460-grade preheating-free welding maritime work steel and preparation method thereof

Abstract

The invention discloses 460-grade preheating-free welding maritime work steel and a preparation method thereof, and belongs to the technical field of metal materials. The steel comprises the following chemical components in percentage by mass: 0.04 to 0.06 percent of C, 0.15 to 0.50 percent of Si, 1.75 to 1.85 percent of Mn, less than or equal to 0.008 percent of P, less than or equal to 0.003 percent of S, 0.012 to 0.02 percent of Ti, less than or equal to 0.015 percent of Al, 0.25 to 0.35 percent of Ni, 0.20 to 0.28 percent of Cu, 0.20 to 0.25 percent of Cr and the balance of Fe and inevitable impurities. A low-carbon and high-manganese component design is adopted, the S460MLO super-thick steel plate with the maximum thickness capable of reaching 100 mm is produced through a continuous casting billet, the carbon equivalent Ceq is smaller than or equal to 0.45, and high strength, high toughness and high welding performance are integrated. The base metal and welding toughness of the thick steel plate produced by the TMCP process are improved through the component and inclusion regulation and control technology, the process is simple, the production cost is low, the production efficiency is high, preheating before welding can be avoided, energy is saved, consumption is reduced, and the method is environmentally friendly.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy and relates to a 460-grade preheat-free welding marine engineering steel and a preparation method thereof. Background Art

[0003] Traditional marine engineering steel usually needs to be preheated to 80-120℃ before welding to ensure toughness after welding. However, due to the large-scale marine engineering equipment and the characteristics of outdoor welding, preheating before welding has become increasingly difficult to achieve. There is no mature case of preheat-free welding for the production of S460MLO products with a maximum thickness of 100mm using continuous casting billets. Summary of the invention

[0004] The object of the present invention is to provide a 460-grade preheat-free welded marine engineering steel and a preparation method thereof, wherein the representative steel grade is S460MLO and the thickness is 50-100 mm. In particular, no preheating before welding can be achieved.

[0005] The technical solution of the present invention: A 460-grade preheat-free welding marine steel, the chemical composition of which is C=0.04%~0.06%, Si=0.15%~0.50%, Mn=1.75%~1.85%, P≤0.008%, S≤0.003%, Ti=0.012%~0.02%, Al≤0.015%, Ni=0.25%~0.35%, Cu=0.20%~0.28%, Cr=0.20%~0.25%, and the rest is Fe and unavoidable impurities, Ceq=[C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15] ≤ 0.45, the steel plate is S460MLO extra thick steel plate with a thickness of 50~100mm, the yield strength of the steel is 483~501Mpa, the tensile strength is 596~618MPa, the elongation is 21.45~24.28%, the impact energy of the parent material at -50℃ is 267~338J, and the welding impact energy at -40℃ is 224~286J.

[0006] A method for preparing 460-grade preheat-free welded marine steel, the key process steps are as follows: (1) Smelting: The smelting raw materials are pre-treated by KR molten iron and then smelted in a converter, and 200-300gk of ferrosilicon and 1.8 tons of metallic manganese are added; no aluminum wire is fed after the converter taps out steel; after the LF furnace arrives at the station and delivers the electrochemical slag for the first time, the oxygen content is determined and controlled at 80-100ppm, 300-400gk of ferrotitanium is added first, and then 30-50m of aluminum wire is fed, and finally 100m of calcium wire is fed; then white slag is made to adjust the composition; after refining, VD vacuum treatment is carried out to break the air and determine the hydrogen content ≤2.0ppm; finally, it is cast into a continuous casting billet with a thickness of ≥300mm; (2) Heating: reheat the continuous casting billet to 1100~1140℃, soaking time 20~30min; (3) Rolling: After leaving the furnace, two-stage rolling is carried out: the first stage of rough rolling has a final rolling temperature of ≥980°C, and the second stage of fine rolling has a final rolling temperature controlled at 760~780°C; (4) Cooling: Use water cooling for rapid cooling, and the red-return temperature after cooling is 350~420℃.

[0007] The technical principle of the present invention is as follows: the present invention adjusts the oxygen content of the converter and the order of adding alloys during the steelmaking process, modifies the inclusions in the molten steel, forms fine inclusions mainly composed of titanium, magnesium, calcium oxides and composite inclusions, provides ferrite and bainite phase deformation nuclei in the subsequent rolling cooling and welding cooling phase transformation, promotes phase transformation, and effectively cuts the original austenite grains, thereby achieving the purpose of refining the grains and improving the low-temperature toughness and welding toughness of the steel plate.

[0008] Beneficial effects of the present invention: 1) The present invention uses continuous casting billets to produce high-toughness marine engineering steel plates with low-temperature impact requirements of -40°C and below, with a maximum thickness of 100mm. While ensuring product quality, no preheating before welding can be achieved. 2) The present invention improves the parent material and welding toughness of thick-gauge steel plates produced by the TMCP process through composition and inclusion control technology, with simple procedures, low production costs, energy saving and consumption reduction, improved welding efficiency, and improved welding environment, providing metallurgical ideas for the TMCP process to produce high-strength, tough, and easy-to-weld extra-thick steel plates. 3) The method of the present invention produces a new type of economical, low-carbon and environmentally friendly steel material with a yield strength of 483~501Mpa, a tensile strength of 596~618MPa, an elongation of 21.45~24.28%, a -50°C parent material impact energy of 267~338J, and a -40°C welding impact energy of 224~286J. It can be widely used in the manufacture of thick plates in multiple fields such as shipbuilding, wind power, bridges, and construction. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 Metallographic structure photograph of the steel plate of Example 1 of the present invention.

[0010] Figure 2 Metallographic structure photograph of the steel plate of Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0011] The invention discloses a 460-grade preheat-free welded marine steel and a preparation method thereof, which is smelted in a 120t converter, refined in an LF furnace, vacuum treated in a VD furnace, and cast into a 300mm thick continuous casting billet, and then rolled into a finished product on a 5000mm double-frame medium and thick plate production line. The following is further described by examples and comparative examples. The chemical composition of the steel plates in the examples and comparative examples is shown in Table 1.

[0012] The key process steps and parameters of the example and comparative example steel plates are as follows. Example 1

[0013] The thickness of the steel plate is 100 mm. The preparation process is as follows: (1) Smelting: The smelting raw materials are pre-treated with KR molten iron and then smelted in a converter. No aluminum iron is added when the converter is tapped. 213 gk of ferrosilicon and 1.8 tons of metallic manganese are added for deoxidation. No aluminum wire is fed after the converter is tapped. No aluminum-containing deoxidizer is added when the LF furnace is powered on for the first time at the station. The oxygen content is controlled at 92 ppm after the first power-on slag is regulated. First, 323 gk of ferrotitanium is added, then 32 m of aluminum wire is fed, and finally 100 m of calcium wire is fed. Then Make white slag and adjust the composition; after refining, perform VD vacuum treatment to break the air and set the hydrogen content to 1.5ppm; finally cast it into a continuous casting billet with a thickness of 300mm; (2) Heating: reheat the continuous casting billet to 1139℃, and soak it for 26min; (3) Rolling: after leaving the furnace, carry out two-stage rolling: the first stage rough rolling has a final rolling temperature of 1028℃, and the second stage fine rolling has a final rolling temperature of 765℃; (4) Cooling: rapid cooling by water cooling, and the red-returning temperature after cooling is 385℃.

[0014] Comparative Example 1 The thickness of the steel plate is 100 mm. The preparation process is as follows: (1) Smelting: the smelting raw materials are pre-treated with KR molten iron and then smelted in a converter. When the converter is tapped, 600 gk aluminum iron is added for deoxidation. Normal deoxidation and alloying are carried out when the LF furnace is powered on for the first time at the station. After refining, VD vacuum treatment is carried out to break the air and determine the hydrogen content to be 1.4 ppm. Finally, it is cast into a continuous casting billet with a thickness of 300 mm. (2) Heating: the continuous casting billet is reheated to 1135°C, and the soaking time is 24 minutes. (3) Rolling: After being discharged from the furnace, two-stage rolling is carried out: the first stage rough rolling has a final rolling temperature of 1025°C, and the second stage fine rolling has a final rolling temperature of 766°C. (4) Cooling: rapid cooling is carried out by water cooling, and the red-returning temperature after cooling is 383°C. Example 2

[0015] The thickness of the steel plate is 80 mm. The preparation process is as follows: (1) Smelting: The smelting raw materials are pre-treated with KR molten iron and then smelted in a converter. No aluminum iron is added when the converter is tapped. 201 gk of ferrosilicon and 1.8 tons of metallic manganese are added for deoxidation. No aluminum wire is fed after the converter is tapped. No aluminum-containing deoxidizer is added when the LF furnace is powered on for the first time at the station. The oxygen content is controlled at 89 ppm after the first power-on slag is regulated. First, 322 gk of ferrotitanium is added, then 33 m of aluminum wire is fed, and finally 100 m of calcium wire is fed. Then Make white slag and adjust the composition; after refining, perform VD vacuum treatment to break the air and determine the hydrogen content to be 1.8ppm; finally cast it into a continuous casting billet with a thickness of 300mm; (2) Heating: reheat the continuous casting billet to 1135℃, and soak it for 25min; (3) Rolling: after leaving the furnace, carry out two-stage rolling: the first stage rough rolling final rolling temperature is 1012℃, and the second stage fine rolling final rolling temperature is 772℃; (4) Cooling: rapid cooling by water cooling, and the red-return temperature after cooling is 402℃.

[0016] Comparative Example 2 The thickness of the steel plate is 80 mm. The preparation process is as follows: (1) Smelting: The smelting raw materials are pre-treated with KR molten iron and then smelted in a converter. No aluminum iron is added when the converter is tapped. 201 gk of ferrosilicon and 1.8 tons of metallic manganese are added for deoxidation. No aluminum wire is fed after the converter is tapped. No aluminum-containing deoxidizer is added when the LF furnace is powered on for the first time at the station. The oxygen content is controlled at 89 ppm after the first power-on slag is regulated. First, 322 gk of ferrotitanium is added, then 33 m of aluminum wire is fed, and finally 100 m of calcium wire is fed. Then Make white slag and adjust the composition; after refining, perform VD vacuum treatment to break the air and determine the hydrogen content to 1.8ppm; finally cast it into a continuous casting billet with a thickness of 300mm; (2) Heating: reheat the continuous casting billet to 1208℃, and soak it for 25min; (3) Rolling: after leaving the furnace, carry out two-stage rolling: the first stage rough rolling final rolling temperature is 1028℃, and the second stage fine rolling final rolling temperature is 769℃; (4) Cooling: rapid cooling by water cooling, the red return temperature after cooling is 405℃. Example 3

[0017] The thickness of the steel plate is 50 mm. The preparation process is as follows: (1) Smelting: The smelting raw materials are pre-treated with KR molten iron and then smelted in a converter. No aluminum iron is added when the converter is tapped. 205 gk of ferrosilicon and 1.8 tons of metallic manganese are added for deoxidation. No aluminum wire is fed after the converter is tapped. No aluminum-containing deoxidizer is added when the LF furnace is powered on for the first time at the station. The oxygen content is controlled at 85 ppm after the first power-on slag is quenched. First, 326 gk of ferrotitanium is added, then 36 m of aluminum wire is fed, and finally 100 m of calcium wire is fed. Then Make white slag and adjust the composition; after refining, perform VD vacuum treatment to break the air and determine the hydrogen content to be 1.4ppm; finally cast it into a continuous casting billet with a thickness of 300mm; (2) Heating: reheat the continuous casting billet to 1136℃, and soak it for 25min; (3) Rolling: after leaving the furnace, carry out two-stage rolling: the first stage rough rolling has a final rolling temperature of 1020℃, and the second stage fine rolling has a final rolling temperature of 778℃; (4) Cooling: rapid cooling by water cooling, and the red-returning temperature after cooling is 416℃.

[0018] Comparative Example 3 The thickness of the steel plate is 50 mm. The preparation process is as follows: (1) Smelting: the smelting raw materials are pre-treated with KR molten iron and then smelted in a converter. When the converter is tapped, 600 gk aluminum iron is added for deoxidation. Normal deoxidation and alloying are carried out when the LF furnace is powered on for the first time at the station. After refining, VD vacuum treatment is carried out to break the air and determine the hydrogen content to be 1.6 ppm. Finally, it is cast into a continuous casting billet with a thickness of 300 mm. (2) Heating: the continuous casting billet is reheated to 1208°C, and the soaking time is 25 min. (3) Rolling: After being discharged from the furnace, two-stage rolling is carried out: the first stage rough rolling final rolling temperature is 1023°C, and the second stage fine rolling final rolling temperature is 815°C. (4) Cooling: Rapid cooling by water cooling is adopted, and the red-returning temperature after cooling is 605°C.

[0019] Table 1 Chemical composition and Ceq (wt, %) of the steel plates in the examples and comparative examples .

[0020] Table 2 Comprehensive mechanical properties of the steel plates of the examples and comparative examples .

[0021] The base materials and welding performance of the steel plates of Examples 1, 2 and 3 of the present invention are good. The metallographic structure of the steel plates of the examples is observed, and the microstructure is mainly composed of acicular ferrite + granular bainite, with fine and uniform grains. Figure 1 As shown. The low temperature impact toughness and welding toughness of the comparative steel plate are poorer than those of the embodiment. Comparative Example 1 is ordinary S460MLO marine steel, and the 100mm extra-thick steel plate produced by traditional deoxidation and rolling process, the parent material and the impact performance after welding can not meet the requirements, and the metallographic structure is large granular and plate-like bainite, as shown in FIG. Figure 2As shown; Comparative Example 2 has the same composition and smelting process as Example 2, but high temperature heating is used, which causes the effective inclusions formed in the smelting process to partially dissolve, and does not provide sufficient nucleation particles during the cooling phase change, resulting in a decrease in the impact performance of the parent material, and the toughness after welding does not meet the requirements; and the steel in Comparative Example 3 is Q420qE, a bridge plate, which uses traditional smelting technology and rolling methods, and its toughness for preheat-free welding does not meet the requirements. Therefore, it is difficult to stably produce marine steel plates that meet the requirements of low-temperature toughness and preheat-free welding toughness in industrial production using traditional smelting and rolling processes, which fully demonstrates the ingenuity, consideration and uniqueness of the present invention in composition and process design.

Claims

1. A 460-grade preheat-free welded marine steel, characterized in that: The chemical composition of steel is C=0.04%~0.06%, Si=0.15%~0.50%, Mn=1.75%~1.85%, P≤0.008%, S≤0.003%, Ti=0.012%~0.02%, Al≤0.015%, Ni=0.25%~0.35%, Cu=0.20%~0.28%, Cr=0.20%~0.25%, the rest is Fe and unavoidable impurities, Ceq=[C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15] ≤ 0.45, S460MLO extra thick steel plate with a thickness of 50~100mm, the yield strength of the steel is 483~501Mpa, the tensile strength is 596~618MPa, the elongation is 21.45~24.28%, the impact energy of the parent material at -50℃ is 267~338J, and the welding impact energy at -40℃ is 224~286J.

2. A method for preparing 460-grade preheat-free welded marine steel, characterized in that: The key process steps are as follows: (1) Smelting: The smelting raw materials are pre-treated by KR molten iron and then smelted in a converter, and 200-300gk of ferrosilicon and 1.8 tons of metallic manganese are added; no aluminum wire is fed after the converter taps out steel; after the LF furnace arrives at the station and delivers the electrochemical slag for the first time, the oxygen content is determined and controlled at 80-100ppm, 300-400gk of ferrotitanium is added first, and then 30-50m of aluminum wire is fed, and finally 100m of calcium wire is fed; then white slag is made to adjust the composition; after refining, VD vacuum treatment is carried out to break the air and determine the hydrogen content ≤2.0ppm; finally, it is cast into a continuous casting billet with a thickness of ≥300mm; (2) Heating: reheat the continuous casting billet to 1100~1140℃, soaking time 20~30min; (3) Rolling: After leaving the furnace, two-stage rolling is carried out: the first stage of rough rolling has a final rolling temperature of ≥980°C, and the second stage of fine rolling has a final rolling temperature controlled at 760~780°C; (4) Cooling: Use water cooling for rapid cooling, and the red-return temperature after cooling is 350~420℃.

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