CN118910512A - Production method of preheating-free welding NM450 wear-resistant steel plate - Google Patents
Production method of preheating-free welding NM450 wear-resistant steel plate Download PDFInfo
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Abstract
A process for preparing the wear-resistant NM450 steel without preheating includes such steps as proportionally mixing C＝0.19％～0.20％,Si＝0.25％～0.45％,Mn＝1.10％～1.20％,P≤0.012％,S≤0.003％,Cr＝0.65％～0.70％,Nb＝0.015％～0.020％,Ti＝0.008％～0.016％,AlT＝0.070％～0.090％,B＝0.0014％～0.0020％,H≤0.0015％,N≤0.0050％,O≤0.0015％, Fe with inevitable impurities, and CEV less than or equal to 0.54%. The process steps comprise converter smelting, LF refining, RH or VD vacuum degassing, continuous casting, heating, rolling and heat treatment. The thickness of the produced NM450 wear-resistant steel plate covers 6-20 mm, the surface hardness is 420-480 HBW, the yield strength is more than or equal to 1180MPa, the tensile strength is more than or equal to 1400MPa, the elongation is more than or equal to 16%, and the diameter of 6a is 90 degrees, so that the impact AKV at minus 40 ℃ is more than or equal to 50J; the toughness performance after the preheating-free welding is good.
Description
Technical Field
The invention belongs to the technical field of metallurgy, and relates to a preheating-free welding NM450 wear-resistant steel plate and a production method thereof.
Technical Field
The wear-resistant steel is widely applied to various fields of metallurgy, mines, building materials, railways and the like, and plays an important role in the important parts of equipment such as mining dumpers, coal mine scraper conveyors, bulldozers, excavators, mixers, loaders and the like, which are subjected to wear. The wear-resistant material has a severe service environment, so that the wear-resistant material is required to have extremely high strength, hardness, wear resistance and low-temperature impact toughness, so that the service life of equipment is prolonged, the replacement period of parts is shortened, and the operation time is greatly prolonged. With the light weight of mechanical equipment and the emergence of complicated design demands, higher requirements are put forward on the welding forming performance in the processing and manufacturing processes of the wear-resistant steel, namely the service life of application equipment of the wear-resistant steel is longer, and maintenance and shutdown caused by maintenance are reduced, so that the investment is reduced. The higher the hardness of the wear-resistant steel is, the better the wear resistance is, but the difficulty of welding processing is increased. The 450 HB-grade wear-resistant steel belongs to a medium-high grade wear-resistant variety, the Brinell hardness of the surface is 420-480 HB, the content of C, cr, mo, ni and other alloy elements is relatively high in component design, the carbon equivalent of the steel plate is generally more than 0.50%, the problem caused by the fact that the welding processing is difficult, the tendency of cold cracking of the material is obvious, and the welding heat affected zone is easy to soften and embrittle to brittle fracture of a welding joint.
To avoid such problems, manufacturers often employ a combination of increasing the preheat temperature and tightly controlling the welding process; but preheating before welding can increase energy consumption and cost and greatly reduce welding processing and forming efficiency. The invention discloses a preheating-free welding method suitable for 500HB wear-resistant steel, aiming at the preheating-free welding method of 500 HB-level wear-resistant steel plates, by designing a groove of a welding joint, adopting a 50 kg-level welding wire, a 80 kg-level welding wire and a wear-resistant steel welding wire to form gradient transition, the welding of the wear-resistant steel is completed, compared with the traditional wear-resistant steel welding joint, preheating before welding and heat treatment after welding are not needed, the welding process is simpler and higher in university, the welding deformation is controllable, and the generation of welding cracks is reduced; meanwhile, the welding wire with gradient transition strength is selected, so that the production cost is saved compared with the whole process of applying the wear-resistant and abrasion-resistant steel welding wire. The patent focuses on the matching and welding method of the welding wire for preheating-free welding of 500HB wear-resistant steel, and is not applicable to the intensity level of the NM450 wear-resistant steel plate for preheating-free welding.
Chinese patent CN116586816a discloses an arc welding rod for preheating-free welding of 1000MPa high-strength steel and a preparation method thereof, wherein the arc welding rod is adopted to weld 1000MPa high-strength steel, the strength of a welded joint is not lower than 1000MPa, and meanwhile, no crack is generated during room temperature welding; the invention solves the problems of insufficient toughness and strength of a welding joint in the welding process of 1000 MPa-level ultra-high strength steel and weld cracking in the welding process, and the invention focuses on an arc welding rod for preheating-free welding of 1000 MPa-level ultra-high strength steel and a preparation method thereof, and cannot meet the strength level of a preheating-free welding NM450 wear-resistant steel plate.
Disclosure of Invention
The invention aims to provide a production method of a preheating-free welding NM450 wear-resistant steel plate, the produced wear-resistant steel plate is of NM450 grade, the thickness of the wear-resistant steel plate is 6-20 mm, the surface hardness of the wear-resistant steel plate is 420-480 HBW, the yield strength is more than or equal to 1180MPa, the tensile strength is more than or equal to 1400MPa, the elongation is more than or equal to 16%, the diameter of 6a is 90 degrees cold bending, the impact AKV at-40 ℃ is more than or equal to 50J, and the toughness performance after preheating-free welding is good.
The technical scheme of the invention is as follows:
A production method of high-strength high-toughness wear-resistant steel comprises the following chemical components of C＝0.19％～0.20％,Si＝0.25％～0.45％,Mn＝1.10％～1.20％,P≤0.012％,S≤0.003％,Cr＝0.65％～0.70％,Nb＝0.015％～0.020％,Ti＝0.008％～0.016％,AlT＝0.070％～0.090％,B＝0.0014％～0.0020％,H≤0.0015％,N≤0.0050％,O≤0.0015％, weight percent of Fe and unavoidable impurities, wherein CEV is less than or equal to 0.54 percent. The key process steps comprise:
(1) Smelting in a converter: the top-bottom combined blown converter is controlled to have the tapping temperature of 1575-1592 ℃, the tapping P of the converter is less than or equal to 0.012 percent, a deoxidizer and an alloy are added in the tapping process for deoxidizing alloying, wherein the alloy adopts a low P alloy, and the expansion P of molten steel is avoided;
(2) Refining: the chemical components of the ladle molten steel are accurately adjusted after the LF furnace is powered on and heated up, then the ladle molten steel enters an RH furnace or a VD furnace for vacuum treatment, and the outbound measurement molten steel gas H is less than or equal to 0.0015%, N is less than or equal to 0.0050% and O is less than or equal to 0.0015%;
(3) Continuous casting: the superheat degree of the tundish, the temperature of a continuous casting furnace is less than or equal to 20 ℃, the temperature of a casting furnace is less than or equal to 25 ℃, the internal quality of a continuous casting billet is improved by adopting a dynamic soft pressing or heavy pressing technology in continuous casting, and the thickness dimension of the continuous casting billet is 180-260 mm and the width dimension is 2000-2300 mm;
(4) Heating: the temperature of the preheating section is 650-800 ℃, the temperature of the heating section is 1100-1240 ℃, the temperature of the soaking section is 1150-1230 ℃, and the furnace time is 180-300 min;
(5) Rolling: adopting two-stage controlled rolling, wherein the rough rolling temperature is 1150-980 ℃, the cumulative compression ratio of rough rolling is more than or equal to 2.2, the thickness of an intermediate billet is 60-80 mm, the initial rolling temperature of finish rolling of 12mm is less than or equal to 960 ℃, the initial rolling temperature of finish rolling of 20mm is less than or equal to 900 ℃, the cumulative compression ratio of finish rolling is more than or equal to 3.5, and the final rolling temperature of finish rolling is 760-830 ℃;
(6) And (3) heat treatment: quenching and tempering are adopted, the quenching heating temperature is 880-900 ℃, the heating speed is 1.6-2.2 min/mm, the heat preservation time is 10-30 min, and the quenching cooling rate is 20-40 ℃/s; tempering heating temperature is 200-220 ℃, heating speed is 3.5-4.0 min/mm, and heat preservation time is 10-25 min.
The principle of the invention:
The wear-resistant steel has the comprehensive characteristics of high strength, high hardness, low temperature high toughness, good stretching and impact after preheating-free welding, and good bending processability. The action and mechanism of the main alloying elements in the chemical composition of the steel of the present invention are described below.
The C range is controlled to ensure that the surface hardness range of the steel plate meets the target requirement; the hardenability of the steel plate is improved through the addition of Mn, B, si, cr elements, so that the steel plate structure is ensured to be uniform; the strength performance of the steel plate is improved by combining structure strengthening and alloy strengthening; the grain is refined by combining precipitates of Nb, ti and Al with reasonable rolling heat treatment process rules so as to achieve the aim of improving the toughness and hardness; meanwhile, the P, S, H, N, O of molten steel is strictly controlled, and the invention effectively combines scientific alloy element proportion and reasonable rolling heat treatment process, thereby ensuring that the steel plate has excellent mechanical property, welding property and processing property. The design reasons of the main additive elements are as follows:
the carbon element can effectively improve the strength of the steel, increase the hardenability and remarkably improve the surface hardness of the wear-resistant steel plate; however, too high carbon adversely affects the toughness, cold formability, and weldability of the steel. Based on the comprehensive consideration, the carbon content of the invention is controlled to be 0.19-0.20%.
Manganese is the most effective alloy element for improving hardenability, dissolves into ferrite to have solid solution strengthening effect, and can improve heat treatment performance of steel, refine pearlite grains and improve strength and hardness of steel. The addition of a certain amount of manganese to the steel is beneficial, but the content is not too high; the Mn is an element easy to segregate, in the solidification process of molten steel, mn element can enable molten steel to gather at the solidification end to form center segregation, so that coarse cementite appears in the core of the steel plate, the core performance is unfavorable, meanwhile Mn can reduce the martensitic transformation temperature in the material, when Mn is accumulated in a segregation zone to reach a certain proportion, high-hardness microstructures such as martensite and bainite can be generated in the cooling process after welding, and the toughness is obviously reduced. Based on the comprehensive consideration, the manganese content of the invention is controlled to be 1.10-1.20%.
The silicon is good in reducing agent and deoxidizer in the steelmaking process, and is easy to form solid solution in ferrite, so that the strength of steel, especially the yield strength, is improved, but when the Si content is too high, the low-temperature toughness is reduced, and meanwhile, the iron scale on the surface of the steel plate is difficult to remove. The Si content of the steel is controlled within the range of 0.25-0.45%, which is beneficial to the comprehensive performance.
The phosphorus element has strong solid solution strengthening effect, so that the strength and hardness of the steel are obviously improved, but the phosphorus is an easily segregated element, the tempering brittleness is increased, and the low-temperature toughness of the steel is very unfavorable. Therefore, the content of phosphorus in the steel should be strictly controlled, and the P in the steel of the present invention should be controlled to be 0.012% or less.
The sulfur element is used as a harmful element in steel, has hot cracking tendency, and sulfide inclusion obviously reduces the toughness of the steel, so that the S content is as low as possible. S in the steel is controlled within 0.003%.
Niobium has extremely strong affinity with nitrogen and carbon in steel, and can form an extremely stable Nb (C, N) compound with the niobium. Nb (C, N) particles dispersed along the austenite grain boundary can greatly improve the coarsening temperature of original austenite grains, thereby refining ferrite grains and improving impact toughness and strength. The Nb of the invention is controlled to be 0.015-0.020%.
Titanium is a strong carbide forming element, has extremely strong binding force with carbon and nitrogen, and can strongly block the migration of austenite grain boundaries when Ti and N produce stable TiN in the solidification process of steel, thereby refining austenite grains; ti and C are combined to generate TiC, so that the precipitation strengthening effect can be achieved. The Ti content of the invention is controlled to be 0.008-0.016%.
Chromium is one of the basic elements of the wear-resistant steel, and has the advantages of improving hardenability, strengthening matrix by solid solution, refining grains, and improving the strength, hardness and wear resistance of the steel; and can obviously improve the oxidation resistance of steel and promote the corrosion resistance of steel. The Cr content of the invention is controlled to be 065-0.70%.
Aluminum acts as a deoxidizer in the steel and can play a role in refining grains. The Al content of the invention is controlled to be 0.070% -0.090%.
Boron is a key element for improving the hardenability of the steel plate, and the hardenability can be obviously improved by only adding a small amount of B (0.0008-0.0030%) into the steel. Therefore, the addition of a small amount of B into the quenched and tempered steel can effectively replace some expensive hardenability alloy elements. But the B content in the wear-resistant steel should not exceed 0.0040 percent, otherwise, non-solid solution boride is easy to generate to cause boron embrittlement. The B content of the invention is controlled to be 0.0014 to 0.0020 percent.
The main innovation point of the invention is that: by adopting a low CEV component design and combining a strict rolling control process, a quenching and low-temperature tempering heat treatment process, a preheating-free welding process-performance evaluation is carried out in the research and development process, and a preheating-free NM450 wear-resistant steel plate with excellent parent metal performance and welding performance is developed. The beneficial effects are that: the NM450 wear-resistant steel produced by the method has excellent toughness, wear resistance and preheating-free welding forming performance. The mechanical properties are as follows: the surface hardness is 420-480 HBW, the yield strength is more than or equal to 1120MPa, the tensile strength is more than or equal to 1370MPa, the elongation is more than or equal to 11.5%, and the 6a diameter 90-degree cold bending and the impact AKV at-40 ℃ is more than or equal to 32J are satisfied. After preheating-free welding, the tensile strength of the butt joint is more than or equal to 780MPa, and the impact energy of a welding line and a heat affected zone at-5 ℃ in a Charpy V-shaped notch test is respectively as follows: 83J/75J/97J, 109J/94J/117J, 138J/156J/185J. The steel plate produced by the method can be used for wear-resistant parts and structural parts of excavators, bulldozers, loaders, dumpers, scraper conveyors and the like, has excellent mechanical properties and excellent welding formability, and is a green steel product with great prospect.
Drawings
FIGS. 1 and 2 are photographs showing metallographic structures of steels produced in example 1 and example 2, respectively;
FIG. 3 is a graph showing the hardness distribution of a steel sheet of the example after non-preheating welding.
Detailed Description
Example 1:
A production method of a preheating-free welding NM450 wear-resistant steel plate comprises the steps of smelting a steel plate with the thickness of 12mm rolled by 1 furnace NM450 wear-resistant steel, wherein the chemical composition weight percentage of the steel is shown in table 1; the method comprises the following key process steps:
(1) Smelting in a converter: smelting by adopting a top-bottom combined blown converter, wherein the tapping temperature is 1581 ℃, the tapping endpoint P content of the converter is 0.010%, alloying is carried out in the tapping process, deoxidizers such as aluminum iron, aluminum blocks and the like are added, and alloys such as low-carbon ferrochrome, manganese and the like are added;
(2) Refining: heating the LF furnace and adjusting components, heating the LF furnace to 1600 ℃ after the components are adjusted, discharging, vacuumizing the VD furnace, keeping the vacuum for 17min, performing soft blowing and standing for 19min after the vacuum breaking, and sampling and detecting H=0.00012%, N=0.0031% and O=0.0011%;
(3) Continuous casting: the liquidus of the molten steel is about 1509 ℃, the tundish temperature is controlled at 1513-1526 ℃, and the thickness of the casting blank section is multiplied by the width=260×2090mm;
(4) Heating: the heating system is as follows: the preheating section is 710 ℃, the heating section is 1120-1240 ℃, the soaking section is 1170-1219 ℃, the slab tapping temperature is 1230 ℃, and the furnace time is 210min;
(5) Rolling: rolling a steel plate with the specification of 12 x 210mm (thickness x width), adopting two-stage controlled rolling, and the rolling technological parameters are shown in table 2;
(6) And (3) heat treatment: quenching and heating the single-row cloth at the target temperature of 890 ℃; the tempering heating target temperature is 210 ℃, and the detailed heat treatment parameters are shown in table 3.
Preheating-free welding experiment: specific process parameters of the preheating-free welding are shown in Table 4. The detection results of the mechanical properties of the obtained steel plate parent metal are shown in Table 5; the tensile and impact performance results after preheating-free welding are shown in Table 6; the hardness profile is shown in FIG. 3 and the test results are shown in Table 7.
Example 2:
A production method of a preheating-free welding NM450 wear-resistant steel plate comprises the steps of smelting a steel plate with the thickness of 20mm rolled by 1 furnace NM450 wear-resistant steel, wherein the chemical composition weight percentage of the steel is shown in table 1; the method comprises the following key process steps:
(1) Smelting in a converter: smelting by adopting a top-bottom combined blown converter, wherein the tapping temperature is 1578 ℃, the tapping endpoint P content of the converter is 0.009%, alloying is carried out in the tapping process, deoxidizing agents such as aluminum iron, aluminum blocks and the like are added, and alloys such as low-carbon ferrochrome, manganese and the like are added;
(2) Refining: heating the LF furnace and adjusting components, heating the LF furnace to 1602 ℃ after the components are adjusted, discharging the LF furnace, vacuumizing the LF furnace, maintaining vacuum for 16min, performing soft blowing and standing for 17min after the vacuum breaking, and sampling and detecting H=0.00013%, N=0.0037% and O=0.0010%;
(3) Continuous casting: the liquidus line of the molten steel is about 1510 ℃, the ladle temperature is controlled at 1517-1528 ℃, and the thickness of the casting blank section is multiplied by the width=260×2090mm;
(4) Heating: the heating system is as follows: 700 ℃ of a preheating section, 1100-1230 ℃ of a heating section, 1165-1220 ℃ of a soaking section, 1216 ℃ of a plate blank tapping temperature and 238min of furnace time;
(5) Rolling: rolling a steel plate with the specification of 20 x 2200mm (thickness x width), adopting two-stage controlled rolling, wherein the rolling technological parameters are shown in table 2;
(6) And (3) heat treatment: quenching and heating the single-row cloth at the target temperature of 890 ℃; the tempering heating target temperature is 210 ℃, and the detailed heat treatment parameters are shown in table 3.
Preheating-free welding experiment: specific process parameters of the preheating-free welding are shown in Table 4. The detection results of the mechanical properties of the obtained steel plate parent metal are shown in Table 5; the tensile and impact performance results after preheating-free welding are shown in Table 6; the hardness profile is shown in FIG. 3 and the test results are shown in Table 7.
Table 1 mass percent of chemical composition (wt.%)
| Examples | C | Si | Mn | P | S | AlT | Cr | Nb | Ti | B | Pcm | CEV |
| 1 | 0.20 | 0.31 | 1.12 | 0.010 | 0.0006 | 0.077 | 0.66 | 0.016 | 0.016 | 0.0014 | 0.31 | 0.52 |
| 2 | 0.20 | 0.28 | 1.13 | 0.009 | 0.0016 | 0.079 | 0.65 | 0.018 | 0.013 | 0.0018 | 0.31 | 0.52 |
Table 2 parameters of the rolling process
| Examples | Thickness mm | Thickness of blank is mm | Intermediate billet mm | Finish rolling start temperature DEG C | Finishing temperature (DEG C) |
| 1 | 12 | 260 | 70 | 950 | 830 |
| 2 | 20 | 260 | 75 | 890 | 811 |
TABLE 3 heat treatment process parameters
Table 4 preheating-free welding process parameters
Table 5 example base material mechanical properties test results
TABLE 6 mechanical Property results after preheating-free welding
TABLE 7 hardness results after preheating-free welding
Claims (1)
1. A production method of preheating-free welding NM450 wear-resistant steel is characterized by comprising the following steps: the weight percentage of the chemical components of the steel is C＝0.19％～0.20％,Si＝0.25％～0.45％,Mn＝1.10％～1.20％,P≤0.012％,S≤0.003％,Cr＝0.65％～0.70％,Nb＝0.015％～0.020％,Ti＝0.008％～0.016％,AlT＝0.070％～0.090％,B＝0.0014％～0.0020％,H≤0.0015％,N≤0.0050％,O≤0.0015％,, and the balance of Fe and unavoidable impurities, wherein CEV is less than or equal to 0.54 percent; the key process steps comprise:
(1) Smelting in a converter: the top-bottom combined blown converter is controlled to have the tapping temperature of 1575-1592 ℃, the tapping P of the converter is less than or equal to 0.012 percent, a deoxidizer and an alloy are added in the tapping process for deoxidizing alloying, wherein the alloy adopts a low P alloy, and the expansion P of molten steel is avoided;
(2) Refining: the chemical components of the ladle molten steel are accurately adjusted after the LF furnace is powered on and heated up, then the ladle molten steel enters an RH furnace or a VD furnace for vacuum treatment, and the outbound measurement molten steel gas H is less than or equal to 0.0015%, N is less than or equal to 0.0050% and O is less than or equal to 0.0015%;
(3) Continuous casting: the superheat degree of the tundish, the temperature of a continuous casting furnace is less than or equal to 20 ℃, the temperature of a casting furnace is less than or equal to 25 ℃, the internal quality of a continuous casting billet is improved by adopting a dynamic soft pressing or heavy pressing technology in continuous casting, and the thickness dimension of the continuous casting billet is 180-260 mm and the width dimension is 2000-2300 mm;
(4) Heating: the temperature of the preheating section is 650-800 ℃, the temperature of the heating section is 1100-1240 ℃, the temperature of the soaking section is 1150-1230 ℃, and the furnace time is 180-300 min;
(5) Rolling: adopting two-stage controlled rolling, wherein the rough rolling temperature is 1150-980 ℃, the cumulative compression ratio of rough rolling is more than or equal to 2.2, the thickness of an intermediate billet is 60-80 mm, the initial rolling temperature of finish rolling of 12mm is less than or equal to 960 ℃, the initial rolling temperature of finish rolling of 20mm is less than or equal to 900 ℃, the cumulative compression ratio of finish rolling is more than or equal to 3.5, and the final rolling temperature of finish rolling is 760-830 ℃;
(6) And (3) heat treatment: quenching and tempering are adopted, the quenching heating temperature is 880-900 ℃, the heating speed is 1.6-2.2 min/mm, the heat preservation time is 10-30 min, and the quenching cooling rate is 20-40 ℃/s; the tempering heating temperature is 200-220 ℃, the heating speed is 3.5-4.0 min/mm, the heat preservation time is 10-25 min, the surface hardness of the wear-resistant steel is 4420-480 HBW, the yield strength is more than or equal to 1180MPa, the tensile strength is more than or equal to 1400MPa, the elongation is more than or equal to 16%, the 6a diameter 90 DEG cold bending is satisfied, and the impact AKV at-40 ℃ is more than or equal to 50J.
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