A crane boom steel with a yield strength of ≥ 1000 mpa and a production method

Abstract

A crane boom steel with yield strength greater than or equal to 1000 MPa, which has the following components and wt%: C: 0.165-0.185%, Si: 0.02-0.15%, Mn: 1.15-1.25%, P: less than or equal to 0.015%, S: less than or equal to 0.002%, Als: 0.025-0.050%, Nb: 0.010-0.020%, Ti: 0.010-0.025%, Cr: 0.35-0.45%, Mo: 0.42-0.48%, V: 0.035-0.045%, B: 0.0010-0.0025%, Ca: 0.0010-0.0030%, N: less than or equal to 0.0050%, T[O]: less than or equal to 0.0030%, H: less than or equal to 0.00025%; the production method comprises the following steps: molten iron desulfurization, converter smelting, bottom argon blowing, LF furnace refining, RH vacuum treatment, casting into a blank, heating the cast blank, rough rolling, finish rolling, coiling after cooling, and heat treatment.The present application has the advantages of guaranteeing yield strength greater than or equal to 1000 MPa, tensile strength of 1050-1200 MPa, elongation A after breaking greater than or equal to 10%, longitudinal impact energy KV2 at-40 DEG C greater than or equal to 50 J, and less addition of valuable elements.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of crane steel and production method, specifically belongs to a kind of crane boom steel with yield strength ≥1000MPa and production method. BACKGROUND

[0002] High-strength steel for engineering machinery has strict requirements on steel quality due to its harsh use environment and stress conditions. In terms of performance, in order to ensure the safety of use during loading, there are higher requirements on the strength performance and impact performance of the steel. The heat treatment process requires uniform temperature and uniform cooling, and the finishing and straightening process can eliminate or greatly reduce the deformation that has already occurred, balance and reduce internal stress, etc. In addition, there are strict requirements on the welding performance of the steel plate and the post-weld deformation, and the post-weld deformation of the crane boom is required to be no more than 4 mm. More importantly, in order to reduce the weight of the equipment, reduce fuel consumption, and improve work efficiency, and with the intensification of international competition, the development requirements of high-performance, large-scale and lightweight engineering machinery, the strength level of engineering machinery steel is higher, and it is more widely used. Especially for the crane boom made of high-strength and easy-to-weld structural steel, the requirements have become the development trend. Obviously, for the high-alloy steel currently used to manufacture the boom of the crane, there is always a trade-off between high strength, easy weldability and economic performance, so it cannot meet the development requirements in this field. For example, according to the search:

[0003] The document with Chinese patent application number CN201110098008.2, "A yield strength 960MPa grade ultra-high strength steel and its production method", discloses a yield strength 960MPa grade ultra-high strength steel and its production method, the chemical composition is as follows in terms of weight percentage: C: 0.07-0.09%; Si: 0.15-0.25%; Mn: 1.00-1.20%; Cr: 1.05-1.15%; Mo: 0.15-0.20%; Al: 0.01-0.06%; P: ≤0.02%; S: ≤0.01%; N: ≤0.008%; the rest is Fe and unavoidable impurities; the production method is: smelting, casting into billet; heating to 1150-1250℃; final rolling temperature is 840-900℃; final cooling temperature is 640-700℃; quenching and tempering treatment is carried out, quenching heating temperature is 880-920℃, holding time is 20-60min, tempering heating temperature is 150-450℃, holding time is 90-180min. The material meets the performance requirements of 960MPa ultra-high strength steel, and has good elongation and impact toughness. As can be seen from the examples, the impact energy at -40℃ is 21-35J, which is lower than the present application and cannot meet the requirements of long-term service in extremely cold weather.

[0004] The document of Chinese patent application No. CN201110096170.0, "Ultra-high strength steel with yield strength 1100MPa-1200MPa and its production method", provides an ultra-high strength steel with yield strength 1100MPa-1200MPa and its production method, the chemical composition (wt%) of which is: C: 0.15-0.18%; Si: 0.20-0.25%; Mn: 0.85-1.25%; Cr: 0.20-0.60%; Mo: 0.45-0.65%; V: 0.035-0.060%; Nb: 0.015-0.020%; Ni: 0-0.55%; Cu: 0-0.035%; Al: 0.01-0.06%; P: ≤0.015%; S: ≤0.01%; N: ≤0.008%, and the rest is Fe and inevitable impurities. The production method is: smelting and casting into a casting blank; heating the casting blank to 1150-1250℃, the final rolling temperature is 860-920℃; the coiling temperature is 650-750℃; the quenching heating temperature is 880-930℃, the holding time is 20-90min, the tempering heating temperature is 100-450℃, the holding time is greater than 90min, and the slow cooling or air cooling is to room temperature. The steel plate produced according to the composition and process of the present application has a yield strength of 1150MPa-1230MPa, a tensile strength of 1250MPa-1340MPa, an elongation of 11%-13.5%, and an impact energy value at -40℃ of 21J-34J. As shown in its examples, it adds higher Ni and Mo, and the cost is higher, although the yield strength and tensile strength are higher than those of the present application, the yield strength and tensile strength of the present application can meet the performance requirements of crane boom steel. However, its impact energy value at -40℃ is 21J-34J, which is lower than that of the present application, and cannot meet the requirements of long-term service in extremely cold weather.

[0005] The document of Chinese patent application No. CN201110071217.8, "A kind of excellent plasticity HT960 steel plate and its manufacturing method", provides a kind of excellent plasticity HT960 steel plate and its manufacturing method, and its component weight percentage is: C: 0.07%~0.12%, Si≤0.15%, Mn: 0.80%~1.20%, P≤0.012%, S≤0.0030%, Cr: 0.30%~0.60%, Mo: 0.30%~0.60%, Ni: 1.00%~1.60%, Cu: 0.15%~0.45%, B: 0.0008%~0.0016%, Ti: 0.006%~0.014%, Nb: 0.010%~0.030%, Als: 0.025%~0.060%, V: 0.030%~0.060%, N: ≤0.0060%, O≤0.0040%, Ca: 0.001%~0.004%, the rest iron and inevitable inclusions. By TMCP+ tempering heat treatment process, the ultra-high strength steel plate with excellent weldability, tensile strength≥960MPa, yield strength≥900MPa, -60℃ Charpy transverse impact energy (single value)≥47J, fracture elongation δ5≥15% and uniform elongation Ag≥6% is obtained. It adds higher Mo, Ni, Cu elements, and the alloy cost is higher. In addition, the TMCP rolling process has many disadvantages, the capacity requirements of rolling mill and open equipment are extremely high, and the uniformity of plate shape and coiling length and width direction performance is difficult to guarantee.

[0006] The document of Chinese patent application No. CN201110410802.6, "A kind of yield strength 1000MPa grade quenched and tempered ultra-high strength steel and its manufacturing method", provides a kind of yield strength 1000MPa grade quenched and tempered ultra-high strength steel and its manufacturing method, and its chemical composition is (weight), C: 0.15%~0.20%; Si: 0.10%~0.40%; Mn: 1.00%~1.50%; Cr: 0.30%~0.50%; Mo: 0.30%~0.50%; Ni: 0.20%~0.50%; B: 0.0010%~0.0030%; Nb: 0.010%~0.030%; V: 0.030%~0.050%; Ti: 0.010%~0.020%; Alt: 0.030%~0.050%; P: ≤0.020%; S: ≤0.010%. The steel can meet the performance requirements of 1000MPa grade quenched and tempered ultra-high strength steel. It adds higher Ni element, and the alloy cost is higher.

[0007] The document with Chinese patent application number CN201210430148.X, "A production method of ultra-high strength steel plate", provides a production method of ultra-high strength steel plate, adopting a process route of converter steelmaking→secondary refining→continuous casting→heating→rolling→accelerated cooling→heat treatment. The chemical mass percentage composition of the steel is: C=0.25-0.27, Si=0.75-0.85, Mn=1.45-1.55, P≤0.015, S≤0.010, Alt≤0.020, Nb=0.02-0.03, V=0.05-0.06, Ti=0.045-0.060, Mo=0.55-0.65, B=0.0017-0.0022. The component design of the steel plate of the present application is simple, without adding a large amount of alloying elements, thereby reducing the production cost of the ultra-high strength steel plate; the Ti oxide metallurgical technology is adopted to improve the welding performance of the steel plate; the steel plate is treated by Q+P to have a microstructure of ultra-fine lath martensite+nanoscale lath residual austenite and precipitated complex carbides, and the comprehensive performance of the strength and plasticity of the steel plate is superior to that of dual-phase steel, TRIP steel and general martensitic steel; the steel plate is quenched by a roller quenching machine to have good plate shape; the process is simple and the technology is easy to implement, thereby solving the problem that the traditional quenching and tempering cannot produce ultra-high strength steel plate, and realizing batch production of 1600MPa grade ultra-high strength steel plate. The Si content added in the composition is very high, which is easy to cause FeO skin on the surface of the steel plate, and the surface quality is poor, and the Mn, Mo, V and Ti components are higher than those of the present application, and the cost is higher.

[0008] The document with Chinese patent application number CN201510323916.5, "1300MPa grade ultra-high strength steel and preparation method thereof", provides a 1300MPa grade ultra-high strength steel and a preparation method thereof, belonging to the technical field of engineering machinery steel manufacturing. The preparation method mainly includes slab smelting, slab casting, slab heating, steel plate rolling and heat treatment process steps. The advantage is that: by designing a reasonable component system, on the basis of adding appropriate amount of alloying elements, through optimized rolling and heat treatment process, the prepared ultra-high strength engineering machinery structural steel has low cost, simple process, and has the advantages and prospects of batch production and application. The Si content added is relatively high, which is easy to cause FeO skin on the surface of the steel plate, and the surface quality is poor, and the added Ni component is relatively high, and the cost is higher.

[0009] The document with Chinese patent application number CN201710481010.5, "A yield strength greater than 1400MPa ultra-high strength steel plate and its production method", provides a yield strength greater than 1400MPa ultra-high strength steel plate. The chemical composition of the steel plate includes C: 0.22-0.30%, Si: 0.10-0.50%, Mn: 0.8-1.40%, Nb: 0.010-0.040%, V: 0.020-0.050%, Ti: ≤0.008%, Al: 0.05-0.09%, Ni: 0.8-2.0%, Cr: 0.30-0.70%, Mo: 0.30-0.70%, B: 0.001-0.005%, Ca: 0.001-0.005%, P ≤0.010%, S ≤0.003%, O ≤0.002%, N ≤0.004%, H ≤0.00015%, and the balance is Fe and unavoidable impurity elements. The production process is: converter or electric furnace steelmaking-LF refining-VD or RH vacuum degassing-Ca treatment-continuous casting-slow cooling-heating-rolling-quenching-low temperature tempering. The steel plate has good low temperature toughness, and the yield strength is greater than 1400MPa. The high Si content added in the composition is easy to produce FeO skin on the surface of the steel plate, and the surface quality is poor. The high Ni content added is high in cost. SUMMARY

[0010] The present application is to overcome the deficiencies in the prior art, and to provide a crane boom steel with yield strength ≥1000MPa and a production method, which has a yield strength ≥1000MPa, a tensile strength of 1050-1200MPa, an elongation A ≥10%, a longitudinal impact energy KV2 ≥50J at -40℃, and a small amount of valuable element addition.

[0011] The measures to achieve the above-mentioned purposes are:

[0012] A crane boom steel with yield strength ≥1000MPa, which has the following components and weight percentage contents: C: 0.165-0.185%, Si: 0.02-0.15%, Mn: 1.15-1.25%, P: ≤0.015%, S: ≤0.002%, Als: 0.025-0.050%, Nb: 0.010-0.020%, Ti: 0.010-0.025%, Cr: 0.35-0.45%, Mo: 0.42-0.48%, V: 0.035-0.045%, B: 0.0010-0.0025%, Ca: 0.0010-0.0030%, N ≤0.0050%, T[O] ≤0.0030%, H ≤0.00025%, and the balance is Fe and unavoidable inclusions.

[0013] Preferably: the weight percentage content of Cr is 0.38-0.41%.

[0014] Preferably: the weight percentage content of V is 0.038-0.042%.

[0015] A production method of a crane boom steel with a yield strength ≥1000MPa, comprising the steps of:

[0016] 1) hot metal desulphurization, desulphurization target: S≤0.001%, the exposed surface of the hot metal after slagging is not less than 90%, when slagging is performed twice or more, the time between each two times of slagging is required to be not less than 6min;

[0017] 2) performing converter smelting, and controlling the end point temperature of smelting to be 1610-1630℃, and the end point oxygen to be 0.035-0.075%; adding aluminum iron for deoxidization when tapping the converter, and the adding amount is based on the principle of making the Als in the end point molten steel to be 0.025-0.045%;

[0018] 3) performing bottom argon blowing, and controlling the Als in the molten steel at the end of argon blowing to be 0.040-0.060%;

[0019] 4) performing LF furnace refining, and controlling S in the molten steel to be ≤0.002%, and Als to be 0.040-0.070%;

[0020] 5) adopting SiCa for RH vacuum treatment, during which: the vacuum circulation time is controlled to be 25-35min, the vacuum degree is controlled to be ≤15Pa, and the temperature at the end of vacuum is controlled to be 1548-1558℃; and CaSi wire is added according to 0.50-0.70kg / t.s for calcium treatment at the end of vacuum treatment;

[0021] 6) performing casting into a billet under the protection of a protective slag: during which: the billet drawing speed is controlled to be 0.9-1.3m / min, the fluctuation range of the molten steel surface of the crystallizer is within ±3mm; the crystallizer taper is controlled to be 1.19-1.24%, the cooling water flow of the wide surface of the crystallizer is controlled to be 3380-3550L / min, and the cooling water flow of the narrow surface of the crystallizer is controlled to be 620-640L / min; the superheat degree of the molten steel is ≤15℃, and the tundish temperature is 1518-1528℃;

[0022] 7) heating the cast billet, and controlling the cast billet into the furnace temperature to be 1230-1290℃;

[0023] 8) performing rough rolling, and controlling the rough rolling temperature to be 1080-1120℃;

[0024] 9) performing finish rolling, and controlling the finish rolling temperature to be 880-920℃ to end the rolling;

[0025] 10) after cooling, coiling and controlling the coiling temperature at 610-650℃;

[0026] 11) heat treatment, during which: controlling the quenching temperature at 890-910℃, quenching holding time at 6-8min; tempering temperature at 490-510℃, tempering holding time at 12-15min.

[0027]

[0028] The physical property requirements of the protective slag are: basicity at 1.17-1.27, viscosity at 0.05-0.15 Pa·S at 1300℃, and melting point at 1040-1100℃.

[0029] The roles and mechanisms of the raw materials and main processes in the application

[0030] Carbon (C): a conventional strengthening element, which can improve the yield strength and tensile strength, and increase the hardness of the steel, but too high carbon will reduce the plasticity and impact toughness. The more suitable carbon addition amount is 0.165-0.185%.

[0031] Manganese (Mn): Mn is a more economical alloying element, which is dissolved in ferrite and austenite, can expand the austenite region, greatly reduces the martensite transformation temperature of the steel, reduces the phase change speed of the steel, effectively improves the hardenability of the steel, increases the content of residual austenite, and can significantly improve the yield and tensile strength of the steel, and improve the cold bending performance. However, when the manganese content is too high, the plasticity and welding performance of the steel will be reduced, and central segregation will occur. The more suitable manganese addition amount is 1.15-1.25%.

[0032] Silicon (Si): silicon has a strong chemical reaction with oxygen in steel, which can make the pure ferrite grains in the steel small and uniformly distributed, improve the strength of the steel, and improve the corrosion resistance and oxidation resistance of the steel. However, too high silicon will reduce the plasticity and welding performance, and the more suitable silicon addition amount is 0.02-0.15%.

[0033] Niobium (Nb): can optimize the grain boundary structure, promote the precipitation hardening of the steel, adjust the morphology of non-metallic inclusions in the steel and improve the boundary morphology, make the grain boundary fine and reduce its number, thereby improving the toughness and plasticity of the steel. It can improve the strength and hardness of the steel, improve the oxidation resistance of the steel, and improve the processability and plasticity of the steel. However, too high niobium will reduce the toughness of the steel, resulting in uneven carburized layer. The more suitable niobium addition amount is 0.010-0.020.

[0034] ​Titanium (Ti): Titanium is one of the strong ferrite forming elements, which reduces the austenite phase region. Titanium has a strong affinity with nitrogen, oxygen and carbon, and is a good deoxidizing and degassing agent and an effective element for fixing nitrogen and carbon. Titanium and carbon form TiC with high stability, and TiC particles can prevent steel grain growth and coarsening, and have the effect of refining the grain. However, too high titanium content can reduce the toughness of the steel. The more appropriate titanium addition amount is 0.010-0.025%.

[0035] Chromium (Cr): Chromium easily forms a continuous solid solution, reducing the austenite phase region. Chromium and carbon form various carbides, which are not easy to decarburize during heat treatment, and can increase the hardenability of the steel, and can improve the strength of the steel in the rolled state. Chromium can form a relatively dense protective layer on the surface of the steel, which can protect the matrix and effectively improve the weather resistance of the steel. However, too high chromium content in the steel can deteriorate the toughness of the steel plate and reduce the weldability of the steel. The more appropriate chromium addition amount is 0.35-0.45%, preferably 0.38-0.41%.

[0036] Molybdenum (Mo): Molybdenum can improve hardenability and thermal strength, and is a strong hardenability element. It can improve the tempering stability of the steel, prevent temper brittleness, and improve the plasticity of the steel. It can form a solid solution with iron elements, which can significantly improve the strength and hardness of the steel. It can improve the corrosion resistance of the steel. However, too high molybdenum will reduce the oxidation resistance of the steel and increase the deformation resistance of the steel to hot working. Therefore, the more appropriate molybdenum addition amount is 0.42-0.48%.

[0037] Vanadium (V): Vanadium and iron can form a continuous solid solution, which strongly reduces the austenite phase region. By controlling the austenitizing temperature, the amount of vanadium in austenite and the amount of undissolved carbides can be changed, and the actual grain size of the steel can be improved, which can improve the hardenability of the steel. Vanadium and carbon can form stable refractory carbides, which can maintain fine grain structure at high temperatures and greatly reduce the overheating sensitivity of the steel. It can improve the toughness, hardness and wear resistance of the steel. However, too high vanadium content can lead to the appearance of aggregated carbides, which can reduce the strength, and the precipitation of carbides in the grain can reduce the room temperature toughness. The more appropriate vanadium addition amount is 0.035-0.045%, preferably 0.038-0.042%.

[0038] Boron (B): The main role of boron element is to improve the hardenability of the steel. A small amount of boron can significantly improve the hardenability of the steel. Boron can reduce the chemical heterogeneity of continuous casting billets, refine columnar crystals, and ultimately form the best metallographic structure, while reducing the effect of aging hardening. However, too much boron can easily accumulate at the grain boundaries, which can reduce the grain boundary binding energy, making the steel plate more prone to intergranular fracture under impact load, and reducing the low temperature impact energy of the steel plate. The more appropriate boron addition amount is 0.0010-0.0025%.

[0039] Aluminum (Al): Aluminum is the main deoxidizing element in steel, which can significantly reduce the oxygen content in steel, and the combination of aluminum and nitrogen forms AlN, which can effectively refine the grain. However, when the aluminum content in steel exceeds 0.05%, it is easy to cause the obvious increase of aluminum oxide inclusions, which reduces the cleanliness of the steel and is not conducive to the toughness of the steel. The appropriate addition amount of aluminum is 0.025-0.050% respectively. Preferably, it is 0.030-0.040%.

[0040] Phosphorus, sulfur (P, S): Phosphorus easily leads to cold brittleness of steel; sulfur easily causes hot brittleness; therefore, the content of phosphorus and sulfur in steel should be reduced as much as possible.

[0041] Nitrogen, oxygen, hydrogen (N, O, H): Nitrogen, oxygen, and hydrogen are important indicators for measuring the purity of molten steel, and nitrogen, oxygen, and hydrogen are easy to form inclusions and pores, leading to cracks in steel and affecting the service life of steel. Therefore, the content of nitrogen, oxygen, and hydrogen in steel should be reduced as much as possible.

[0042] Calcium (Ca): Calcium treatment is mainly used for denaturation treatment of inclusions that cannot be removed in steel, changes the morphology of high-melting-point aluminum oxide inclusions, forms low-melting-point calcium-aluminum compounds, improves the purity of molten steel, and reduces the influence of inclusions on the performance of steel. Improve the casting performance of molten steel.

[0043] The reason why the present application controls the desulfurization target S≤0.001% and the bare surface of molten iron after slagging is not less than 90% is that the desulfurization of molten iron makes the target S≤0.001%, in order to reduce the sulfur content of molten iron entering the converter, thereby reducing the sulfur content in the molten steel in the LF furnace, reducing the pressure of desulfurization in the LF furnace, and the bare surface of molten iron after slagging is not less than 90% in order to clean the slag and prevent incomplete slagging from causing subsequent steel slag to return sulfur.

[0044] The reason why the present application controls the smelting endpoint temperature at 1610-1630℃ and the endpoint oxygen at 0.035-0.075% is that the main raw material for smelting molten steel in the converter is molten iron and scrap steel. If the smelting endpoint temperature is too low, the scrap steel will not be completely melted. If the smelting endpoint temperature is too high, it is not conducive to the removal of phosphorus in the molten steel, which will lead to excessive phosphorus. Dephosphorization requires a relatively low temperature. If the endpoint oxygen is too low, the oxidizing property of the molten steel is insufficient, which is not conducive to the removal of phosphorus in the molten steel. If the endpoint oxygen is too high, the molten steel will be over-oxidized, which will lead to high nitrogen and fast erosion of the inner wall of the converter.

[0045] The reason why the present application controls the Als in the molten steel at 0.040-0.060% at the end of argon blowing is to make the subsequent desulfurization in advance to form reducing slag, and the subsequent desulfurization must require the reducing property of the slag.

[0046] The application adopts SiCa for RH vacuum treatment, during which: the vacuum circulation time is controlled in 25-35 min, the vacuum degree is controlled in ≤15 Pa, and the temperature at the end of vacuum treatment is controlled in 1548-1558℃; the CaSi wire is added in accordance with 0.50-0.70 kg / t.s for calcium treatment at the end of vacuum treatment, because the circulation time and vacuum degree parameters are strictly controlled in the vacuum circulation process, the nitrogen content in the steel can be further reduced, the harmful impurities and gases can be further removed, the purity of the molten steel is improved, and the low-temperature impact toughness of the steel is improved.

[0047] The application controls the drawing speed in 0.9-1.3 m / min, the fluctuation range of the crystallizer liquid surface is within ±3 mm, the crystallizer taper is controlled in 1.19-1.24%, the cooling water flow of the wide surface of the crystallizer is in 3380-3550 L / min, the cooling water flow of the narrow surface of the crystallizer is in 620-640 L / min, the overheating degree of the molten steel is ≤15℃, and the tundish temperature is in 1518-1528℃, because the drawing speed is lower than 0.9 m / min, the phenomenon of drawing stoppage is easy to occur, the drawing stoppage of the casting blank on the roller bed of the continuous casting machine also causes damage to the continuous casting machine, the drawing speed is higher than 1.3 m / min, and the drawing speed is too fast to cause leakage. When the fluctuation range of the crystallizer liquid surface exceeds ±3 mm, the crystallizer slag rolling is easy to cause secondary pollution to the molten steel. When the crystallizer taper is lower than 1.19 or higher than 1.24, the casting blank is easy to produce cracks to cause the casting blank to be scrapped. When the cooling water flow of the wide surface and the narrow surface of the crystallizer is too high, the blank shell at the outlet of the crystallizer is thinned, and the risk of leakage is increased. When the overheating degree of the molten steel and the tundish temperature are too high, the casting blank is easy to produce center segregation.

[0048] The application controls the casting blank temperature in 1230-1290℃, because the temperature is too low to cause low toughness. The temperature is too high to cause defects such as surface oxidation, deformation, pores, cracks and the like, and the quality is affected. The energy consumption is increased.

[0049] The application controls the rough rolling temperature in 1080-1120℃, because the rough rolling temperature is too low to cause the material to be too hard, the rolling force is required to be large, and the plate shape is not easy to control. The rough rolling temperature is too high to cause defects such as strong oxidation of the steel, decarburization, exposure and oxidation of the skin bubble, overburning and the like, and the steel is scrapped in serious cases.

[0050] The present application controls the quenching temperature at 890-910 DEG C, the quenching holding time at 6-8 min; the tempering temperature at 490-510 DEG C, and the tempering holding time at 12-15 min. If the quenching temperature is too low, the phase change temperature cannot be reached, the quenching requirement cannot be met, and the strength and hardness are insufficient. If the quenching temperature is too high, the steel material becomes brittle and cracks. If the quenching holding time is too short, the structure after cooling is not uniform, and the steel material cracks. If the quenching holding time is too long, the size is deformed, the grain size is increased, the grain boundary is thickened, and the hardness, strength and toughness are reduced. If the tempering temperature is too high, the surface of the steel material is decarburized, cracks, the hardness, strength and toughness are reduced. If the tempering temperature is too low, the stress and brittleness of the steel material are too large, the structure of the steel material is not fully transformed, and the toughness is reduced. If the tempering holding time is too short, the structure is not uniform, the grain growth is not uniform, and the performance indexes such as strength and toughness are unstable. If the tempering holding time is too long, the hardness, strength and toughness are reduced.

[0051] Compared with the prior art, the present application has the advantages that the yield strength is greater than or equal to 1000 MPa, the tensile strength is 1050-1200 MPa, the elongation A after fracture is greater than or equal to 10%, the longitudinal impact energy KV2 at-40 DEG C is greater than or equal to 50 J, and the addition amount of valuable elements is small. DETAILED DESCRIPTION

[0052] The present application will be described in detail as follows:

[0053] Table 1 is a list of chemical components of each embodiment and the comparative example of the present application;

[0054] Table 2 is a list of main process parameters of each embodiment and the comparative example of the present application;

[0055] Table 3 is a list of performance detection conditions of each embodiment and the comparative example of the present application.

[0056] Each embodiment of the present application is produced according to the following steps

[0057] 1) Desulfurization of molten iron, desulfurization target: S≤0.001%, the exposed surface of molten iron after slagging is not less than 90%, and when the slagging is performed twice or more, the residence time between every two times of slagging is required to be not less than 6 min;

[0058] 2) Converter smelting is performed, and the smelting end point temperature is controlled at 1610-1630 DEG C, the end point oxygen is 0.035-0.075%; aluminum iron is added for deoxidization when the converter is tapped, and the addition amount is based on the principle that the Als in the end point molten steel is 0.025-0.045%;

[0059] 0.075%; aluminum iron is added for deoxidization when the converter is tapped, and the addition amount is based on the principle that the Als in the end point molten steel is 0.025-0.045%;

[0060] 3) Bottom argon blowing is performed, and the Als in the molten steel at the end of argon blowing is controlled at 0.040-0.060%;

[0061] 4) LF furnace refining is carried out, and the content of S in the molten steel is controlled to be ≤0.002%, and the content of Als is controlled to be in the range of 0.040-0.070%;

[0062] 5) SiCa is used for RH vacuum treatment, during which: the vacuum circulation time is controlled to be in the range of 25-35 min, the vacuum degree is controlled to be ≤15 Pa, and the temperature at the end of vacuum treatment is controlled to be in the range of 1548-1558℃; CaSi wire is added at the end of vacuum treatment according to 0.50-0.70 kg / t.s for calcium treatment;

[0063] 6) casting into a blank is carried out under the protection of a protective slag, during which: the blank drawing speed is controlled to be in the range of 0.9-1.3 m / min, the crystallizer steel liquid surface fluctuation range is within ±3 mm; the crystallizer taper is controlled to be in the range of 1.19-

[0064] 1.24%, the crystallizer wide surface cooling water flow is controlled to be in the range of 3380-3550 L / min, the crystallizer narrow surface cooling water flow is controlled to be in the range of 620-640 L / min; the molten steel superheat is ≤15℃, and the tundish temperature is in the range of 1518-1528℃;

[0065] 7) the cast blank is heated, and the cast blank furnace entry temperature is controlled to be in the range of 1230-1290℃;

[0066] 8) rough rolling is carried out, and the rough rolling temperature is controlled to be in the range of 1080-1120℃;

[0067] 9) finish rolling is carried out, and the finish rolling temperature is controlled to be in the range of 880-920℃ to end the rolling;

[0068] 10) after cooling, coiling is carried out, and the coiling temperature is controlled to be in the range of 610-650℃;

[0069] 11) heat treatment is carried out, during which: the quenching temperature is controlled to be in the range of 890-910℃, the quenching holding time is controlled to be in the range of 6-

[0070] 8 min; the tempering temperature is controlled to be in the range of 490-510℃, and the tempering holding time is controlled to be in the range of 12-15 min.

[0071] Table 1 lists the chemical components of each embodiment of the present application and the comparative examples (wt%)

[0072]

[0073]

[0074] Table 2 lists the main process parameters of each embodiment of the present application and the comparative examples

[0075]

[0076] Continued Table 2-1

[0077]

[0078]

[0079] Table 2-2 (Continued)

[0080]

[0081] Table 2-3 (Continued)

[0082]

[0083]

[0084] Table 3 Main performance test statistics of various embodiments of the present application and comparative examples

[0085]

[0086] As can be seen from Table 3, by strictly controlling the process parameters of hot metal desulphurization, converter smelting, LF refining, RH vacuum, continuous casting, hot rolling, heat treatment quenching, tempering, etc., the crane steel described in the present application can have a yield strength of ≥1000 MPa, a tensile strength of 1050-1200 MPa, an elongation A of ≥10%, and a longitudinal impact energy KV2 of ≥50 J at -40℃, thereby meeting the requirements for long-term service in extremely cold weather. By optimizing the content of alloying elements, canceling the Ni element, and reducing the content of other alloying elements, the alloy cost can be reduced by more than 30%.

[0087] The specific embodiments are only the best examples, and are not a limiting implementation of the technical solutions of the present application.

Claims

1. A crane boom steel with a yield strength ≥1000MPa, comprising the following components and weight percentages: C: 0.165%, Si: 0.02%, Mn: 1.15%, P: 0.012%, S: 0.0011%, Alt: 0.025%, Nb: 0.010%, Ti: 0.01%, Cr: 0.35%, Mo: 0.42%, V: 0.035%, B: 0.0010%, Ca: 0.0012%, N: 0.0035%, O: 0.0021%, H: 0.0002%, balance Fe and inevitable impurities; production method: 1) hot metal desulphurization, desulphurization target: S: 0.0007%, hot metal exposed surface after slagging is not less than 90%, when two or more times of slagging is performed, the time between every two times of slagging is 10 min; 2) converter smelting is performed, and the smelting end point temperature is controlled at 1625℃, the end point oxygen is 0.054%; aluminum iron is added for deoxidization when the converter is tapped, and the addition amount is such that the Als in the end point molten steel is 0.026%; 3) bottom argon blowing is performed, and the Als in the molten steel at the end of argon blowing is controlled at 0.051%; 4) LF furnace refining is performed, and the S in the molten steel is controlled at 0.0009%, and the Als is controlled at 0.049%; 5) SiCa is used for RH vacuum treatment, during which: the vacuum circulation time is controlled at 34 min, the vacuum degree is controlled at: 12 Pa, and the temperature at the end of vacuum is controlled at 1557℃; at the end of vacuum treatment, CaSi wire is added at 0.52 kg / t.s for calcium treatment; 6) casting into a billet is performed under the protection of a protective slag: during which: the casting speed is controlled at 1.2 m / min, the crystallizer molten steel surface fluctuation is -3 mm; the crystallizer taper is controlled at 1.2%, the crystallizer wide surface cooling water flow is 3406 L / min, the crystallizer narrow surface cooling water flow is 626 L / min; the molten steel superheat is 13℃, and the tundish temperature is 1526℃; 7) the cast billet is heated, and the cast billet heating temperature is controlled at 1255℃; 8) rough rolling is performed, and the rough rolling temperature is controlled at 1097℃; 9) finish rolling is performed, and the finish rolling temperature is controlled at 898℃ to end the rolling; 10) after cooling, coiling is performed, and the coiling temperature is controlled at 628℃; 11) heat treatment is performed, during which: the quenching temperature is controlled at 895℃, the quenching holding time is 6 min; the tempering temperature is 495℃, and the tempering holding time is 12 min. 0.05%, Mn: 1.17%, P: 0.011%, S: 0.002%, Alt: 0.028%, Nb: 0.011%, Ti: 0.012%, Cr: 0.36%, Mo: 0.43%, V: 0.036%, B: 0.0011%, Ca: 0.0015%, N: 0.0038%, O: 0.0023%, H: 0.00022%, balance Fe and inevitable impurities; production method: 1) hot metal desulphurization, desulphurization target: S: 0.0008%, hot metal exposed surface after slagging is not less than 90%, when two or more times of slagging is performed, the time between every two times of slagging is 9 min; 2. A crane boom steel having a yield strength of > 1000 MPa, the composition and weight percent contents of which are: C: 0.167%, Si: 2) converter smelting is performed, and the smelting end point temperature is controlled at 1630℃, the end point oxygen is 0.062%; aluminum iron is added for deoxidization when the converter is tapped, and the addition amount is such that the Als in the end point molten steel is 0.028%; ​ ​ 3) bottom argon blowing is performed, and Als in the molten steel at the end of the argon blowing is controlled to be 0.052%; 4) LF furnace refining is performed, and S in the molten steel is controlled to be 0.0018%, and Als is controlled to be 0.053%; 5) SiCa is used for RH vacuum treatment, during which, vacuum circulation time is controlled to be 32 min, vacuum degree is controlled to be 14 Pa, and temperature at the end of the vacuum treatment is controlled to be 1553 ℃; CaSi wire is added at the end of the vacuum treatment according to 0.55 kg / t.s for calcium treatment; 6) casting is performed under the protection of the protective slag, during which, the casting speed is controlled to be 1.3 m / min, the molten steel surface fluctuation in the mold is 2 mm, the mold taper is controlled to be 1.19%, the wide surface cooling water flow in the mold is 3511 L / min, the narrow surface cooling water flow in the mold is 640 L / min, the molten steel superheat is 9 ℃, and the tundish temperature is 1522 ℃; 7) the cast blank is heated, and the cast blank heating temperature is controlled to be 1249 ℃; 8) rough rolling is performed, and the rough rolling temperature is controlled to be 1090 ℃; 9) finish rolling is performed, and the finish rolling temperature is controlled to be 891 ℃ to end the rolling; 10) after cooling, coiling is performed, and the coiling temperature is controlled to be 621 ℃; 11) heat treatment is performed, during which, the quenching temperature is controlled to be 892 ℃, the quenching holding time is controlled to be 7 min, the tempering temperature is controlled to be 492 ℃, and the tempering holding time is controlled to be 13 min.

3. A crane boom steel with a yield strength ≥ 1000 MPa, the components and weight percentage contents of which are: C: 0.168%, Si: 0.08%, Mn: 1.2%, P: 0.01%, S: 0.0015%, Alt: 0.031%, Nb: 0.015%, Ti: 0.0014%, Cr: 0.38%, Mo: 0.44%, V: 0.038%, B: 0.0013%, Ca: 0.0016%, N: 0.004%, O: 0.0019%, H: 0.00025%, and the balance being Fe and inevitable inclusions; a production method comprises the following steps: 1) hot metal desulfurization, desulfurization target: S: 0.0009%, the bare surface of the hot metal after slagging is not less than 90%, and the residence time between two times of slagging is 8 min when the slagging is performed two times or more; 2) converter smelting is performed, and the smelting end temperature is controlled to be 1622 ℃, and the end oxygen is 0.068%; aluminum iron is added for deoxidization when the converter is tapped, and the addition amount is such that the Als in the end molten steel is 0.035%; 3) bottom argon blowing is performed, and the Als in the molten steel at the end of the argon blowing is controlled to be 0.045%; 4) LF furnace refining is performed, and S in the molten steel is controlled to be 0.0013%, and Als is controlled to be 0.044%; 5) SiCa is used for RH vacuum treatment, during which, vacuum circulation time is controlled to be 33 min, vacuum degree is controlled to be 13 Pa, and temperature at the end of the vacuum treatment is controlled to be 1554 ℃; CaSi wire is added at the end of the vacuum treatment according to 0.56 kg / t.s for calcium treatment; 6) casting is performed under the protection of the protective slag, during which, the casting speed is controlled to be 1.1 m / min, the molten steel surface fluctuation in the mold is 2 mm, the mold taper is controlled to be 1.19%, the wide surface cooling water flow in the mold is 3511 L / min, the narrow surface cooling water flow in the mold is 640 L / min, the molten steel superheat is 9 ℃, and the tundish temperature is 1522 ℃; ​ ​ ​ The face wave is 1 mm; the taper of the crystallizer is controlled at 1.22%, the cooling water flow of the wide face of the crystallizer is 3400 L / min, the cooling water flow of the narrow face of the crystallizer is 627 L / min; the superheat of the molten steel is 10 ℃, and the temperature of the tundish is 1523 ℃; 7) heating the cast blank and controlling the heating temperature of the cast blank at 1252 ℃; 8) rough rolling and controlling the rough rolling temperature at 1092 ℃; 9) finish rolling and controlling the finish rolling temperature at 893 ℃ to end the rolling; 10) coiling after cooling and controlling the coiling temperature at 624 ℃; 11) heat treatment, during which: controlling the quenching temperature at 898 ℃, the quenching holding time at 8 min; the tempering temperature at 498 ℃, and the tempering holding time at 14 min. ​

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