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The causes on lower impact toughness of weld for 10 mm thick 700 MPa grade square and rectangular welded pipe welded with high frequency resistance are analyzed with such inspection and analytical equipment as metallographic microscope, impact testing machine, scanning electron microscope and energy dispersive spectrometer. The results showed that there were such endogenous inclusions as silicate and titanium nitride as well as foreign inclusion that is mainly manganese oxide at the weld, the combined effect of which causes impact absorbing energy at room temperature of weld to be less than 8 J. Subsequently, the weld quality of square and rectangular welded pipe is improved, impact absorbing energy of weld is increased to about 20 J by taking such measures as strengthening control level of steelmaking process and increasing upset force of high frequency resistance welding. In straightening and sizing process, cracking rate of square and rectangular welded pipe is decreased from 8% to 3%.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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