CN109055683B - Vacuum grading gas quenching method for D6AC ultrahigh-strength steel thin-wall shell - Google Patents
Vacuum grading gas quenching method for D6AC ultrahigh-strength steel thin-wall shell Download PDFInfo
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- CN109055683B CN109055683B CN201811250345.7A CN201811250345A CN109055683B CN 109055683 B CN109055683 B CN 109055683B CN 201811250345 A CN201811250345 A CN 201811250345A CN 109055683 B CN109055683 B CN 109055683B
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/56—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering characterised by the quenching agents
- C21D1/613—Gases; Liquefied or solidified normally gaseous material
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/18—Hardening; Quenching with or without subsequent tempering
- C21D1/19—Hardening; Quenching with or without subsequent tempering by interrupted quenching
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
- C21D1/773—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material under reduced pressure or vacuum
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D6/00—Heat treatment of ferrous alloys
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/0068—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for particular articles not mentioned below
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Abstract
The invention provides a vacuum grading gas quenching method for a D6AC ultrahigh-strength steel thin-wall shell, which comprises the step of quenching D6AC ultrahigh-strength steel at 6.7 multiplied by 10‑2Heating to 900 ℃ under Pa vacuum degree, cooling the D6AC ultrahigh-strength steel to 50 ℃ in four steps under the protection of high-purity nitrogen at 2bar, discharging from the furnace and air cooling. The invention adopts a vacuum grading gas quenching method, can prevent decarburization by heat treatment, improve mechanical property and reduce deformation, and simultaneously adopts high-purity nitrogen to replace quenching oil, and the high-purity nitrogen is prepared from air, so that the preparation is convenient, clean and pollution-free.
Description
Technical Field
The invention relates to a quenching method.
Background
The microstructure of the D6AC ultra-high strength steel after quenching and tempering is sorbite, has high yield ratio, good ductility and notch toughness, can still keep higher strength at high temperature, and is mainly used for solid rocket engine shells, booster shells and the like. The shell of the solid rocket engine and the shell of the booster belong to thin-wall long cylinder parts, the requirements on the dimensional accuracy and the mechanical property of the shell are high after heat treatment, and large thermal stress and structural stress are generated after conventional heat treatment, and the stress causes large deformation or microcracks of the thin-wall shell, so that the dimensional accuracy and the stability of the shell are influenced. When the austenite bay is adopted for the stepped cooling quenching, the temperature cannot be automatically adjusted when the austenite bay is kept warm, the operation difficulty is high, in addition, the stepped quenching process can only carry out the classification on the austenite bay, the transformation from high temperature to pearlite and the transformation from martensite can not be controlled, the stepped thermal stress and the structure stress can not be reduced, and the temperature of the thin-wall shell is uneven when the temperature is reduced in the air atmosphere. Meanwhile, the thin-wall shell is heated in the air atmosphere, so that the decarburization problem exists, and the mechanical property of the material is influenced. In addition, the oil quenching has large pollution and cannot meet the requirement of environmental protection. Therefore, the quenching process of the D6AC ultrahigh-strength steel severely restricts the production of the thin-wall shell, and a safe, stable, reliable and environment-friendly heat treatment method must be found.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides the vacuum grading gas quenching method of the D6AC ultrahigh-strength steel thin-wall shell, which can prevent decarburization during heat treatment, improve the mechanical property and reduce deformation, and meanwhile, high-purity nitrogen is adopted to replace quenching oil and is prepared from air, so that the preparation is convenient, clean and pollution-free.
The technical scheme adopted by the invention for solving the technical problem comprises the following steps:
1) at 6.7X 10-2～1.33×10-3Heating the thin-wall shell to 650-720 ℃ at a heating rate of 8-15 ℃/min under a vacuum degree of Pa, and preserving heat for 30-60 min;
2) at 6.7X 10-2～1.33×10-3Heating the thin-wall shell to 880-900 ℃ at a heating rate of 8-15 ℃/min under a vacuum degree of Pa, and preserving heat for 90-120 min;
3) under 2bar of nitrogen, cooling the thin-wall shell to 780-750 ℃ at a cooling rate of 15-25 ℃/min;
4) under 2bar of nitrogen, cooling the thin-wall shell to 600 ℃ at a cooling rate of 200-400 ℃/min, and then cooling to 520 ℃ at a cooling rate of 1-2 ℃/min;
5) cooling the thin-wall shell to 320-290 ℃ at a cooling rate of 180-300 ℃/min under 2bar of nitrogen;
6) and (3) cooling the thin-wall shell to below 50 ℃ at a cooling rate of 5-8 ℃/min under 2bar of nitrogen, discharging and air cooling.
The thin-wall shell after quenching is tempered, is protected by nitrogen, is kept at 550 +/-10 ℃ for 120 +/-10 min, and is discharged from a furnace for air cooling.
The purity of the nitrogen gas is 99.99%.
The invention has the beneficial effects that:
firstly, after austenite transformation is finished at 880-900 ℃, a precooling quenching method is adopted to cool to 780-750 ℃ at a cooling rate of 15-25 ℃/min, precooling before quenching can reduce thermal stress, so that deformation and cracking tendency of a thin-wall shell are reduced; meanwhile, the precooling quenching can also increase the hardening layer of the shell, improve the comprehensive performance of the shell and improve the service performance of the shell;
secondly, when the shell is cooled to 600 ℃ at 780-750 ℃ at a cooling rate of 200-400 ℃/min and cooled at a cooling speed higher than the critical cooling speed, pearlite transformation at 740-610 ℃ can be inhibited, and by rapidly cooling to a certain temperature of an austenite bay area at 610-510 ℃, pearlite is prevented from being generated due to slow cooling rate, and the mechanical property of the shell is reduced;
thirdly, cooling at a cooling rate of 1-2 ℃/min in an austenite bay interval of 600-520 ℃, so that the quenching temperature is reduced, the thermal stress is further reduced, and the quenching deformation tendency is reduced;
fourthly, after cooling at the temperature of 600-520 ℃, cooling to 320-290 ℃ at the cooling rate of 180-300 ℃/min, and when cooling at the cooling rate higher than the critical cooling rate, inhibiting the transformation of upper bainite, and improving the comprehensive mechanical property of the shell;
fifthly, cooling from 320-290 ℃ to below 50 ℃ at a cooling rate of 5-8 ℃/min, and cooling at a lower cooling rate in a martensite transformation zone, so that the transformation of martensite is slower, the surface tensile stress is reduced, the deformation is reduced, the quenching crack is prevented, and the structure stress is reduced;
sixthly, nitrogen is used as a quenching medium, so that the preparation is convenient, the environmental pollution is reduced, and the cleaning process is omitted;
and seventhly, the vacuum quenching method is adopted, so that the decarburization problem of the thin-wall shell is reduced, the mechanical performance of the shell is improved, and the safety and the stability of the thin-wall shell are improved.
Drawings
FIG. 1 is a schematic diagram of the quenching process of the present invention.
Detailed Description
The present invention will be further described with reference to the following drawings and examples, which include, but are not limited to, the following examples.
The invention provides a quenching method of a D6AC ultrahigh-strength steel thin-wall shell, which can improve the mechanical property and reduce the deformation, is pollution-free, clean and environment-friendly, and comprises the following steps:
1) loading the thin-wall shell into a vacuum high-pressure gas quenching furnace at 6.7X 10-2Pa～1.33×10-3Heating to 650-720 ℃ at a heating rate of 8-15 ℃/min under a vacuum degree of Pa, and preserving heat for 30-60 min;
2) after the heat preservation is finished, heating to 880-900 ℃ at the heating rate of 8-15 ℃/min, and preserving the heat for 90-120 min;
3) after the heat preservation is finished, cooling to 780-750 ℃ at a cooling rate of 15-25 ℃/min by using 2bar of high-purity nitrogen (the purity is 99.99%);
4) cooling to 600 ℃ at a cooling rate of 200-400 ℃/min, and then cooling to 520 ℃ at a cooling rate of 1-2 ℃/min;
5) after cooling, cooling to 320-290 ℃ at a cooling rate of 180-300 ℃/min;
6) cooling from 320-290 ℃ to below 50 ℃ at a cooling rate of 5-8 ℃/min, and discharging and air cooling.
7) High-temperature tempering: tempering the quenched thin-wall shell, adopting high-purity nitrogen gas for protection (the purity is 99.99 percent), preserving the heat at 550 +/-10 ℃ for 120min +/-10 min, discharging and air cooling.
The above steps 1) and 2) are both 6.7X 10-2Pa～1.33×10-3Heating under Pa vacuum degree; the above steps 3) to 6) were all cooled under 2bar of high purity nitrogen.
The vacuum grading gas quenching method for the D6AC ultrahigh-strength steel thin-wall shell improves the dimensional precision and the mechanical property of the thin-wall shell, reduces pollution, and increases the safety and the stability of the thin-wall shell.
The following examples were used to demonstrate the beneficial effects and analysis of the present invention:
the first embodiment is as follows:
the vacuum grading gas quenching method for the D6AC ultrahigh-strength steel thin-wall shell is specifically carried out according to the following steps: according to the invention, the D6AC ultrahigh-strength steel is processed at 6.7 x 10 in two steps-2Heating to 900 ℃ under Pa vacuum degree, preserving heat for 90min, and cooling to 780 ℃ with 2bar of high-purity nitrogen at a cooling rate of 15 ℃/min; cooling to 600 deg.C at a cooling rate of 200 deg.C/min, and cooling to 1 deg.C/minCooling to 520 deg.C; after cooling, cooling to 320 ℃ at a cooling rate of 180 ℃/min; cooling from 320 deg.C to below 50 deg.C at a cooling rate of 5 deg.C/min, and air cooling. After gas quenching, adopting high-purity nitrogen for protection, preserving heat for 120min +/-10 min at the temperature of 550 +/-10 ℃, discharging and air cooling.
In the first embodiment, the tensile strength of the processed D6AC ultrahigh-strength steel matrix sample is between 1610MPa and 1640MPa, and the elongation after fracture is 13.9-14.9%; the tensile strength of the welding sample is between 1620MPa and 1640 MPa; the radial runout of five sections of the shell after quenching is respectively as follows: 0.8mm, 1.2mm, 1.5mm, 1.0mm, 0.6 mm.
Example two:
the vacuum grading gas quenching method for the D6AC ultrahigh-strength steel thin-wall shell is specifically carried out according to the following steps: according to the invention, the D6AC ultrahigh-strength steel is processed at 6.7 x 10 in two steps-2Heating to 900 ℃ under Pa vacuum degree, preserving heat for 90min, and cooling to 780 ℃ with 2bar of high-purity nitrogen at a cooling rate of 15 ℃/min; cooling to 600 deg.C at a cooling rate of 200 deg.C/min, and cooling to 520 deg.C at a cooling rate of 1 deg.C/min; after the heat preservation is finished, cooling to 290 ℃ at a cooling rate of 180 ℃/min; cooling from 290 deg.C to below 50 deg.C at a cooling rate of 5 deg.C/min, and air cooling. After gas quenching, adopting high-purity nitrogen for protection, preserving heat for 120min +/-10 min at the temperature of 550 +/-10 ℃, discharging and air cooling.
The tensile strength of the ultrahigh-strength steel matrix sample D6AC treated in the second embodiment is 1650-1660 MPa, and the elongation after fracture is 13.4-14.1%; the tensile strength of the welding sample is between 1660MPa and 1670 MPa; the radial runout of five sections of the shell after quenching is respectively as follows: 0.8mm, 1.3mm, 1.6mm, 1.0mm, 0.8 mm.
Example three:
the vacuum grading gas quenching method for the D6AC ultrahigh-strength steel thin-wall shell is specifically carried out according to the following steps: according to the invention, the D6AC ultrahigh-strength steel is processed at 6.7 x 10 in two steps-2Heating to 900 ℃ under Pa vacuum degree, preserving heat for 90min, and cooling to 750 ℃ with 2bar of high-purity nitrogen at a cooling rate of 25 ℃/min; cooling to 600 deg.C at a cooling rate of 400 deg.C/min, and cooling to 2 deg.CCooling to 520 ℃ at a cooling rate of/min; after cooling, cooling to 320 ℃ at a cooling rate of 300 ℃/min; cooling from 320 ℃ to below 50 ℃ at a cooling rate of 8 ℃/min, discharging and air cooling. After gas quenching, adopting high-purity nitrogen for protection, preserving heat for 120min +/-10 min at the temperature of 550 +/-10 ℃, discharging and air cooling.
The tensile strength of the ultrahigh-strength steel matrix sample D6AC treated in the third embodiment is between 1610MPa and 1640MPa, and the elongation after fracture is 14.0-14.8%; the tensile strength of the welding sample is between 1610MPa and 1630 MPa; the radial runout of five sections of the shell after quenching is respectively as follows: 0.7mm, 1.2mm, 1.6mm, 1.4mm, 0.8 mm.
Example four:
the vacuum grading gas quenching method for the D6AC ultrahigh-strength steel thin-wall shell is specifically carried out according to the following steps: according to the invention, the D6AC ultrahigh-strength steel is processed at 6.7 x 10 in two steps-2Heating to 900 ℃ under Pa vacuum degree, preserving heat for 90min, and cooling to 750 ℃ with 2bar of high-purity nitrogen at a cooling rate of 25 ℃/min; cooling to 600 deg.C at a cooling rate of 400 deg.C/min, and cooling to 520 deg.C at a cooling rate of 2 deg.C/min; after cooling, cooling to 290 ℃ at a cooling rate of 300 ℃/min; cooling from 290 deg.C to below 50 deg.C at cooling rate of 8 deg.C/min, and air cooling. After gas quenching, adopting high-purity nitrogen for protection, preserving heat for 120min +/-10 min at the temperature of 550 +/-10 ℃, discharging and air cooling.
After four treatments, the tensile strength of the ultrahigh-strength steel matrix sample D6AC is 1620MPa to 1660MPa, and the elongation after fracture is 13.5 percent to 14.3 percent; the tensile strength of the welding sample is 1640-1670 MPa; the radial runout of five sections of the shell after quenching is respectively as follows: 0.8mm, 1.4mm, 1.7mm, 1.3mm, 0.9 mm.
Comparison experiment one:
heating the D6AC ultrahigh-strength steel to 900 ℃, preserving heat for 40min at 900 ℃, performing austenitization, then performing oil quenching to room temperature, and preserving heat for 120min at 550 ℃ by adopting high-purity nitrogen protection after oil quenching; wherein, the inside and the outside of the shell are protected by protective paint for quenching.
After the first comparative experiment, the tensile strength of the ultrahigh-strength steel matrix sample D6AC is 1550-1650 MPa, and the elongation after fracture is 10.2-13.6%; the tensile strength of the welding sample is 1560 MPa-1660 MPa; the radial runout of five sections of the shell after quenching is respectively as follows: 1.2mm, 3.0mm, 3.3mm, 2.1mm, 1.3 mm.
Comparative experiment two:
heating the D6AC ultrahigh-strength steel to 900 ℃, preserving heat for 40min at 900 ℃, cooling to 550 ℃ in air after austenitizing is completed, then carrying out oil quenching to room temperature, and preserving heat for 120min at 550 ℃ by adopting high-purity nitrogen protection after oil quenching; wherein, the inside and the outside of the shell are protected by protective paint for quenching.
The tensile strength of the D6AC ultrahigh-strength steel matrix sample treated by the comparative experiment II is between 1540MPa and 1630MPa, and the elongation after fracture is 11.0 to 13.9 percent; the tensile strength of the welding sample is between 1540MPa and 1640 MPa; the radial runout of five sections of the shell after quenching is respectively as follows: 1.0mm, 2.3mm, 2.7mm, 1.6mm, 1.1 mm.
The implementation effect analysis of the invention comprises the following steps:
compared with the first comparative experiment and the second comparative experiment, the tensile strength, the elongation after fracture and the tensile strength of the base sample of the shell treated in the first to the fourth examples are more uniform and stable in distribution, and the elongation after fracture is higher. Meanwhile, the radial runout change of the thin-wall shell after quenching is smaller.
Therefore, the D6AC ultrahigh-strength steel thin-wall shell treated by the method has the advantages of higher tensile strength and elongation after fracture, more uniform distribution, better consistency and more stability of products, good combination of strong plasticity and wide application in the production of solid rocket engine shells.
Claims (3)
1. A vacuum grading gas quenching method for a D6AC ultrahigh-strength steel thin-wall shell is characterized by comprising the following steps:
1) at 6.7X 10-2～1.33×10-3Heating the thin-wall shell to 650-720 ℃ at a heating rate of 8-15 ℃/min under a vacuum degree of Pa, and preserving heat for 30-60 min;
2) at 6.7X 10-2～1.33×10-3The thin-wall shell is heated at a temperature of 8-15 ℃/min under the Pa vacuum degreeHeating to 880-900 ℃ at the heating rate, and keeping the temperature for 90-120 min;
3) cooling the thin-wall shell to 780-750 ℃ at a cooling rate of 15-25 ℃/min in a quenching furnace under the nitrogen pressure of 2 bar;
4) cooling the thin-wall shell to 600 ℃ at a cooling rate of 200-400 ℃/min in a quenching furnace under the nitrogen pressure of 2bar, and then cooling to 520 ℃ at a cooling rate of 1-2 ℃/min;
5) cooling the thin-wall shell to 320-290 ℃ at a cooling rate of 180-300 ℃/min in a quenching furnace under the nitrogen pressure of 2 bar;
6) and (3) cooling the thin-wall shell to below 50 ℃ at a cooling rate of 5-8 ℃/min in the quenching furnace under the nitrogen pressure of 2bar, discharging and air cooling.
2. The vacuum staged gas quenching method for the D6AC ultra-high strength steel thin-wall shell as claimed in claim 1, wherein: and (3) tempering the quenched thin-wall shell, preserving the heat for 120 +/-10 min at 550 +/-10 ℃ by adopting nitrogen protection, discharging and air cooling.
3. The vacuum staged gas quenching method for the D6AC ultra-high strength steel thin-wall shell as claimed in claim 1, wherein: the purity of the nitrogen is 99.99%.
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