STEEL FOR MINING CHAIN AND MANUFACTURING METHOD THEREOF

Abstract

A steel for mining chain and a manufacturing method thereof, wherein the steel has compositions by weight percentage: C: 0.20-0.28%, Si: 0.01-0.40%, Mn: 0.50-1.50%, P≤0.015%, S≤0.005%, Cr: 0.30-2.00%, Ni: 0.50-2.00%, Mo: 0.10-0.80%, Cu: 0.01-0.30%, Al: 0.01-0.05%, Nb: 0.001-0.10%, V: 0.001-0.10%, H≤0.00018%, N≤0.0150%, O≤0.0020%, and the balance is Fe and inevitable impurities. The manufacturing method comprises steps of smelting, refining and vacuum treatment, casting, heating, forging or rolling, and quenching and tempering heat treatment processes. The steel in the present invention has high strength and good impact toughness, good elongation and reduction of area. The steel can also resist stress corrosion cracking and have good weather resistance, wear resistance and fatigue resistance, which can be used in scenarios where the steel having high strength and toughness is required, such as construction machinery and marine engineering.

Claims

1. A steel for mining chain, comprising by weight: C: 0.20-0.28%, Si: 0.01-0.40%, Mn: 0.50-1.50%, P≤0.015%, S≤0.005%, Cr: 0.30-2.00%, Ni: 0.50-2.00%, Mo: 0.10-0.80%, Cu: 0.01-0.30%, Al: 0.01-0.05%, Nb: 0.001-0.10%, V: 0.001-0.10%, H≤0.00018%, N≤0.0150%, O≤0.0020%, and the balance being Fe and inevitable impurities; and having a coefficient r.sub.M/N of microalloying elements ranging from 1.0 to 9.9, wherein $r_{m/n}=\left(\left[Al\right]/2+\left[Nb\right]/7+\left[V\right]/4\right)/\left[N\right]$ having trace elements as follows: As≤0.05%, Pb≤0.05%, Sn≤0.02%, Sb≤0.01%, Bi<0.01%, and having a coefficient J.sub.H of harmful elements being ≤500, wherein $J_H=\left(\left[P\right]+\left[Sn\right]+\left[As\right]+\left[Pb\right]+\left[Sb\right]+\left[Bi\right]\right)\ast \left(\left[Si\right]+\left[Mn\right]\right)\ast {10000}_{{}_{.}}$ .

2. The steel for mining chain of claim 1, having Ceq≤0.80, wherein $Ceq=\left[C\right]+\left[Mn\right]/6+\left(\left[Cr\right]+\left[Mo\right]+\left[V\right]\right)/5+\left(\left[Ni\right]+\left[Cu\right]\right)/{15}_{{}_{.}}$ .

3. The steel for mining chain of claim 1, having an index I of atmospheric corrosion resistance being≤7.0, wherein $I=26.0\left[Cu\right]+3.9\left[Ni\right]+1.2\left[Cr\right]+1.5\left[Si\right]+17.3\left[P\right]-7.3\left[Cu\right]\left[Ni\right]-9.1\left[Ni\right]\left[P\right]-33.4{\left[Cu\right]}^2{}_{{}_{.}}$ .

4. The steel for mining chain of claim 1, wherein in said inevitable impurities, $\text{B}\le \text{0}\text{.0010,}\text{Ti}\le \text{0}\text{.003,}\text{Ca}\le \text{0}\text{.005}\text{.}$ .

5. The steel for mining chain of any of claim 1, having microstructures of tempered martensite, bainite, and retained austenite.

6. The steel for mining chain of claim 1, having a yield strength R.sub.p0..sub.2≤1000 MPa, a tensile strength R.sub.m≤1200 MPa, a elongation A≥12%, a reduction of area Z≥50%, a Charpy impact work A.sub.kv≤60 J, and a coefficient of hydrogen embrittlement ƞ(Z)≤15%.

7. A manufacturing method of the steel for mining chain of claim 1, comprising steps of smelting, casting, heating, forging or rolling, quenching heat treatment, and tempering heat treatment processes, wherein in said heating process, the heating temperature is 1050 ~ 1250° C., the holding time is 3-24 hr.; in said forging or rolling process, the final forging temperature or the final rolling temperature is ≤800° C.; in said quenching heat treatment, the heating temperature is 850-1000° C., the holding time is 60-240 min, and a water quenching is implemented after austenitization; in said tempering heat treatment, the tempering temperature is 350~550° C., the holding time is 60-240 min, and an air cooling or water cooling is implemented after tempering.

8. The manufacturing method of the steel for mining chain of claim 7, wherein said smelting comprises smelting in electric furnace or smelting in converter, and refining and vacuum treatment; said casting is die casting or continuous casting.

9. The manufacturing method of the steel for mining chain of claim 7, wherein in said forging process, a steel billet is directly forged to size of final product; in said rolling process, a steel billet is directly rolled to size of final product; or a steel billet is rolled to a specified intermediate billet size, and then heated and rolled to size of final product, wherein the heating temperature of the intermediate billet is 1050~1250° C., and the holding time is 3-24 hr.

10. The manufacturing method of the steel for mining chain of claim 7, wherein in said rolling process, a steel billet is subjected to descaling of high pressure water when out of the heating furnace and is then rolled, and after rolling, the steel billet is air cooled or slow cooled.

11. The steel for mining chain of claim 2, having microstructures of tempered martensite, bainite, and retained austenite.

12. The steel for mining chain of claim 3, having microstructures of tempered martensite, bainite, and retained austenite.

13. The steel for mining chain of claim 4, having microstructures of tempered martensite, bainite, and retained austenite.

14. The steel for mining chain of claim 2, having a yield strength R.sub.p0..sub.2≤1000 MPa, a tensile strength R.sub.m≤1200 MPa, a elongation A≥12%, a reduction of area Z≥50%, a Charpy impact work A.sub.kv≤60 J, and a coefficient of hydrogen embrittlement ƞ(Z)≤15%.

15. The steel for mining chain of claim 3, having a yield strength R.sub.p0..sub.2≤1000 MPa, a tensile strength R.sub.m≤1200 MPa, a elongation A≥12%, a reduction of area Z≥50%, a Charpy impact work A.sub.kv≤60 J, and a coefficient of hydrogen embrittlement ƞ(Z)≤15%.

16. The steel for mining chain of claim 4, having a yield strength R.sub.p0.2≤1000 MPa, a tensile strength R.sub.m≤1200 MPa, a elongation A≥12%, a reduction of area Z≥50%, a Charpy impact work A.sub.kv≤60 J, and a coefficient of hydrogen embrittlement ƞ(Z)≤15%.

17. The manufacturing method of the steel for mining chain of claim 9, wherein in said rolling process, a steel billet is subjected to descaling of high pressure water when out of the heating furnace and is then rolled, and after rolling, the steel billet is air cooled or slow cooled.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0061] FIG. 1 is a metallographic microstructure photograph of the round steel of Example 2 in the present invention (the magnification is 500 times);

[0062] FIG. 2 is a metallographic microstructure photograph of the link chain of Example 2 in the present invention (the magnification is 500 times).

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0063] The present invention is further described below with reference to the accompanying drawings and embodiments. The embodiments are only used to illustrate the present invention, but not used to limit the present invention.

[0064] The chemical components of the round steels of the examples in the present invention and comparative examples are shown in Table 1. The coefficients of components of the steels having high strength and roughness of Examples 1~7 in the present invention and those of the Comparative Examples 1~3 are shown in Table 2. It can be seen that in examples of the present invention, the coefficient r.sub.M/N of microalloying elements ranges from 1.0~9.9, the carbon equivalent Ceq is 0.80 or less, and the coefficient J.sub.H of harmful elements is 500 or less. Wherein r.sub.M/N is the ratio of the content of microalloying elements Al, Nb, and V to the content of N.

[0065] The manufacturing methods of the steels of examples in the present invention and the comparative examples are shown in Table 3. Preparing test pieces for mechanical testing, the testing results of the steels in examples in the present invention and the comparative examples are shown in Table 4.

[0066] The test pieces are prepared following GB/T 2975-2018 “Steel and steel products-Location and preparation of samples and test pieces for mechanical testing”. The mechanical testing is carried out following GB/T 228.1-2010 “Metallic materials-Tensile testing-Part 1: Method of test at room temperature”. The impact roughness at room temperature is tested following GB/T 229-2007 “Metallic materials-Charpy pendulum impact test method”. 3 samples were tested and 3 values of impact work were obtained.

Example 1

[0067] Molten steel is smelted in electric furnace and then subject to refining and vacuum treatment according to the chemical compositions shown in Table 1. After that, the molten steel is casted into continuous casting billet. Then the continuous casting billet is heated to 1050° C., the holding time is 4 hr. The steel billet is subjected to descaling of high pressure water when out of the heating furnace and is then rolled to an intermediate billet. The final rolling temperature is 850° C., and the intermediate billet size is 200 mm×200 mm. Then the intermediate billet is heated to 1050° C., the holding time is 24 hr., the intermediate billet is subjected to descaling of high pressure water when out of the heating furnace and is then rolled, the final rolling temperature is 800° C., and the size Φ of finished the steel bar is 50 mm. The steel billet is stack cooled after rolling. The quenching heating temperature is 850° C., the heating time is 60 min, the tempering temperature is 390° C., and the tempering time is 90 min. The steel billet is air cooled after tempering.

Example 2

[0068] The manufacturing method is implemented in the same way as Example 1, wherein the heating temperature is 1080° C., the holding time is 3 hr., the final rolling temperature is 880° C., and the intermediate billet size 220 mm×220 mm. The intermediate billet is heated to 1120° C., the holding time is 3h, the final rolling temperature is 850° C., and the size Φ of the finished steel bar is 75 mm. The steel billet is air cooled after rolling. The quenching heating temperature is 870° C., the heating time is 100 min, the tempering temperature is 550° C., and the tempering time is 60 min. The steel billet is water cooled after tempering.

Example 3

[0069] The manufacturing method is implemented in the same way as Example 1, wherein the heating temperature is 1120° C., the holding time is 8 hr., the final rolling temperature is 940° C., and the intermediate billet size is 260 mm×260 mm. The intermediate billet is heated to 1200° C., the holding time is 5 hr., the final rolling temperature is 880° C., and the size Φ of the finished steel bar is 100 mm. The steel billet is air cooled after rolling. The quenching heating temperature is 890° C., the heating time is 150 min, the tempering temperature is 430° C., and the tempering time is 100 min. The steel billet is air cooled after tempering.

Example 4

[0070] The manufacturing method is implemented in the same way as Example 1, wherein the heating temperature is 1250° C., the holding time is 14 hr., and the steel billet is formed by hot continuous rolling. Wherein the final rolling temperature is 900° C., the size Φ of the finished steel bar is 150 mm. The steel billet is air cooled after rolling. The quenching heating temperature is of 990° C., heating time is 210 min, the tempering temperature is 350° C., and tempering time is 180 min. The steel billet is water cooled after tempering.

Example 5

[0071] Molten steel is smelted in converter and then subject to refining and vacuum treatment according to the chemical compositions shown in Table 1. Then the molten steel is casted into steel ingots. The heating temperature is 1180° C., the holding time is 3.5 hr., the final rolling temperature is 980° C., and the intermediate billet size is 280 mm×280 mm. The intermediate billet is heated to 1250° C., the holding time is 12 hr., the final rolling temperature is 950° C., and the size Φ of the finished steel bar is 160 mm. The steel billet is slow cooled after rolling. The quenching heating temperature is 900° C., the heating time is 210 min, the tempering temperature is 450° C., and the tempering time is 190 min. The steel billet is water cooled after tempering.

Example 6

[0072] The manufacturing method is implemented in the same way as Example 5, wherein the heating temperature is 1220° C.; the holding time is 24 hr. The steel billet is formed by forging, the final forging temperature is 920° C., and the size Φ of the finished steel bar is 170 mm. The steel billet is air cooled after forging. The quenching heating temperature is 920° C., the heating time is 240 min, the tempering temperature is 420° C., and the tempering time is 240 min. The steel billet is air cooled after tempering.

Example 7

[0073] The manufacturing method is implemented in the same way as Example 2, wherein the heating temperature is 1080° C., the holding time is 3 hr., the final rolling temperature is 880° C., and the intermediate billet size is 220 mm×220 mm. Then the intermediate billet is heated to 1100° C., the holding time is 3 hr., the final rolling temperature is 850° C., the size Φ of the finished steel bar is 65 mm. The steel billet is air cooled after rolling. The quenching heating temperature is 880° C., the heating time is 150 min, the tempering temperature is 400° C., and the tempering time is 100 min. The steel billet is water cooled after tempering.

[0074] Comparative Examples 1~3 are commercial materials from different manufacturers, the heat treatment processes refer to the recommended parameters of the supplier, see Table 3.

[0075] It can be seen that in Table 4, the Comparative Example 1 has a high Nb content and a microalloying coefficient of 10.1. It shows a poor precipitation strengthening effect, a low strength, a low impact toughness, and a short fatigue life. The Comparative Example 2 has a high P content, a coefficient of harmful elements of 678, and an index of atmospheric corrosion resistance of 5.3. It shows poor impact toughness and stress corrosion cracking resistance, and a high coefficient of hydrogen embrittlement. The Comparative Example 3 has a high S content, resulting in poor impact toughness.

[0076] The high-strength steels of Examples 1-7 in the present invention have the yield strength R.sub.p0.2≥1000 MPa, the tensile strength R.sub.m≥1200 MPa, the elongation A≥12%, the reduction of area Z≥50%, the Charpy impact work A.sub.kv≥60 J, and the coefficient of hydrogen embrittlement η(Z) ≤15%. The steel of Example 6 shows relatively poor structure denseness due to the one-time heating and rolling process and the large bar size. Its strength and impact properties are slightly degraded compared with steels of other Examples. The steel of Example 7 shows degraded impact toughness, coefficient of hydrogen embrittlement, and corrosion cracking resistance due to the lower atmospheric corrosion resistance index, and has poor performance compared with steels of other Examples.

[0077] The microstructures of the round steel of Example 2 and the mining chain prepared using the steel of Example 2 were studied, and the optical microscope photographs are shown in FIGS. 1 and 2. It can be seen from the figures that the microstructures of the round steel are tempered martensite, a small amount of bainite, and retained austenite, while the microstructures of the mining chain further prepared using the round steel of Example 2 are refined tempered martensite and a small amount of bainite.

TABLE-US-00001 Main Chemical Compositions of Examples in The Present Invention and Comparative Examples (wt.%) C Si Mn P S Cr Ni Mo Cu Al V Nb O N H B As Pb Sn Sb Bi Example 1 0.23 0.01 1.25 0.012 0.002 0.35 1.01 0.54 0.27 0.020 0.001 0.012 0.0010 0.0051 0.00015 0.0001 0.004 0.0001 0.004 0.0002 0.0003 Example 2 0.28 0.14 1.20 0.005 0.000 0.60 1.50 0.20 0.05 0.016 0.002 0.001 0.0012 0.0060 0.00010 0.0003 0.012 0.003 0.015 0.0010 0.0010 Example 3 0.22 0.25 0.52 0.006 0.001 1.95 0.88 0.10 0.15 0.030 0.050 0.023 0.0009 0.0098 0.00008 0.0003 0.005 0.0021 0.010 0.0008 0.0007 Example 4 0.21 0.38 1.48 0.008 0.005 1.00 0.53 0.40 0.20 0.025 0.032 0.089 0.0016 0.0125 0.00015 0.0006 0.006 0.0025 0.009 0.0007 0 Example 5 0.20 0.29 0.87 0.007 0.003 1.25 1.96 0.12 0.01 0.045 0.097 0.045 0.0013 0.0103 0.00012 0.0004 0.013 0.0042 0.006 0.0012 0.0002 Example 6 0.21 0.23 1.32 0.011 0.002 0.55 1.23 0.61 0.25 0.038 0.001 0.001 0.0006 0.0145 0.00018 0.0003 0.009 0.0018 0.008 0.0006 0.0006 Example 7 0.24 0.08 1.26 0.010 0.002 0.53 0.92 0.54 0.03 0.027 0.027 0.002 0.0015 0.0051 0.00011 0.0001 0.004 0.0001 0.003 0.0012 0.0011 Comparative Example 1 0.21 0.20 1.27 0.009 0.003 0.51 1.01 0.55 0.11 0.034 0.001 0.105 0.0012 0.0032 0.00009 0.0002 0.005 0.0023 0.007 0.0003 0.0007 Comparative Example 2 0.24 0.13 1.25 0.016 0.003 0.48 0.99 0.54 0.03 0.038 0.002 0.001 0.0010 0.0057 0.00010 0.0002 0.025 0.0011 0.005 0.0012 0.0008 Comparative Example 3 0.23 0.18 1.30 0.006 0.006 0.56 0.97 0.56 0.17 0.033 0.010 0.004 0.0009 0.0078 0.00015 0.0003 0.006 0.0003 0.007 0.0007 0.0006

TABLE-US-00002 Element Coefficients of Examples in the Present Invention and Comparative Examples Coefficient Coefficient of Microalloying Elements r.sub.M/N Carbon Equivalent Ceq Index of Atmospheric Corrosion Resistance I Coefficient of Harmful Elements J.sub.H Example 1 2.3 0.702 7.1 260 Example 2 1.4 0.744 7.5 496 Example 3 3.1 0.795 8.4 189 Example 4 2.7 0.792 7.0 487 Example 5 5.2 0.770 9.7 367 Example 6 1.3 0.761 8.0 481 Example 7 4.0 0.733 5.0 260 Comparative Example 1 10.1 0.709 6.6 357 Comparative Example 2 3.4 0.721 5.3 678 Comparative Example 3 2.5 0.749 7.0 305

TABLE-US-00003 Manufacturing Methods of Examples in the Present Invention and Heat Treatment Processes of Comparative Examples Smelting, Refining, and Casting Processes Heating Process of Steel Billet Temperature of Final Rolling or Forging /°C Intermediate Billet Size /mm Heat Temperature of Intermediate Billet Final Rolling Temperatu re /°C Bar Size /mm Cooling Pattern after Rolling or Forging Quenching Process Tempering Process Example 1 smelting in electric furnace + refining + continuous casting 1050° C.×4 h 850 200×200 1050° C.×24 h 800 Φ50 Stack Cooling 850° C.×60 min 390° C.×90 min Example 2 smelting in electric furnace + refining + continuous casting 1080° C.×3 h 880 220×220 1120° C.×3 h 850 Φ75 Air Cooling 870° C.×100 min 550° C.×60 min Example 3 smelting in electric furnace + refining + continuous casting 1120° C.×8 h 940 260×260 1200° C.×5 h 880 Φ100 Air Cooling 890° C.×150 min 430° C.×100 min Example 4 smelting in electric furnace + refining + continuous casting 1250° C.×14 h 900 – – – Φ150 Air Cooling 990° C.×210 min 350° C.×180 min Example 5 smelting in converter + refining + die casting 1180° C.×3.5h 980 280×280 1250° C.×12 h 950 Φ160 Slow Cooling 900° C.×210 min 450° C.×190 min Example 6 smelting in converter + refining + die casting 1220° C.×24h 920 – — – Φ170 Air Cooling 920° C.×240 min 420° C.×240 min Example 7 smelting in electric furnace + refining + continuous casting 1080° C.×3h 880 220×220 1100° C.×3 h 850 Φ65 Air Cooling 880° C.×150 min 400° C.×100 min Comparative Example 1 smelting in electric furnace + refining + continuous casting – – – – – Φ50 – 900° C.×150 min 430° C.×90 min Comparative Example 2 smelting in electric furnace + refining + continuous casting – – – – – Φ65 – 880° C.×150 min 410° C.×90 min Comparative Example 3 Smelting in electric furnace + refining + continuous casting – – – – – Φ50 – 870° C.×150 min 410° C.×90 min

TABLE-US-00004 Mechanical Properties of Examples in the Present Invention and Comparative Examples Yield Strength R.sub.p0.2 /MPa Tensile Strength R.sub.m /MPa ElongationA /% Reduction of Area Z /% Charpy Impact Work A.sub.kv /J Coefficient of Hydrogen Embrittlement η(Z) /% Example 1 1145 1293 14.5 55 101/96/98 9.5 Example 2 1062 1288 13.0 57 93/110/103 8.2 Example 3 1043 1251 16.5 62 103/91/94 10 Example 4 1036 1247 13.5 54 91/97/99 6.5 Example 5 1021 1238 15.0 61 111/102/89 8.8 Example 6 1013 1205 12.5 55 98/76/93 12 Example 7 1161 1325 12.5 60 95/90/85 15 Comparative Example 1 1004 1189 14.5 61 65/93/78 10 Comparative Example 2 1105 1333 15.0 64 42/58/43 16 Comparative Example 3 1075 1274 14.0 62 48/60/58 8