How is the workpiece double-liquid quenched? How can it be ensured that the workpiece does not deform after quenching? The double-liquid quenching method involves taking the quenched workpiece out from the quenching temperature, first cooling it in a fast cooling agent to rapidly overcool the austenite close to the martensite transformation region, and then cooling it in a slower cooling agent. This process generally starts with water and then oil.
The advantage of the double-liquid quenching method is rapid cooling in the unstable austenite region and slow cooling within the martensite transformation region. Consequently, both the organizational stress and thermal stress are relatively small. Therefore, this quenching method can be applied to high carbon steel tools with complex shapes that have limited hardenability. However, there are disadvantages to using this quenching method. First, it's difficult to determine the dwell time in the first quenching agent. If the dwell time is too long, excessive internal stress may occur, losing the significance of double-liquid quenching. On the other hand, if the dwell time is too short, there is a risk of transformation into pearlite-like structures in the second cooling agent, failing to meet the requirements. Sometimes, although the surface reaches martensite, the central part remains at a high temperature with residual heat. In such cases, when the workpiece is transferred from the first cooling agent to the second, there could be heating from inside out, causing inappropriate surface tempering. Additionally, during the transfer between the two cooling liquids, the temperature distribution across different parts of the workpiece becomes uneven, which might lead to quenching defects. Therefore, workers performing this type of quenching must possess sufficient experience and skilled techniques; otherwise, it is challenging to achieve the expected results.
During double-liquid quenching, the parts are typically cooled in water to 300°C and then placed in oil or air for further cooling. For carbon tool steels, the cooling time in water is generally about one second per 3 mm effective thickness or diameter. For more complex-shaped workpieces, this time can be reduced to one second per 4-5 mm effective thickness or diameter. When using the double-liquid quenching method, the hardened layer depth is usually shallower than single-liquid quenching.
For large-section alloy steel workpieces with relatively simple shapes, to increase the hardened layer depth, the water-oil double-liquid quenching method can also be used. The dwell time of the alloy steel workpiece in water should be based on the center layer being cooled to around 300-350°C, approximately 1.5-3 seconds per millimeter of effective thickness, with larger sections taking the upper limit and smaller ones the lower limit. If the required dwell time in water is too long due to the size of the workpiece, the total necessary dwell time can be divided into two stages: first cooling in water for a certain period, then cooling briefly in air, and continuing cooling in water. This reduces the temperature difference between the surface layer and the center layer, avoiding cracking of the workpiece. However, attention must be paid to ensure that during the air cooling process, the heat from the center does not dissipate outward, causing improper surface tempering, which would affect the quality of the quenched workpiece.
High-frequency quenching equipment in various models can perform different quenching processes for different workpieces. For inquiries, please contact 13937100064 or visit our official website at www.guoyunwu.com. Technical consultations are available via QQ number 513925465.