TPT January 2013

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January 2013 99
Article
plate, strip and hot section steel, and not contain the rolls for
rolling steel pipe and cold roll formed steel.
New high chromium alloy casting roll researched and
manufactured by Shandong Province Sifang Technical
Development Co Ltd (SDSF) is different from the above
mentioned forged alloy roll, and the roll has greater advantages
in terms of roll quality, service life, production method and
production cost and the roll has remarkable effect in energy
saving and material saving.
New roll manufactured by SDSF had been extensively used
to all key enterprises for producing seamless steel pipe and
many large-scale enterprises for producing HFW/ERWwelding
steel pipe and cold roll formed steel, and the market share of
straightening roll for seamless pipe manufactured by SDSF
is up to 80 per cent in China. New roll has been exported to
many countries in Asia, Europe, Africa and new roll has been
appraised as a “quality product” by China Cold Roll Formed
Steel Association of China, the Iron and Steel Association and
Tianjing Steel Pipe Co Ltd.
This new technology has achieved proprietary intellectual
property rights and two Chinese invention patents and one
Chinese utility model patent, two invention patents and also
two utility model patents are being applied for. This new
technology has created excellent foundations for developing
advanced alloy roll with national independent brands.
The project of “The researching and application of new roll for
steel pipe and cold roll formed steel” has won second prize in
the China metallurgy science and technology awards, second
prize for the Shandong province scientific and technical
progress and first prize at the Jinan city scientific and technical
invention awards.
3 Researching and developing of
new roll for straightening steel
pipe, HFW/ERW welding steel
pipe and cold roll formed steel
3.1 The principle of researching and developing
The roll is one of the main consumption parts in rolling steel
production. The roll quality is not only related to production cost
and productivity of rolling steel, but also reflects the quality of
rolled steel to a great degree. With the development of rolling
technology and continuously increasing of rolling mill speed
and automation level, the service condition of roll is changed
due to rigour on a day-by-day basis and the production process
has a high requirement for quality of roll. The marked trend
for enhancing the quality of roll is to increase the composition
content of alloy elements, such as the use of high chromium
alloy roll in the 1970s and the use of high speed steel roll in
the 1980s. Because of high alloying of roll material the roll is
difficult to forge in production.
With continuous development and successive success of new
processes and advanced equipment the centrifugal casting
process of roll was held by many countries in the world in
1970s and the centrifugal casting roll process was successfully
developed by many enterprises at home in the 1980s, and this
roll could replace some imported product and part of this roll
could be exported. The external layer of centrifugal complex
casting roll is high alloying casting iron or high alloying casting
steel, and it has high hardness, excellent wear resistant and
excellent heat crack resistance properties.
At the present the back up roll for heat rolling plate and
strip steel by centrifugal complex casting method has been
successfully manufactured at home, its weight is up to more
than 80 tons for every piece and it has achieved good effects[2] .
The centrifugal complex casting roll for cold rolling plate and
strip steel has also been successfully manufactured at home
and it has also achieved good effects[3].
Before the 1980s high speed steel roll was produced using the
forging method. High speed steel casting roll has won a great
success in managing to achieve a fast development in recent
years, but this method was usually only used to produce circle
roll under many condition.
Through researching and testing many times the experiment
principle is determined as following: suitable for the working
environment and up to as ideal a state as possible using a
simple process and saving material and energy resources.
The design plan of high chromium alloy casting roll made
using the above principles is different from that of foreign
forging steel roll and high chromium alloy roll for rolling plate
and strip steel.
3.2 The researching and developing of roll material and
preparation method
If utilising casting method with original chemical composition
of D2, X155CrVMo121, SKD11 or Cr12MoV roll the property
of this roll is certainly very poor compared to that of forging
method and the product can not satisfy the requirement of
production. Because of having certain limitations in the way
of heat crack resistance and wear resistance, and meeting
severe challenge of high speed steel roll[4], high chromium
alloy casting iron roll used extensively in heat steel mill
for plate and strip steel before the 1990s is continuously
decreased in used number in heat mill of late years, so it has
certain problems in adhering to design plan of high chromium
casting iron roll.
Through systematically analysing the service condition and
service features of straightening steel pipe roll, HFW/ERW
welding pipe roll and cold roll formed steel roll, the new high
chromium alloy material and shaped method of casting roll
were confirmed. Through adding strength carbide elements
and modification agents used to change shape and distribution
of carbide and to fine crystal, which can enhance the wear
resistance of material in essence, the new high chromium alloy
material in serial that can be suitable for working condition of
speedily cooling and speedily heating and normal temperature
was developed. Since alloying of Mo, Nb elements, etc, the
comprehensive property of roll is increased.
C and Cr are the most essential and most important elements in
high chromium material. Their content determines the number
of carbide, the ratio between M7C3 carbide and total carbide,
hardness, toughness and quenching degree of material.