Process for on-line quenching of seamless steel tube using residual heat and manufacturing method

Abstract

An process for the on-line quenching of seamless steel tube using residual heat, a method for manufacturing a seamless steel tube, and a seamless steel tube. The process for the on-line quenching of a seamless steel tube comprises the following steps: when the temperature of a tube is higher than Ar3, evenly spraying water along a circumferential direction of the tube so as to continuously cool the tube to be not higher than T° C., the cooling rate being controlled to be E1° C./s to E2° C./s to obtain a microstructure with martensite as the main composition, wherein T=Ms−95° C., Ms represents the martensitic phase transition temperature, E1=20×(0.5−C)+15×(3.2−Mn)−8×Cr−28×Mo−4×Ni−2800×B, and E2=96×(0.45−C)+12×(4.6−Mn), and the C, Mn, Cr, Ni, B and Mo in the equations each represents the mass percentages of corresponding elements in the seamless steel tube.

Claims

1. A process for the on-line quenching of seamless steel tube using residual heat, consisting of the following steps: cooling the tube when the temperature of tube is higher than Ar3 by spraying water evenly along the circumferential direction of the tube so as to continuously cool the tube to be at least 120° C. but not higher than a threshold temperature that is 95° C. less than the martensitic phase transition temperature, ceasing cooling before the tube reaches a temperature of lower than 120° C., wherein the cooling rate is controlled to be between a range of E1° C./s and E2° C./s that is based on the mass percentage of corresponding elements of the seamless steel tube to obtain a microstructure with martensite as the main composition, wherein
E1=20×(0.5−C)+15×(3.2−Mn)−8×Cr−28×Mo−4×Ni−2800×B,
E2=96×(0.45−C)+12×(4.6−Mn), and wherein C, Mn, Cr, Ni, B and Mo in the equations each represent the mass percentage of corresponding elements of the seamless steel tube, and wherein the seamless steel tube comprises the following composition by mass percentage: C: 0.17%-0.3%, Mn: 0.45%-1.65%, Cr: 0-1.05%, Mo: 0-0.23%, B: 0-0.0025%, and Ni: 0-1.05%.

2. The process for the on-line quenching of seamless steel tube according to claim 1, wherein the total amount of alloying elements of the seamless steel tube is not more than 5% by mass, said alloying elements being at least one selected from C, Mn, Cr, Mo, Ni, Cu, V, Nb and Ti.

3. The process for the on-line quenching of seamless steel tube according to claim 2, wherein the total amount of alloying elements of the seamless steel tube is 0.2% to 5% by mass.

4. The process for the on-line quenching of seamless steel tube according to claim 1, wherein the phase ratio of martensite is not less than 90%.

5. A method for manufacturing a seamless steel tube using residual heat, comprising the following steps: (1) manufacturing the billet; (2) forming the billet into tube; (3) cooling the tube by the process for the on-line quenching of seamless steel tube according to claim 1; and (4) tempering.

6. The method for manufacturing seamless steel tube according to claim 5, wherein in the step (4), the tempering temperature is not less than 400° C., the tempering time is not less than 30 min.

7. The method for manufacturing seamless steel tube according to claim 5, wherein in the step (2), the billet is heated to 1100° C. to 1300° C., maintained for 1-4 hours, followed by piercing, successive rolling, stretch reducing or sizing, so as to obtain the tube.

Description

DETAILED DESCRIPTION

(1) The process for the on-line quenching of seamless steel tube using residual heat and the method for manufacturing a seamless steel tube according to the present invention will be further explained and described accompanying drawings and the specific Example as follow, and the this explanation and description shall not be deemed to limit to the technical solution of the present invention.

Examples A1-A7 and Comparative Examples B1-B5

(2) The seamless steel tubes of the above Examples A1 to A7 were obtained by the following steps:

(3) (1) Manufacturing the billet: smelting according to the mass percentage of each chemical element listed in Table 1, casting it into an ingot and forging the ingot into the billet.

(4) (2) forming the billet into tube: the billet is heated to 1100° C. to 1130° C. and maintained for 1 to 4 hours, followed by piercing, rolling, stretch reducing or sizing, so as to obtain the tube.

(5) (3) use the process for the on-line quenching of seamless steel tube using residual heat: when the temperature of tube is higher than Ar3, evenly spraying water along the circumferential direction of the tube so as to continuously cool the tube to be not higher than T° C., the cooling rate being controlled from E1° C./s to E2° C./s to obtain a microstructure with martensite as the main composition, wherein T=Ms−95° C., Ms represents the martensitic phase transition temperature, E1=20×(0.5−C)+15×(3.2−Mn)−8×Cr−28×Mo−4×Ni−2800×B. E2=96×(0.45−C)+12×(4.6−Mn), C, Mn, Cr, Ni, B and Mo in the equations each represent the mass percentage of corresponding elements of the seamless steel tube.

(6) (4) tempering: the tempering temperature is not less than 400° C., the tempering time is not less than 30 min.

(7) In order to demonstrate the implementation effect of the online-control cooling process of the present invention, the process steps of manufacturing the billet and the tube for Comparative Example B1-B5 are the same as that for Example of the invention, whereas the process parameters of control cooling process for Comparative Example B1-B5 are outside the protection scope of the present technical solution. In addition, the treatment of the tube in the Comparative Example is not the on-line quenching, but completely cooled to room temperature and then heated to Ar3 and then began to quench.

(8) Table 1 lists each mass percentage of the chemical elements of the seamless steel tubes of Examples A1 to A7 and Comparative Examples B1 to B5.

(9) TABLE-US-00001 TABLE 1 (wt %, the margin is Fe and other unavoidable impurity elements) Steel No. model C Mn Cr Mo B Ni A1 16Mn 0.17 1.65 — — — A2 20Mn2 0.2 1.6 — — — A3 20Mn2 0.2 1.6 — — — A4 30CrMo 0.3 0.45 1.05 0.23 — A5 30CrMo 0.3 0.45 1.05 0.23 — A6 20Mn2B 0.21 1.64 — — 0.0025 A7 20CrNi 0.2 0.55 0.9  — — 1.05 B1 20Mn2 0.2 1.6 — — — B2 20Mn2 0.2 1.6 — — — B3 20Mn2 0.2 1.6 — — — B4 20Mn2 0.2 1.6 — — — B5 30CrMo 0.3 0.45 1.05 0.23 —

(10) Table 2 lists the specific process parameters for the methods for manufacturing seamless steel tube of Examples A1-A7 and Comparative Examples B1-B5.

(11) TABLE-US-00002 TABLE 2 Start Final Heating Ar3 cooling cooling The phase ratio tempering temper- heating temper- temper- temper- Cooling of the martensite temper- tempering ature time ature ature Ms T ature E1 E2 rate after quenching ature time No. (° C.) (h) (° C.) (° C.) (° C.) (° C.) (° C.) (° C./s) (° C./s) (° C./s) (%) (° C.) (min) A1 1150 1.4 835 930 410 315 220 29.85 62.28 61 94 500 60 A2 1250 2.5 740 920 400 305 290 30 60 42 96 450 45 A3 1200 2 740 880 400 305 120 30 60 38 98 550 50 A4 1280 2.8 763 960 345 250 190 30.41 64.2 34 92 620 70 A5 1140 3.5 763 830 345 250 200 30.41 64.2 44 95 640 80 A6 1260 2.5 736 970 270 175 160 22.2 58.56 36 93 660 35 A7 1220 3 750 920 410 315 265 48.75 72.6 64 96 580 45 B1 1250 2 740 725 400 305 100 30 60 48 42 500 60 B2 1250 2 740 860 400 305 250 30 60 24 38 450 60 B3 1250 2 740 940 400 305 380 30 60 46 26 550 60 B4 1250 2 740 800 400 305 180 30 60 66 — B5 1250 2 763 890 345 250 160 30.41 64.2 70 —

(12) Various performance tests were conducted on the seamless steel tubes of Example A1-A7 and Comparative Example B1-B5, and the results are shown in Table 3. Wherein the yield strength data are average value obtained according to the API standard after the seamless steel tube of Example A1-A7 and the seamless steel tube of Comparative Example B1-B6 are processed into API arc-shaped samples. The impact sample was test by the standard impact sample of the seamless steel tube of Example A1-A7 and Comparative Example B1 to B6 processed into 10 mm*10 mm*55 mm size, V-notch at 0° C. In addition, the hardness after quenching cooling of each Example and Comparative Example was measured by a Rockwell hardness test.

(13) Table 3 lists the seamless steel tube performance data for each of the Examples and Comparative Examples.

(14) TABLE-US-00003 Impact HRC Yield energy hardness Strength (full size after Crack/ Rp0.2 sample) No. quenching yes or no (MPa ) at 0° C. (J) A1 39 no 492 185 A2 42 no 785 106 A3 44 no 645 118 A4 46 no 798 162 A5 49 no 762 177 A6 43 no 606 154 A7 42 no 672 148 B1 35 no 421 167 B2 33 no 596 98 B3 33 no 568 112 B4 — yes — — B5 — yes — —

(15) As can be seen from Table 2, the phase ratio of martensite of the seamless steel tubes for all Examples A1-A7 is ≥90% after the on-line quenching. As can be seen from Table 3, the yield strength of the seamless steel tubes for Examples A1-A7 is ≥492 MPa, the impact energy at 0° C. thereof are all higher than 106J. and the hardness of HRC after quenching are higher than 39, and there is no creaking.

(16) As can be seen from Table 2 and Table 1, the component ratios of the chemical elements for all Example and Comparative Example have no difference, but the method for manufacturing of the Example and Comparative Example are significantly different. Therefore, the performance of the seamless tube of Example A1-A7 is superior to that of Comparative Example B1-B6 overall. In addition, as can be seen from Table 2 and Table 3, the quenching starting temperature of Comparative Example B1 is lower than the Ar3 temperature so that the steel of Comparative Example B1 precipitates proeutectoid ferrite, reducing its hardness after quenching and affecting the strength of seamless steel tube also. The cooling rate of Comparative Example B2 is lower than the cooling rate range defined in the present technical solution, and the final cooling temperature of Comparative Example B3 was higher than the T° C. of the present invention, thus the desired microstructure with high ratio of martensite of seamless steel tube could not be obtained in Comparative Example B2 and B3, which will affect the performance. In addition, the cooling rate of Comparative Example B4 is higher than the cooling rate range defined in the present technical solution, so that the steel tube cracked, and no suitable steel tube can be obtained.

(17) It is to be noted that the above Example are only a specific embodiments of the present invention. Apparently, the invention is not limited to the above embodiments, and there are may be many similar variations. A person skilled in the art can directly derive or associate all the variations from the content disclosed by the invention, all of which shall be covered by the protection scope of the invention.