CN108950148B

CN108950148B - Method for improving radial structure and performance uniformity of G115 steel large-caliber thick-wall pipe

Info

Publication number: CN108950148B
Application number: CN201810853351.5A
Authority: CN
Inventors: 刘正东; 陈正宗; 徐松乾; 包汉生; 赵海平; 雷丙旺; 杨钢
Original assignee: Central Iron and Steel Research Institute
Current assignee: Central Iron and Steel Research Institute
Priority date: 2018-07-30
Filing date: 2018-07-30
Publication date: 2020-07-21
Anticipated expiration: 2038-07-30
Also published as: CN108950148A

Abstract

A method for improving radial structure and performance uniformity of a G115 steel large-caliber thick-wall pipe belongs to the technical field of steel materials. The process comprises the following steps: adopting a hot extruded tube blank, normalizing: charging at 400-600 ℃, heating to 980-1000 ℃ at a heating speed of 100-120 ℃/h, keeping the temperature for 0.5-1 min/mm, heating to 1030-1080 ℃ at 130-150 ℃/h, keeping the temperature for 1-3 h, and air cooling or water quenching to room temperature; a tempering system: charging at a temperature of less than or equal to 600 ℃, heating to a tempering temperature of 780 +/-10 ℃ at a heating speed of 120-150 ℃/h, keeping the temperature for 3-5 h, and air cooling to room temperature. The method has the advantages that the radial temperature field of the thick-wall pipe is improved, the crystal grains are not easy to coarsen, and the radial structure and performance uniformity of the thick-wall pipe is greatly improved.

Description

Method for improving radial structure and performance uniformity of G115 steel large-caliber thick-wall pipe

Technical Field

The invention belongs to the technical field of steel materials, and particularly relates to a method for improving radial structure and performance uniformity of a G115 steel large-caliber thick-wall pipe, which improves the radial structure uniformity of the G115 steel large-caliber thick-wall pipe with the wall thickness of 60-150 mm, and is particularly suitable for manufacturing related pipelines of a 630-650 ℃ steam parameter supercritical (supercritical) thermal power generating unit.

Background

The improvement of steam parameters of the thermal power generating unit is the most important measure for improving the heat efficiency of the unit and realizing coal saving and emission reduction.

The patent Z L201210574445.1 '650 ℃ steam temperature ultra-supercritical thermal power unit steel and a preparation method thereof' are novel martensite heat-resistant steels which are independently developed in China and can be used for 650 ℃ steam parameter ultra-supercritical thermal power units, the enterprise brand is G115, the room temperature tensile property, the impact property, the high temperature mechanical property and the durability of the martensite heat-resistant steels are far higher than those of P92 steel in GB5310 and ASME standards, meanwhile, the martensite heat-resistant steels are also higher than those of CN 101680065B 'ferrite heat-resistant steels' (namely SAVE12AD) under the same conditions, the durability strength value of the martensite heat-resistant steels G115 which are independently developed in China can be used for 620 ℃ to 650 ℃ steam temperature large-caliber boiler pipes, and the martensite heat-resistant steels become unique demonstration materials of 630 ℃ to 650 ℃ ultra-supercritical thermal power units in China and have important driving and selectable significance for promoting the practical development of China today.

At present, the specifications of large-caliber thick-wall seamless tubes for ultra-supercritical power station boilers are 273 mm-1066 mm in outer diameter and 20 mm-130 mm in wall thickness. The method for producing the large-caliber thick-wall heat-resistant steel pipe and the heat-resistant alloy pipe mainly adopts a vertical hot extrusion method, and has obvious advantages compared with the traditional method, and the method is described in patent CN 101706019B. The production and manufacture of the novel martensite heat-resistant steel G115 large-caliber thick-wall pipe also adopt a vertical hot extrusion technology.

Patent CN 106216415B "method for improving wall thickness uniformity of large-caliber thick-wall pipe in vertical hot extrusion process", achieves the purpose of improving the wall thickness uniformity of large-caliber thick-wall pipe in vertical hot extrusion process by a pipe blank with a specific shape and combining optimization control of thermal deformation parameters in extrusion process.

The traditional heat treatment method of the G115 steel large-caliber thick-wall pipe is shown in figure 1, crystal grains are easily large, radial structure and performance are uneven, the larger the wall thickness of the steel pipe is, the larger the crystal grains are, the more serious the radial structure and performance unevenness are, the example of a 630 ℃ ultra-supercritical unit demonstration project of 2 × 1000MW is taken, a novel martensite heat-resistant steel G115 material is taken as a main steam pipeline, the calculated pipeline wall thickness can reach 150mm, if the conventional heat treatment method is adopted, the crystal grains are large, the difference of structures and the performance at different radial positions is obvious, and the service safety of the 630 ℃ ultra-supercritical boiler is seriously influenced.

Patent CN 103938134B, "method for improving radial structure uniformity of heat-resistant alloy thick-wall extruded tube", utilizes induction heating to realize radial temperature difference before extrusion of heat-resistant alloy, and compensate for temperature difference between inner and outer surfaces in the extrusion process, so as to achieve the purpose of uniform radial structure after extrusion of heat-resistant alloy tube.

Patent CN 103614524 a, "a heat treatment method for obtaining high durability of martensite heat-resistant steel", through a secondary tempering heat treatment process, the size of an initial precipitated phase is small, and the number is increased, so that in a long-term service process, the pinning action of precipitated relative dislocation and lath boundary can be maintained at a high level, and the durability of a sample is higher than that after the treatment of a traditional heat treatment system.

Patent CN 101956055A, "a heat treatment method for a heat-resistant steel pipe with a large diameter and a thick wall", relates to a heat treatment method for controlling the cooling rate through the temperature range of 900-400 ℃ according to different outer diameters and wall thicknesses.

Patent CN 101899556B "heat treatment method for refining and coarsening crystal grains of ferritic heat-resistant steel for high temperature bearing": a heat treatment method for refining and coarsening grains of 10Cr9Mo1VNbN or 10Cr9MoW2VNbBN ferrite heat-resistant steel is provided.

At present, very few reports on radial structure and performance uniformity of large-caliber thick-wall steel pipes are reported at home and abroad. The industrial trial production of 10 times of G115 steel large-caliber thick-wall pipes is developed in China, the industrial manufacturing level is the forefront all over the world, the heat treatment level of the thick-wall pipes belongs to the frontier field, and the problem is solved by the people in the first-line engineering science and technology of China. Along with the approaching of the construction period of 630 ℃ ultra-supercritical coal-fired demonstration power plant in China, the novel martensite heat-resistant steel G115 is the only material of the main steam pipeline of the demonstration unit, so that the radial structure and the performance uniformity of the G115 steel large-caliber thick-wall pipe are improved, and the large-caliber thick-wall pipe heat treatment method which is simple in process, short in production period and low in energy consumption is provided.

Disclosure of Invention

The invention aims to provide a method for improving radial structure and performance uniformity of a G115 steel large-caliber thick-wall pipe, solves the problem of non-uniform radial structure and performance of a novel martensite heat-resistant steel G115 large-caliber thick-wall pipe with the wall thickness of 60-150 mm, and overcomes the defects in the prior art.

The technical scheme adopted by the invention for solving the technical problem comprises the following steps:

(1) a normalizing system: charging the hot extruded tube blank at 400-600 ℃, heating to 980-1000 ℃ at a heating speed of 100-120 ℃/h, keeping the temperature for 0.5-1 min/mm, heating to 1030-1080 ℃ at 130-150 ℃/h, keeping the temperature for 0.5-0.8 min/mm, keeping the temperature for 1-3 h, and air cooling or water quenching to room temperature;

(2) a tempering system: charging at 400-600 ℃, heating to the tempering temperature of 780 +/-10 ℃ at the heating speed of 120-150 ℃/h, keeping the temperature for 3-5 h, and air-cooling to the room temperature.

The chemical components of the G115 steel are as follows in percentage by mass (wt%): 0.07-0.10% of C; si is less than or equal to 0.5 percent; 0.3-0.7% of Mn; p is less than or equal to 0.004 percent; s is less than or equal to 0.002%; 8.5-9.5% of Cr; 2.5-3.5% of W; 2.5-3.5% of Co; 0.03-0.07% of Nb; v is 0.10-0.30%; 0.8-1.0% of Cu; n is 0.007-0.011%; b0.011-0.020%; ni is less than or equal to 0.01 percent; al is less than or equal to 0.005 percent; ti is less than or equal to 0.01 percent; zr is less than or equal to 0.01 percent; the balance being Fe;

the wall thickness of the martensite heat-resistant steel large-caliber thick-wall pipe is 60-150 mm.

The gist of the invention is based on the following recognition:

for heat-resistant steel, a certain grain size requirement is crucial to the steel's endurance strength properties and strength-toughness matching, and therefore, the grain size of the novel martensitic heat-resistant steel must be reasonably controlled. Research shows that the novel martensite heat-resistant steel G115 belongs to 9Cr-3W-3Co series ferrite heat-resistant steel, and A thereof_C3The point was 890 ℃. When the heating temperature exceeds 890 ℃, the novel martensite heat-resistant steel is austenitized, and the austenitizing process comprises three aspects, namely nucleation, growth and component homogenization of austenite. The higher the austenitizing temperature, the more pronounced the austenite growth and the coarser the crystal grains.

A G115 large-caliber pipe with the wall thickness of 90mm adopts a traditional heat treatment heating method, and when the temperature of the outer surface reaches 1080 ℃ and the temperature of the inner surface reaches 930 ℃. When the inner wall completely reaches the set temperature of 1080 ℃, the penetration time is required to be about 2 hours, for example, the heat preservation time is 1 hour, at the moment, the heat preservation time of the outer surface is 3 hours, and the heat preservation time of the inner surface is only 1 hour. The temperature rise at the wall thickness and the inner surface of the steel pipe 1/2 is transmitted by continuous heat conduction along the wall thickness direction through the outer surface. At such high temperatures of 1080 ℃, the temperature field from the outer surface to the inner surface is not uniform, which tends to cause radial grain size non-uniformity.

The grain size observation of the G115 steel after 1 hour of heat preservation at 980 ℃ and 1000 ℃ is shown in fig. 2 and 3. It can be seen that after the heat preservation is carried out for 1 hour at 980 ℃ and 1000 ℃, the grain size of the G115 steel pipe is uniform and fine, and the average grain size is about 3-5 um. In order to reduce the temperature field difference in the normalizing process of the inner surface and the outer surface, if the temperature field difference is thoroughly preserved at 980-1000 ℃, the temperature field difference in the austenitizing process of the inner surface and the outer surface can be effectively reduced, and the radial tissue uniformity is further improved.

The invention has the advantages and beneficial effects that: the invention greatly improves the temperature field of the G115 steel large-caliber thick-wall pipe in the normalizing heating process by step heating, not only improves the radial temperature field of the thick-wall pipe, but also ensures that crystal grains are not easy to coarsen, and greatly improves the uniformity of the radial structure and performance of the thick-wall pipe. Meanwhile, the heat treatment process is simple in flow, short in production period and low in energy consumption. By adopting the technical scheme of the invention, the average grain size of the G115 large-caliber thick-wall pipe (the wall thickness is 60-150 mm) is 3-6 grades, and the radial structure and the performance uniformity are good. Meanwhile, the room-temperature mechanical properties are as follows: tensile strength properties: tensile strength R at a test temperature of 23 DEG C_m(σ_b) More than or equal to 760 MPa; yield strength R_p0.2(σ_0.2) Not less than 620 MPa. Impact toughness property: impact energy A at a test temperature of 20 DEG C_KVThe thickness is more than or equal to 50J. Compared with the prior art, the performance difference reduction rate is more than 50%. Meanwhile, the heat treatment process is simple in flow, short in production period and low in energy consumption.

Drawings

FIG. 1 is a graph of a normal heat treatment process specified by the prior art standard for G115 steel.

FIG. 2 is a graph showing the curve of the novel heat treatment process of the G115 steel.

FIG. 3 is a metallographic structure diagram of G115 steel after austenitizing at 980 ℃.

FIG. 4 is a metallographic structure diagram of G115 steel after austenitizing at 1000 ℃.

FIG. 5 is a metallographic structure of a large-caliber thick-walled tube of G115 steel after heat treatment according to the prior art.

FIG. 6 is a metallographic structure diagram of 1/4 wall thickness in a G115 steel large-caliber thick-walled tube (wall thickness 90mm) after heat treatment according to the invention.

FIG. 7 is a metallographic structure chart of a G115 steel large-caliber thick-wall pipe (wall thickness 90mm)1/2 after heat treatment according to the invention.

FIG. 8 is a metallographic structure diagram of the G115 steel large-caliber thick-wall pipe (wall thickness 90mm) at the outer 1/4 wall thickness after heat treatment according to the invention.

Detailed Description

The present invention will be further described with reference to specific examples, but is not limited to the examples.

Example 1

The novel martensite heat-resistant steel (G115) provided by the embodiment of the invention comprises the following main components in percentage by weight: c: 0.080%; cr: 8.99 percent; si: 0.30 percent; mn: 0.50 percent; co: 3.01 percent; w: 2.81 percent; v: 0.21 percent; nb: 0.53 percent; n: 0.008 percent; b: 0.014%; cu: 0.8 percent; p: 0.001 percent; s: 0.0005%; ni: 0.01 percent; al: 0.005 percent; ti: 0.01 percent; zr: 0.01 percent; the balance being Fe.

The invention smelts 40 tons of molten steel according to the EAF + L F + VD technique of the above-mentioned composition, pours 3 steel ingots, chooses two of them to carry on the vertical hot extrusion, two products specification are outer diameter phi 590mm × wall thickness 90mm × long 6000mm G115 heavy-calibre thick wall heat-resisting steel pipe, one is implemented according to the prior art, another is implemented according to the process of the invention.

The prior art is implemented as follows: charging at 550 ℃, heating to 1080 ℃ at 130 ℃/h after thorough preservation, preserving heat for 2 hours, then preserving heat for 1 hour, and quickly performing water quenching to room temperature after discharging; and then, tempering the steel pipe, namely, charging the steel pipe at the temperature of 550 ℃, rapidly heating to 780 ℃, preserving heat for 4 hours, discharging and air cooling.

The special process of the invention is as follows: charging at 550 deg.C, heating to 1000 deg.C at 110 deg.C/h, maintaining for 0.8min/mm, rapidly heating to 1080 deg.C at 150 deg.C/h, maintaining for 0.5min/mm, maintaining for 1h, and water quenching to room temperature; and then the steel pipe is tempered, namely the steel pipe is heated to 780 ℃ at the heating rate of 150 ℃/h at the furnace temperature of 550 ℃, is kept warm for 4 hours, is taken out of the furnace and is cooled to the room temperature by air.

And (3) carrying out subsequent different treatments on the two G115 steel pipes subjected to the same extrusion process. The metallographic structure of the structure after the conventional heat treatment is shown in FIG. 5; the metallographic structure of the heat treated steel sheet is shown in fig. 6-8. The mechanical properties and the difference between the properties of the G115 large-caliber thick-wall pipe after the conventional heat treatment and the heat treatment of the invention are shown in tables 1 and 2 respectively.

TABLE 1

TABLE 2

The difference reduction rate in table 2 is given by equation (1). As can be seen from Table 2, the reduction rate of the radial performance difference of the extruded tube produced by the special process of the invention is 70-80% compared with the conventional process, and the radial structure and performance of the heat-resistant alloy extruded tube produced by the process of the invention are obviously superior to those of the heat-resistant alloy extruded tube produced by the conventional process.

Claims

1. A method for improving radial structure and performance uniformity of a G115 steel large-caliber thick-wall pipe is characterized by comprising the following steps:

(1) adopting a hot extruded tube blank, normalizing: charging at 400-600 ℃, heating to 980-1000 ℃ at a heating speed of 100-120 ℃/h, keeping the temperature for 0.5-1 min/mm, heating to 1030-1080 ℃ at 130-150 ℃/h, keeping the temperature for 1-3 h, and air cooling or water quenching to room temperature;

(2) a tempering system: charging at 400-600 ℃, heating to the tempering temperature of 780 +/-10 ℃ at the heating speed of 120-150 ℃/h, keeping the temperature for 3-5 h, and air cooling to the room temperature;

the G115 steel comprises the following chemical components in percentage by mass: 0.07-0.10% of C; si is less than or equal to 0.5 percent; 0.3-0.7% of Mn; p is less than or equal to 0.004 percent; s is less than or equal to 0.002%; 8.5-9.5% of Cr; 2.5-3.5% of W; 2.5-3.5% of Co; 0.03-0.07% of Nb; v is 0.10-0.30%; 0.8-1.0% of Cu; n is 0.007-0.011%; b0.011-0.020%; ni is less than or equal to 0.01 percent; al is less than or equal to 0.005 percent; ti is less than or equal to 0.01 percent; zr is less than or equal to 0.01 percent; the balance of Fe and other inevitable impurities;

the wall thickness of the G115 steel large-caliber thick-wall pipe is 60-150 mm.