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WALZEN IRLE Materials - Overview
The following listed roll materials represent the WALZEN IRLE standard material index.
It results from over 190 years of experience in hundreds of thousands successfully done orders for nearly every thinkable industrial rolling application.
Regarding stability, surface hardness and wear resistance properties all following roll materials can be adjusted to the customers specific mill conditions.
G — Grey Iron
I — Indefinite - Compound Casting
K — Chilled Cast Iron - Single Poured
K — Chilled Cast Iron - Compound
KT — Chilled Cast Iron - Compound
KSC — Chilled Cast Iron - Compound
SP — Single Poured and Compound
SA — Single Poured and Compound
SP/A H — Single Poured
SM — Centrifugal Compound Cast
CR — Chrome Iron
KSTV
ST — Steel Casting
ST 0i — Steel Casting - induction hardened
STG — Steel Casting Graphite
SST — Special Steel
FS — Forged Steel
NI-Hard — Ni-Hard
ICRO — Icrodur
G — Grey Iron
Microstructure and main properties
Grey cast rolls have a perlitic basic structure with lamella graphite over the whole barrel diameter. If special demands are put upon the wear resistance, cementite deposits can exist in the matrix in case of respective chemical consistency. Distinguishing properties of the grey iron rolls are:
- very good heat conductivity
- temperature change stability
- good gripping ability
- low decrease of hardness
- relatively low wear resistance.
I — Indefinite - Compound Casting
Microstructure and main properties
The essential feature of the indefinite roll is a microstructure which is aimed from the roll surface towards the roll core.
The microstructural components cementite and graphite are arranged in a cellular way vertically to the roll surface.
The graphite proportion continuously increases from the barrel surface to the barrel core and the proportion of free cementite decreases in the same direction.
The metallic basic matrix of indefinite rolls is formed perlitic or bainitic in the hardness range of 340-540 HV. Due to the special matrix and the continuous decrease of hardness from the barrel surface towards the core, indefinite rolls with a surface hardness of up to about 540 HV are suitable for indenting of deep calibres.
Indefinite rolls of up to 540 HV are mainly applied as single poured rolls.
In case they are exposed to high wear and mechanical or thermal loads they can also be manufactured as statically poured or centrifugally cast compound rolls with grey cast iron- or nodular iron cores.
K — Chilled Cast Iron - Single Poured
Microstructure and main properties
Single poured chilled cast iron rolls consist of a hardened layer of white cast graphite free cementite and the metallic matrix. The thickness of the usable chilled layer can be up to 20 mm depending on the roll diameter. The core material is grey solidified and consists mainly of a perlitic matrix with lamella graphite. Between the outer chilled shell and the core there is a mottled iron zone consisting of grey and white solidified microstructures.
The surface hardness and the wear resistance of the chilled cast iron is determined by the amount of ledeburit in the microstructure and the structure of the matrix. A perlitic, bainitic or martensitic matrix can be obtained using special alloying elements. An increase in the hardness and wear resistance will cause a decrease in the thermal and mechanical capability. The quality grade K30 describes the proportion of cementite in the microstructure.
K — Chilled Cast Iron - Compound
Microstructure and main properties
Compound poured chilled cast iron rolls consist of a hardened layer of white cast graphite free cementite (ledeburit) and the metallic matrix. The surface hardness and wear resistance is defined by the amount of cemintite in the matrix and the formation of the metallic matrix.
A perlitic, bainitic or martensitic matrix can be obtained using special alloying elements. An increase in the hardness and wear resistance will cause a decrease in the thermal and mechanical capability.
The quality grade K30 describes the proportion of cementite in the microstructure.
The thickness of the wear resistant coating on the compound rolls can be adjusted according to the degree of utilization . The core and journal material of the compound roll can consist of grey cast iron (G) or nodular iron (S).
The strength and bending strength of the roll can be adjusted according to the different operating conditions.
KT for calender rolls in the paper industry — Chilled Cast Iron - Compound
Microstructure and main properties
The microstructure of the compound cast quality "K" has a cementite part of about 50% and in the "KT" quality it is 30-40%. This means that the "KT" quality has a slightly lower wear resistance, but it is suitable for higher temperatures (roll-surface temperatures > 160°C).
Before the compound rolls are put into use, the possible thermal and mechanical tension must be calculated for each individual application, so that a foolproof material selection is ensured. The rolls can be delivered with cast-poured journals or screwed on ones.
KSC for calender rolls in the paper industry — Chilled Cast Iron - Compound
Microstructure and main properties
The microstructure of KSC roll materials are similar to the chilled cast iron.
The wear resistance layer (shell layer in compound rolls) consists of cementite (ledeburit) and the metallic matrix.
The matrix is bainitic/martensitic due to the high proportion of alloying elements (Cr, Ni, Mo). Depending upon the degree of alloying there can be varying amounts of austenite in the matrix. This matrix mix increases the corrosion resistance compared to the lower alloyed chilled cast iron materials. Although KSC-alloys cannot be compared to rust-free materials.
The wear resistance of the KSC-material is determined by the large amount of cementite and the hardness of the metallic matrix and compared to chilled cast iron this has a positive and increasing influence.
KSC-rolls can only be cast in the lower diameter- and hardness range (Ø max. 600 mm; KSC-520) as single-cast rolls.
Due to the high proportion of alloying elements is the risk of breakage increased, therefore all other rolls must be manufactured using a compound cast with the journals and core material made of grey iron or nodular iron.
The KSC-rolls are manufactured with cast journals or screwed on forged steel journals with a hardness range of between 400-660 HV.
KSC-rolls are used when special demands are put upon the corrosion and/or wear resistance.
SP — Nodular Iron - perlitic, Single Poured and Compound
Microstructure and main properties
In nodular cast iron rolls the graphite has a nodular function, which causes significant increase in mechanical strength and ductility compared to grey lamella qualities. Apart from the nodular graphite and depending upon the required wear resistance, variable amounts of cementite in the microstructure can be found.
The amount of cementite decreases from the barrel surface to the core of the roll and the nodular graphite simultaneously increases.
Nodular cast iron rolls are used mainly as single-poured rolls. In case of especially high wear resistance demands and mechanical or thermal resistance, they can be manufactured as statically cast or as centrifugal cast compound rolls with a high strength nodular core.
SA — Nodular Iron - acicular, Single Poured and Compound
Microstructure and main properties
In nodular cast iron rolls the graphite has a nodular function, which causes significant increase in mechanical strength and ductility compared to grey lamella qualities.
Apart from the nodular graphite and depending upon the required wear resistance, variable amounts of cementite in the microstructure can be found. The amount of cementite decreases from the barrel surface to the core of the roll and the nodular graphite simultaneously increases.
The metallic matrix is in SA-nodular cast iron rolls acicular. The acicular matrix is adjusted by alloys of Ni and Mo and compared to the perlitic matrix it has a higher tensile strength and wear resistance. The hardness, tensile-strength and viscosity of this material can be optimally adjusted to the respective applications by tempering- or start-annealing. In case of especially high wear resistance demands and mechanical or thermal resistance, the nodular cast iron rolls can be manufactured as statically cast or as centrifugal cast compound rolls.
SP/A H — Nodular Iron - annealed, Single Poured
Microstructure and main properties
In nodular cast iron rolls the graphite has a nodular function, which causes a significant increase in mechanical strength and ductility compared to grey lamella qualities.
Apart from the nodular graphite and depending upon the required wear resistance, variable amounts of cementite in the microstructure can be found. The matrix is either ferritic/perlitic, perlitic or bainitic.
The ductility and the thermal resistance of the material is increased by carrying out a special annealing process to the qualities SP/A-280H, -320H, -360H and -400H.
The heat treatment results in a homogeneous matrix over the whole roll cross section with a low radial hardness loss.
The nodular cast iron rolls SP/A -280H, -320H, -360H and -400H can be annealed for the manufacture of larger roll profiles in a pre-calibrated condition. This means that hereby on the roll surface, pressure residual stress can be fixed even in deeper calibre cuts, which counteracts cracking.
SM — Nodular Iron - martensitic, Centrifugal Compound Cast
Microstructure and main properties
In nodular cast iron rolls the graphite has a nodular function, which causes significant increase in mechanical strength and ductility compared to grey lamella qualities. Apart from the nodular graphite and depending upon the required wear resistance, variable amounts of cementite in the microstructure can be found. The amount of cementite decreases from the barrel surface to the core of the roll and the nodular graphite simultaneously increases.
The metallic matrix is in SM-nodular cast iron rolls martensitic.
The high hardness of the martensite and the cementite in the matrix determines the very good wear resistance of the MS-nodular cast iron rolls.
The thermal sensitivity is relatively high, so that good cooling conditions are necessary when using the roll.
As the SM-nodular cast iron rolls are quite brittle, they are only manufactured as centrifugally cast compound rolls with tough nodular cast iron cores.
CR — Chrome Steel - Chrome Iron
Microstructure and main properties
The microstructure of the wear resistant chrome cast alloys consists of chromium rich eutectic carbides of the M7C3 or M23C6 type, in a matrix of pearlite or martensite with finely dispersed secondary carbides.
Due to the special structures of the CR-carbides the chrome cast materials have far superior mechanical strength and higher ductility in comparison to other carbide materials.
Further positive properties are high pressure and thermal resistance. The amount of Cr-carbides in the Cr-material is variable in a wide range. Increasing amounts of Cr-carbides increase the wear resistance and on the other hand ductility and mechanical strength decreases. The quality grade CR5 describes the proportional amount of eutectic Cr-carbides in the microstructure. By using heat treatment and depending upon the amount of Cr-carbides, surface hardness of up to 700 HV can be reached. The decrease in hardness in the usable shell layer is very low.
For use in the flat rolling mills, the Cr-rolls are only manufactured as centrifugal cast compound rolls with grey cast iron or nodular iron cores. For profile roll mills they are used as single-poured rolls.
KSTV Chrome Steel - Special Material for calender rolls in the paper industry
Microstructure and main properties
Using a special casting treatment for the KSTV-rolls it is possible to achieve high temperature stability properties. KSTV-rolls can be used with roll surface temperatures of >200°C. The temperature difference between the heating medium and the roll surface may not exceed max. ± 70-80°C.
Due to their technological properties the KSTV-rolls can be dimensioned as chilled cast iron rolls with low diameters and wall thickness. This means that due to their weight reduction they can be beneficial not only in new machines but also when modernising old ones.
The KSTV-rolls are delivered with screwed on forged iron steel journals.
ST — Steel Casting
Microstructure and main properties
Depending upon the chemical composition and heat treatment steel cast rolls have a perlitic or bainitic matrix. The main alloying elements are Cr, Ni, Mo, V and W which depending upon the application of the roll are additionally alloyed in various amounts.
The description ST-0 is valid for under eutectoid to near eutectoid materials with a C-content <0,8 %.
These materials are distinguished by high strength and breaking strength.
The surface temperature of the steel cast roll is adjusted by the type of heat treatment and the chemical composition and can be in the range of 180 - 420 HV.
The decrease in hardness within the working layer is negligible.
Steel cast rolls can be annealed in a pre-calibrated condition for the manufacturing of larger profiles. This means that hereby on the roll surface, pressure residual stress can be fixed even in deeper calibre cuts, which counteracts cracking. Apart from that, this special annealing achieves lower hardness loss and thereby good wear resistance up to the end diameter of the roll.
ST 0i — Steel Casting - induction hardened
Microstructure and main properties
The ST0i calender rolls are made of a high creep-resistant cast steel especially developed for paper calender rolls. Special ST0i properties: high strength, toughness and security against fracture. Special metallurgical treatments provide high material cleanness and a low amount of non-metallic inclusions.
With a special adjustment of the chemical composition ST0i provides mechanical and physical material properties for paper calender rolls, which fulfil very high operating demands (stresses).
An excellent wear resistance will be achieved by inductive surface hardening. In the non hardened section the hardness will be 280-320 HV and in the hardened layer a surface hardness up to 640 HV can be reached. Due to the high tempering strength of ST0i, the surface hardness is constant up to a working temperature of 320°C. The depth of hardening amounts ca. 6 mm.
The microstructure of the hardened layer (i) consists of a tempered fine-grained martensite and the core out of eutectoid steel.
STG — Steel Casting Graphite
Microstructure and main properties
The graphited steel cast iron rolls are associated with the over eutectoid materials due to their C-content.
By carrying out a specific treatment to the steel cast, a part of the carbon content is released when solidifying as free graphite.
Essential alloying elements are Si, Cr, Mn, Ni and Mo which depending upon the application of the roll are additionally alloyed in varying amounts.
The matrix of the graphited steel cast rolls STGO consists of a perlitic matrix , with max. 5 % carbide and graphite.
The proportion of carbide and graphite can be adjusted from the chemical composition and the type of heat treatment. Thereby adjusted to the thermal and the wear resistance of the material and the application.
Graphited steel cast rolls are distinguished in comparison to the graphite free rolls as follows:
-
high cracking resistance
- good wear resistance
- good surface conditions.
The good material properties of the graphited cast steel roll can be additionally improved by annealing in a pre-calibrated condition. This means that hereby on the roll surface, pressure residual stress can be fixed even in deeper calibre cuts, which counteracts cracking. Apart from that, this special annealing achieves lower hardness loss and thereby good wear resistance up to the end diameter of the roll.
The surface hardness of the STGO rolls can be adjusted in the range of 180 - 380 HV.
SST — Special Steel
Microstructure and main properties
The SST alloyed materials are associated with the high-working-speed steel (HSS).
The main alloying elements are C, Cr, V, W and Mo. The matrix of these materials consist after the most sophisticated heat treatment of the martensic elementary matrix in which the carbide of the vanadium (VC) molybdenum (Mo2C), Tungsten (W2C) and mixed carbide (M6C) can be found finely distributed. These special carbides are characterized by their extremely high hardness (up to 3000 HV) and cause these materials to have a very high wear resistance.
Further positive properties of the SST materials are:
- good tempering properties (up to 550°C)
- high heat stability
- constant hardness throughout the usable roll section
- strongly improved shape accuracy of the products with minimal wear in combination with very good surface structure.
The performance of the rolls compared to the usual qualities can be improved multi-fold (up to 6 x) by using the SST-materials.
FS for Rolls in the Paper Industry — Forged Steel
Microstructure and main properties
Forged steel rolls consist of composed martensit on the hardened surface and the core and journal material consists of a homogeneous heat treatable matrix. Due to special metallurgic steps the roll surface has a matrix with the highest degree of cleanliness.
After forging, tempering and pre-machining the hardness of the roll barrel and the required roll surface hardness are implemented. This procedure is carried out mainly using the induction hardening method , although other hardening processes are possible. The hardening depth is normally a minimum of 6 - 8 mm.
The following main points determine the quality and chemical composition of the forged steel rolls:
- roll diameter
- surface hardness
- thickness of the hardened layer
- running temperature in the calender
For the known applications the two qualities FS1 and FS2 have proven to be successful.
The quality FS1 is used for rolls with a surface hardness of up to 620 HV and the quality FS2 is used for rolls with a roll surface hardness of 600 HV to 700 HV.
Other possibilities are available for special requirements such as the surface hardness, hardening depth or the running temperature of the roll.
NI-Hard — Ni-Hard
Microstructure and main properties
The Ni-Hard-materials consist of a chrome carbide in a martenistic elementary matrix.
The casting of the materials can take place either in sand or chill-moulds respectively permanent moulds. The fine grain achieved by chill- moulding leads to better impact strength properties.
The materials are relatively good in tempering, so that the applications take place up to temperatures of up to 400 °C as long as no temperature shocks occur. NI-Hard I and Ni-Hard II-materials differentiate in the carbon content, whereas the NI-Hard IV-material contains chrome-special carbides (M7C3). With respect to impact fatigue strength, the Ni-Hard IV-material is superior to the NI-Hard I- and NI-Hard II materials.
All NI-Hard materials show a low hardness decrease over the entire wall thickness.
ICRO — Icrodur
Microstructure and main properties
The icrodur material is characterised by a very fine grain microstructure. By using special carbide developers an almost eutectic M7C3 / M23C6 - carbide structure in martensitic matrix is created.
The material can be supplied as a single poured cast as well as compound cast version with grey cast iron core or nodular cast iron core.
Apart from highest wear resistance Icrodur is characterized by extremely low decrease in hardness over the working layer.
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