Process analysis of normalizing 61500020012R crankshaft using high-frequency induction annealing furnace

61500020012R The crankshaft is a key component of the power output of the internal combustion engine of heavy-duty trucks. It is subject to huge bending and torsional stress during operation. The normalizing hardness value is an important mechanical performance index of normalized parts, and its level directly affects the strength, toughness and service life of the crankshaft.

61500020012R crankshaft normalizing can be carried out by using a high-frequency induction annealing furnace. There are no fire sealing and heat preservation devices on the front and rear furnace doors. The crankshaft is continuously loaded transversely perpendicular to the length of the furnace bottom. The original production method is continuous discharging, and the cooling method required by the process is air cooling. Since the last pair of burners are located at a high position and are 2 to 3 crankshaft rotation radii away from the rear furnace door, the temperature of the last continuous crankshaft in the rear furnace door drops significantly, causing the crankshaft to become darker after coming out of the furnace. The high temperature radiometer measured it to be 700 At about ℃, the hardness after air cooling is 4.6~4.9. Later, manual pulling was used to pull the 850~880℃ through-fired crankshaft directly to the fan for cooling. The result was a pass rate of 60%. Those with a normalized hardness value between 4.5~4.7 could only be sold at a reduced price, which not only greatly reduced corporate profits, It also affects the corporate image and weakens the company's market competitiveness.

Through careful observation and in-depth analysis of the production process, and through communication and demonstration with the R&D leaders and professional technicians, our company determined to improve the high-frequency induction annealing furnace to ensure the temperature of the parts coming out of the oven, and change the cooling method to fully refine the grains. Adjust and strictly control the heating temperature and the holding time after the parts reach temperature to prevent austenite grains from growing, thereby affecting the normalizing grain refinement effect. Process improvements are made in three aspects to improve product quality and stabilize mass production.

The process of parts processing using high-frequency induction annealing furnace is: blanking - forging - normalizing - hardness detection - shot blasting - machining - surface quenching - nitriding - inspection - finished product storage.

Normalizing technical requirements: The hardness testing point is the big head parting surface, genuine products are 4.0~4.5, defective products are 4.5~4.7; normalizing metallographic structure sampling location: 1/3 radius from the big head to the surface, identified according to national standards.

When using a high-frequency induction annealing furnace to normalize parts, if the heating temperature is too high and the holding time is too long, the austenite grains will grow and the grain boundaries will be reduced, which will reduce the nucleation rate during pearlite transformation; cooling after normalizing Low speed will reduce the degree of supercooling of pearlite transformation and reduce the driving force of pearlite phase transformation. Both of these aspects will affect the refinement of grains by normalizing, making the pearlite lamellae thicker after normalizing, thus making the material The resistance to plastic deformation is reduced, and the performance test is low hardness.

The heat preservation performance of the high-frequency induction annealing furnace is not good, and the furnace is shut down for heat preservation when the operators have a group meal, which causes the temperature of the normalized parts to drop when they come out of the furnace. If the temperature of the parts is lower than the austenite transformation point and higher than the eutectoid point of the material, during the cooling process The pro-eutectoid transformation will occur, and the precipitation of the pro-eutectoid phase of 45 steel, that is, ferrite, will also reduce the normalizing hardness.