CN112961973A - Stainless steel pipe doped with element cerium P92 and postweld cyclic heat treatment method thereof - Google Patents
Stainless steel pipe doped with element cerium P92 and postweld cyclic heat treatment method thereof Download PDFInfo
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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
- C21D9/50—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for welded joints
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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
- C21D1/78—Combined heat-treatments not provided for above
- C21D1/785—Thermocycling
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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
- C21D6/004—Heat treatment of ferrous alloys containing Cr and Ni
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- 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
- C21D6/005—Heat treatment of ferrous alloys containing Mn
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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
- C21D6/008—Heat treatment of ferrous alloys containing Si
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
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Abstract
The invention discloses a stainless steel pipe doped with cerium P92 and a post-welding circulating heat treatment method thereof, wherein the stainless steel pipe doped with cerium after welding is preheated and subjected to heat preservation treatment; heating the treated steel pipe and carrying out heat preservation treatment; then heating the steel pipe to 830-850 ℃, and preserving heat for 0.4-0.6 h; cooling the steel pipe to 750-770 ℃, and preserving heat for 0.4-0.6 h; repeating the heating and cooling two cycles; and then carrying out heat preservation treatment, and then cooling the steel pipe to room temperature to complete the post-welding circulating heat treatment of the doped element cerium P92 stainless steel pipe. On the basis of P92 steel components, a proper amount of rare earth element cerium is added, and the circulating heat treatment method disclosed by the invention is adopted, so that the formation and growth of delta ferrite in the structure are inhibited, the solid solution strengthening degree is improved, the structure is improved, and the tensile strength and the lasting strength of the material are improved.
Description
Technical Field
The invention belongs to the technical field of machining, and particularly relates to a stainless steel pipe doped with cerium P92 and a post-welding circulating heat treatment method thereof.
Background
With the development of ultra-supercritical thermal generator sets, the performance of P91 steel can not meet the production requirements gradually. On the basis of P91 steel alloy components, 1.5-2.0% of W is added to replace part of Mo, so as to improve the solid solution strengthening effect, and meanwhile, a trace amount of B is added, so that novel P92 steel for the high-temperature section of the supercritical boiler is developed.
Rare earth elements are known as industrial vitamins, cerium has the content of about 0.0046 percent in earth crust, is the highest abundance of the rare earth elements, has irreplaceable excellent performance, plays a great role in improving product performance and increasing product varieties, and is widely applied to the fields of metallurgy, petrochemical industry, new materials and the like.
The microstructure and the structure of the metal material are cast by the heat treatment process, and the microstructure and the structure determine the mechanical properties of the metal material, which is the guarantee of the product quality.
In field installation, the steel pipes need to be connected together by welding, and welded steel pipe welded joints have poor tensile strength and impact resistance and can be in service after heat treatment.
Delta ferrite, which is high temperature ferrite, is relatively rare at normal temperature, but in some stainless steels, remains from delta ferrite to normal temperature. However, since delta ferrite is brittle, easily causes cracks in working and service, and easily causes pitting corrosion, it is generally controlled as a harmful additive.
Disclosure of Invention
The technical problem to be solved by the present invention is to provide a cerium-doped P92 stainless steel tube and a post-welding cyclic heat treatment method thereof, wherein a proper amount of cerium is added based on the components of P92 stainless steel to improve the tensile strength and impact toughness of the P92 steel tube.
The invention adopts the following technical scheme:
a post-weld circulating heat treatment method for a stainless steel pipe doped with element cerium P92 comprises the following steps:
s1, preheating the welded stainless steel pipe doped with the element cerium and carrying out heat preservation treatment;
s2, heating the steel pipe processed in the step S1 and carrying out heat preservation treatment;
s3, heating the steel pipe processed in the step S2 to 830-850 ℃, and preserving heat for 0.4-0.6 hour;
s4, cooling the steel pipe processed in the step S3 to 750-770 ℃, and preserving heat for 0.4-0.6 hour;
s5, repeating the steps S3 and S4 for two cycles;
s6, performing heat preservation treatment after the two cycles of the step S5 are completed, then cooling the steel pipe to room temperature, and completing the post-welding circular heat treatment of the cerium-doped P92 stainless steel pipe.
Specifically, in step S1, the preheating temperature is 150-250 ℃, and the heat preservation time is 9-11 hours.
Further, the temperature rise rate in the preheating process is not more than 150 ℃ per hour.
Specifically, in step S1, the mass fraction of the doping element cerium is 0.1% to 0.4%.
Specifically, in step S2, the temperature is raised to 750-770 ℃, and the heat preservation time is 0.9-1.1 hours.
Further, the temperature rise speed in the temperature rise process is not more than 150 ℃ per hour.
Specifically, in step S6, the heat preservation time is 0.4 to 0.6 hour.
Specifically, in step S6, the cooling rate in the cooling process is not more than 120 ℃.
According to another technical scheme, the stainless steel pipe doped with the cerium P92 comprises the following components in percentage by mass: 0.07 to 0.13 percent of C, 8.5 to 9.5 percent of Cr, less than or equal to 0.4 percent of Ni, 0.3 to 0.6 percent of Mn, 1.5 to 2.0 percent of W, 0.3 to 0.6 percent of Mo, 0.15 to 0.25 percent of V, less than or equal to 0.5 percent of Si, 0.1 to 0.4 percent of Ce, the balance of Fe and inevitable impurity elements.
Specifically, the average size of delta ferrite is 7.4-17.6 microns, the volume ratio of the delta ferrite is 0.082-0.180%, the tensile strength is 646-665 MPa, and the lasting strength is 119-126 MPa.
Compared with the prior art, the invention has at least the following beneficial effects:
a post-welding circulating heat treatment method for a stainless steel pipe doped with cerium P92 can effectively reduce the content of harmful phase delta ferrite in a structure and the average size of the delta ferrite, thereby improving the tensile strength and the lasting strength of P92 steel.
Further, preheating and heat preservation are carried out to avoid premature failure of the material due to large internal stress generated by the material caused by overhigh heat treatment temperature.
Furthermore, the temperature rise speed is not more than 150 ℃ per hour, so that the cracking caused by local stress due to overlarge temperature difference between the inner side and the outer side of the material and non-uniform strain caused by overhigh temperature rise speed is prevented.
Furthermore, 0.1-0.4 mass percent of cerium is doped, so that the aggregation of ferrite forming elements can be effectively inhibited, and the formation and growth of delta ferrite in the structure are inhibited.
Further, the material is heated to below the austenite transformation temperature and kept warm, so as to prepare for subsequent cycle heat treatment.
Furthermore, the temperature rise speed is not more than 150 ℃ per hour, so that the cracking caused by local stress due to overlarge temperature difference between the inner side and the outer side of the material and non-uniform strain caused by overhigh temperature rise speed is prevented.
Furthermore, the heat preservation time is set to be 0.4-0.6 hours, so that the delta ferrite is preferentially transformed to austenite under the condition that the temperature of the material is higher than the austenite transformation temperature.
Furthermore, the cooling speed is not more than 120 ℃ per hour, so that the internal structure of the material is homogenized, and larger internal stress cannot be generated.
Furthermore, on the basis of the P92 steel component, rare earth elements are added to improve the solid solution strengthening degree and the structure.
In conclusion, the invention adds a proper amount of rare earth element cerium on the basis of P92 steel components, and adopts the circulating heat treatment method listed by the invention to inhibit the formation and growth of delta ferrite in the structure, improve the solid solution strengthening degree, improve the structure and improve the tensile strength and the lasting strength of the material.
The technical solution of the present invention is further described in detail by the accompanying drawings and embodiments.
Drawings
FIG. 1 is a schematic view of a heat treatment step according to the present invention;
fig. 2 is a scanning electron micrograph of a welded joint of a steel pipe corresponding to examples 1 to 5 of the present invention, in which (a) is a microstructure of a joint to which no cerium is added, (b) is a microstructure of a joint to which 0.1% by mass of cerium is added, (c) is a microstructure of a joint to which 0.2% by mass of cerium is added, (d) is a microstructure of a joint to which 0.3% by mass of cerium is added, and (e) is a microstructure of a joint to which 0.4% by mass of cerium is added;
FIG. 3 is a curve showing the change of the average size of the harmful phase delta ferrite to the volume ratio of the harmful phase delta ferrite at the welded joint of the steel pipe according to examples 1 to 5 of the present invention with the addition of cerium;
FIG. 4 is a graph showing the variation of the tensile strength and the endurance strength of the welded joint of the steel pipe according to examples 1 to 5 of the present invention with the addition of cerium.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It will be understood that the terms "comprises" and/or "comprising," when used in this specification and the appended claims, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
It is also to be understood that the terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used in the specification of the present invention and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.
It should be further understood that the term "and/or" as used in this specification and the appended claims refers to and includes any and all possible combinations of one or more of the associated listed items.
Various structural schematics according to the disclosed embodiments of the invention are shown in the drawings. The figures are not drawn to scale, wherein certain details are exaggerated and possibly omitted for clarity of presentation. The shapes of various regions, layers and their relative sizes and positional relationships shown in the drawings are merely exemplary, and deviations may occur in practice due to manufacturing tolerances or technical limitations, and a person skilled in the art may additionally design regions/layers having different shapes, sizes, relative positions, according to actual needs.
The invention provides a stainless steel pipe doped with cerium P92 and a post-welding circulating heat treatment method thereof, wherein the stainless steel pipe doped with cerium is preheated and insulated on the basis of SA335-P92 brand components; then heating and insulating the steel pipe; heating and insulating the treated steel pipe; then cooling and preserving heat of the steel pipe; and after repeating the two cycles of heating and cooling, cooling the steel pipe after heat preservation, and finishing the cyclic heat treatment. Compared with the original P92 stainless steel tube, the harmful phase delta ferrite structure in the welding joint of the P92 stainless steel tube doped with cerium is optimized through the circular heat treatment provided by the invention, and the tensile strength and the impact toughness of the steel tube are improved.
The invention relates to a stainless steel pipe doped with cerium P92, which comprises the following chemical components in percentage by mass: c (0.07-0.13), Cr (8.5-9.5), Ni (less than or equal to 0.4), Mn (0.3-0.6), W (1.5-2.0), Mo (0.3-0.6), V (0.15-0.25), Si (less than or equal to 0.5), Ce (0.1-0.4), and the balance of Fe and inevitable impurity elements.
Referring to fig. 1, a post-weld circulation heat treatment method for a stainless steel pipe doped with cerium P92, the performance of the welded joint of the heat-treated steel pipe meeting the requirement of the pipe for the high-temperature section of a supercritical boiler, includes the following steps:
s1, preheating the welded steel pipe to 150-250 ℃, and preserving heat for 9-11 hours;
the mass fraction of the doping element cerium is 0.1-0.4%, and the temperature rise speed in the preheating process is not more than 150 ℃ per hour.
S2, heating the steel pipe processed in the step S1 to 750-770 ℃, and preserving heat for 0.9-1.1 hours;
the temperature rise speed in the temperature rise process is not more than 150 ℃ per hour.
S3, heating the steel pipe processed in the step S2 to 830-850 ℃, and preserving heat for 0.4-0.6 hour;
s4, cooling the steel pipe processed in the step S3 to 750-770 ℃, and preserving heat for 0.4-0.6 hour;
s5, repeating the steps S3 and S4 for two cycles, and then carrying out the step S6;
s6, continuously preserving the heat for 0.4-0.6 hour, and cooling the steel pipe to 25 ℃.
The cooling speed in the cooling process is not more than 120 ℃ per hour.
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. The components of the embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations. Thus, the following detailed description of the embodiments of the present invention, presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1:
the doped element cerium P92 steel tube comprises the following chemical components in percentage by mass: c (0.112), Cr (8.831), Ni (0.235), Mn (0.409), W (1.936), Mo (0.386), V (0.209), Si (0.241), the balance being Fe and unavoidable impurity elements.
The steel pipe postweld heat treatment method comprises the steps of heating up 1, preserving heat 2, heating up 3, preserving heat 4 and cooling down 5, wherein a steel pipe welding joint sequentially undergoes the steps of heating up 1, preserving heat 2, heating up 3, preserving heat 4 and cooling down 5.
The step 1 of heating comprises the steps of heating the steel pipe from 25 ℃ to 165 ℃ and preserving heat for 10 hours, wherein the heating speed in the preheating process is 140 ℃ per hour.
The step 2 of holding comprises holding the treated steel tube at 165 ℃ for 16.5 hours.
The temperature rise 3 step comprises the steps of heating the treated steel pipe from 165 ℃; then the temperature of the steel pipe is raised to 760 ℃, and the steel pipe is kept for 1 hour, wherein the temperature raising speed in the temperature raising process is 140 ℃ per hour.
The heat preservation 4 step comprises; heating the treated steel pipe to 840 ℃ and preserving heat for 0.5 hour; the steel tube was then cooled to 760 ℃ and held for 60.5 hours.
And repeating the heating and cooling steps 5, wherein the two steps comprise two cycles, the temperature of the treated steel pipe is cooled to 25 ℃ from 760 ℃ after heat preservation, the cooling speed in the cooling process is not more than 120 ℃ per hour, and the cooling time is 30.5 hours. The cyclic heat treatment was completed at 85 ℃ per hour.
Example 2:
the doped element cerium P92 steel tube comprises the following chemical components in percentage by mass: c (0.112), Cr (8.831), Ni (0.235), Mn (0.409), W (1.936), Mo (0.386), V (0.209), Si (0.241), Ce (0.1), and the balance Fe and unavoidable impurity elements.
The steel pipe postweld heat treatment method comprises the steps of heating up 1, preserving heat 2, heating up 3, preserving heat 4 and cooling down 5, wherein a steel pipe welding joint sequentially undergoes the steps of heating up 1, preserving heat 2, heating up 3, preserving heat 4 and cooling down 5.
The step 1 of heating comprises the steps of heating the steel pipe from 25 ℃ to 165 ℃ and preserving heat for 10 hours, wherein the heating speed in the preheating process is 140 ℃ per hour.
The step 2 of holding comprises holding the treated steel tube at 165 ℃ for 16.5 hours.
The temperature rise 3 step comprises the steps of heating the treated steel pipe from 165 ℃; then the temperature of the steel pipe is raised to 760 ℃, and the steel pipe is kept for 1 hour, wherein the temperature raising speed in the temperature raising process is 140 ℃ per hour.
The heat preservation 4 step comprises; heating the treated steel pipe to 840 ℃ and preserving heat for 0.5 hour; the steel tube was then cooled to 760 ℃ and held for 60.5 hours.
And repeating the heating and cooling steps 5, wherein the two steps comprise two cycles, the temperature of the treated steel pipe is cooled to 25 ℃ from 760 ℃ after heat preservation, the cooling speed in the cooling process is not more than 120 ℃ per hour, and the cooling time is 30.5 hours. The cyclic heat treatment was completed at 85 ℃ per hour.
Example 3:
the doped element cerium P92 steel tube comprises the following chemical components in percentage by mass: c (0.112), Cr (8.831), Ni (0.235), Mn (0.409), W (1.936), Mo (0.386), V (0.209), Si (0.241), Ce (0.2), and the balance Fe and unavoidable impurity elements.
The steel pipe postweld heat treatment method comprises the steps of heating up 1, preserving heat 2, heating up 3, preserving heat 4 and cooling down 5, wherein a steel pipe welding joint sequentially undergoes the steps of heating up 1, preserving heat 2, heating up 3, preserving heat 4 and cooling down 5.
The step 1 of heating comprises the steps of heating the steel pipe from 25 ℃ to 165 ℃ and preserving heat for 10 hours, wherein the heating speed in the preheating process is 140 ℃ per hour.
The step 2 of holding comprises holding the treated steel tube at 165 ℃ for 16.5 hours.
The temperature rise 3 step comprises the steps of heating the treated steel pipe from 165 ℃; then the temperature of the steel pipe is raised to 760 ℃, and the steel pipe is kept for 1 hour, wherein the temperature raising speed in the temperature raising process is 140 ℃ per hour.
The heat preservation 4 step comprises; heating the treated steel pipe to 840 ℃ and preserving heat for 0.5 hour; the steel tube was then cooled to 760 ℃ and held for 60.5 hours.
And repeating the heating and cooling steps 5, wherein the two steps comprise two cycles, the temperature of the treated steel pipe is cooled to 25 ℃ from 760 ℃ after heat preservation, the cooling speed in the cooling process is not more than 120 ℃ per hour, and the cooling time is 30.5 hours. The cyclic heat treatment was completed at 85 ℃ per hour.
Example 4:
the doped element cerium P92 steel tube comprises the following chemical components in percentage by mass: c (0.112), Cr (8.831), Ni (0.235), Mn (0.409), W (1.936), Mo (0.386), V (0.209), Si (0.241), Ce (0.3), the balance Fe, and unavoidable impurity elements.
The steel pipe postweld heat treatment method comprises the steps of heating up 1, preserving heat 2, heating up 3, preserving heat 4 and cooling down 5, wherein a steel pipe welding joint sequentially undergoes the steps of heating up 1, preserving heat 2, heating up 3, preserving heat 4 and cooling down 5.
The step 1 of heating comprises the steps of heating the steel pipe from 25 ℃ to 165 ℃ and preserving heat for 10 hours, wherein the heating speed in the preheating process is 140 ℃ per hour.
The step 2 of holding comprises holding the treated steel tube at 165 ℃ for 16.5 hours.
The temperature rise 3 step comprises the steps of heating the treated steel pipe from 165 ℃; then the temperature of the steel pipe is raised to 760 ℃, and the steel pipe is kept for 1 hour, wherein the temperature raising speed in the temperature raising process is 140 ℃ per hour.
The heat preservation 4 step comprises; heating the treated steel pipe to 840 ℃ and preserving heat for 0.5 hour; the steel tube was then cooled to 760 ℃ and held for 60.5 hours. And repeating the heating and cooling steps 5, wherein the two steps comprise two cycles, the temperature of the treated steel pipe is cooled to 25 ℃ from 760 ℃ after heat preservation, the cooling speed in the cooling process is not more than 120 ℃ per hour, and the cooling time is 30.5 hours. The cyclic heat treatment was completed at 85 ℃ per hour.
Example 5:
the doped element cerium P92 steel tube comprises the following chemical components in percentage by mass: c (0.112), Cr (8.831), Ni (0.235), Mn (0.409), W (1.936), Mo (0.386), V (0.209), Si (0.241), Ce (0.4), the balance Fe, and unavoidable impurity elements.
The steel pipe postweld heat treatment method comprises the steps of heating up 1, preserving heat 2, heating up 3, preserving heat 4 and cooling down 5, wherein a steel pipe welding joint sequentially undergoes the steps of heating up 1, preserving heat 2, heating up 3, preserving heat 4 and cooling down 5.
The step 1 of heating comprises the steps of heating the steel pipe from 25 ℃ to 165 ℃ and preserving heat for 10 hours, wherein the heating speed in the preheating process is 140 ℃ per hour.
The step 2 of holding comprises holding the treated steel tube at 165 ℃ for 16.5 hours.
The temperature rise 3 step comprises the steps of heating the treated steel pipe from 165 ℃; then the temperature of the steel pipe is raised to 760 ℃, and the steel pipe is kept for 1 hour, wherein the temperature raising speed in the temperature raising process is 140 ℃ per hour.
The heat preservation 4 step comprises; heating the treated steel pipe to 840 ℃ and preserving heat for 0.5 hour; the steel tube was then cooled to 760 ℃ and held for 60.5 hours.
(ii) a And repeating the heating and cooling steps 5, wherein the two steps comprise two cycles, the temperature of the treated steel pipe is cooled to 25 ℃ from 760 ℃ after heat preservation, the cooling speed in the cooling process is not more than 120 ℃ per hour, and the cooling time is 30.5 hours. The cyclic heat treatment was completed at 85 ℃ per hour.
As described in examples 2, 3, 4, and 5, the steel pipes to which 0.1%, 0.2%, 0.3%, and 0.4% by mass fraction of cerium was added were reduced in average size of the harmful phase δ ferrite by 24.14%, 43.53%, 68.11%, and 49.57%, respectively, in volume percentage of δ ferrite by 10.03%, 35.14%, 59.44%, and 44.86%, respectively, in tensile strength at 650 ℃ by 0.94%, 3.59%, 3.91%, and 2.19%, and in permanent strength at 650 ℃ and 90MPa by 2.59%, 8.62%, 7.76%, and 4.31%, respectively, as compared with the steel pipes to which no cerium was added as described in example 1.
Please refer to fig. 2, which shows the metallographic structure of the results obtained in examples 1 to 5. Referring to FIG. 3, the results of examples 1 to 5 show the average size of δ ferrite and the ratio of precipitation. Referring to FIG. 4, the results of examples 1-5 are shown, respectively, the tensile strength and the endurance strength of the material. As described in examples 2, 3, 4, and 5, the steel pipes to which 0.1%, 0.2%, 0.3%, and 0.4% by mass fraction of cerium was added were reduced in average size of the harmful phase δ ferrite by 24.14%, 43.53%, 68.11%, and 49.57%, respectively, in volume percentage of δ ferrite by 10.03%, 35.14%, 59.44%, and 44.86%, respectively, in tensile strength at 650 ℃ by 0.94%, 3.59%, 3.91%, and 2.19%, and in permanent strength at 650 ℃ and 90MPa by 2.59%, 8.62%, 7.76%, and 4.31%, respectively, as compared with the steel pipes to which no cerium was added as described in example 1.
TABLE 1 Main comparison data of tests on welded joints obtained using conventional heat treatment method after welding and the cyclic heat treatment method after welding given in the present invention
On the basis of the components of the P92 stainless steel, a proper amount of cerium is added, and the stainless steel pipe doped with a proper amount of cerium is welded and then is subjected to heat treatment according to the method provided by the invention, so that the stainless steel pipe has excellent comprehensive performance. Compared with the conventional postweld heat treatment method for raising the temperature to 760 ℃ and preserving the heat for a period of time, the average size of the harmful phase delta ferrite of the welding joint obtained by adopting the postweld circulating heat treatment method provided by the invention is reduced by 7.57%, the volume percentage of the delta ferrite is reduced by 9.82%, the tensile strength at 650 ℃ is improved by 1.11%, and the lasting strength at 650 ℃ and 90MPa is improved by 2.65%.
In summary, according to the cerium-doped P92 stainless steel tube and the post-weld cyclic heat treatment method thereof of the present invention, the steel tube with 0.1%, 0.2%, 0.3%, 0.4% of cerium by mass fraction is added, compared with the steel tube without cerium added in example 1, the average size of the harmful phase δ ferrite is respectively reduced by 24.14%, 43.53%, 68.11%, 49.57%, the volume ratio of the δ ferrite is respectively reduced by 10.03%, 35.14%, 59.44%, 44.86%, the tensile strength at 650 ℃ is respectively improved by 0.94%, 3.59%, 3.91%, 2.19%, and the permanent strength at 650 ℃ and 90MPa is respectively improved by 2.59%, 8.62%, 7.76%, 4.31%.
The above-mentioned contents are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereby, and any modification made on the basis of the technical idea of the present invention falls within the protection scope of the claims of the present invention.
Claims (10)
1. A post-welding circulating heat treatment method for a stainless steel pipe doped with cerium P92 is characterized by comprising the following steps:
s1, preheating the welded stainless steel pipe doped with the element cerium and carrying out heat preservation treatment;
s2, heating the steel pipe processed in the step S1 and carrying out heat preservation treatment;
s3, heating the steel pipe processed in the step S2 to 830-850 ℃, and preserving heat for 0.4-0.6 hour;
s4, cooling the steel pipe processed in the step S3 to 750-770 ℃, and preserving heat for 0.4-0.6 hour;
s5, repeating the steps S3 and S4 for two cycles;
s6, performing heat preservation treatment after the two cycles of the step S5 are completed, then cooling the steel pipe to room temperature, and completing the post-welding circular heat treatment of the cerium-doped P92 stainless steel pipe.
2. The method according to claim 1, wherein in step S1, the preheating temperature is 150-250 ℃ and the holding time is 9-11 hours.
3. The method of claim 2, wherein the pre-heating is performed at a rate of no more than 150 ℃ per hour.
4. The method according to claim 1, wherein in step S1, the mass fraction of the doping element cerium is 0.1-0.4%.
5. The method according to claim 1, wherein in step S2, the temperature is raised to 750-770 ℃ and the holding time is 0.9-1.1 hours.
6. The method of claim 5, wherein the temperature is raised at a rate of no more than 150 ℃ per hour.
7. The method according to claim 1, wherein the holding time in step S6 is 0.4-0.6 hours.
8. The method according to claim 1, wherein in step S6, the cooling rate of the cooling process is not more than 120 ℃ per hour.
9. Stainless steel tube doped with the element cerium P92 for use in the method according to claim 1, comprising, in mass%: 0.07 to 0.13 percent of C, 8.5 to 9.5 percent of Cr, less than or equal to 0.4 percent of Ni, 0.3 to 0.6 percent of Mn, 1.5 to 2.0 percent of W, 0.3 to 0.6 percent of Mo, 0.15 to 0.25 percent of V, less than or equal to 0.5 percent of Si, 0.1 to 0.4 percent of Ce, the balance of Fe and inevitable impurity elements.
10. The stainless steel tube doped with cerium P92 as claimed in claim 9, wherein the average size of delta ferrite is 7.4-17.6 μm, the volume ratio of delta ferrite is 0.082-0.180%, the tensile strength is 646-665 MPa, and the permanent strength is 119-126 MPa.
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