Method for manufacturing seamless steel pipe or tube
A technology for seamless steel pipes and manufacturing methods, which is applied in the field of manufacturing seamless steel pipes and high-Cr seamless steel pipes, can solve the problems of reduced yield and reduced production efficiency, and achieve the effect of suppressing internal broken defects
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Embodiment 1
[0091] A steel ingot having the chemical composition shown in Table 1 was subjected to block rolling by a usual method to form a round billet with a diameter of 225 mm. In addition, steels A1 and B1 in Table 1 are steels of examples of the present invention whose chemical components are within the range specified by the present invention. On the other hand, the Cr of steel A2 ＊ and Cr of steel B2 ＊ Steel whose content is outside the range specified in the present invention.
[0092] (Table 1)
[0093] Next, after loading the round steel billets of the above-mentioned various steel sizes into the heating furnace, they are heated under the conditions shown in Table 2, and the piercing efficiency and the front end draft ratio of the plug are respectively 52% and 7.7%. The method is to use a piercer to perform piercing and rolling to produce a tube blank with an outer diameter of 230mm and a wall thickness of 20mm. In addition, the furnace time represented by the above-mention...
reference example 1
[0101] At a soaking temperature of 1200°C, the steel A1 round steel billet with a diameter of 225mm produced in Example 1 was heated, and the time in the furnace was 180 minutes, and then the piercing efficiency and plug tip shown in Table 4 Draft ratio Piercing and rolling were carried out with a piercing machine to produce a tube with an outer diameter of 230 mm and a wall thickness of 20 mm. In addition, when the draft ratio at the front end of the plug was 2.8% in the piercing condition numbers 4, 8, and 12 of Table 4, piercing and rolling could not be performed due to poor bite.
[0102] (Table 4)
[0103] It was investigated whether or not internal cracking defects occurred in each of the shells of the piercing condition numbers 1 to 3, 5 to 7, and 9 to 11 of Table 4 obtained in this way. That is, as in the case of Example 1, first, the occurrence site of the inner surface defect was identified and marked by ultrasonic flaw detection, and then the site was cut and visua...
Embodiment 2
[0108] At a soaking temperature of 1200°C, the steel A1 produced in the above-mentioned embodiment 1 is heated to a round steel billet with a diameter of 225mm, and the time in the furnace is 150 minutes, and then the surface roughness Rz of the roll of the piercing machine is adjusted. JIS It was pierced and rolled to 45 to 210 μm, and an outer diameter of 230 mm and a wall thickness of 20 mm were produced. In addition, with regard to the roughness condition numbers of the respective rolls in Table 5, the plug front end draft ratio at the time of piercing and rolling with a piercing machine was 5.6%.
[0109] (table 5)
[0110] The inner surface properties of each of the obtained blank tubes were investigated. That is, as in the case of Example 1, first, the occurrence site of the inner surface defect was identified and marked by ultrasonic flaw detection, and then the site was cut and visually inspected for evaluation. Furthermore, the occurrence of outer surface defects a...
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Abstract
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