CN113322368A - Manufacturing method for eliminating overheating of 35CrNi3MoV large-scale cylinder forging - Google Patents

Abstract

The invention relates to a manufacturing method for eliminating overheating of a 35CrNi3MoV large-scale cylinder forging, aiming at the overheated large-scale cylinder forging with the diameter phi of 1100mm and the wall thickness of not more than 400mm, a heat treatment method of repeatedly fluctuating heating temperature in a pearlite region and an austenite region is adopted to refine grains, and the manufacturing method comprises the following specific steps: preheating a workpiece at 650 +/-20 ℃, raising the full-power temperature to 10-20 ℃ above AC3, carrying out heat preservation according to the effective section of the workpiece and the calculation of 2-4h/100mm after temperature equalization, and ensuring that the central temperature of the workpiece reaches 810 +/-10 ℃; cooling the workpiece to a pearlite transformation area of 650 +/-10 ℃, and preserving heat according to 4-8h/100mm times of normal heat preservation time; after the heat preservation at 650 +/-10 ℃, the full-power temperature is raised to 810 +/-10 ℃, the repetition times are determined according to the coarse crystal degree, and a heat treatment method that the heating temperature repeatedly fluctuates in a pearlite area and an austenite area is adopted, so that the aims of refining crystal grains, improving and cutting off the tissue inheritance are achieved, and the problem of grain refining which cannot be solved by adopting multiple normalizing of large-size cylinder forgings is solved.

Description

Manufacturing method for eliminating overheating of 35CrNi3MoV large-scale cylinder forging

Technical Field

The invention belongs to the technical field of large-scale forging heat treatment, and particularly relates to a manufacturing method for eliminating overheating of a 35CrNi3MoV large-scale cylinder forging, which can cut off tissue inheritance to achieve grain refinement and can solve the problem of overheating of a large-scale forging with a large diameter phi 1100mm and a wall thickness of not more than 400mm by adopting a conventional multi-normalizing heat treatment process.

Background

The 35CrNi3MoV cylinder forging has the advantages of large specification, large size of the required steel ingot, slow crystallization process, serious segregation of the steel ingot, uneven structure and components and other internal defects caused by part selection crystallization results, long forging period, more heating times, uneven deformation, slow heating speed and long retention time in a high-temperature area. After the forging is cooled, the equilibrium structure is difficult to obtain, and a relatively fast heating speed cannot be obtained when reheating is carried out through a critical zone, so that coarse prior austenite grains are easy to inherit. The large crystal grains not only cause the performance of the large forging to be poor, the service life to be reduced, and the ultrasonic flaw detection is grass-shaped waves, thereby covering the internal defects of the forging and influencing the judgment of the internal quality condition of the workpiece by ultrasonic waves.

Disclosure of Invention

The invention aims to overcome the defects in the prior art and provide a manufacturing method for eliminating overheating of a 35CrNi3MoV large-scale cylinder forging, which can effectively solve the problems of cutting structure inheritance and coarse grains of the large-scale cylinder forging and the repeated fluctuation of heating temperature in a pearlite region and an austenite region, and can refine the grains.

The technical scheme of the invention is realized as follows:

a manufacturing method for eliminating overheating of a 35CrNi3MoV large-scale cylinder forging piece is characterized in that aiming at the overheated large-scale cylinder forging piece with the diameter phi of 1100mm and the wall thickness of not more than 400mm, a heat treatment method with the heating temperature repeatedly fluctuating in a pearlite region and an austenite region is adopted to refine grains, and the manufacturing method specifically comprises the following steps:

step 1), preheating a workpiece at 650 +/-20 ℃, raising the temperature to 10-20 ℃ above AC3 at full power, carrying out heat preservation according to the effective section of the workpiece by 2-4h/100mm after temperature equalization, and ensuring that the central temperature of the workpiece reaches 810 +/-10 ℃;

step 2), cooling the workpiece to a pearlite transformation area of 650 +/-10 ℃, and preserving heat according to 4-8h/100mm times of normal heat preservation time;

and 3) after the heat preservation at 650 +/-10 ℃, raising the temperature at full power to 810 +/-10 ℃, and determining the repetition times according to the coarse crystal degree.

Compared with the prior art, the invention has the following advantages:

by adopting a heat treatment method of repeatedly fluctuating heating temperature in a pearlite area and an austenite area, the aims of refining crystal grains, improving and cutting off tissue inheritance are achieved, and the problem of grain refining which cannot be solved by adopting multiple normalizing for large-size cylinder forgings is solved. The invention heats the workpiece to a temperature slightly higher than Ac3, can retain a large amount of carbide particles, increase the nucleation rate of cooled pearlite, spheroidize needle austenite, lose original orientation and cut off tissue inheritance.

Detailed Description

The following examples are intended to describe the invention in detail, and these examples are merely illustrative of the best mode of carrying out the invention and do not limit the scope of the invention in any way.

The mechanism of the invention is that according to the temperature of the 35CrNi3MoV large-scale cylinder forging near the heating AC3 line, more unmelted carbide particles are preserved, the nucleation rate of cooled pearlite is increased, meanwhile, the initially formed fine austenite is used for air cooling to the pearlite area, and the needle-shaped austenite is spheroidized after repeated times (more than 2 times), loses the original orientation, cuts off the tissue inheritance, and finally achieves the purpose of refining grains.

Therefore, the invention can adopt the method that after the workpiece is preheated, the full power is heated to 10-20 ℃ above AC3, after the workpiece is homogenized and insulated, the workpiece is air-cooled to a pearlite area, and the normal insulation time is 2-4 times. The process is repeated for more than 2 times according to the coarsening degree of the crystal grains.

Therefore, the grain refinement of the 35CrNi3MoV large-scale cylinder forging is realized as follows: preheating a workpiece at 650 +/-20 ℃, then raising the full power temperature to 10-20 ℃ above AC3, after temperature equalization, calculating according to (2-4) h/100mm of the effective section of the workpiece, and preserving heat to ensure that the central temperature of the workpiece reaches 810 +/-10 ℃. Cooling the workpiece to a pearlite transformation area of 650 +/-10 ℃, and preserving heat according to 4-8h/100mm times of normal heat preservation time. After the heat preservation at 650 +/-10 ℃, the full-power temperature is raised to 810 +/-10 ℃, and the repetition times are determined according to the coarse crystal degree.

Example 1: a cylinder forging with the specification of phi 1100 multiplied by phi 700 multiplied by 800mm is forged and then subjected to conventional one-time normalizing and tempering preheating treatment, and the detection results after quenching and tempering are as follows:

the process method for grain refinement comprises the following steps:

feeding the overheated cylinder forging (with unqualified grain size) into a furnace at the temperature of less than or equal to 650 ℃, keeping the temperature at 650 +/-10 ℃ for 4 hours, raising the full power to 810 +/-10 ℃, keeping the temperature for 10 hours after homogenizing, cooling to 650 +/-10 ℃, and keeping the temperature for 6 hours at the temperature; then heating to 810 +/-10 ℃ at full power, carrying out homogenization and heat preservation for 10 hours, carrying out air cooling to 650 +/-10 ℃, carrying out heat preservation for 6 hours at the temperature, carrying out furnace cooling to 400 ℃ at the temperature of less than or equal to 30 ℃, carrying out air cooling to room temperature, and carrying out pretreatment to spheroidize the needle-shaped austenite, improve the tissue inheritance of the needle-shaped austenite, increase the nucleation rate of pearlite and provide good tissue conditions for subsequent tempering.

The pretreated cylinder forging is subjected to heating quenching at 860 +/-10 ℃ and tempering at 550-620 ℃, and the detection result is as follows:

example 2: a cylinder forging with the specification of phi 1200 multiplied by phi 500 multiplied by 1000mm is forged and then subjected to conventional secondary normalizing and tempering preliminary heat treatment, and the detection results after quenching and tempering are as follows:

the process method for grain refinement comprises the following steps:

feeding the cylinder forging with the upper grain size not more than 650 ℃ into a furnace, keeping the temperature at 650 +/-10 ℃ for 4 hours, raising the full power to 810 +/-10 ℃, keeping the temperature for 8.5 hours after homogenizing, air-cooling to 650 +/-10 ℃, and keeping the temperature at the temperature for 12 hours; then heating to 810 +/-10 ℃ at full power, carrying out homogenization and heat preservation for 9 hours, carrying out air cooling to 650 +/-10 ℃, carrying out heat preservation for 12 hours at the temperature, carrying out furnace cooling to 400 ℃ at the temperature of less than or equal to 30 ℃, carrying out air cooling to room temperature, and carrying out pretreatment on the mixture to spheroidize the needle-shaped austenite, improve the tissue inheritance of the needle-shaped austenite, increase the nucleation rate of pearlite and provide good tissue conditions for subsequent tempering.

The pretreated cylinder forging is subjected to heating quenching at 860 +/-10 ℃ and tempering at 550-620 ℃, and the detection result is as follows;

the grain size detection result shows that the large-size cylinder forging is pretreated by conventional normalizing and tempering, the crystal grains are coarsened after quenching and tempering, the nucleation rate of the cooled pearlite is increased by adopting a heat treatment method that the heating temperature repeatedly fluctuates in a pearlite area and an austenite area, and simultaneously the needle-shaped austenite is spheroidized, loses the original orientation and cuts off the tissue inheritance, so that the aims of improving and cutting off the tissue inheritance are achieved, and the problem of overheating (crystal grain refinement) which cannot be solved by adopting multiple times of normalizing of the large-size cylinder forging is solved.

Claims (1)

1. The manufacturing method for eliminating overheating of the 35CrNi3MoV large-scale cylinder forging is characterized in that aiming at the overheated large-scale cylinder forging with the diameter phi of 1100mm and the wall thickness of not more than 400mm, a heat treatment method with the heating temperature repeatedly fluctuating in a pearlite region and an austenite region is adopted to refine grains, and the method specifically comprises the following steps:

step 1), preheating a workpiece at 650 +/-20 ℃, raising the temperature to 10-20 ℃ above AC3 at full power, carrying out heat preservation according to the effective section of the workpiece by 2-4h/100mm after temperature equalization, and ensuring that the central temperature of the workpiece reaches 810 +/-10 ℃;

step 2), cooling the workpiece to a pearlite transformation area of 650 +/-10 ℃, and preserving heat according to 4-8h/100mm times of normal heat preservation time;

and 3) after the heat preservation at 650 +/-10 ℃, raising the temperature at full power to 810 +/-10 ℃, and determining the repetition times according to the coarse crystal degree.