Tham khảo tài liệu 'engineering materials 2e volume2 episode 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Case studies in steels 141 Molten lead held at 900 C Fig. . Austenitising a striking face. Postscript Although there is a British Standard for hammers there is no legislation in the UK which compels retailers to supply only standard hammers. It is in fact quite difficult to get standard hammers over the counter . But reputable makers spot check their hammers because they will not knowingly sell improperly heat-treated hammers. Further reading K. E. Easterling Introduction to the Physical Metallurgy of Welding Butterworth 1983. D. T. Llewellyn Steels - Metallurgy and Applications 2nd edition Butterworth-Heinemann 1994. Problems The heat exchanger in a reformer plant consisted of a bank of tubes made from a low-alloy ferritic steel containing weight carbon. The tubes contained hydrocarbon gas at high pressure and were heated from the outside by furnace gases. The tubes had an internal diameter of 128 mm and a wall thickness of 7 mm. Owing to a temperature overshoot one of the tubes fractured and the resulting gas leak set the plant on fire. When the heat exchanger was stripped down it was found that the tube wall had bulged over a distance of about 600 mm. In the most expanded region of the bulge the tube had split longitudinally over a distance of about 300 mm. At the edge of the fracture the wall had thinned down to about 3 mm. Metallurgical sections were cut from the tube at two positions i immediately next to the fracture surface half-way along the length of the split ii 100 mm away from the end of the split in the part of the tube which although slightly expanded was otherwise intact. 142 Engineering Materials 2 The microstructure at position ii consisted of grains of ferrite and colonies of pearlite. It was noticed that the pearlite had started to spheroidise see Problem . The microstructure at position i consisted of grains of ferrite and grains of lower bainite in roughly equal proportions. Estimate the temperatures to which the tube been .
