Many factors affecting the mechanical properties of forgings after quenching after heat, including heating temperature, forging deformation temperature (the beginning of forging〉, the final forging temperature, deformation, deformation rate, the final forging to the quenching of the residence time before quenching, quenching medium and tempering temperature, etc.. Today, the main to understand the deformation rate, forging residence time, quenching medium and high temperature tempering temperature on the mechanical properties of forgings after quenching after heat.
The deformation speed depends mainly on the equipment used, commonly used
forging equipment deformation speed is as follows:
Die forging hammer: 4 m/s - 7 m/s
Inertia screw press: 0.5m / s 1.2 m/s
Hot forging with mechanical press: 0.6 m/s - 1.5 m/s
Hydraulic press: 0.02 m/s - 0.03 m/s
With the increase of deformation speed, strength changes are more complex, when the deformation speed is small (0.7m/s~2.8m/s), with the increase of deformation speed, the more difficult to recrystallize in the process of deformation, so the deformation strengthening effect will increase with the increase of the deformation speed, but strengthened to a certain extent, with the strength of the further increase in the deformation speed is large enough when the deformation of the heat generated during the deformation of the temperature will be raised And make the recrystallization process can be carried out, so the strength is no longer with the increase in deformation speed and increase, and may even decline; when the deformation speed is greater, the strength of the deformation speed with the increase and further increase, at the same time, plasticity is the first to increase and then reduce, and later do not change with the increase in deformation volume.
Forging in the forging forming after autotuning and correction, so it must stay for a period of time to quenching, stay time is shorter, the more retained deformation strengthening effect. But after forging time on the mechanical properties of forgings more complex, and its austenitization heating temperature, deformation temperature. If you do not require forging after-heat quenching can improve the toughness of steel and only hope that the resulting performance is not lower than the level of ordinary tempering, it is entirely possible to extend the residence time after forging, so forging after-heat quenching can also be used for free forgings.
Final forging quenching before the impact of mechanical properties of the residence time with the forging material and forging process and different. Carbon steel in the forging process dynamic response and dynamic recrystallization will be completed, stay after forging will not only recrystallization, and will even gather recrystallization, so the forging should be quenched as soon as possible; for alloy steels, especially the deformation temperature is lower, deformation variable is small, not easy to recrystallization, forging after appropriate stay will be conducive to the formation of polygonalization of the structure of the strength to improve the strength, so as to obtain the best strength and toughness with. When the stay time is too long will make the forging strength decline. In short, the final forging to quenching stay time according to the specific requirements of the performance of forgings, generally should not be long. Can be tested to find the appropriate residence time after forging.
Quenching medium not only affects the mechanical properties of forgings, metallurgical organization, but also may produce deformation and cracks, so it is necessary to choose the appropriate quenching medium, and maintenance and maintenance of quenching medium. Ideal quenching medium cooling characteristics: carbon steel and low alloy steel at 650 ℃ above the austenite is more stable, to a slower rate of cooling, in order to reduce the workpiece due to the temperature difference between the temperature caused by the temperature stresses inside and outside; at 650 ℃ ~ 450 ℃, the requirements of a sufficiently fast cooling rate (more than the critical cooling rate) should be less than 400 ℃ should be cooled slowly to reduce organizational stresses, to prevent excessive deformation and quenching cracks. Quenching and cooling, in order to obtain martensite or bainite organization, must be fast cooling. But the same is to obtain martensite, a variety of steel critical cooling rate is not the same, too fast cooling, will cause excessive internal stress, causing deformation or even cracking.
As mentioned earlier, the forging heat quenching if used and ordinary tempering heat treatment of the same tempering temperature, its plasticity and toughness indicators than ordinary tempering heat treatment is low. And ordinary quenching, with the tempering temperature increases, strength and hardness decline, plasticity and toughness is increased, so as long as the tempering temperature is increased, you can make the plasticity and toughness of forging heat quenching and ordinary quenching is comparable or slightly higher. Forging afterheat quenching has a high temper resistance, in order to get and ordinary quenching after tempering the same toughness and hardness, forging afterheat quenching of high temperature tempering temperature than the ordinary quenching tempering temperature generally need to increase 40 ℃ - 80 ℃, so that you can get a better overall mechanical properties.
The above high-temperature deformation heat treatment on the organization and mechanical properties of the forging and deformation after reply and recrystallization, reply and recrystallization can be eliminated high-temperature deformation of the reinforcing effect of high-temperature deformation of the forging organization and mechanical properties of the impact of the degree of deformation of the forging will be as the model with the recuperation and recrystallization of the gradual weakening of the process, or even disappeared, so in the determination of forging heat quenching process parameters should be noted.
