Product category:
Metals and materials, stockholding
News Release from: Bohler Special Steels | Subject: Bohler W400VMR tool steels
Edited by the Manufacturingtalk Editorial
Team on 07 February 2002
Advanced melting produces extra clean
tool steels
The advanced melting technology traditionally associated with the production of 'super alloys' is now lending itself to the manufacture of tool steels, particularly in hot work types.
Bohler has been recognised as the world's largest producer of tool steels for many years, whilst being a major supplier of 'super alloys' for industries such as the aerospace and chemical industry, where cleanliness of material is of paramount importance The advanced melting technology traditionally associated with the production of Super Alloys is now lending itself to the manufacture of Bohler's tool steel range, particularly in hot work tool steels where 'extra clean' material offers substantial benefits to the tool user for medium to long run tooling
This article was originally published on Manufacturingtalk on 28 May 2007 at 8.00am (UK)
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The production route by which a hot work tool steel has been manufactured should increasingly be taken into consideration when selecting the appropriate material.
The tool steel manufacturing process, be it conventional melting, electro slag remelting (ESR) or vacuum remelting (VMR), has a great influence on the microstructure, cleanliness and homogeneity of the material, thus imparting positive effects on mechanical properties such as toughness, thermal conductivity and hence improved tool life.
A fundamental problem associated with conventional melting techniques employed in tool steel manufacture is the inhomogeneity of the cast ingot.
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Complex alloys such as tool steels segregate during cooling and crystallisation, causing macro segregation in the steel structure, resulting in areas of different chemical composition over the cross section and the concentration of non-metallic inclusions.
Consequently, this produces "banding" which is familiar to hot work tool steel users.
It is this banding which causes the difference in toughness between longitudinal and transverse directions.
Vacuum remelting of tool steels enhances the cleanliness of the steel and the homogeneity of the microstructure, thus significantly reducing the problem of banding.
The homogenised structure also imparts improved toughness, which allows the hardness of the tool to be increased without any fall off in toughness normally associated with conventionally melted tool steels.
This is significant to tool users as this higher hardness can be exploited to increase resistance to abrasive wear and erosion whilst maintaining the toughness required to combat heat checking.
Bohler W400VMR offers an increase of 67% in toughness over 1.2343 ESR material at working temperature, reducing the risk of failure due to gross cracking, whilst delaying the onset of heat checking.
In diecasting, surface temperatures reach peaks of over 500degC and it is the added toughness of the die at these temperatures which means that heat checking is delayed, and when heat checking cracks do appear, they do not propagate as quickly due to homogenised steel structure.
For hot work applications particularly in pressure diecasting where long tool life is required, this can be best achieved by selecting Bohler W400 VMR, especially where heat checking is the limiting factor on tool life.
(This was Manufacturingtalk's Top Story on 6 February 2002).
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