can reach SEP 1921 E/e grade in ultrasonic testing.

A: If the forging ratio is less than 4:1, the cast carbide network remains and causes segregation, hurting toughness and polishing performance. Multi-direction repeated upsetting and drawing above 4:1 breaks coarse angular carbide clusters (8–18 μm) into fine and evenly distributed particles. It improves the isotropic performance and mold service life of 1.2379 steel.

A: After heating to 800–850°C in spheroidizing annealing, slow cooling to 600°C at 10°C/h followed by air cooling helps form uniform spheroidal pearlite. A faster cooling rate will form lamellar carbides and reduce machinability. The 10°C/h cooling rate is critical for full spheroidization and hardness ≤255 HB.

A: Cryogenic treatment at -70 to -80°C after quenching promotes the transformation of retained austenite into martensite. It raises the hardness of DIN 1.2379 by 1–3 HRC and reduces microstructure change during service. Dimensional stability is greatly improved, which suits precision molds.

A: SEP 1921 E/e grade is a stricter inspection standard than regular D/d grade, requiring smaller defect equivalent. ESR grade 1.2379 material usually meets E/e grade, which corresponds to ASTM A388 with FBH max. 5 mm defect equivalent. It means fewer internal cracks, pores and inclusions inside the material, suitable for high-load precision molds.

Conclusion

DIN 1.2379 production includes EAF melting, LF+VD refining and ESR remelting. It is shaped by heating, rolling or forging (including three upsetting and three drawing). Then it goes through spheroidizing annealing, quenching & tempering and cryogenic treatment. We provide the quality test of 1.2379 material in the whole process. We also provide after processing such as saw cutting, peeling, turning, milling and grinding. The team of Keyspark Steel offers custom ESR grade and long-term after-sales service to guarantee material performance.

More DIN 1.2379 Resources

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    These are our related articles if you want to learn more tool steel comparison:

    1. 1.2379 Steel – The Electroslag Remelting (ESR) Principle
    2. How Does Vacuum Degassing Refining Improve Material 1.2379?

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