Sucker rod steel and manufacturing method therefor

Abstract

A sucker rod steel, a heat treatment process therefor, and a manufacturing method comprising the heat treatment process are provided. The sucker rod steel comprises, in mass percent, the following chemical elements: C: 0.10˜0.20%, Si: 0.40˜0.80%, Mn: 0.20˜0.60%, Mo: 0.36˜0.46%, Cr: 6.15˜7.10%, Al: 0.015˜0.035%, Nb: 0.02˜0.06%, and N: 0.008˜0.015%, with the balance being Fe and other inevitable impurities. The microstructure of the sucker rod steel is tempered martensite and nanoscale precipitates. The grain size is higher than grade 10, the tensile strength is 920˜1320 Mpa, and the AKU2 impact energy is greater than or equal to 180 J.

Claims

1. A sucker rod steel, comprising the following chemical elements in mass percent: C: 0.10˜0.20%, Si: 0.40˜0.80%, Mn: 0.20˜0.60%, Mo: 0.36˜0.46%, Cr: 6.15˜6.97%, Al: 0.015˜0.035%, Nb: 0.02˜0.06%, and N: 0.008˜0.015%, with the balance being Fe and other inevitable impurities, wherein the microstructure of the sucker rod steel is tempered martensite and nanoscale precipitates and the precipitates include carbonitrides of Cr and Fe, wherein the sucker rod steel has a tensile strength of 920˜1320 MPa.

2. The sucker rod steel according to claim 1, wherein the nanoscale precipitates comprise granular precipitates.

3. The sucker rod steel according to claim 2, wherein the granular precipitates have a particle size of 10˜20 nm.

4. The sucker rod steel according to claim 2, wherein the granular precipitates comprise carbonitrides of Cr, Mn and Nb.

5. The sucker rod steel according to claim 1, wherein the carbonitrides of Cr and Fe are rod-shaped.

6. The sucker rod steel according to claim 5, wherein the precipitates have a length of 60˜80 nm and a width of 10˜20 nm.

7. The sucker rod steel according to claim 1, wherein the sucker rod steel has a grain size of higher than grade 10.

8. The sucker rod steel according to claim 1, wherein the sucker rod steel has an AKU2 of 180 J or more.

9. A heat treatment process of the sucker rod steel according to any one of claims 1 to 6, 7 and 8, comprising the steps of: induction hardening: passing the sucker rod steel through an intermediate frequency induction heater to heat the sucker rod steel to 850˜950° C. and keep for a holding time of 1˜5 min, and then cooling the sucker rod steel by oil quenching at an oil temperature of 20˜50° C.; induction tempering: passing the sucker rod steel through an intermediate frequency induction heater to heat the sucker rod steel to 520˜650° C. and keep for a holding time of 1.5˜5 min, and then air cooling the sucker rod steel to room temperature.

10. The heat treatment process according to claim 9, wherein, in the step(s) of the induction hardening and/or the induction tempering, passing the sucker rod steel through an intermediate frequency induction heater with a frequency of 20˜30 KHz at a speed of 0.5˜1 m/min.

11. A method for manufacturing sucker rod steel, comprising the heat treatment process according to claim 9.

12. A method for manufacturing sucker rod steel, comprising the heat treatment process according to claim 10.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a photograph showing the metallographic structure of the sucker rod steel of Example A5.

(2) FIG. 2 is a photograph showing the metallographic structure of the nanoscale precipitates of the sucker rod steel of Example A5.

DETAILED DESCRIPTION

(3) The sucker rod steel and the manufacturing method thereof according to the present invention will be further explained and illustrated below with reference to the accompanying drawings and specific Examples. However, the explanations and illustrations do not unduly limit the technical solutions of the present invention.

Examples A1˜A9

(4) The sucker rod steels of Examples A1˜A9 were prepared by the following steps:

(5) (1) smelting: the mass percent of each chemical element is as shown in Table 1, primary smelting was carried out by using a converter or an electric arc furnace, after the primary smelting, external refining, vacuum refining RH or VD was carried out by ladle furnace, and then continuous casting or die casting was carried out to obtain a rough slab;

(6) (2) The rough slab was hot processed and rolled into the sucker rod steel by a rolling mill;

(7) (3) The sucker rod steel from step (2) was subjected to a heat treatment process, wherein the process specifically includes: induction hardening: passing the sucker rod steel through an intermediate frequency induction heater to heat the sucker rod steel to 850˜950° C. and keep for a holding time of 1˜5 min, then cooling the sucker rod steel by oil quenching at an oil temperature of 20˜50° C.; induction tempering: passing the sucker rod steel through an intermediate frequency induction heater to heat the sucker rod steel to 520˜650° C. and keep for a holding time of 1.5˜5 min, then air cooling the sucker rod steel to room temperature.

(8) Wherein, in the induction hardening step and the induction tempering step, the sucker rod steel passed through the intermediate frequency induction heater at a speed of 0.5 m/min, and the intermediate frequency induction heater is a hollow copper pipe with a frequency of 20˜30 KHz. In addition, in the induction hardening step and the induction tempering step, an infrared induction temperature measurement system was used for temperature control.

(9) It should be noted that when the sucker rod steel is rolled, it may be rolled into a bar or a wire rod according to the specific conditions of each Example.

(10) Table 1 lists the mass percent of each chemical element in the sucker rod steel of each Example.

(11) TABLE-US-00001 TABLE 1 (wt %, the balance is Fe and other inevitable impurity elements other than P and S) Example C Mn Si Cr Al Mo S P Nb N A1 0.1 0.47 0.43 6.5 0.028 0.36 0.002 0.018 0.02 0.009 A2 0.19 0.57 0.57 6.15 0.035 0.39 0.02 0.02 0.03 0.012 A3 0.13 0.49 0.7 6 0.015 0.39 0.01 0.009 0.06 0.008 A4 0.11 0.4 0.68 7.1 0.028 0.4 0.015 0.007 0.06 0.015 A5 0.16 0.2 0.8 6.78 0.029 0.45 0.008 0.008 0.04 0.012 A6 0.19 0.6 0.48 6.99 0.038 0.38 0.002 0.006 0.03 0.015 A7 0.2 0.25 0.66 6.97 0.018 0.46 0.018 0.017 0.05 0.014 A8 0.18 0.36 0.78 6.89 0.029 0.39 0.016 0.017 0.04 0.013 A9 0.19 0.38 0.42 6.99 0.032 0.44 0.017 0.01 0.05 0.01

(12) Table 2 lists the specific process parameters of the manufacturing method of the Examples.

(13) TABLE-US-00002 TABLE 2 Temper- Holding Cooling Heating Holding ature of time of temperature temper- time of induction induction of oil ature of induction hardening hardening quenching induction tempering Example (° C.) (min) (° C.) (° C.) (min) A1 950 2.5 35 570 2.5 A2 930 1 35 600 5 A3 940 2 35 650 4 A4 920 4.5 40 550 4.5 A5 920 3.5 35 600 3.5 A6 900 1.5 35 630 3 A7 890 5 50 550 2.5 A8 870 1.5 35 530 2 A9 850 5 35 520 1.5

(14) The sucker rod steels of the above Examples were sampled and manufactured into sucker rods. The sucker rods were subjected to various performance tests, and the performance parameters obtained from the tests are listed in Table 3.

(15) Table 3 lists the performance parameters of the sucker rods made of the sucker rod steels of the Examples.

(16) TABLE-US-00003 TABLE 4 Tensile impact Grain strength energy size Example (MPa) AKU2(J) (grade) A1 1310 190 10 A2 1070 210 11 A3 1000 220 10 A4 1275 198 10 A5 1090 230 11 A6 975 208 11 A7 1250 209 11 A8 1090 210 11 A9 980 206 10

(17) Note: AKU2 was measured by GB229 metal Charpy notched impact test method, Aku2 represents the impact absorbing energy of a U-notch sample with a depth of 2 mm, and the unit is J.

(18) As can be seen from Table 3, the sucker rod steels of the Examples of the present invention have a grain size higher than grade 10, a tensile strength of 920˜1320 MPa and an Aku2 of 180 J or more, which greatly satisfy the use requirements of the oil well.

(19) FIG. 1 is a photograph showing the metallographic structure of the sucker rod steel of Example 5. As can be seen from FIG. 1, the microstructure of the sucker rod steel of Example 5 is tempered martensite and nanoscale precipitates.

(20) The nanoscale precipitates can be further referred to FIG. 2. FIG. 2 is a photograph showing the metallographic structure of the nanoscale precipitates of the sucker rod steel of Example 5. As can be seen from FIG. 2, the sucker rod steel of Example 5 precipitates a large amount of nanoscale precipitates, and the nanoscale precipitates include granular precipitates 1, 2 and short rod-shaped precipitates 3, 4, 5. Among them, the granular precipitates 1 and 2 are carbonitrides of Cr, Mn, and Nb, and the short rod-shaped precipitates 3, 4 and 5 are carbonitrides of Cr and Fe.

(21) It should be noted that the above are merely illustrative of specific Examples of the invention. It is obvious that the present invention is not limited to the above Examples, but has many similar variations. All modifications that are directly derived or associated by those skilled in the art are intended to be within the scope of the present invention.