EFFECT OF NITROGEN CONTENT ON MICRO-STRUCTURE AND IMPACT TOUGHNESS OF COARSE CRYSTAL HEAT AFFECTED ZONE OF LOW CARBON Mo-V-Ti-B MICRO-ALLOYED STEEL UNDER HIGH HEAT INPUT CONDITION
EFFECT OF NITROGEN CONTENT ON MICRO-STRUCTURE AND IMPACT TOUGHNESS OF COARSE CRYSTAL HEAT AFFECTED ZONE OF LOW CARBON Mo-V-Ti-B MICRO-ALLOYED STEEL UNDER HIGH HEAT INPUT CONDITION
The influence of nitrogen content on the area of thermal impact zone of low-carbon Mo-V-Ti-B micro-alloy steel was studied by Gleeble.The results show,under the condition of 100 kJ/cm heat input,the impact energies in the-20 ℃ HAZ of 85N,110N and 144N test steels are 186 J,97 J and 57 J,respectively.With the increase of nitrogen content in the test steel,the impact work of the test steel decreases gradually.When the nitrogen content increased from 85 ppm to 110 ppm,the thermal affected area of welding low-carbon Mo-V-Ti-B micro-alloy steel changed from massive ferrite+a large amount of needle ferrite to a small amount of needle ferrite,and the tissue coarsened,so the impact work in the thermal affected area of coarse ferrite was reduced.When the nitrogen content further increased from 110 ppm to 144 ppm,coarse crystal thermal influence area organization from massive ferrite+a small amount of needle ferrite into massive ferrite+beads,although bulk ferrite grain refinement,but the"hard phase"pearlite content increases in tissue,and the size of the body is larger,"hard phase"beads and matrix in the impact sample deformation deformation of uncoordinated,resulting in crack initiation,causing impact work further decline.
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