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Acta Metall Sin  2016, Vol. 52 Issue (7): 890-896    DOI: 10.11900/0412.1961.2015.00584
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EFFECTS OF HEAT INPUT ON THE MICROSTRUC-TURE AND IMPACT TOUGHNESS OF WELD METAL PROCESSED BY A NEW FLUXNOVEL FLUX CORED WIRE WELD
Fengyu SONG1,Yanmei LI2,Ping WANG1(),Fuxian ZHU2
1 Key Laboratory of Electromagnetic Processing of Materials, Ministry of Education, Northeastern University, Shenyang 110819, China.
2 State Key Laboratory of Rolling and Automation, Northeastern University, Shenyang 110819, China.
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Abstract  

In recent years, the components tend to be large-scale and large-span. In order to improve the welding construction efficiency and reduce production costs, the high input welding methods, such as automatic gas electric vertical welding, submerged arc welding, electro slag welding, etc., have been widely used in manufacturing fields, like shipbuilding, buildings, bridges, petrochemical and marine structures, etc.. The domestic iron and steel enterprises and research institutes have cooperated successively to develop a number of heat input welding steel with heat input greater than 400 kJ/cm. However, at present, the welding materials which can be matched with these special steels are still dependent on import. In order to change this passive situation, a new type of flux cored wire has been independently developed in this research. The effects of heat input on the microstructure and impact toughness of the weld metal have been investigated through laboratory tests. The results demonstrate that under the condition of large heat input welding, a large number of fine inclusions are formed and distributed randomly in the weld metal. Substantial amount of interlocked acicular ferritic grains are found around the inclusions, contributing to the high impact toughness for the weld metal. With the increase of heat input value, the number of fine inclusions (smaller than 1 μm) decreases and the tendency of inclusion assembly and growth is found to accelerate. Simultaneously, the nucleation points of acicular ferrite decreased and the grain size of acicular ferrite increased slightly in the weld metal. The impact toughness was deteriorated mildly as well.

Key words:  weld metal      high heat input      acicular ferrite      toughness     
Received:  13 November 2015     
Fund: Supported by National Natural Science Foundation of China (No.51174058)

Cite this article: 

Fengyu SONG,Yanmei LI,Ping WANG,Fuxian ZHU. EFFECTS OF HEAT INPUT ON THE MICROSTRUC-TURE AND IMPACT TOUGHNESS OF WELD METAL PROCESSED BY A NEW FLUXNOVEL FLUX CORED WIRE WELD. Acta Metall Sin, 2016, 52(7): 890-896.

URL: 

https://www.ams.org.cn/EN/10.11900/0412.1961.2015.00584     OR     https://www.ams.org.cn/EN/Y2016/V52/I7/890

Heat input Current Voltage Welding speed Mass fraction / %
(kJcm-1) A V (mmmin-1) C Si Mn Al S B O Ti Fe
205 370 35 38 0.08 0.30 1.85 0.41 0.017 0.008 0.060 0.080 Bal.
276 460 38 38 0.09 0.28 2.02 0.40 0.017 0.008 0.061 0.073 Bal.
341 479 45 38 0.09 0.30 1.97 0.40 0.017 0.008 0.061 0.071 Bal.
425 598 45 38 0.08 0.32 1.93 0.40 0.017 0.008 0.061 0.092 Bal.
Table 1  Process parameters of gas-electric vertical welding and chemical compositions of weld metal
Heat input Rm Rp0.2 Rm/Rp0.2 δ Akv(-40 ℃)
(kJcm-1) MPa MPa % J
205 605 440 0.72 24 90
276 663 500 0.75 24 79
341 600 480 0.80 24 71
425 640 470 0.73 24 65
Table 2  Mechanical properties of the weld metal with different heat inputs
Fig.1  EBSD orientation images (a, c) and grain boundary character distributions (b, d) of welded metal with heat inputs of 276 kJ/cm (a, b) and 425 kJ/cm (c, d)
Fig.2  OM (a, c, e, g) and SEM (b, d, f, h) images of the weld metal with heat inputs of 205 kJ/cm (a, b), 276 kJ/cm (c, d), 341 kJ/cm (e, f) and 425 kJ/cm (g, h)
Fig.3  TEM image of an inclusion promoted acicular ferrite (AF) nucleation (a) and EDS analyses of points A~C (b) in weld metal with heat input of 276 kJ/cm
Fig.4  TEM image of an inclusion promoted AF nucleation (a) and EDS analyses of points A~C (b) in weld metal with heat input of 341 kJ/cm
Fig.5  EPMA back scattering image of inclusions distribution in weld metal with heat input of 205 kJ/cm
Fig.6  Inclusions distribution statistical figure of the weld metal
Fig.7  Schematic of AF nucleation in the weld metal
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