CN112626316A - Heat treatment method for improving G115 impact toughness of novel martensite heat-resistant steel and application - Google Patents
Heat treatment method for improving G115 impact toughness of novel martensite heat-resistant steel and application Download PDFInfo
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- CN112626316A CN112626316A CN201910904153.1A CN201910904153A CN112626316A CN 112626316 A CN112626316 A CN 112626316A CN 201910904153 A CN201910904153 A CN 201910904153A CN 112626316 A CN112626316 A CN 112626316A
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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
- C21D1/25—Hardening, combined with annealing between 300 degrees Celsius and 600 degrees Celsius, i.e. heat refining ("Vergüten")
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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
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Abstract
The invention provides a heat treatment method for improving the impact toughness of novel martensite heat-resistant steel G115 and application thereof, wherein a secondary hardening and tempering process is adopted, wherein the first hardening and tempering process comprises the following steps: charging the martensite heat-resistant steel G115 at the temperature of 400-700 ℃, heating to 1000-1150 ℃ at the heating speed of less than or equal to 100 ℃/h, preserving heat, calculating the heat preservation time according to the thickness of not less than 2min/mm, and cooling to room temperature by water cooling or air cooling; tempering is carried out, the charging temperature ranges from 400 ℃ to 700 ℃, the temperature is raised to 760 ℃ to 780 ℃ at the heating speed of less than or equal to 100 ℃/h for heat preservation, the heat preservation time is calculated according to the thickness of not less than 1min/mm, and the air cooling is carried out to the room temperature; and (3) hardening and tempering for the second time: keeping the temperature at 1030-1100 ℃ for more than or equal to 1h, and cooling the mixture to room temperature by water or air; tempering temperature is 760-795 ℃, the heat preservation time is more than or equal to 3h, and air cooling is carried out to the room temperature. Compared with the traditional heat treatment process, the impact energy is obviously improved after the two-time tempering process is adopted, and the room-temperature tensile strength and the high-temperature tensile strength at 650 ℃ are both improved to a certain extent.
Description
Technical Field
The invention relates to the technical field of heat-resistant steel, in particular to a heat treatment method for improving the impact toughness of novel martensite heat-resistant steel G115 and application thereof, which are suitable for heat treatment of large-caliber pipes, forgings, castings and the like for ultra-supercritical power stations with the temperature of more than 600 ℃.
Background
Coal-fired power generation is an important component of power supply structures both now and for some period of time in the future. Along with the transformation and upgrading of coal power, a high-steam-parameter ultra-supercritical power station with high capacity, high efficiency, low emission and low energy consumption becomes a development direction for building and modifying a thermal power generating unit in the future. On the other hand, at present, China has become the world with the largest installed quantity and total capacity of 600 ℃ ultra-supercritical power stations, and the 630-. The heat-resistant material is a bottleneck problem which restricts the development of the coal-electric unit to higher parameters, and the ultra-supercritical thermal power unit puts higher requirements on the performance of the heat-resistant material along with the increase of the steam temperature and the steam pressure.
A novel martensite heat-resistant steel G115 independently developed in China, such as the Chinese invention patent with the publication number of CN103045962B, is guided by a multi-element composite strengthening theory, the strength of the invention steel is further improved by adding a precipitation type element Cu, the metallurgical strengthening effect of B is fully exerted to further improve the strength and toughness of a crystal boundary of the invention steel at a high temperature, and meanwhile, Ni and Al are controlled, and the proportion between B and N elements is controlled. The material is the only material which can be selected in main steam pipelines of 630 ℃ ultra-supercritical coal-fired demonstration units in China, and is selected as ' first batch application demonstration instruction directory of important new materials (version 2018) ' by the Ministry of industry and trust '. In the aspect of heat treatment process, the seamless steel tube for the high-pressure boiler generally adopts a normalizing and high-temperature tempering process (see GB5310 for details). In the industrial trial-manufacturing process of the G115 steel, the impact toughness value range is about 20-50J by adopting a common quenching and high-temperature tempering process, the impact energy is unstable, the safety margin is small, and the requirement of long-term stable service of a high-pressure boiler container product is difficult to meet. Therefore, the impact toughness of the G115 steel is improved, and the good comprehensive performance of the G115 steel is obtained, so that the method has very important engineering significance.
Chinese patent publication No. CN108998650A discloses that the impact toughness of a G115 large-diameter pipe is improved by adjusting the deformation temperature; the literature, "influence of normalizing temperature on the structure and the room temperature strength of the G115 steel" researches the influence of normalizing temperature of the G115 steel at 1065-1120 ℃ on the structure and the room temperature strength.
Chinese patent publication No. CN 101805819B, "a method for thermal refining of thick steel plate for pressure vessel", discloses a method for obtaining good strength and elongation matching of thick steel plate by secondary thermal refining.
Chinese patent document CN 103074482B, a secondary hardening and tempering process of 'a regeneration method of a scrap Cr5 forged steel working roll' is applied to the regeneration method of the scrap Cr5 forged steel working roll.
Disclosure of Invention
The invention aims to provide a heat treatment method for improving the impact toughness of novel martensite heat-resistant steel G115, which can improve the impact energy of the G115 steel from 20-50J in the traditional process to more than 120J, improve the tensile strength at room temperature by 50-80MPa and improve the tensile strength at high temperature of 650 ℃ by 20-40 MPa.
The technical problem to be solved can be implemented by the following technical scheme.
A heat treatment method for improving the impact toughness of novel martensite heat-resistant steel G115 comprises the following steps:
(1) first tempering:
charging the martensite heat-resistant steel G115 at the temperature of 400-700 ℃, heating to 1000-1150 ℃ at the heating speed of less than or equal to 100 ℃/h, preserving heat, calculating the heat preservation time according to the thickness of not less than 2min/mm, and cooling to room temperature;
tempering the martensite heat-resistant steel G115 subjected to the steps, charging at the temperature of 400-700 ℃, heating to 760-780 ℃ at the heating speed of less than or equal to 100 ℃/h for heat preservation, and air-cooling to room temperature, wherein the heat preservation time is calculated according to the thickness of not less than 1 min/mm;
(2) and (3) hardening and tempering for the second time:
and (3) carrying out secondary hardening and tempering on the martensite heat-resistant steel G115 subjected to the primary hardening and tempering, wherein the hardening and tempering conditions are as follows:
keeping the temperature at 1030-1100 ℃ for more than or equal to 1h, and cooling the mixture to room temperature by water or air; tempering temperature is 760-795 ℃, the heat preservation time is more than or equal to 3h, and air cooling is carried out to the room temperature.
As a further improvement of the technical scheme, the quenching (or normalizing) temperature of the first quenching and tempering is controlled to be Ac3+ 100-150 ℃.
After the treatment of passing through the light, the impact energy of the G115 steel can be improved to more than 120J from 20-50J in the traditional process, and meanwhile, the tensile strength at room temperature is improved by 50-80MPa, and the tensile strength at high temperature of 650 ℃ is improved by 20-40 MPa.
The invention aims to solve another technical problem and provides an application of the heat treatment method in heat treatment of large-diameter pipes, forgings or castings used in ultra-supercritical power stations with the temperature of above 600 ℃.
The mechanical property of the G115 steel adopting the secondary hardening and tempering process can reach the following value:
(1) the impact energy at room temperature is more than or equal to 120J;
(2) room temperature tensile properties: rp0.2 is more than or equal to 580MPa, and Rm is more than or equal to 720 MPa;
(3) high temperature tensile Property at 650 ℃: rp0.2 is more than or equal to 300MPa, and Rm is more than or equal to 350 MPa.
Drawings
FIG. 1 shows a metallographic structure of a sample obtained by secondary hardening and tempering in example 1 of the present invention.
FIG. 2 shows the metallographic structure of example 2 of the present invention after the secondary quenching and tempering process.
FIG. 3 shows the metallographic structure after the secondary quenching and tempering process in example 3 of the present invention.
Fig. 4 shows a metallographic structure of a comparative example after a conventional process was used.
Detailed Description
The following describes embodiments of the present invention in further detail with reference to the accompanying drawings.
The invention provides a heat treatment method for improving the impact toughness of novel martensite heat-resistant steel G115 by adopting a secondary quenching and tempering process (namely, twice quenching and tempering), and realizes that the secondary quenching and tempering heat treatment is adopted in the field of materials for pressure boilers to obtain good comprehensive properties such as impact toughness, strength and the like.
The G115 steel is generally smelted by adopting 40 tons of EAF + LF + VD processes, is poured into steel ingots, is forged into phi 500-phi 900 bars, is hot extruded into large-caliber pipes, and is finally subjected to quenching and tempering heat treatment. The invention is to heat treat G115 rod or large-diameter pipe by the following method.
(1) First tempering:
charging the martensite heat-resistant steel G115 at the temperature of 400-700 ℃, heating to 1000-1150 ℃ at the heating speed of less than or equal to 100 ℃/h, preserving heat for at least 2min/mm, and air-cooling to room temperature;
tempering the martensite heat-resistant steel G115 subjected to the steps, charging at the temperature of 400-700 ℃, heating to 760-780 ℃ at the heating speed of less than or equal to 100 ℃/h for heat preservation, and air-cooling to room temperature, wherein the heat preservation time is calculated according to the thickness of not less than 1 min/mm;
(2) and (3) hardening and tempering for the second time:
and (3) carrying out secondary hardening and tempering on the martensite heat-resistant steel G115 subjected to the primary hardening and tempering, wherein the hardening and tempering conditions are as follows:
keeping the temperature at 1030-1100 ℃ for more than or equal to 1h, and cooling to room temperature by water; tempering at 760-795 deg.c for 3 hr or more, and air cooling to room temperature.
Wherein the second tempering system is G115 traditional heat treatment process. The invention develops a secondary hardening and tempering process on the basis of the traditional process, namely, twice hardening and tempering are adopted, and the metallurgical principle is as follows:
the quenching (or normalizing) temperature of the first quenching and tempering is controlled to be Ac3+ 100-150 ℃, so that precipitated phases are fully dissolved, alloy elements are fully homogenized, the uniformity of the structure is greatly improved, a large amount of fine and uniform carbides can be precipitated by the first tempering treatment, more nucleation positions can be provided for the austenitizing process of the second quenching and tempering, and crystal boundaries can be pinned in the process of austenite growth to prevent the growth of austenite crystal grains. Therefore, the first thermal refining treatment well lays a cushion for the second thermal refining treatment from the material microstructure, so that the grains of the second thermal refining treatment are further refined, and the impact toughness is greatly improved.
The novel martensite heat-resistant steel (G115) in the embodiment of the invention is smelted by adopting 40 tons of EAF + LF + VD processes, is poured into a steel ingot, is then manufactured into a large forging and a large-caliber pipe, and is finally subjected to quenching and tempering heat treatment. Examples 1 and 2 are G115 heavy forgings with a specification of phi 600 mm; example 3 is a G115 large-bore pipe with the specification of phi 530 multiplied by 115 mm; the comparative example is a G115 heavy forging adopting the traditional quenching and tempering process, and the specification is phi 600 mm.
Specific examples are as follows.
Example 1:
first tempering: setting the charging temperature to 650 ℃, charging the G115 forging with the specification of phi 600mm, heating to 1140 ℃ at the temperature of 100 ℃/h, preserving heat for 3 hours, and air-cooling to room temperature after discharging; and then tempering, setting the tempering charging temperature to 500 ℃, heating to 780 ℃ at 100 ℃/h, preserving the heat for 5 hours, discharging and air cooling.
The G115 forging subjected to the first hardening and tempering is subjected to the second hardening and tempering described below.
And (3) hardening and tempering for the second time: quenching and tempering treatment are carried out according to the traditional process, namely heating to 1050 ℃ at a speed of 100 ℃/h, keeping the temperature for 1 hour, and water quenching is carried out to room temperature after discharging; and then tempering treatment is carried out, the charging temperature is 500 ℃, the temperature is rapidly heated to 780 ℃, the temperature is kept for 3 hours, and the steel is discharged from the furnace and cooled in air.
Example 2:
first tempering: setting the charging temperature to 600 ℃, charging the G115 forged piece with the specification of phi 600mm, heating to 1100 ℃ at the speed of 90 ℃/h, preserving heat for 5 hours, and air-cooling to room temperature after discharging; and tempering, wherein the tempering charging temperature is 500 ℃, the heating is carried out to 780 ℃ at the speed of 100 ℃/h, the heat preservation is carried out for 5 hours, and the steel plate is taken out of the furnace and cooled in air.
The G115 forging subjected to the first hardening and tempering is subjected to the second hardening and tempering described below.
And (3) hardening and tempering for the second time: quenching and tempering treatment are carried out according to the traditional process, namely heating to 1050 ℃ at a speed of 100 ℃/h, keeping the temperature for 1 hour, and water quenching is carried out to room temperature after discharging; and then tempering treatment is carried out, the charging temperature is 500 ℃, the temperature is rapidly heated to 780 ℃, the temperature is kept for 5 hours, and the steel is discharged from the furnace and cooled in air.
Example 3:
first tempering: setting the charging temperature to 600 ℃, charging G115 large-caliber pipes with the specification of phi 530 multiplied by 115mm, heating to 1400 ℃ at the rate of 100 ℃/h, preserving heat for 2 hours, and air-cooling to room temperature after discharging; and tempering, wherein the tempering charging temperature is 500 ℃, the heating is carried out to 780 ℃ at the speed of 100 ℃/h, the heat preservation is carried out for 5 hours, and the steel plate is taken out of the furnace and cooled in air.
The G115 forging subjected to the first hardening and tempering is subjected to the second hardening and tempering described below.
And (3) hardening and tempering for the second time: quenching and tempering treatment are carried out according to the traditional process, namely heating to 1050 ℃ at a speed of 100 ℃/h, keeping the temperature for 1 hour, and water quenching is carried out to room temperature after discharging; and then tempering treatment is carried out, the charging temperature is 500 ℃, the temperature is rapidly heated to 780 ℃, the temperature is kept for 3 hours, and the steel is discharged from the furnace and cooled in air.
Comparative example:
the method is implemented according to the traditional process: charging at 650 ℃, heating to 1050 ℃ at 100 ℃/h, keeping the temperature for 1 hour, discharging, and water-quenching to room temperature; and then tempering the forging, quickly heating to 780 ℃ at the charging temperature of 500 ℃, preserving heat for 3 hours, discharging and air cooling.
Table 1 below shows the heat treatment process technology and performance comparison of the inventive examples and comparative examples. It can be seen that the impact energy of the G115 steel is improved to more than 120J from 20-50J in the traditional process by adopting the secondary quenching and tempering process, meanwhile, the tensile strength at room temperature is improved by 50-80MPa, and the tensile strength at high temperature of 650 ℃ is improved by 20-40 MPa.
Comparing and observing the figures 1-4, the G115 steel can be found to have obvious grain refinement and more dispersed precipitated phases after the secondary tempering process is adopted, and the reason for greatly improving the performance after the secondary tempering is presumed.
Table 1: heat treatment process and mechanical properties of examples and comparative examples
Claims (3)
1. A heat treatment method for improving the impact toughness of novel martensite heat-resistant steel G115 is characterized by comprising the following steps:
(1) first tempering:
charging the martensite heat-resistant steel G115 at the temperature of 400-700 ℃, heating to 1000-1150 ℃ at the heating speed of less than or equal to 100 ℃/h, preserving heat for at least 2min/mm, and air-cooling or water-cooling to room temperature;
tempering the martensite heat-resistant steel G115 subjected to the steps, charging at the temperature of 400-700 ℃, heating to 760-780 ℃ at the heating speed of less than or equal to 100 ℃/h, preserving heat, and air cooling to room temperature, wherein the heat preservation time is calculated according to the thickness of not less than 1 min/mm;
(2) and (3) hardening and tempering for the second time:
and (3) carrying out secondary hardening and tempering on the martensite heat-resistant steel G115 subjected to the primary hardening and tempering, wherein the hardening and tempering conditions are as follows:
keeping the temperature at 1030-1100 ℃ for more than or equal to 1h, and cooling the mixture to room temperature by water or air; tempering temperature is 760-795 ℃, the heat preservation time is more than or equal to 3h, and air cooling is carried out to the room temperature.
2. The heat treatment method for improving the G115 impact toughness of the novel martensitic heat-resistant steel as claimed in claim 1, wherein the quenching or normalizing temperature of the first quenching and tempering is controlled to be Ac3+ 100-150 ℃.
3. Use of the heat treatment method of claim 1 or 2 in the heat treatment of large-bore pipes, forgings or castings for ultra supercritical power stations at temperatures above 600 ℃.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN113249552A (en) * | 2021-05-26 | 2021-08-13 | 河南中原特钢装备制造有限公司 | Quenching and tempering heat treatment process for improving flaw detection clutter of 2Cr13 rotor |
| CN114875214A (en) * | 2022-06-01 | 2022-08-09 | 东北大学 | Heat treatment method of COST-FB2 steel large forging |
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN113249552A (en) * | 2021-05-26 | 2021-08-13 | 河南中原特钢装备制造有限公司 | Quenching and tempering heat treatment process for improving flaw detection clutter of 2Cr13 rotor |
| CN113249552B (en) * | 2021-05-26 | 2023-03-31 | 河南中原特钢装备制造有限公司 | Quenching and tempering heat treatment process for improving flaw detection clutter of 2Cr13 rotor |
| CN114875214A (en) * | 2022-06-01 | 2022-08-09 | 东北大学 | Heat treatment method of COST-FB2 steel large forging |
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