Heat treatment method of martensite precipitation hardening stainless steel 06Cr15Ni5Cu2Ti
Technical Field
The invention belongs to the technical field of ferrous metallurgy, and particularly relates to a heat treatment method of martensite precipitation hardening stainless steel 06Cr15Ni5Cu2 Ti.
Background
Precipitation hardening stainless steel (PH steel) refers to a high-strength stainless steel, which is called PH steel for short, and is characterized in that different types and quantities of strengthening elements are added on the basis of chemical components of the stainless steel, and different types and quantities of carbides, nitrides, carbonitrides and intermetallic compounds are precipitated in the precipitation hardening process, so that the strength of the steel is improved, and sufficient toughness is maintained. Precipitation hardening stainless steels may be classified into martensite type, semi-austenite type and austenite type 3 types according to the metallographic structure of their matrix. The 06Cr15Ni5Cu2Ti steel is a novel martensite precipitation hardening stainless steel using Cu as precipitation hardening element, a martensite structure can be obtained by air cooling to room temperature after solid solution, and Cu-rich intermetallic compounds are precipitated in the aging process to generate precipitation hardening. The 06Cr15Ni5Cu2Ti martensite precipitation hardening stainless steel has higher strength, excellent plasticity and toughness, good corrosion resistance and welding performance, is suitable for manufacturing important bearing parts such as an aircraft engine combustion chamber, a conical beam mounting side frame and the like, and is a material used for a long time in the aviation industry.
After hot working, martensitic precipitation hardening stainless steel needs to be softened to reduce the hardness so that it can be easily cold deformed and used for machining. For martensitic precipitation hardening stainless steel, the steel has certain plastic deformation capacity after solution treatment and overaging treatment. Solution treatment is not claimed as a means for softening a semi-finished product in principle, because the microstructure after solution treatment is lath-like martensite, high internal stress due to volume expansion remains, the steel has high crack sensitivity, surface cracks are easily induced from surface scratches, and the crack propagation speed is extremely high, which often results in scrapping of the whole batch of steel due to cracks. The over-aging treatment has better softening effect than the solution treatment, but the treatment time is generally not shorter than 20h and longer.
Disclosure of Invention
The invention solves the technical problem that the prior martensite precipitation hardening stainless steel has high hardness after hot processing and is not easy to be subjected to cold deformation and mechanical processing.
The technical scheme for solving the problems is to provide a heat treatment method of martensite precipitation hardening stainless steel 06Cr15Ni5Cu2Ti, which comprises the following steps:
a. solution treatment: heating 06Cr15Ni5Cu2Ti steel to 1000 +/-10 ℃, preserving heat for 1-2 hours, and then air-cooling to room temperature;
b. and (3) adjusting: heating the 06Cr15Ni5Cu2Ti steel subjected to solution treatment to a temperature between Ac1 and Ac3, preserving the heat for 0.5-1 hour, and then air-cooling to room temperature;
c. aging treatment: and (3) keeping the temperature of the adjusted 06Cr15Ni5Cu2Ti steel at a temperature lower than Ac1 for 0.5-1h, and then cooling the steel to room temperature in air.
Wherein, the chemical components of the 06Cr15Ni5Cu2Ti steel are less than or equal to 0.08 percent of carbon, less than or equal to 0.70 percent of silicon, less than or equal to 1.0 percent of manganese, less than or equal to 0.02 percent of phosphorus, less than or equal to 0.018 percent of sulfur, 13.50 to 14.80 percent of chromium, 4.8 to 5.8 percent of nickel, 1.75 to 2.50 percent of copper, 0.03 to 0.15 percent of titanium and the balance of iron and impurities in percentage by mass.
Where Ac1 is the austenite transformation start temperature during heating, and Ac3 is the austenite transformation end temperature during heating.
Wherein the temperature of the adjusting treatment is controlled to be 640-660 ℃.
Preferably, the temperature of the conditioning treatment is controlled at 650 ℃.
Wherein the temperature of the aging treatment is 550 ℃.
The invention has the beneficial effects that:
after the solution treatment, the temperature is adjusted between Ac1 and Ac3, so that part of austenite phase begins to appear in the 06Cr15Ni5Cu2Ti steel and certain precipitated phase is contained; after the solution treatment and the adjustment treatment, the aging treatment is carried out at the temperature slightly lower than Ac1 in a shorter time, at the moment, reversed austenite appears, a fine dispersed strengthening phase exists, and the toughness and comprehensive performance are better; according to the invention, through a large number of experiments, the temperature and time of the adjustment treatment and the aging treatment are strictly controlled, the tensile strength is 1030MPa, the yield strength is 940MPa, and the impact energy is 162J, so that the martensite precipitation hardening stainless steel 06Cr15Ni5Cu2Ti achieves the softening effect, and meanwhile, a certain strength is maintained, and the martensite precipitation hardening stainless steel is easy to cold deform and machine for use.
Detailed Description
The invention provides a heat treatment method of martensitic precipitation hardening stainless steel 06Cr15Ni5Cu2Ti, which comprises the following steps:
a. solution treatment: heating 06Cr15Ni5Cu2Ti steel to 1000 +/-10 ℃, preserving heat for 1-2 hours, and then air-cooling to room temperature;
b. and (3) adjusting: heating the 06Cr15Ni5Cu2Ti steel subjected to solution treatment to a temperature between Ac1 and Ac3, preserving the heat for 0.5-1 hour, and then air-cooling to room temperature;
c. aging treatment: and (3) keeping the temperature of the adjusted 06Cr15Ni5Cu2Ti steel at a temperature lower than Ac1 for 0.5-1h, and then cooling the steel to room temperature in air.
In the heat treatment process, the austenite phase is completely austenitized after the solution treatment, a part of austenite phase begins to appear after the adjustment treatment, the austenite phase contains a certain precipitated phase, and the reversed austenite phase appears after the aging treatment, and the fine dispersed strengthening phase exists, so that the toughness and the comprehensive performance are better.
Wherein, the chemical components of the 06Cr15Ni5Cu2Ti steel are calculated by mass percent and are less than or equal to 0.08 percent of carbon, less than or equal to 0.70 percent of silicon, less than or equal to 1.0 percent of manganese, less than or equal to 0.02 percent of phosphorus, less than or equal to 0.018 percent of sulfur, 13.50 to 14.80 percent of chromium, 4.8 to 5.8 percent of nickel, 1.75 to 2.50 percent of copper, 0.03 to 0.15 percent of titanium, and the balance of iron and impurities.
Where Ac1 is the austenite transformation start temperature during heating, and Ac3 is the austenite transformation end temperature during heating.
Wherein the temperature of the adjusting treatment is controlled to be 640-660 ℃.
Preferably, the temperature of the conditioning treatment is controlled at 650 ℃.
Wherein the aging treatment temperature is just lower than Ac 1.
Preferably, the temperature of the aging treatment is controlled to 550 ℃.
The invention is further illustrated and described by the following examples.
A hot rolled open billet of 06Cr15Ni5Cu2Ti steel was selected, the main components and the contents of which are shown in Table 1. The transformation characteristic temperatures AC1, AC3 and Ms (martensite start point) of the steel are shown in Table 2 after being tested by a formastor FII high temperature phase transformation instrument. The 06Cr15Ni5Cu2Ti steel was heat-treated in different processes in the following examples and comparative examples according to the above transformation characteristic temperature, and the mechanical properties of the treated samples were tested according to the national standard GB/T228.1-2010, and the test results are shown in Table 3.
TABLE 1
Steel grade
|
C
|
Si
|
Mn
|
P
|
S
|
Cr
|
Mo
|
Ni
|
Cu
|
Ti
|
06Cr15Ni5Cu2Ti
|
0.05
|
0.40
|
0.50
|
0.0043
|
0.0031
|
14.8
|
0.07
|
5.05
|
2.01
|
0.18 |
TABLE 2
Critical point of
|
Ac1
|
Ac3
|
Ms
|
Temperature of
|
565
|
700
|
175 |
Comparative example 1: heating the 06Cr15Ni5Cu2Ti steel sample to 1000 ℃ in a heating furnace, preserving heat for 1.5h, and then cooling to room temperature in air.
Comparative example 2: heating the 06Cr15Ni5Cu2Ti steel sample to 1000 ℃ in a heating furnace, preserving heat for 1.5h, then air-cooling to room temperature, carrying out aging treatment for 0.5h at 550 ℃, and air-cooling to room temperature.
Examples 1 to 4 were prepared by heating a 06Cr15Ni5Cu2Ti steel sample in a heating furnace to 1000 ℃ and holding the temperature for 1.5 hours, then air-cooling to room temperature, adjusting the temperature at 580 ℃, 600 ℃, 650 ℃ and 700 ℃ for 1 hour, respectively, air-cooling to room temperature, aging the sample after adjustment at 550 ℃ for 0.5 hour, and air-cooling to room temperature.
Comparative example 3: heating a 06Cr15Ni5Cu2Ti steel sample in a heating furnace to 1000 ℃, preserving heat for 1.5h, then cooling in air to room temperature, carrying out conditioning treatment for 1h at 800 ℃, cooling in air to room temperature, carrying out aging treatment for 0.5h on the conditioned sample at 550 ℃, and cooling in air to room temperature.
Comparative example 4: heating a 06Cr15Ni5Cu2Ti steel sample in a heating furnace to 1000 ℃, preserving heat for 1.5h, then cooling in air to room temperature, carrying out conditioning treatment at 850 ℃ for 1h, cooling in air to room temperature, carrying out aging treatment on the conditioned sample at 550 ℃ for 0.5h, and cooling in air to room temperature.
TABLE 3
As can be seen from the above comparative examples 1 and 2, the 06Cr15Ni5Cu2Ti steel had an air-cooled tensile strength of 1060MPa, a yield strength of 980MPa, an impact energy of 120J, and a microhardness of 361.5 after being solutionized at 1000 ℃ for 1.5 h; after the solution treatment, the tensile strength of the alloy is 1093MPa, the yield strength is 1040MPa, the impact energy is 115J, and the microhardness value is 388.8 after the aging treatment is directly carried out at 550 ℃.
The microstructure after the solution treatment is lath martensite, no precipitated phase is generated, the strength is lower than that of an aging state, but high stress formed by volume expansion remains in the lath martensite, the crack sensitivity of the steel is strong, and surface cracks are easily induced from surface scratches; the strength is improved after aging treatment, and the steel contains fine dispersed strengthening phases through analysis of a scanning electron microscope and a transmission electron microscope, so that the steel is high in strength and is not suitable for cold deformation and machining.
After the solution treatment at 1000 ℃, the temperature is adjusted between Ac1 and Ac3 once, and then the aging treatment is carried out, so that the strength is reduced to a certain extent, and the ductility and toughness are improved, wherein when the adjustment treatment temperature is 650 ℃, the tensile strength is 1030MPa, the yield strength is 940MPa, the impact energy is 162J, the strength is reduced, but the ductility and toughness are greatly improved, and through analysis of an X-ray, a scanning electron microscope and a transmission electron microscope, the sample contains 10% of austenite content and has a certain fine dispersed strengthening phase, so that the sample has high strength and high toughness.