Through macro-morphology,chemical analysis,metallographic examination,hardness testing and scanning electron microscope observation,the properties and causes of cracks in welded joints of small-diameter thick-walled pipes of 12Cr1 MoVG under the condition of low temperature and no preheating were studied.The results showed that under the low ambient temperature,no preheating before welding,and high heat input of the welding line,the residual stress at the weld seam increased and the plastic deformation capacity weakened.Furthermore,the appearance of vacancies at the austenite grain boundaries resulted in transverse cracking of the weld root layer perpendicular to the weld direction.For small-diameter thick-walled 12Cr1MoVG steel pipes,cracking of the weld seam can be effectively avoided by preheating before welding,controlling the interlayer temperature,post-weld heat treatment,adjusting the welding parameters,and reducing the welding heat input.
12Cr1MoVG steelsmall-diameter thick-walled pipespreheating before weldingwelding line energyresidual stressplastic deformation capacitytransverse crack
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