A cold rolling method for seamless tubes made of tungsten-containing high-alloy austenitic heat-resistant steel

Abstract

This invention discloses a cold rolling method for seamless tubes made of tungsten-containing high-alloy austenitic heat-resistant steel, comprising the following steps: S1, billet preparation; S2, primary cold rolling; S3, intermediate heat treatment; S4, secondary cold rolling; S5, finished product heat treatment; S6, finished product inspection. In S1, the billet preparation step includes: S11, billet material selection and heat treatment; S12, billet cooling treatment; S13, billet straightening, end-flattening, and pickling treatment; S14, billet surface inspection and grinding treatment. This invention can reduce the risk of cold rolling cracking in seamless tubes made of tungsten-containing high-alloy austenitic heat-resistant steel, ensuring product quality while reducing production costs.

Description

Technical Field

[0001] This invention belongs to the field of steel material processing technology, specifically relating to a cold rolling method for seamless tubes of tungsten-containing high-alloy austenitic heat-resistant steel. Background Technology

[0002] 06Cr22Ni25W3Cu3Co2MoNbN is a tungsten-containing high-alloy austenitic heat-resistant steel developed by adding a certain amount of alloying elements such as W, Nb, and Cu to the traditional austenitic heat-resistant steel TP310H. Compared with conventional austenitic stainless steel, the tungsten-containing high-alloy austenitic heat-resistant steel has a high-temperature creep strength of not less than 96.6 MPa after 100,000 hours extrapolated from 700℃. It also has good resistance to high-temperature steam corrosion, high-temperature flue gas corrosion, and coal ash corrosion, making it the preferred material for advanced ultra-supercritical superheaters and screen reheaters.

[0003] To achieve high dimensional accuracy and good surface finish, stainless steel pipes are usually produced using cold rolling. During cold rolling, the material is subjected to strong external forces and deforms, causing a large number of dislocations to form and become entangled in the metal grains. This results in a significant increase in strength and hardness, a sharp decrease in plasticity and toughness, and an increase in brittleness, which can cause problems for subsequent processing or use.

[0004] The primary solution is to effectively eliminate the internal stress caused by previous hot or cold working processes through heat treatment, thereby restoring the material's plasticity and toughness. Compared to conventional 300 series austenitic stainless steel, tungsten-containing high-alloy austenitic heat-resistant steel contains higher levels of Cr and Ni, as well as large amounts of W, Cu, Co, Mo, Nb, and N, with a total alloy content exceeding 57%. This high alloy content increases the difficulty of material processing, especially the addition of large amounts of W, Co, Nb, and N, which not only increases the material's strength and hardness but also reduces its plasticity and toughness, making it more prone to cracking during cold rolling than conventional 300 series stainless steel.

[0005] In actual production, when using conventional cold rolling methods to produce seamless tubes of tungsten-containing high-alloy austenitic heat-resistant steel, serious processing problems such as splitting, network cracks on the inner and outer walls, and point cracks in the finished tubes occur, resulting in an extremely low first-pass inspection pass rate (<10%) and making production exceptionally difficult. Summary of the Invention

[0006] In order to solve all or part of the above problems, the purpose of this invention is to provide a cold rolling method for seamless tubes of tungsten-containing high-alloy austenitic heat-resistant steel, which can reduce the risk of cold rolling cracking of seamless tubes of tungsten-containing high-alloy austenitic heat-resistant steel, thus ensuring product quality and reducing production costs.

[0007] This invention provides a cold rolling method for seamless tubes made of tungsten-containing high-alloy austenitic heat-resistant steel, comprising the following steps: S1, tube blank preparation; S2, cold rolled in one step; S3, intermediate heat treatment; S4, double cold rolling; S5, finished product heat treatment; S6, Finished product inspection; In S1, the tube blank preparation steps include: S11, tube blank material selection and heat treatment; S12, tube blank cooling treatment; S13, tube blank straightening, end flattening, and pickling treatment; S14, Inspection and grinding of tube blank surface.

[0008] Optionally, in S11, the mass percentage of the chemical composition of the tube blank is: C: 0.03-0.08%, Si≤0.40%, Mn≤0.50%, P≤0.020%, S≤0.008%, Cr: 18.0-25.0%, Ni: 21.5-31.0%, N: 0.10-0.35%, B: 0.003-0.009%, Nb: 0.30-0.65%, Cu: 2.0-4.0%, W: 1.0-5.0%, Co: 1.0-4.0%, Mo≤0.40%, Al≤0.04%, with the remainder being Fe and unavoidable impurities.

[0009] Optionally, in S11, the tube blank is heat-treated by a heating furnace, while the heating temperature is controlled at 1120-1200℃, and the holding time is set according to the tube blank wall thickness of 1.5min / mm.

[0010] Optionally, in S12, the heat-treated tube blank is subjected to rapid cooling treatment, while the average grain diameter is adjusted to 31.2-88.4 μm.

[0011] Optionally, in S14, during the blank grinding process, the grinding depth is controlled to be no more than 3% of the blank wall thickness, and the transition between the blank and the un-grinded area is smooth with a width-to-depth ratio of no less than 6.

[0012] Optionally, in S2, the total deformation amount and total deformation passes are set according to the finished steel pipe specifications and billet specifications, and the elongation coefficient between passes is controlled to be <2.5, the surface reduction rate is controlled to be <50%, and the single-pass feed amount is controlled to be 4-5mm / pass, while the diameter reduction rate / wall reduction rate of the cold rolling pass η value is controlled to be close to 1.

[0013] Optionally, in S3, the tube blank is heat-treated in a heating furnace, with the heating temperature controlled at 1120-1200℃ and the holding time at 30-60min, and the heat-treated tube blank is then subjected to rapid cooling.

[0014] Optionally, in S4, the total deformation amount and total number of deformation passes are set according to the finished steel pipe specifications and billet specifications, and the elongation coefficient between passes is controlled to be <2.5, the reduction rate is controlled to be <50%, and the single-pass feed amount is controlled to be 4-5mm / pass, while the diameter reduction rate / wall reduction rate of the cold rolling pass η value is controlled to be close to 1.

[0015] Optionally, in S5, the finished tube is heat-treated by a heating furnace, while the heating temperature is controlled at 1220±5℃ and the holding time is set according to the tube blank wall thickness of 1min / mm. The finished tube after heat treatment is then subjected to rapid cooling treatment.

[0016] As can be seen from the above technical solution, the cold rolling method for seamless tubes of tungsten-containing high-alloy austenitic heat-resistant steel provided by the present invention has the following advantages: This cold rolling method can reduce the risk of cold rolling cracking in seamless tubes of tungsten-containing high-alloy austenitic heat-resistant steel, improve the first-pass inspection pass rate of finished tubes, enhance the quality stability and reliability of products, and achieve good economic benefits.

[0017] Other features and advantages of the present invention will be set forth in the following description. Attached Figure Description

[0018] The accompanying drawings are provided to further understand the technical solutions of the present invention and constitute a part of the specification. They are used together with the embodiments of the present invention to explain the technical solutions of the present invention, and do not constitute a limitation on the technical solutions of the present invention.

[0019] Figure 1 This is a process flow diagram of an embodiment of the present invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present invention can be arbitrarily combined with each other.

[0021] like Figure 1 The illustration shows an embodiment of the present invention, which discloses a cold rolling method for seamless tubes made of tungsten-containing high-alloy austenitic heat-resistant steel, comprising the following steps: S1, tube blank preparation; S2, cold rolled in one step; S3, intermediate heat treatment; S4, double cold rolling; S5, finished product heat treatment; S6, Finished product inspection.

[0022] The specific steps of the cold rolling method in this embodiment are as follows: billet preparation → process lubrication → first cold rolling → tube degreasing → intermediate heat treatment → tube pickling, inner and outer surface inspection, and end-forming → process lubrication → second cold rolling → tube degreasing → finished product heat treatment → finished tube pickling, inner and outer surface inspection, non-destructive testing, and end-forming inspection → physical and chemical property testing. Since process lubrication, tube degreasing, tube pickling, inner and outer surface inspection, end-forming, non-destructive testing, and physical and chemical property testing are all conventional processes, they will not be described in detail here.

[0023] In S1, the tube blank preparation steps include: S11, tube blank material selection and heat treatment; S12, tube blank cooling treatment; S13, tube blank straightening, end flattening, and pickling treatment; S14, Inspection and grinding of tube blank surface.

[0024] In S11, when selecting tube blanks, the required chemical composition by mass percentage is as follows: C: 0.03-0.08%, Si≤0.40%, Mn≤0.50%, P≤0.020%, S≤0.008%, Cr: 18.0-25.0%, Ni: 21.5-31.0%, N: 0.10-0.35%, B: 0.003-0.009%, Nb: 0.30-0.65%, Cu: 2.0-4.0%, W: 1.0-5.0%, Co: 1.0-4.0%, Mo≤0.40%, Al≤0.04%, with the remainder being Fe and unavoidable impurities.

[0025] In S11, during the heat treatment of the tube blank, the tube blank is heat-treated by a heating furnace such as a chamber furnace or a roller hearth furnace. The heating temperature is controlled at 1120-1200℃, and the holding time is set according to the tube blank wall thickness of 1.5min / mm. For example, if the tube blank wall thickness is 10mm, the holding time is 15min.

[0026] In S12, after the tube blank undergoes heat treatment, it is subjected to rapid cooling to eliminate internal stresses introduced by the previous hot or cold working process. Simultaneously, the average grain diameter is adjusted to 31.2-88.4 μm, and harmful precipitates (Cr) are dissolved. 23 C6 is equal).

[0027] In S14, if there are defects such as oxide scale, cracks, folds, pits, pits, and heavy scale on the inner and outer surfaces of the tube blank, when the tube blank is ground, the grinding depth shall be controlled to be no more than 3% of the tube blank wall thickness, and the transition between the tube blank and the unground area shall be smooth with a width-to-depth ratio of no less than 6, in order to prevent new fine cracks or folds from appearing during the cold rolling process.

[0028] In S2, the total deformation amount and total number of deformation passes are set according to the finished steel pipe specifications and billet specifications, and the elongation coefficient between passes is controlled to be <2.5 and the reduction rate to be <50% to prevent network cracks or point cracks on the inner and outer walls during cold rolling. Simultaneously, the feed rate per pass is controlled to be 4-5 mm / pass to reduce the number of roll passes, lower the tendency for work hardening cracking, and prevent rolling stalls and head splitting. Furthermore, the diameter reduction rate / wall reduction rate of the cold rolling pass is controlled to be close to 1 to ensure the surface quality of the cold-rolled steel pipe.

[0029] In S3, the tube blank is heat-treated by a heating furnace such as a chamber furnace or roller hearth furnace, with the heating temperature controlled at 1120-1200℃ and the holding time at 30-60min. The heat-treated tube blank is then subjected to rapid cooling (water cooling or water + mist cooling) to eliminate cold work hardening, adjust grain size, dissolve harmful precipitates, and after annealing, it undergoes straightening, sawing, pickling and other finishing processes to obtain a semi-finished product.

[0030] In S4, the total deformation amount and total number of deformation passes are set according to the finished steel pipe specifications and billet specifications, and the elongation coefficient between passes is controlled to be <2.5, the reduction rate is controlled to be <50%, and the single-pass feed amount is controlled to be 4-5mm / pass. At the same time, the diameter reduction rate / wall reduction rate of the cold rolling pass η value is controlled to be close to 1.

[0031] In S5, the finished tubes are heat-treated by heating furnaces such as roller hearth furnaces, car bottom furnaces or chamber furnaces, while the heating temperature is controlled at 1220±5℃ and the holding time is set according to the tube blank wall thickness 1min / mm. The finished tubes after heat treatment are then subjected to rapid cooling treatment.

[0032] The above measures can effectively solve the problem of cold rolling cracking in seamless tubes of tungsten-containing high-alloy austenitic heat-resistant steel, improve the first-pass inspection pass rate of finished tubes, and produce seamless steel tubes with stable quality and reliable safety. To further illustrate this application, the following are specific embodiments: Example 1 Production Φ54 8.6mm tungsten-containing high-alloy austenitic heat-resistant steel seamless tube S1, select Φ95 A 15mm tube blank, with the following chemical composition by mass percentage: C: 0.07%, Si: 0.23%, Mn: 0.42%, P: 0.019%, S: 0.001%, Cr: 22.31%, Ni: 26.1%, N: 0.23%, B: 0.006%, Nb: 0.45%, Cu: 2.8%, W: 3.4%, Co: 1.5%, Mo: 0.29%, Al: 0.021%.

[0033] Meanwhile, the tube blank is heat-treated at a target temperature of 1180℃ and held for 23 minutes before being air-cooled. The heat-treated tube blank is then pickled, inspected, ground, cut to length, and trimmed to ensure that there are no defects such as oxide scale, cracks, folds, pits, pits, or overlapping on the inner and outer surfaces of the tube blank.

[0034] S2, the tube blank undergoes a single cold rolling process, the first pass starting from Φ95. 15mm cold rolled to Φ76 12mm, inter-pass elongation coefficient is 1.56, surface reduction rate is 36%, pass feed is controlled at 4mm, and cold rolling pass η value (diameter reduction rate / wall reduction rate) is 1.0.

[0035] S3. The tube blank undergoes intermediate heat treatment. The degreased cold-rolled tube is sent to the intermediate process for solution heat treatment. The heating furnace is a roller hearth furnace with a heating temperature of 1180±10℃ and a holding time of 40min. After annealing, the tube blank undergoes straightening, sawing, pickling and other finishing processes to obtain the semi-finished product.

[0036] S4, the tube blank undergoes a second cold rolling process, the second pass starting from Φ76. 12mm cold rolled to Φ54 The diameter is 8.6mm, the elongation coefficient between passes is 1.97, the reduction rate is 49%, the feed amount per pass is controlled at 5mm, and the cold rolling pass η value (diameter reduction rate / wall reduction rate) is 1.02.

[0037] S5 uses a roller hearth furnace to heat treat the finished pipes. After the steel pipes reach the target heat treatment temperature of 1220±5℃, they are held at the temperature for 9 minutes. After holding, they are removed from the furnace and cooled by water.

[0038] S6, to perform performance testing on the flattened pipe.

[0039] Testing revealed that the seamless tubes made of tungsten-containing high-alloy austenitic heat-resistant steel produced using the aforementioned cold rolling method were free of defects such as splitting, internal and external wall network cracks, and point cracks in the finished tubes, and the products met the requirements.

[0040] Example 2 Production Φ70 10mm diameter tungsten-containing high-alloy austenitic heat-resistant steel seamless tube S1, select Φ108 A 15mm tube blank, with the following chemical composition by mass percentage: C: 0.06%, Si: 0.18%, Mn: 0.37%, P: 0.019%, S: 0.001%, Cr: 23.1%, Ni: 25.8%, N: 0 .22%, B: 0.007%, Nb: 0.42%, Cu: 2.9%, W: 3.5%, Co: 1.6%, Mo: 0.30%, Al: 0.019%.

[0041] Meanwhile, the tube blank is heat-treated at a target temperature of 1180℃ and held for 23 minutes before being air-cooled. The heat-treated tube blank is then pickled, inspected, ground, cut to length, and trimmed to ensure that there are no defects such as oxide scale, cracks, folds, pits, pits, or overlapping on the inner and outer surfaces of the tube blank.

[0042] S2, the tube blank undergoes a single cold rolling process, with the first pass starting from Φ108. 15mm cold rolled to Φ92 The diameter is 13mm, the elongation coefficient between passes is 1.36, the reduction rate is 26%, the feed rate per pass is controlled at 4mm, and the cold rolling pass η value (diameter reduction rate / wall reduction rate) is 1.11.

[0043] S3. The tube blank is subjected to intermediate heat treatment. The degreased cold-rolled tube is sent to the intermediate process for solution heat treatment. The heating furnace is a roller hearth furnace with a heating temperature of 1180±10℃ and a holding time of 45min. After annealing, the semi-finished product is obtained after straightening, sawing, pickling and other finishing processes.

[0044] S4, the tube blank undergoes a second cold rolling process, the second pass starting from Φ92. 13mm cold rolled to Φ70 The diameter is 10mm, the elongation coefficient between passes is 1.71, the reduction rate is 42%, the feed amount per pass is controlled at 5mm, and the cold rolling pass η value (diameter reduction rate / wall reduction rate) is 1.04.

[0045] S5 uses a roller hearth furnace to heat treat the finished pipes. After the steel pipes reach the target heat treatment temperature of 1220±5℃, they are held for 10 minutes. After holding, they are removed from the furnace and cooled by water.

[0046] S6, to perform performance testing on the flattened pipe.

[0047] Testing revealed that the seamless tubes made of tungsten-containing high-alloy austenitic heat-resistant steel produced using the aforementioned cold rolling method were free of defects such as splitting, internal and external wall network cracks, and point cracks in the finished tubes, and the products met the requirements.

[0048] As can be seen from the above, the cold rolling method can effectively eliminate the surface defects of tungsten-containing high-alloy austenitic heat-resistant steel seamless pipes, improve the first-pass inspection pass rate of finished pipes, produce seamless steel pipes with stable quality and reliable safety, and reduce production costs.

[0049] It should be noted that, unless otherwise stated, the technical or scientific terms used in this invention should have the ordinary meaning as understood by one of ordinary skill in the art.

[0050] Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly defined.

[0051] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. The present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A cold rolling method for seamless tubes of tungsten-containing high-alloy austenitic heat-resistant steel, characterized in that, Includes the following steps: S1, tube blank preparation; S2, cold rolled in one step; S3, intermediate heat treatment; S4, double cold rolling; S5, finished product heat treatment; S6, Finished product inspection; In S1, the tube blank preparation steps include: S11, tube blank material selection and heat treatment; S12, tube blank cooling treatment; S13, tube blank straightening, end flattening, and pickling treatment; S14, Inspection and grinding of tube blank surface.

2. The cold rolling method according to claim 1, characterized in that, In S11, the chemical composition of the tube blank by mass percentage is: C: 0.03-0.08%, Si≤0.40%, Mn≤0.50%, P≤0.020%, S≤0.008%, Cr: 18.0-25.0%, Ni: 21.5-31.0%, N: 0.10-0.35%, B: 0.003-0.009%, Nb: 0.30-0.65%, Cu: 2.0-4.0%, W: 1.0-5.0%, Co: 1.0-4.0%, Mo≤0.40%, Al≤0.04%, with the remainder being Fe and unavoidable impurities.

3. The cold rolling method according to claim 1, characterized in that, In S11, the tube blank is heat-treated by a heating furnace, while the heating temperature is controlled at 1120-1200℃ and the holding time is set according to the tube blank wall thickness of 1.5min / mm.

4. The cold rolling method according to claim 1, characterized in that, In S12, the heat-treated tube blank is subjected to rapid cooling, while the average grain diameter is adjusted to 31.2-88.4 μm.

5. The cold rolling method according to claim 1, characterized in that, In S14, during the blank grinding process, the grinding depth is controlled to be no more than 3% of the blank wall thickness, and the transition between the blank and the un-grinded area is smooth with a width-to-depth ratio of no less than 6.

6. The cold rolling method according to claim 1, characterized in that, In S2, the total deformation amount and total number of deformation passes are set according to the finished steel pipe specifications and billet specifications, and the elongation coefficient between passes is controlled to be <2.5, the reduction rate is controlled to be <50%, and the single-pass feed amount is controlled to be 4-5mm / pass. At the same time, the diameter reduction rate / wall reduction rate of the cold rolling pass η value is controlled to be close to 1.

7. The cold rolling method according to claim 1, characterized in that, In S3, the tube blank is heat-treated in a heating furnace, with the heating temperature controlled at 1120-1200℃ and the holding time at 30-60min. The heat-treated tube blank is then subjected to rapid cooling.

8. The cold rolling method according to claim 1, characterized in that, In S4, the total deformation amount and total number of deformation passes are set according to the finished steel pipe specifications and billet specifications, and the elongation coefficient between passes is controlled to be <2.5, the reduction rate is controlled to be <50%, and the single-pass feed amount is controlled to be 4-5mm / pass. At the same time, the diameter reduction rate / wall reduction rate of the cold rolling pass η value is controlled to be close to 1.

9. The cold rolling method according to claim 1, characterized in that, In S5, the finished tube is heat-treated in a heating furnace, with the heating temperature controlled at 1220±5℃ and the holding time set according to the tube blank wall thickness of 1min / mm. The finished tube after heat treatment is then subjected to rapid cooling.

Images