Steel for coiled tubing with low yield ratio and ultra-high strength and preparation method thereof

Abstract

Steel for coiled tubing with a low yield ratio and ultra-high strength and a preparation method thereof, wherein the chemical composition of the steel in mass percentage is: C: 0.05-0.16%, Si: 0.1-0.9%, Mn: 1.25-2.5%, P≤0.015%, S≤0.005%, Cr: 0.51-1.30%, Nb: 0.005-0.019%, V: 0.010-0.079%, Ti: 0.01-0.03%, Mo: 0.10-0.55%, Cu: 0.31-0.60%, Ni: 0.31-0.60%, Ca: 0.0010-0.0040%, Al: 0.01-0.05%, N≤0.008%, and the rest being Fe and inevitable impurity elements. The chemical composition combines the technologies of low temperature finishing rolling and low temperature coiling to obtain an MA constituent+bainite+ferrite multiphase structure. The steel has a low yield ratio and ultra-high strength with the following specific properties: yield strength≥620 MPa, tensile strength≥750 MPa, elongation≥11%, and yield ratio≤0.83, and is suitable for manufacturing coiled tubing with ultra-high strength having a grade of 110 ksi or higher.

Claims

1. A steel for coiled tubing with low yield ratio and ultra-high strength, comprising the following chemical composition in percentage by mass: C: 0.05-0.16%, Si: 0.1-0.9%, Mn: 1.25-2.5%, P≤0.015%, S≤0.005%, Cr: 0.51-1.30%, Nb: 0.005-0.019%, V: 0.020-0.079%, Ti: 0.01-0.03%, Mo: 0.10-0.55%, Cu: 0.31-0.60%, Ni: 0.31-0.60%, Ca: 0.0010-0.0040%, Al: 0.01-0.05%, N≤0.008%, and the rest being Fe and inevitable impurity elements, and wherein the steel for coiled tubing with low yield ratio and ultra-high strength has a yield strength (R.sub.p0.2) of 620 MPa or more, a tensile strength (R.sub.m) of 750 MPa or more, an elongation (A.sub.50) of 11% or more and a yield ratio (R.sub.p0.2/R.sub.m) of 0.83 or less.

2. The steel for coiled tubing with low yield ratio and ultra-high strength as claimed in claim 1, wherein the steel for coiled tubing with low yield ratio and ultra-high strength has a microstructure consisting of MA constituents+bainite+ferrite multiphase structure.

3. A manufacturing method of the steel for coiled tubing with low yield ratio and ultra-high strength as claimed in claim 1, comprising the following steps: 1) conducting electric furnace or converter smelting, external refining and continuous casting of the chemical components recited in claim 1, wherein the external refining comprises LF desulfurization and RH vacuum degassing, the RH vacuum degassing time is 5 min or more; and during the continuous casting process, degree of superheat is controlled to 15-30° C. and sedation time is controlled to 8-17 min; 2) hot rolling, wherein heating temperature is 1200-1260° C., final rolling temperature is 840-920° C. and coiling temperature is 450-550° C.; and 3) pickling and oiling, wherein coil loading temperature is 70° C. or less, pickling temperature is 65-80° C. and pickling time is 45-100 seconds; thereby producing the steel with low yield ratio and ultra-high strength of claim 1.

4. The manufacturing method of the steel for coiled tubing with low yield ratio and ultra-high strength as claimed in claim 3, wherein the steel for coiled tubing with low yield ratio and ultra-high strength has a microstructure consisting of MA constituents+bainite+ferrite multiphase structure.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a typical microstructure of Example 4 of the present invention.

DETAILED DESCRIPTION

(2) The present invention is further described below with reference to the Examples and the FIGURE.

(3) Table 1 shows the composition of the steel of the Examples of the present invention, Table 2 shows the main process parameters of the steel of the Examples of the present invention, and Table 3 shows the properties of the steel of the Examples of the present invention.

(4) The process route of the Examples of the present invention is: smelting.fwdarw.external refining.fwdarw.continuous casting.fwdarw.reheating slabs.fwdarw.controlling the rolling.fwdarw.cooling.fwdarw.coiling.fwdarw.coil loading.fwdarw.pickling.fwdarw.coating oil.

(5) It can be seen from FIG. 1 that the steel structure manufactured by the present invention is an MA constituents+bainite+ferrite multiphase structure.

(6) As can be seen from Table 3, the steel manufactured by the present invention has a yield strength (R.sub.p0.2) of 620 MPa or more, a tensile strength (R.sub.m) of 750 MPa or more, an elongation (A.sub.50) of 11% or more and a yield ratio (R.sub.p0.2/R.sub.m) of 0.83 or less. Moreover, the steel has a good surface quality, a thickness uniformity and a manufacturability that is more easily achieved, and can be used to manufacture coiled tubing with ultra-high strength which is suitable for deep wells and exploitation of unconventional oil and gas.

(7) TABLE-US-00001 TABLE 1 unit: wt % C Mn Si S P Nb Ti Cu Ni Mo Cr Ca Alt V N Example 1 0.051 2.45 0.51 0.0021 0.011 0.017 0.022 0.60 0.31 0.32 0.51 0.0023 0.035 0.015 0.007 Example 2 0.070 1.80 0.63 0.0018 0.009 0.014 0.028 0.55 0.48 0.11 0.58 0.0015 0.020 0.078 0.004 Example 3 0.160 1.25 0.75 0.0015 0.012 0.006 0.020 0.35 0.32 0.22 1.29 0.0019 0.040 0.020 0.004 Example 4 0.110 1.50 0.32 0.0011 0.011 0.018 0.010 0.32 0.32 0.12 0.63 0.0013 0.030 0.040 0.004 Example 5 0.090 1.90 0.16 0.0012 0.008 0.016 0.015 0.50 0.42 0.55 0.55 0.0018 0.026 0.060 0.004 Example 6 0.140 1.40 0.25 0.0008 0.013 0.019 0.013 0.31 0.31 0.13 0.75 0.0023 0.030 0.060 0.004 Example 7 0.085 2.20 0.11 0.0020 0.012 0.009 0.015 0.45 0.56 0.10 0.52 0.0023 0.038 0.030 0.004

(8) TABLE-US-00002 TABLE 2 RH degassing degree of sedation heating final rolling coiling coil loading pickling mode of time superheat time temperature temperature temperature temperature temperature pickling smelting (min) (° C.) (min) (° C.) (° C.) (° C.) (° C.) (° C.) time (s) Example 1 Converter 5 28 11 1220 843 480 70 65 80 Example 2 Converter 8 25 17 1250 873 505 30 70 70 Example 3 Converter 7 16 9 1215 915 535 60 80 50 Example 4 Converter 8 25 17 1240 870 520 30 75 70 Example 5 Converter 5 28 11 1230 850 510 70 75 80 Example 6 Converter 6 20 10 1255 900 475 25 65 90 Example 7 Converter 6 20 10 1245 885 460 20 70 90

(9) TABLE-US-00003 TABLE 3 R.sub.p0.2/MPa R.sub.m/MPa A.sub.50/% R.sub.p0.2/R.sub.m Example 1 803 1163 13 0.69 Example 2 698 884 16 0.79 Example 3 898 1230 12 0.73 Example 4 658 850 17 0.77 Example 5 854 1182 14 0.72 Example 6 723 1003 15 0.72 Example 7 778 1089 14 0.71