Vacuum arc and electroslag remelting process 3

[rapid1348]

Hi everybody
Can anyone explain in brief to me the difference between these two processes and also in which process the quality of the product is better?

Kind Regards

 

[richardbuss]

Hi Rapid,

Vacuum Arc Remelting is melting done under a vacuum. Its used for alloying elements that oxidise easily. Lots of uses for alloys made in this way in the airline industry.

In the ESR process you take an ingot and pass an electric current through it. It slowly melts and drips through a slag and a new ingot is built up underneath. This gives a uniform steel structure with little carbide segregation in the ingot core. Nice for things like aluminium extrusion dies.

Regards
RIchard

 

[rapid1348]

Hi Richard

Thanks for your valuable post.

In fact, our vendor of the steam turbine driver of a compressor has changed the material of the blades from A422-2 to A422-3 and the difference was in the manufacturing process which A422-2 is by vacuum arc and the A422-3 is by electroslag.I did like to know the difference and would appereciate it if you kindly let me know your opinion about this change in the material production procedure.Regarding your explanantion of the vacuum arc remelting process and its application it looks like that this process is better that the other one.

Cheers

Rapid

 

[metengr]

In making comparisons between these two types of melting practices, the ESR process can be used for compressor blades in your application. I know that in the past, VAR was the choice by the aircraft industry to produce rotating blades from superalloy compositions. The VAR provided advantages like; no crucible reaction, low gas content, very low inclusion content, superior macro soundness and chemical homogeneity.

ESR has caught on for manufacturing rotating blades and turbine rotor steels. Superalloys that were manufactured by the ESR process consisted of slabs for re-rolling into sheet products. In ESR melting, the slag protects the molten metal from contamination by the surrounding atmosphere. The slag provides a cleaning action and is more effective for desulphurization. The reported advantages of ESR include; minimized macro and micro segregation, minimized porosity and micro shrinkage, good surface finish and low metallic inclusion content.

Of course, depending on the application, you can combine melting practices like VIM with VAR and/or ESR to achieve triple melting (TM) for extra cleanliness.

 

[rapid1348]

Hi Metengr

Thanks for your response it was very useful.I understand that ESR can also be used in the construction of turbine blades.

Cheers

Rapid

 

[yates]

Strictly speaking, both VAR and ESR are remelting and not melting processes. An ingot (often cylindrical, often produced by VIM) is first produced. This ingot is then used as an electrode - both VAR and ESR are known generically as consumable electrode remelt processes - using either a vacuum (VAR) or a floating slag layer (ESR) to prevent formation of oxides during the remelt phase. Most, although not all, aerospace material specifications do not distinguish between VAR or ESR but refer to 'consumable electrode remelt processes' when such a process is desired.

 

[rd400guy]

Interesting tidbit - VAR is still the primary remelt process for aerospace in the US. Almost all other countries that produce aerospace and other high-performance alloys have switched to primarily ESR, especially Japan.

With respect to high alloy steels such as tool steels, Hitachi's YXR grades (ESR high-speed steels, also called "matrix steels") have a microstructure superior to air-melt grades, and higher toughness numbers thanks to ESR's even distribution of smaller carbides and lower inclusion content. ESR in tool steels seems to be bridging the gap (in performance and cost) between air-melt and much more expensive PM steels like Crucible's CPM grades.

In contrast, although VAR does help with microcleanliness, the process can still leave large non-metallic inclusions in the ingot. This can usually be controlled by careful processing of the electrode.