Heat treatment process for large 35CrMo steel axis forgings

Abstract

The invention discloses a heat treatment process for large 35CrMo steel axis forgings. The heat treatment process comprises the following steps of: performing one-time forging on the forgings at the temperature of higher than 800DEG C, and performing air cooling until the surface temperature is 500-600DEG C; heating to the temperature of between 870 and 880DEG C, keeping the temperature for 3.8 to 4 hours, taking out of a furnace, vertically putting into water at a speed of 2-3 meters per second, pulling out at a speed of 3-5 meters per second after the forgings are completely put into the water, and performing air cooling to normal temperature; preliminarily cutting, heating to the temperature of between 600 and 620DEG C, and keeping the temperature for 0.4 to 0.6 hour, continuously heating to the temperature of between 830 and 850DEG C, keeping the temperature for 3.4 to 3.6 hours, taking out of the furnace, vertically putting into an AQ251 solution at a speed of 2-3 meters per second, and cooling to room temperature; and heating to the temperature of between 680 and 690DEG C, keeping the temperature for 5.5 to 6 hours, taking out of the furnace and performing air cooling. By the heat treatment process, the internal stress of the forgings can be effectively controlled in the heating process, plastic deformation and internal cracks are avoided, the heating time for the forgings is effectively shortened, and energy consumption is reduced.

Description

technical field [0001] The invention relates to a processing method for a steel shaft forging, in particular to a heat treatment process for a large shaft forging made of 35CrMo steel. Background technique [0002] Large shaft forgings generally refer to forgings with a weight of more than 5 tons and a diameter of more than 200mm. The material of the steel ingot is generally medium carbon alloy steel. Due to the heavy weight of such forgings and the use of many materials, it is necessary to strictly control the occurrence of waste products during the processing of parts. In the heat treatment process, the temperature difference between the inside and the surface of the forging is strictly controlled to prevent the forging from cracking due to excessive stress inside the forging; at the same time, due to the large size of the part and the slow heat dissipation, it is also necessary to try to shorten the time spent in the heat treatment process. time taken. [0003] In the h...

AI Technical Summary

Problems solved by technology

[0004] One is that due to the insufficient processing capacity of machine tools and the slow speed of forging and forming, it is necessary to carry out segmental heating and segmental forming of forgings, that is, multi-fire segmental forging and forming. When the forging is finally completed, the temperature of most areas of the forging is already very high. Low, or even if it is formed by one-fire forging, the temperature of the forging has dropped to room temperature before heat treatment

In this way, when the subsequent normalizing heating is performed, it is necessary to take a long heating time and consume more energy to heat up the forging in stages to prevent excessive stress inside the forging and cause cracking

[0005] The second is to carry out normalizing heating directly after the primary forging is completed. At this time, since the lowest temperature on the surface of the forging is still higher than the specified final forging temperature (above 800°C), there is a higher temperature in the core, and at this time, direct normalizing When heated by fire, the core of the forging will be under high temperature for a long time, which will easily lead to coarse grains in the core of the forging and reduce the mechanical properties of the material.

[0006] The third is that in the cooling process of the heat treatment air environment, other methods are often not used, but simply cooled in the air. Since the diameter and length of the large shaft forgings are relatively large, the heat dissipation speed is slow, and more man-hours are spent.

Images