TPT July 2011

A rticle

Innovation and development of roll for steel pipe and cold roll forming steel Yuan Houzhi, Liu Xingyi, Zhang Ning – Shandong Province Sifang Technical Development Co Ltd, China

Abstract High chromium alloy casting rolls for steel pipe straightening, HFW/ ERW welding pipe and cold roll forming steel, researched and developed by Shandong Province Sifang Technical Development Co Ltd, successfully meet the requirements of producing high-grade alloy pipe and fit the advanced steel pipe production mills. The utilisation property and service life of high chromium alloy casting roll is comparable to the forged steel rolls made of materials such as D2, X155CrVMo121 and SKD11. Compared to forged steel rolls, high chromium alloy casting rolls have advantages in method and cost of manufacture. The effects of saving energy and material can be remarkable through utilising high chromium alloy casting roll. 1. General In recent years China has introduced and constructed a lot of steel pipe production lines with a world advanced level – and some of the lines are the first of their kind in the world. [1] Now China’s steel pipe producing and consuming industry is the largest in the world, and the consuming quantity of roll is also the largest in the world. The material design of roll is a basic part of the machinery design. The material used for steel pipe straightening roll, HFW/ERW welding pipe roll and cold roll forming steel roll in traditional design is alloy forging steel. The USA uses D2 and H13 in the design, Germany uses X155CrVMo121, X40CrMoV5-1, uses SKD11 and SKD61, and China uses Cr12MoV, 3Cr2W8V, Cr12, 9Cr2Mo and GCr15. D2, X155CrVMo121and SKD11 are about the same with Cr12MoV. They are cold mould steel with high carbon and high chromium, and it is basic kind of cold mould steel. This kind of steel possesses a high quenching ability, quenching hardness and wear resistance, its wear resistance is 2-3 times higher than common low alloy tool steel, but this kind of steel has higher requirements for smelting, forging and heat treatment and is more difficult to make.

The production of advanced steel pipe mills and high grade alloy steel pipe has a higher requirement to roll – the forging steel rolls which are separately introduced with the mills and produced by China are all affected by different defects. In production D2, X155CrVMo121 and SKD11 forging steel rolls, which are used in advanced rolling pipe mills, specially under the condition of speedily cooling and speedily heating, are all presented with the phenomenon of cracks on the roll face and looseness of roll shaft. See figure 1 and figure 2. Now, Cr12MoV forged steel roll is only used in small size roll for a welding pipe production line at home, the great majority of mills still use a low-class forging steel roll consisted of Cr12, 3Cr2W8V, 9Cr2Mo and GCr15. These rolls have poor wear resistance and the service life is only 1 / 2 – 1 / 3 of the above mentioned imported forging steel roll. The pipe straightening roll, HFW/ERW welding pipe roll and cold roll forming steel roll belong to special-shaped roll. This kind of roll is possessed of the features of complex shape, more size and a small batch. With special HFW/ERW welding pipe roll and cold roll forming steel roll, one drawing is only able to produce 1-2 product, the maximum weight of product can be up to 8-10 tons per piece and minimum weight of product can be up to 5-8kg/piece. This kind of roll is difficult to produce to use of forging tool steel, the inside hole of roll can not be forged and the utilisation factor of material is lower than 50%. D2, X155CrVMo121, SKD11, Cr12MoV materials have a narrow forgeable temperature area and big forged difficulties, so the material has a low utilisation factor and high-energy consumption. Because the roll has a complex shape and big differential on wall thickness, the heat treatment encounters even bigger difficulties. Due to a lot of research that has been collected that studies plate and strip rolls in relation to rolls for steel pipe and cold roll forming steel, China now has around 3,425 patents related to roll. The main area of the above-mentioned patents is plate and strip roll and only 161 patents are for special-shaped roll for pipe and cold roll forming steel. The patent of special-shaped roll is only occupied by 4.75 of all patents. High chromium alloy casting roll researched and manufactured by Shandong Province Sifang Technical Development Co Ltd is different from the above mentioned forged alloy roll, and the roll has greater advantages in the way of roll quality, service life, production method and production cost. The roll manufactured by Shandong Province Sifang Technical Development Co Ltd has been more and more used to production line of steel pipe and cold roll forming steel, specially used to production line with a world advanced level, and has been exported to foreign countries and has got good appreciation.

Figure 1: crack condition of forged SKD11 sizing roll

Figure 2: crack condition of forged D2 straightening roll

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J uly 2011

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