TPT January 2013

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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.

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

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January 2013