1. Phenomenon <br> The coarse crystal state can be seen from the weld or the fracture near the seam (Figure 17-7).
2. Cause Analysis
(1) The preheating is excessive, and the metal in the weld and its vicinity is strongly heated.
(2) The contact is too light during preheating, the intermittent time is too short, and the heat is excessively concentrated on the weld.
(3) The heating zone along the longitudinal direction of the weldment is too wide, and the amount of forging is too small. The upsetting process is not sufficient to cause proper plastic deformation in the near-slit zone, and the superheated metal is not excluded from the weld.
(4) For upsetting and labor saving, the live upset forging continues for a long time, or the upset forging is not possible, causing the metal to overheat.
3. Prevention
(1) Determine the degree of preheating according to the grade, variety and specifications of the steel bar,
And strictly control in production. In order to facilitate the mastery, it is advisable to combine the preheating amount with the number of preheating times. The preheating amount should be 1~2mm, and the number of preheating times is 1~4 times. Through the preheating amount, the preheating start time can be accurately controlled by the scale pointer on the welding machine; the preheating can be controlled in time by counting Stop time.
(2) Adopt low-frequency preheating mode, properly control the contact time, intermittent time and pressing force of preheating, so that the joint can obtain wider low-temperature heating zone, improve joint performance, and not generate large overheating zone.
(3) Strictly control the temperature and retention during upsetting. When the preheating temperature is high, the speed of the entire burning process can be accelerated, and if necessary, the steel bar can be re-clamped and the rapid burning process can be performed again, and the forging amount should be ensured so that the upsetting process can be completed under strong conditions. . Thereby effectively removing the superheated metal.
(4) Strictly control the charging upsetting process. When welding steel bars with large cross-sections, if the operator's physical strength is insufficient, the assistants can be added to coordinate the upsetting, and it is forbidden to adopt the harmful practice of prolonging the charging upsetting process.
2. Cause Analysis
(1) The preheating is excessive, and the metal in the weld and its vicinity is strongly heated.
(2) The contact is too light during preheating, the intermittent time is too short, and the heat is excessively concentrated on the weld.
(3) The heating zone along the longitudinal direction of the weldment is too wide, and the amount of forging is too small. The upsetting process is not sufficient to cause proper plastic deformation in the near-slit zone, and the superheated metal is not excluded from the weld.
(4) For upsetting and labor saving, the live upset forging continues for a long time, or the upset forging is not possible, causing the metal to overheat.
3. Prevention
(1) Determine the degree of preheating according to the grade, variety and specifications of the steel bar,
And strictly control in production. In order to facilitate the mastery, it is advisable to combine the preheating amount with the number of preheating times. The preheating amount should be 1~2mm, and the number of preheating times is 1~4 times. Through the preheating amount, the preheating start time can be accurately controlled by the scale pointer on the welding machine; the preheating can be controlled in time by counting Stop time.
(2) Adopt low-frequency preheating mode, properly control the contact time, intermittent time and pressing force of preheating, so that the joint can obtain wider low-temperature heating zone, improve joint performance, and not generate large overheating zone.
(3) Strictly control the temperature and retention during upsetting. When the preheating temperature is high, the speed of the entire burning process can be accelerated, and if necessary, the steel bar can be re-clamped and the rapid burning process can be performed again, and the forging amount should be ensured so that the upsetting process can be completed under strong conditions. . Thereby effectively removing the superheated metal.
(4) Strictly control the charging upsetting process. When welding steel bars with large cross-sections, if the operator's physical strength is insufficient, the assistants can be added to coordinate the upsetting, and it is forbidden to adopt the harmful practice of prolonging the charging upsetting process.
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