What’s called “Electro Slag Remelting(ESR) in tool steel industry ?

The electroslag remelting (ESR) process is used to remelt and refine steels and various super-alloys, resulting in high-quality ingots. This process can be started up through vacuum induction melting. The ESR process uses the as-cast alloy as a consumable electrode. Electric current (generally AC) is passed between the electrode and the new ingot, which is formed in the bottom Of a water-cooled copper mold. The new ingot is covered in an engineered slag that is superheated by the electric current. The electrode tip is slowly melted from contact with the slag. These metal droplets travel through the slag to the bottom of the water-cooled mold and slowly freeze As the ingot Is directionally solidified upwards from the bottom of the mold. The slag pool floats above the refined alloy, continuously floating upwards as the alloy solidifies. The molten metal is cleaned of impurities that chemically react with the slag or otherwise float to the top of the molten pool as the molten droplets pass through the slag.

Metallurgy of the Electroslag Remelting Process

Due to the superheated slag that is continuously in touch with the electrode tip, a liquid film of metal forms at the electrode tip. As the developing droplets pass through the slag, the metal is cleaned of non-metallic impurities which are removed by chemical reaction with the slag Or by physical flotation to the top of the molten pool. The remaining inclusions in ESR are very small in size and evenly distributed in the remelted ingot.

Slags for ESR are usually based on calcium fluoride (CaF2), Lime (CaO) and alumina (Al2O3). Magnesia (MgO), titania (TiO2) and silica (SiO2) may also be added, depending on the alloy to be remelted. To perform its intended functions, the slag must have some well-defined properties, such as:

• Its melting point must be lower than that of the metal to be remelted;

• It must be electrically efficient;

• Its composition should be selected to ensure the desired chemical reactions;

• It must have suitable viscosity at remelting temperature.

Its advantages are as following :

Ø Highly improve steel pureness

ESR can remove the large non-metallic inclusions very easily, highly improve steel pureness, the plasticity and toughness are also much better than other smelting ways. Cause the molten steel is solidified in the water-cooled mold, cooling rate is fast, thus the ingot composition segregation is very less. Meanwhile as the crystallization of the ingot are gradually proceeds from the bottom to the top, so the structure is homogeneous, no porosity and shrinkage defects.

Ø Good working plasticity

ESR steel have the characteristics of dense microstructure, uniform composition, good working plasticity on wide temperature range. It allows the possibility of low compression ratio, for example 350mm thick flat bars can be produced by a 700mm thick ESR flat ingots.

Ø More excellent performance when steel plate is rolled by ESR ingot

Compared with normal steel plate, the transverse ductility and tenacity of Rolled ESR steel plate is much higher. The anisotropy, fracture toughness, notch sensitivity and low cycle fatigue index{LICFI) are all get significantly improvements.

Ø Good weldability for rolled plates, heat-affected zone get reduced of welded joints

It can leave out the normalizing process of large welding fabrication(High pressure vessel, reactor vessel) After welding.

Ø Well useable performance

ESR rolled steel plate have good resistance to cold brittleness at low temperature

Ø High yield

When producing large heavy plate, ESR ingot have more less mass than normal mould cast steel ingots. The greater tonnage of large heavy plate, the higher utilization ratio of ESR ingot than ordinary steel ingot.

Our mostly produced ESR tool steel grades are as following which mainly be used in aluminium extrusion dies, die casting, glass molds, press molds, knives, cutters etc industries.

H11/1.2343ESR, H13/SKD61/1.2344ESR, 420SS/1.2083ESR, 1.2367ESR, 1.2316ESR

1.2767ESR, D2/SKD11/1.2379ESR, M2/1.3343ESR, A8ESR

Editor : Mr. Jie Yun Lee (Engineer)

Tel: +86 714 3064045, E-mail : sales@altaspecialsteel.com

Company : Alta Special Steel Co.,Ltd

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