Class C steel gears are mainly subjected to dynamic loads or impact loads during operation, so welds are required to have better overall performance. Due to the poor weldability of C-grade steel gears, cold/hot cracks are easily generated during welding. Therefore, several problems must be paid attention to when selecting welding materials: (1) Selecting the chemical composition of the base metal and the strength level is equivalent. Welding material; (2) influence of fusion ratio and cooling rate; (3) influence of heat treatment on mechanical properties of weld; (4) selected welding materials should be able to reduce the hydrogen content in the weld as much as possible.
Based on the above analysis, the 4.0mm alkaline low-hydrogen electrode E5016 and the 1.0mm alloy structural steel wire H08Mn2MoA were selected for testing.
Process test welding specification (1) welding rod material E5016 when using manual arc welding; welding rod diameter 4.0mm; welding current 150180A. (2) welding wire material H08Mn2MoA when CO2 gas shielded welding; welding wire diameter 1.0mm; welding current 140220A; welding voltage 1830V Gas flow rate 615L/min.
The size of the groove of the test piece is Y-shaped groove, and its shape and size are as shown.
Welding process test electrode drying temperature is 250350, baking time is 1h, holding temperature is 100150. Multi-layer multi-pass welding, first layer bottom welding, welding current is 150A. Cover between each bead and bead 1 /31/2. Short arc welding is used for welding. After each weld is welded, the slag is cleaned on the welding surface and the slag on both sides with the air shovel - the groove size of the specimen (the bottom weld is not hammered) ). The preheating temperature during welding is 200250, the interlayer temperature is 200300, and the welding current is 150160A. After the last weld is welded, the weld is required to be 12mm higher than the base metal. After the front surface is welded, the test plate is turned over to remove the root. The arc gouging will cut off the bottom layer, and smooth the surface of the weld and the surface of the base material. Finally, preheat the 190210 and weld it. The welding current is 150A. After the welding, the whole test plate is heated to 200250. Wrap it with asbestos cloth and let the asbestos cloth open after cooling to room temperature.
Welded joints mechanical properties welding method tensile strength / MPa yield strength / MPa elongation 5 / section shrinkage / tensile fracture condition impact work / J hardness / HB manual arc welding 4853901649 broken base material 81178CO2 gas shielded welding 575 not obvious 610 It can be seen from the base material 53215 that the fracture location is in the base metal, indicating that the mechanical properties of the weld are superior to the base metal. The reason for the analysis may be that the preheating temperature is too high, resulting in a coarse Wei's body structure in the heat affected zone, thereby reducing the toughness, and the fracture location is in the heat affected zone. However, the actual pre-heating of the gear is used. The volume of the gear is much larger than that of the test piece. The required preheating temperature should be higher than that of the test piece. Therefore, the preheating temperature at the time of gear repair is determined to be 200,250 (interlayer temperature is 200,300). .
Repair process of gear defects Preparation before welding (1) Before welding, it is required to carefully inspect the defective parts of the gears, confirm the defects and the extents, and record and mark them. (2) The defective part to be welded is ground with a wind wheel, and it is confirmed that the defect has been removed and then repaired, and the transition is required to be smooth, and the surface of the base material is exposed to metallic luster. (3) Clean up the defects and oil and impurities in the vicinity of 100200mm.
Welding specification (1) Welding rod E5016 for manual arc welding; diameter 4.0mm; current 140180A; voltage 1828V. (2) welding wire H08Mn2MoA with CO2 gas shielded welding; diameter 1.0mm; current 140220A; voltage 1830V; gas flow 615L/min .
The welding process operates with multiple layers of multi-pass welding, and the start and end of the weld must be of a quality. The welding current for the first layer of bottom welding can be appropriately adjusted to about 10A. Each weld bead must be covered by 1/3-1/2 between the weld bead. In order to prevent air from invading the weld pool, short arc welding is required for welding. Immediately after welding each weld, use a pneumatic air shovel to carefully clean the surface of the weld and the slag on both sides, and hammer the surface of the weld with a small hammer. After the weld surface of the slag is cleaned, the hammer is hammered first. Punch the sides of the sides evenly to make pitting. After careful observation, if defects are found, the weld should be ground with a wind wheel and reheated and finally welded until no defects are found (Note: the number of repairs per defect cannot exceed 3); If a defect is found, the next seam is welded.
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