CN115747674B - Low-cost hydrogen embrittlement-resistant non-quenched and tempered steel for direct cutting of oversized section, and preparation method and application thereof - Google Patents
Low-cost hydrogen embrittlement-resistant non-quenched and tempered steel for direct cutting of oversized section, and preparation method and application thereof Download PDFInfo
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Abstract
The invention discloses a low-cost hydrogen embrittlement-resistant non-quenched and tempered steel for direct cutting with an oversized section, a preparation method and application thereof, wherein by adding a proper amount of Cu element and controlling rolling and cooling, more VCx precipitated phases with stronger hydrogen capturing capacity and copper-containing precipitated phases with B2 structures are obtained as hydrogen traps on the premise of not obviously improving the alloy cost, so that the hydrogen embrittlement hazard of endogenous hydrogen is reduced; by forming a passivation film on the surface of the steel part, the self-healing trend of the steel part is improved, and the exogenous hydrogen is prevented from entering to form hydrogen embrittlement hazard. Thereby improving the hydrogen embrittlement resistance of the non-quenched and tempered steel for direct cutting with an oversized section with the section diameter exceeding 160 mm.
Description
Technical Field
The invention relates to non-quenched and tempered steel for direct cutting of a super-large section with low cost and hydrogen embrittlement resistance, and a preparation method and application thereof, in particular to non-quenched and tempered steel for direct cutting of a ferrite-pearlite type low cost and hydrogen embrittlement resistance, and a preparation method and application thereof, belonging to the technical field of non-quenched and tempered steel.
Background
The non-quenched and tempered steel for direct cutting can obtain the required mechanical properties after rolling, and is further directly used after cutting, and is mainly used for producing parts such as push rods, hydraulic upright posts and the like. Compared with quenched and tempered steel, the method omits the quenching and tempering process, greatly saves energy consumption and production cost, and is more environment-friendly. With the increase of the cross section of the parts, the quenched and tempered steel has insufficient hardenability, and the microstructure is gradually transformed from tempered sorbite to ferrite-pearlite from the surface to the core. Not only has large tissue change, but also has obvious difference of section mechanical properties. The non-quenched and tempered steel for direct cutting is of ferrite-pearlite structure, and has uniform mechanical properties and higher use safety. However, as the cross section of the non-quenched and tempered steel bar increases, the risk of hydrogen embrittlement cracking increases. Especially, the parts used in weak acid environment are more easily broken due to hydrogen embrittlement under the combined action of endogenous hydrogen and exogenous hydrogen.
Hydrogen embrittlement is a phenomenon that causes brittle failure of metal materials under the combined action of hydrogen and stress, and is extremely harmful to steel parts, particularly high-strength steel. Hydrogen in steel is divided into two parts, endogenous and exogenous. The hydrogen solubility is reduced along with the temperature reduction, so that the hydrogen which is not diffused out can be accumulated in the steel to become endogenous hydrogen. When the steel piece is processed and used in the follow-up process, hydrogen ions and the like can be diffused from the surface of the steel piece to the inside of the steel in a hydrogen-rich environment, become exogenous hydrogen, and cause hydrogen embrittlement together with the endogenous hydrogen. The non-quenched and tempered steel for direct cutting with the super-large section has large cross section area, does not undergo hot working processes such as hot forging, heat treatment and the like after being formed, and has long diffusion distance of endogenous hydrogen outwards, short time and high hydrogen embrittlement risk. The potential for hydrogen embrittlement is further increased if the working environment of the steel is more acidic. Therefore, under the condition of reasonable cost control, the reduction of the risk of hydrogen embrittlement is the safety guarantee of further developing the non-quenched and tempered steel for direct cutting with higher strength and larger sectional area.
In addition to the strict control of hydrogen brought by the solidification process in steel making, adding carbonitrides of microalloy elements such as Nb, V, ti and the like to the steel to increase the number of hydrogen traps is an important method for avoiding hydrogen embrittlement. Dislocation, crystal boundary, phase boundary of second phase particles and matrix are all common hydrogen traps, and hydrogen atoms can be captured and fixed by utilizing the lattice defects, so that the phenomenon that the hydrogen atoms are combined into hydrogen molecules to gather to cause steel cracking is avoided. The larger the lattice defect, the greater the number of hydrogen traps. The second phase particles, especially the non-coherent precipitated phase with larger mismatch degree with the matrix, have large defect density, more hydrogen traps and strongest effect of avoiding hydrogen embrittlement. Chinese patent publication No. CN114645222A obtains high-density nano micro-alloy precipitate by adding micro-alloy elements with mass ratio less than or equal to 1.0% and controlling the proportion of Nb and V elements, and simultaneously improves the mechanical property and hydrogen embrittlement resistance of 40CrNiMo quenched and tempered steel. Chinese patent publication No. CN114908302A improves the strength and hydrogen embrittlement resistance of high strength spring steel by adding 1.3-2.0% of copper and 0.9-1.3% of aluminum to form 2-10nm of B2 structure NiAl and BCC structure Cu. Chinese patent publication No. CN112522610A optimizes and controls V, ti the size of precipitated phase by regulating and controlling forging process, and optimizes the hydrogen embrittlement resistance of the bainite non-quenched and tempered steel. However, no report has been found on improvement of the hydrogen embrittlement resistance of ferrite-pearlite type non-quenched and tempered steel. In addition, the micro-alloy elements or the impurity elements such as Cu and Al of which the content is more than 0.4% or 1% are added in the above patents, so that the cost is obviously increased, and the technological property and mechanical property stability of the steel are difficult to ensure. The Chinese patent ZL201410200432.7 finds that the Cu-containing precipitated phase with a B2 structure with nano size can be precipitated in the silicon steel added with 0.1-0.3% of Cu, so that the magnetic property of the non-oriented silicon steel is improved. It is explained that the addition of less impurity Cu element in the steel also makes it possible to form a second phase to improve the hydrogen embrittlement resistance.
The surface of the steel piece is oxidized to generate a compact protective film which can prevent the entry of exogenous hydrogen to a certain extent. Stainless steel, i.e., a dense oxide film formed by adding at least 10.5% Cr, plays a role in rust prevention and hydrogen prevention, but is too costly. Cu with the concentration of 0.15-0.25% is added into the weathering steel generally, a passivation film is formed on the surface of the steel piece so as to play a role in resisting common atmospheric corrosion, and Cu is generally an impurity element in the steel and has low cost. However, the effect of preventing hydrogen embrittlement by utilizing the effect that Cu is easy to form a weather-proof passivation film on the surface of a steel member has not been seen.
Therefore, the invention provides a method for directly cutting non-quenched and tempered steel by ferrite-pearlite with super-large section, which not only saves cost, but also can effectively avoid hydrogen embrittlement.
Disclosure of Invention
The invention aims to solve the technical problem that the ultra-large section ferrite-pearlite type direct cutting non-quenched and tempered steel with hydrogen embrittlement resistance is obtained by optimizing the type and the quantity of hydrogen traps and inhibiting the diffusion of exogenous hydrogen elements on the basis of not obviously increasing the cost of the existing alloy elements.
Simultaneously, the invention provides a preparation method of non-quenched and tempered steel for direct cutting with a very large section, which has low cost and hydrogen embrittlement resistance, and the method is characterized in that the content and the proportion of V, nb, ti, N are controlled, a proper amount of Cu element is added, and a rolling and cooling control process is combined, so that more VCx precipitated phases with stronger hydrogen capturing capability and copper-containing precipitated phases with a B2 structure are obtained as hydrogen traps on the premise of not obviously improving the alloy cost, and the hydrogen embrittlement hazard of endogenous hydrogen is reduced; by forming a passivation film on the surface of the steel part, the self-healing trend of the steel part is improved, and the damage of hydrogen embrittlement caused by the entering of exogenous hydrogen is prevented, so that the hydrogen embrittlement resistance of the non-quenched and tempered steel for direct cutting of the oversized section with the diameter of 160-300mm is improved.
Meanwhile, the invention provides application of the non-quenched and tempered steel for direct cutting of the oversized-section with low cost and hydrogen embrittlement resistance in a large-scale high-strength steel member.
In order to solve the technical problems, the invention adopts the following technical scheme:
a preparation method of low-cost hydrogen embrittlement-resistant non-quenched and tempered steel for direct cutting of oversized cross section comprises the following steps:
s1: the smelting raw materials mainly comprise scrap steel, and after the Cu element content of molten steel is measured at the final smelting stage, fine copper wires with the diameter of 0.5-2.0 mm are uniformly fed to reach the target Cu content; the target Cu content is: the mass percentage of Cu is 0.25-0.45%; other element control targets are: c:0.30 to 0.50 percent, si:0.35 to 0.65 percent, mn:1.20 to 1.60 percent, V:0.10 to 0.20 percent, nb is less than or equal to 0.01 percent, ti:0.010% -0.050%, N:0.005% -0.008%, S:0.01 to 0.03 percent, and P is less than or equal to 0.02 percent; the mass percentage ratio of Ti to N is more than 3.4;
s2: the temperature of a soaking section in the heating process of the continuous casting billet is 1200-1220 ℃, and the heat preservation time is 5-7 h; the continuous casting blank is a rectangular blank with the section side length of 400-1200 mm;
s3: after the continuous casting billet is discharged from the furnace, high-pressure water is used for descaling, surface oxide skin is removed, and rolling is started immediately; the first 8-10 passes, the reduction of each pass is 50-80mm, and the high-pressure air gun is used for removing the oxide skin on the surface of the billet before each pass of rolling from the second pass; the subsequent pass is not required until a square intermediate blank with the cross section side length of 200-500 mm is rolled;
s4: the intermediate billet is descaled by high-pressure water again when the temperature of the intermediate billet reaches 920-980 ℃, then is rolled into round steel with the diameter of 160-300mm by a finish continuous rolling machine, and the final rolling temperature is 850-880 ℃;
s5: cooling the round steel by passing through water after finishing rolling, cooling to 650-700 ℃ on the surface by 2-3 groups of strong water cooling, and inserting air cooling to return temperature during the period, wherein the surface temperature of each group of strong water cooling round steel after returning temperature is not more than 100 ℃;
s6: slowly cooling the round steel to the surface of 600-620 ℃ by using a heat preservation cover, spraying and cooling the round steel to the surface of 520-550 ℃ by using water mist, and keeping the surface of the round steel at the temperature of 520-550 ℃ for 1-2 min;
s7: cooling the round steel with a straightening function by a stepping cooling bed to 300-350 ℃ on the surface, putting the round steel into a pit, and preserving heat for at least 48 hours to obtain a finished product.
Preferably, during the slow cooling of S6, a copper-containing precipitated phase of B2 structure is formed.
Preferably, the water pressure of the high-pressure water descaling is 30MPa, the pressure of the high-pressure air gun is 20-30 MPa, and the gas of the high-pressure air gun is compressed air.
A non-quenched and tempered steel for direct cutting with ultra-large section, which is low in cost and hydrogen embrittlement resistance, is prepared by the preparation method.
Preferably, the mass percentage of Nb is less than or equal to 0.004 percent.
Preferably, the mass percentage of Cu is 0.30-0.40%.
Preferably, the mass percentage of S is 0.01-0.02%.
Preferably, the mass percentage of Ti is 0.020% -0.028%.
The 1/3 radius longitudinal tensile strength of the finished product is 900-1050 MPa, the yield strength is 650-800 MPa, the elongation after breaking is 15-17%, and the impact power KU is high 2 45～50J。
The non-quenched and tempered steel is applied to large-scale high-strength steel members.
The large-scale high-strength steel member comprises a push rod, a hydraulic upright post, a single crystal furnace upright post, a shaft part for wind power or a large-section power shaft. The selection of the components of the steel billet is based on the following steps:
v: carbonitrides are formed, creating a second phase for strengthening and also acting as hydrogen traps. The more V element in the ferrite-pearlite type non-quenched and tempered steel, the higher the strength grade of the steel, generally about 0.1%. However, after the non-quenched and tempered steel with the oversized section is rolled, the cooling speed is low, the carbonitride of V is easy to gather and grow up, and the V content needs to be properly increased to avoid the strength reduction. The lattice constant of {111} plane of VN and that of {110} plane of ferrite matrix are both 0.204nm, so that a coherent interface is easily formed; and VCx (VCx is V) 2 C and/or V 4 C 3 ) The lattice constant of the alloy is not similar to that of ferrite, only a non-coherent interface can be formed, and the hydrogen trapping effect is stronger. And simultaneously, the VCx precipitation temperature is lower than VN, the dispersion is finer, and the strengthening effect is stronger. It is therefore desirable that most of V precipitates as fine dispersed VCx to ensure strength and hydrogen embrittlement resistance. Therefore, the V element content of the invention is 0.10-0.20%.
Nb: some non-quenched and tempered steels have Nb added at about 0.02% to raise the recrystallization temperature of austenite and thereby refine the room temperature structure. However, nb has a large atomic weight, slowly diffuses in steel, and easily forms a large-sized precipitated phase, and at the same time induces V to form a composite carbonitride with it, thereby significantly reducing the amount of V (C, N) precipitated and the number of hydrogen traps, and requiring strict control of Nb element content. In addition, the cost of Nb is obviously higher than that of other elements, and the reduction of the addition of Nb is also beneficial to the reduction of the raw material cost of the non-quenched and tempered steel. Therefore, the Nb element content is less than or equal to 0.01 percent. Preferably, the mass percentage of Nb is less than or equal to 0.004 percent.
Ti: form stable carbon nitride, refine and heat and austenite crystal grain in the rough rolling process, further refine room temperature structure and improve toughness. The super-large section non-quenched and tempered steel continuous casting blank has large section size, high temperature and long time for heat penetration, so Ti is required to ensure that grains are not coarsened in the heating process. In addition, ti can fix N element, and ensure that V with lower precipitation temperature is precipitated in a VCx form. TiN itself is also a hydrogen trap and can also act to suppress hydrogen embrittlement. Therefore, the Ti element content of the invention is 0.010-0.050%. Preferably, the mass percentage of Ti is 0.020-0.028%.
N: combined with microalloying elements to form more stable nitrides, with TiN, nbN being more used for grain refinement and VN being more used for precipitation strengthening. However, since nitrides have a higher precipitation temperature and a larger size than carbides, strengthening and hydrogen trapping are weak. The N element is added into the non-quenched and tempered steel to convert TiC in the steel into TiN, so that the solid solution temperature of the steel is improved, and the effect of refining grains during heating of a continuous casting blank is ensured. The atomic weight ratio of Ti to N is 3.4, and in order to obtain more VCx, N is ensured to be fixed by Ti as much as possible, and the mass percent ratio of Ti to N is more than 3.4. Therefore, the N element content of the invention is 0.005-0.008%. Preferably, the Ti/N mass percent ratio is > 3.4.
Cu: are generally considered as detrimental elements in steel, which are enriched in scrap steel due to the inability of the steelmaking process to oxidize. When the Cu element content exceeds 0.25%, surface defects are likely to occur during hot working. Cu with the content of less than 0.25% is often added into the weathering steel, so that a passivation layer is formed on the surface of the steel piece, and corrosion resistance is improved. The strength of the steel grade is improved by adding Cu element to form a precipitated phase, and the cost is low. Cu is usually precipitated in the steel in the sequence of bcc→b2→fcc with the best BCC structure strengthening but lowest degree of mismatching and the weakest FCC structure strengthening but highest degree of mismatching, with the B2 structure centered. After Cu element is added, the copper-containing precipitated phase of the B2 structure is precipitated when the round steel is transformed from austenite to ferrite, so that the strength is improved and a hydrogen trap is provided. Meanwhile, a thin passivation film is formed on the surface of the steel in the hot working and using processes of the steel, so that exogenous hydrogen is prevented from entering the steel, and hydrogen embrittlement is avoided in the using process of the steel piece. The copper-containing precipitated phase of the B2 structure can also improve the driving force of solid solution Cu element precipitation on the surface, and once the passivation film is broken, the self-repairing speed of the passivation film of the part is faster. Therefore, in order to improve the hydrogen embrittlement resistance and strength of the non-quenched and tempered steel with the oversized section, the Cu content needs to be further improved to be more than 0.25%. In order to alleviate defects on the surface in the rolling process, the Cu content is not too high, so that the Cu element content is 0.025-0.045 percent. Preferably, the mass percentage of Cu is 0.030-0.040%.
P, sn, sb: impurity elements in steel promote hydrogen embrittlement and are required to be strictly controlled. The content of the P element in the invention is not more than 0.02%. Preferably, the sum of the mass percentages of P, sn and Sb is not more than 0.02%.
The invention discloses a steel billet hot working method, which comprises the following steps:
smelting: the Cu element is enriched in steel, so that the scrap steel is mainly selected for smelting to improve the copper content of the molten steel base, reduce the addition of pure copper and reduce the cost. In addition, after the Cu element content of molten steel is measured at the final stage of smelting, pure copper is added according to the Cu content notch. In order to ensure that the Cu element does not generate macrosegregation, fine copper wires with the diameter of 0.5-2.0 mm are required to be evenly fed.
And (3) heating the continuous casting billet: the section of the continuous casting blank used for the non-quenched and tempered steel with the oversized section is also quite large, and the heat preservation time also needs to be properly prolonged. In order to avoid surface cracking caused by Cu segregation in grain boundaries due to excessive heating temperature, the soaking section temperature of the continuous casting billet is slightly reduced to 1200-1220 ℃, and the heat preservation time is 5-7h.
Rough rolling: because the content of Cu element is high, defects are easy to generate on the surface of the steel billet. Therefore, it is necessary to remove the scale continuously, and to prevent the surface of the billet from being broken and pressed during the rolling of the scale, thereby further promoting the occurrence of surface defects. Therefore, the continuous casting billet water descaling needs to be removed and rolled quickly, so that oxide skin is prevented from being newly generated. And the single-pass secondary deformation is properly controlled in the rolling process, so that the surface defects caused by the deformation of large deformation are reduced. Thus, the reduction of each pass of 8-10 before the invention is 50-80mm. In order to avoid the defect of the surface of the billet caused by the oxide skin generated in the rolling process, the oxide skin on the surface of the billet is removed by using a high-pressure air gun before each pass of rolling from the second pass. The subsequent pass is not required due to small deformation.
And (3) finish rolling: in order to ensure that the oxide skin of the intermediate billet does not cause surface defects, high-pressure water is used for descaling when entering finish rolling. In order to ensure fine bar tissue and improve toughness, the invention requires initial rolling at 950 ℃ and final rolling at 850-880 ℃.
Cooling after rolling: both VCx and copper-containing precipitate phases began to precipitate after finish rolling. The precipitation temperature is high, the size of the precipitation phase is large, and the precipitation strengthening and the improvement of the hydrogen trap density are not facilitated. The phase-to-phase precipitation mode generated in the process of converting austenite into ferrite has larger precipitation power, and the precipitated phase is finer and uniformly distributed. The inter-phase precipitation temperature interval of the component non-quenched and tempered steel is 700-800 ℃, and the core part of the bar is generally 100 ℃ higher than the surface. Therefore, the steel bar is rapidly cooled by water after finish rolling, the interior of the steel bar is promoted to be reduced to 700-800 ℃, and the steel bar is slowly cooled in the temperature range, so that interphase precipitation is promoted to fully occur. The round steel is cooled to 650-700 ℃ by passing through water after final rolling, and air cooling is carried out in a penetrating way during the period of 2-3 groups of strong water cooling until the temperature is returned, wherein the temperature return time is 5-10s each time, the temperature is returned between every two groups of water tanks, and the surface temperature of the round steel subjected to the temperature return by each group of strong water cooling is not more than 100 ℃. The round steel is slowly cooled to the surface of 600-620 ℃ by using a heat preservation cover. The process ensures that the interior of the bar is fully separated out at the temperature range of 700-800 ℃ to obtain uniformly distributed fine VCx and copper-containing precipitated phases, and simultaneously avoids the occurrence of supercooling transformation structures such as bainite and the like on the surface of round steel. And then the water mist is sprayed and cooled to the surface of about 550 ℃, the surface of the round steel is maintained at 520-550 ℃ for about 1-2min, unconverted austenite is converted into fine lamellar pearlite instead of coarse lamellar pearlite, bainite and other unbalanced structures, and the structural uniformity and the toughness of the cross section of the round steel are improved.
The invention has the beneficial effects that:
(1) Strictly controlling the content and proportion of the microalloy elements Ti, nb and N; n is completely combined with Ti element as much as possible, and meanwhile, the composite precipitation of V and Nb is avoided, so that V is precipitated in a non-coherent VCx form; and simultaneously, the precipitation temperature of VCx is lower, and the precipitated phase is more finely dispersed (about 5nm single), so that more hydrogen traps are obtained.
(2) And a proper amount of Cu element is added, so that a large amount of copper-containing precipitated phases (about 5nm single particles and a plurality of particles are agglomerated into a worm shape) of the B2 structure are precipitated in an interphase precipitation mode in the process of converting austenite into ferrite (namely, the process of slowly cooling the steel surface from 650-700 ℃ to 600-620 ℃ by using a heat preservation cover in S6), thereby playing a role in strengthening and increasing hydrogen traps.
(3) The Cu element in solid solution can form an extremely thin passivation film on the surface of the round steel, so that the diffusion of external hydrogen elements into the steel during the use of the steel piece is prevented, and the content of external hydrogen is reduced. Meanwhile, the passivation film also enables the steel piece to have good weather resistance. In the use process, once the passivation film is damaged, the copper-containing precipitated phase of the B2 structure can promote the passivation film to be formed more quickly, and the self-repairing process of the passivation film is accelerated.
(4) Aiming at the non-quenched and tempered steel for direct cutting with the oversized section with the diameter of 160-300mm, which is required to be used in a weak acid environment, the invention can ensure enough grain refining effect and precipitation strengthening effect by regulating and controlling the content and proportion of Ti, nb, V, N element on the premise of not obviously increasing the cost of alloy elements, thereby improving the quantity of VCx with stronger capability of capturing and fixing hydrogen atoms and reducing the quantity of endogenous hydrogen as much as possible. Thereby achieving the effect of improving the toughness and the hydrogen embrittlement resistance of the non-quenched and tempered steel for direct cutting with an oversized section.
(5) According to the invention, by increasing the content of Cu element, a large amount of copper-containing precipitated phases with fine and dispersed B2 structures are formed in steel, and the effects of hydrogen trapping and precipitation strengthening are increased. Meanwhile, an extremely thin passivation film is formed on the surface of the steel part in the use process of the steel part, so that the diffusion of external hydrogen elements into the steel is prevented when the steel part is used, and the content of external hydrogen is reduced. Further reducing the possibility of hydrogen embrittlement of the steel member during use. Meanwhile, the passivation film can also improve the weather resistance of the steel piece.
The invention discloses a low-cost hydrogen embrittlement-resistant non-quenched and tempered steel for direct cutting with an oversized section and a preparation process thereof, wherein the content and the proportion of V, nb, ti, N are controlled, a proper amount of Cu element is added, and simultaneously, a rolling control and cooling control process is combined, so that more VCx precipitated phases with stronger hydrogen capturing capacity and copper-containing precipitated phases with B2 structures are obtained as hydrogen traps on the premise of not obviously improving the alloy cost, and the hydrogen embrittlement hazard of endogenous hydrogen is reduced; by forming a passivation film on the surface of the steel part, the self-healing trend of the steel part is improved, and the exogenous hydrogen is prevented from entering to form hydrogen embrittlement hazard. Thereby improving the hydrogen embrittlement resistance of the non-quenched and tempered steel for direct cutting with the oversized section with the diameter of 160-300 mm.
Drawings
FIG. 1 is a graph showing the austenite stability interval obtained by computer simulation of the composition of the rolled stock of example 1;
FIG. 2 is a graph of the lamellar spacing of pearlite at the 1/3 radius position of the rolled stock of example 1;
FIG. 3 is a plot of copper-containing precipitate phases and diffraction spots of the precipitate phases for the 1/3 radius position B2 structure of the rolled stock of example 1;
FIG. 4 is a graph showing the analysis of the composition of the 1/3 radial position VCx of the rolled stock of example 1.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more clear, the present invention will be described in further detail with reference to the accompanying drawings, comparative examples and examples. The specific embodiments described herein are to be considered in an illustrative sense only and are not intended to limit the invention.
A low-cost hydrogen embrittlement resistant non-quenched and tempered steel for direct cutting with an oversized section has chemical compositions shown in Table 1.
TABLE 1 chemical composition (wt%) (balance Fe and impurity elements)
Wherein the rolling processes of comparative example 1 and example 1 are both: soaking the continuous casting blank at 1210 ℃ for 6 hours, removing scales and surface oxide skin by high-pressure water after discharging, and then starting rolling. The reduction of each pass of the first 8 passes is 60mm, the second pass is started, and a high-pressure air gun is used for removing the surface oxide skin of the billet before each pass of rolling. And rolling to a square billet of 320mm by a subsequent rough rolling process. And (3) when the intermediate billet is heated to the surface 950 ℃, removing scales by using high-pressure water again, and then rolling into round steel with the diameter of 200mm by using a finish continuous rolling machine, wherein the final rolling temperature is 850 ℃. And (3) cooling by passing through water after finishing rolling, cooling to 680 ℃ on the surface by 2 groups of strong water cooling, and inserting air cooling for temperature returning for 5s each time, wherein the temperature returning is carried out between every two groups of water tanks, and the surface temperature of each group of strong water cooling round steel after temperature returning is not more than 100 ℃. When the round steel is slowly cooled to 600 ℃ on the surface by using a heat preservation cover, the water mist is sprayed and cooled to 550 ℃ on the surface, and the surface of the round steel is maintained at 540 ℃ for about 2min. Then cooling the round steel with a step cooling bed with straightening function to the surface of 330 ℃ and then putting the round steel into a pit, and preserving heat for 48 hours to obtain a finished product.
As shown in fig. 1, the austenite stable existence region obtained by computer simulation for the rolled material composition is, as can be seen from fig. 1, the inter-phase precipitation temperature region is: and after finishing rolling, both VCx and copper-containing precipitated phases start to be precipitated, wherein the temperature of the precipitation is high (850 ℃), and the size of the precipitated phases is large, so that the precipitation strengthening and the increase of the hydrogen trap density are not facilitated. The phase-to-phase precipitation mode generated in the process of converting austenite into ferrite has larger precipitation power, and the precipitated phase is finer and uniformly distributed. The inter-phase precipitation temperature interval of the non-quenched and tempered steel of the components of the invention is 700-800 ℃, and the core part of the bar is generally 100 ℃ higher than the surface. Therefore, the steel bar is rapidly cooled by water after finish rolling, the interior of the steel bar is promoted to be reduced to 700-800 ℃, and the steel bar is slowly cooled in the temperature range, so that interphase precipitation is promoted to fully occur. The round steel is cooled to 680 ℃ by passing through water after finish rolling, air cooling is alternated during the period of 2 groups of strong water cooling to return temperature, the temperature return time is 5s each time, the temperature return is carried out between every two groups of water tanks, and the surface temperature of each group of strong water cooling round steel after temperature return is not more than 100 ℃; slowly cooling round steel to 600 ℃ on the surface by using a heat-insulating cover; the process ensures that the inside of the bar is fully subjected to interphase precipitation in the temperature range of 700-800 ℃, as shown in fig. 3 and 4, the uniformly distributed fine VCx and copper-containing precipitation phases are obtained, and meanwhile, the supercooling transformation structures such as bainite and the like are avoided on the surface of the round steel. As shown in fig. 3, the copper-containing precipitated phase of the B2 structure is a metastable phase, the composition is close to Cu: fe=1:1, the particle size is about 5nm, but often several particles are stuck together, and since the copper-containing precipitated phase of the B2 structure is unstable, cu in solid solution in the matrix will reform the passivation film after the surface passivation film is broken. The B2 phase releases Cu into the solid solution, so that the solid solubility of Cu is not reduced, and the formation of a passivation film is promoted. In addition, after the passivation film of the common weathering steel is broken, the solid-solution copper can form the passivation film again, but the solid-solution copper content around the common weathering steel can be reduced, the driving force for forming the film can be reduced, and the time for forming the passivation film after the subsequent breakage can be prolonged. The invention forms a B2 precipitated phase, the B2 precipitated phase can be used as a copper reservoir, and the solid-solution copper element is continuously supplemented to the matrix, so that the driving force for forming the passivation film is not reduced. The present invention can accelerate the self-repairing process. After slow cooling, the water mist is sprayed and cooled to the surface of about 550 ℃, and the surface of the round steel is maintained at 540 ℃ for about 2min, so that unconverted austenite is converted into fine lamellar pearlite instead of coarse lamellar pearlite, bainite and other unbalanced structures as shown in fig. 2, and the structural uniformity and toughness of the cross section of the round steel are improved.
The rolling process of comparative example 2 is: soaking the continuous casting blank at 1210 ℃ for 6 hours, removing scales and surface oxide skin by high-pressure water after discharging, and then starting rolling. The reduction of each pass of the first 8 passes is 60mm, the second pass is started, and a high-pressure air gun is used for removing the surface oxide skin of the billet before each pass of rolling. And rolling to a square billet of 320mm by a subsequent rough rolling process. And (3) when the intermediate billet is heated to the surface 950 ℃, removing scales by using high-pressure water again, and then rolling into round steel with the diameter of 200mm by using a finish continuous rolling machine, wherein the final rolling temperature is 850 ℃. And (3) cooling by passing through water after finish rolling, cooling to the surface of 550 ℃ by 6 groups of strong water cooling, and inserting air cooling for temperature returning for 5s each time, wherein the temperature returning is carried out between every two groups of water tanks, and the surface temperature of each group of strong water cooling round steel after temperature returning is not more than 100 ℃. Then cooling the round steel with a step cooling bed with a straightening function to the surface of 350 ℃, putting the round steel into a pit, and preserving heat for 48 hours to obtain a finished product.
The rolling process of example 2 is: soaking the continuous casting blank at 1220 ℃ for 7 hours, removing scales and surface oxide skin by high-pressure water after discharging, and then starting rolling. The reduction of each pass of the first 10 passes is 80mm, the second pass is started, and a high-pressure air gun is used for removing the oxide skin on the surface of the billet before each pass of rolling. And rolling to a square billet with the thickness of 450mm by a subsequent rough rolling process. And (3) when the intermediate billet is heated to the surface 950 ℃, removing scales by using high-pressure water again, and then rolling into round steel with the diameter of 290mm by using a finish continuous rolling machine, wherein the final rolling temperature is 880 ℃. And (3) carrying out water cooling after finishing rolling, carrying out strong water cooling to the surface 690 ℃, and carrying out air cooling and temperature returning in a penetrating way, wherein the temperature returning time is 10s each time, the temperature returning can be carried out between every two groups of water tanks, and the surface temperature of each group of strong water cooling round steel after temperature returning is not more than 100 ℃. When the round steel is slowly cooled to the surface 620 ℃ by using a heat preservation cover, the water mist is sprayed and cooled to the surface about 550 ℃, and the surface of the round steel is maintained at 520 ℃ for about 2min. Then cooling the round steel with a step cooling bed with a straightening function to the surface of 350 ℃, putting the round steel into a pit, and preserving heat for 48 hours to obtain a finished product.
Example 3 and example 4 differ from example 1 only in the diameter of the final rolled round steel.
In order to characterize the mechanical property and hydrogen embrittlement resistance of the material, a standard tensile sample is taken at the 1/3 radius position of round steel for tensile test, a notch tensile sample is taken, a notch is placed in Walpole corrosion inhibition liquid (hydrochloric acid, sodium acetate and deionized water) for constant load notch tensile test, and the notch tensile delay fracture strength ratio DFSR before and after hydrogen charging is measured. The higher the DFSR value, the stronger the hydrogen embrittlement resistance of the material. Table 2 shows the DFSR values of the mechanical properties and the ratio of the delayed fracture strength of the comparative examples and examples. The mechanical properties of examples 1-4 were not greatly changed, but the hydrogen embrittlement resistance (DFSR) was significantly improved, compared to comparative examples 1 and 2.
TABLE 2 mechanical Properties and delayed fracture Strength ratio
Example 5
A preparation method of low-cost hydrogen embrittlement-resistant non-quenched and tempered steel for direct cutting of oversized cross section comprises the following steps:
the smelting raw materials mainly comprise scrap steel, and fine copper wires with the diameter of 0.5mm are evenly fed after the Cu element content of molten steel is measured at the final smelting stage so as to reach the target Cu content; the target Cu content is: the mass percentage of Cu is 0.30%; soaking the continuous casting blank with the section side length of 800mm multiplied by 1200mm at 1200 ℃ for 5 hours, removing scales and surface oxide skin by high-pressure water after discharging from a furnace, and then starting rolling. The reduction of each pass of the first 9 passes is 50mm, the second pass is started, and a high-pressure air gun is used for removing the surface oxide skin of the billet before each pass of rolling. And rolling to a square billet of 500mm by a subsequent rough rolling process. And (3) when the intermediate billet is heated to 980 ℃ on the surface, removing scales by using high-pressure water again, and then rolling into round steel with the diameter of 300mm by using a finish continuous rolling machine, wherein the final rolling temperature is 860 ℃. And (3) cooling by passing through water after finishing rolling, cooling to the surface 650 ℃ by 2 groups of strong water cooling, and inserting air cooling for temperature returning for 8s each time, wherein the temperature returning time is equal to or less than 100 ℃ after the temperature returning of each group of strong water cooling round steel. When the round steel is slowly cooled to 610 ℃ on the surface by using a heat preservation cover, the round steel is sprayed and cooled to 550 ℃ on the surface by water mist, and the surface of the round steel is maintained at 550 ℃ for about 1min. And then cooling the round steel with a step cooling bed with a straightening function to 300 ℃ on the surface, putting the round steel into a pit, and preserving heat for 50 hours to obtain a finished product.
The low-cost hydrogen embrittlement-resistant non-quenched and tempered steel for direct cutting of oversized cross section comprises the following elements in percentage by mass: 0.30%, si:0.35%, mn:1.20%, V:0.10%, nb:0.004%, ti:0.050%, N:0.005%, cu:0.30%, S:0.01%, P:0.01%, the balance being Fe and unavoidable impurities; ti/N mass percent ratio=10.
The non-quenched and tempered steel of this example is used for large-scale high-strength steel members.
The large high strength steel member includes a pushrod or hydraulic column.
The non-quenched and tempered steel of this example can be used in a weakly acidic environment.
Round steel after rolling has 1/3 radius longitudinal tensile strength of 900MPa, yield strength of 650MPa, elongation after breaking of 15 percent and impact power KU 2 45J。
Example 6:
a preparation method of low-cost hydrogen embrittlement-resistant non-quenched and tempered steel for direct cutting of oversized cross section comprises the following steps:
the smelting raw materials mainly comprise scrap steel, and fine copper wires with the diameter of 2.0mm are evenly fed after the Cu element content of molten steel is measured at the final smelting stage so as to reach the target Cu content; the target Cu content is: the mass percentage of Cu is 0.40%; soaking the continuous casting blank with the section side length of 400mm multiplied by 600mm at 1210 ℃ for 5.5 hours, removing scales and surface oxide skin by high-pressure water after discharging, and then starting rolling. The reduction of each pass of the first 8 passes is 70mm, the second pass is started, and a high-pressure air gun is used for removing the surface oxide skin of the billet before each pass of rolling. And rolling to 200mm square billets by a subsequent rough rolling process. And (3) when the intermediate billet is heated to the surface 920 ℃, removing scales by using high-pressure water again, and then rolling into round steel with the diameter of 160mm by using a finish continuous rolling machine, wherein the final rolling temperature is 870 ℃. And (3) cooling by passing through water after finishing rolling, cooling to the surface 700 ℃ by 3 groups of strong water cooling, and inserting air cooling for temperature returning for 6s each time, wherein the temperature returning is carried out between every two groups of water tanks, and the surface temperature of each group of strong water cooling round steel after temperature returning is not more than 100 ℃. When the round steel is slowly cooled to 615 ℃ on the surface by using a heat preservation cover, the round steel is sprayed and cooled to 520 ℃ on the surface by water mist, and the surface of the round steel is maintained at 520 ℃ for about 1.5min. And then cooling the round steel with a step cooling bed with a straightening function to the surface of 310 ℃ and then putting the round steel into a pit, and preserving heat for 55 hours to obtain a finished product.
The low-cost hydrogen embrittlement-resistant non-quenched and tempered steel for direct cutting of oversized cross section comprises the following elements in percentage by mass: 0.50%, si:0.65%, mn:1.60%, V:0.20%, nb:0.01%, ti:0.018%, N:0.005%, cu:0.40%, S:0.03%, P:0.005%, the balance being Fe and unavoidable impurities; ti/N mass percent ratio = 3.6.
Round steel after rolling with 1/3 radius longitudinal tensile strength of 1050MPa, yield strength of 800MPa, elongation after breaking of 17% and impact power KU 2 50J。
Example 7
This embodiment differs from embodiment 6 only in that:
the low-cost hydrogen embrittlement-resistant non-quenched and tempered steel for direct cutting of oversized cross section comprises the following elements in percentage by mass: 0.44%, si:0.45%, mn:1.55%, V:0.15%, nb:0.003%, ti:0.028%, N:0.008%, cu:0.25%, S:0.02%, P:0.001%, the balance being Fe and unavoidable impurities; ti/N mass percent ratio = 3.5.
Round steel after rolling has 1/3 radius longitudinal tensile strength of 1030MPa, yield strength of 750MPa, elongation after breaking of 16% and impact power KU 2 48J。
Example 8
This embodiment differs from embodiment 6 only in that:
the low-cost hydrogen embrittlement-resistant non-quenched and tempered steel for direct cutting of oversized cross section comprises the following elements in percentage by mass: 0.40%, si:0.50%, mn:1.35%, V:0.15%, nb:0.002%, ti:0.020%, N:0.0055%, cu:0.45%, S:0.015%, P:0.002%, the balance being Fe and unavoidable impurities; ti/N mass percent ratio = 3.6.
Round steel after rolling with 1/3 radius longitudinal tensile strength of 1025MPa, yield strength of 765MPa, elongation after breaking of 16% and impact power KU 2 49J。
It should be appreciated that in the above description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. However, the disclosed method should not be construed as reflecting the intention that: i.e., the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this invention.
While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of the above description, will appreciate that other embodiments are contemplated within the scope of the invention as described herein. Furthermore, it should be noted that the language used in the specification has been principally selected for readability and instructional purposes, and may not have been selected to delineate or circumscribe the inventive subject matter. Accordingly, many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the appended claims. The disclosure of the present invention is intended to be illustrative, but not limiting, of the scope of the invention, which is defined by the appended claims.
The foregoing is only a preferred embodiment of the invention, it being noted that: it will be apparent to those skilled in the art that various modifications and adaptations can be made without departing from the principles of the present invention, and such modifications and adaptations are intended to be comprehended within the scope of the invention.
Claims (8)
1. The preparation method of the non-quenched and tempered steel for direct cutting of the oversized section with low cost and hydrogen embrittlement resistance is characterized by comprising the following steps of:
s1: the smelting raw materials mainly comprise scrap steel, and after the Cu element content of molten steel is measured at the final smelting stage, fine copper wires with the diameter of 0.5-2.0 mm are uniformly fed to reach the target Cu content; the target Cu content is: the mass percentage of Cu is 0.25% -0.45%; other element control targets are: c:0.30% -0.50%, si:0.35% -0.65%, mn:1.20% -1.60%, V:0.10% -0.20%, nb is less than or equal to 0.01%, ti:0.010% -0.050%, N:0.005% -0.008%, S:0.01% -0.03%, P is less than or equal to 0.02%, and the balance is iron and impurity elements; the mass percentage ratio of Ti to N is more than 3.4;
s2: the temperature of a soaking section in the heating process of the continuous casting billet ranges from 1200 ℃ to 1220 ℃, and the heat preservation time ranges from 5 hours to 7 hours; the continuous casting blank is a rectangular blank with the section side length of 400 mm-1200 mm;
s3: after the continuous casting billet is discharged from the furnace, high-pressure water is used for descaling, surface oxide skin is removed, and rolling is started immediately; the rolling method comprises the steps of performing 8-10 times, wherein the rolling reduction of each time is 50-80mm, and removing oxide skin on the surface of a billet by using a high-pressure air gun before rolling each time from the second time; rolling to a square intermediate blank with the cross section side length of 200-500 mm in the subsequent pass;
s4: the intermediate billet is descaled by high-pressure water again when the temperature of the intermediate billet reaches 920-980 ℃, then is rolled into round steel with the diameter of 160-300mm by a finish continuous rolling machine, and the final rolling temperature is 850-880 ℃;
s5: cooling the round steel by passing through water after finishing rolling, cooling to 650-700 ℃ on the surface by 2-3 groups of strong water cooling, and carrying out air cooling and temperature returning in a penetrating way, wherein the temperature returning is carried out between every two groups of water tanks, and the surface temperature of each group of strong water cooling round steel after temperature returning is not more than 100 ℃;
s6: slowly cooling the round steel to the surface of 600-620 ℃ by using a heat preservation cover, spraying and cooling the round steel to the surface of 520-550 ℃ by using water mist, and maintaining the surface of the round steel at the temperature of 520-550 ℃ for 1-2 min;
s7: cooling the round steel with a straightening function by a stepping cooling bed to 300-350 ℃ on the surface, then putting the round steel into a pit, and preserving heat for at least 48 hours to obtain a finished product;
and S6, in the slow cooling process, generating a copper-containing precipitated phase with a B2 structure.
2. The non-quenched and tempered steel for direct cutting with ultra-large section, which is resistant to hydrogen embrittlement at low cost, according to claim 1.
3. The non-quenched and tempered steel as claimed in claim 2, wherein the mass percentage of Nb is not more than 0.004%.
4. The non-quenched and tempered steel according to claim 2, wherein the mass percentage of Cu is 0.30% -0.40%.
5. The non-quenched and tempered steel according to claim 2, wherein the mass percentage of S is 0.01% -0.02%.
6. The non-quenched and tempered steel according to claim 2, wherein the mass percentage of Ti is 0.020% -0.028%.
7. The non-quenched and tempered steel according to claim 2, wherein the 1/3 radius longitudinal tensile strength of the finished product is 900-1050mpa, the yield strength is 650-800 mpa, the elongation after break is 15-17%, and the impact power KU 2 45~50J。
8. The use of the non-quenched and tempered steel as claimed in claim 2 in large-scale high strength steel members,
the large-scale high-strength steel member is characterized by comprising a push rod, a hydraulic upright post or a shaft part for wind power.
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| CN101210298A (en) * | 2006-12-28 | 2008-07-02 | 株式会社神户制钢所 | Steel for high-speed cold working and method for production thereof, and high-speed cold working part and method for production thereof |
| JP2011246784A (en) * | 2010-05-28 | 2011-12-08 | Jfe Steel Corp | Rolled non-heat treated steel bar having excellent strength and toughness and method for producing the same |
| WO2017213166A1 (en) * | 2016-06-07 | 2017-12-14 | 新日鐵住金株式会社 | Rolled steel bar for hot forging |
| CN108246801A (en) * | 2017-12-29 | 2018-07-06 | 钢铁研究总院华东分院 | A kind of big specification non-hardened and tempered steel rolling equipment and its rolling production method |
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| CN101210298A (en) * | 2006-12-28 | 2008-07-02 | 株式会社神户制钢所 | Steel for high-speed cold working and method for production thereof, and high-speed cold working part and method for production thereof |
| JP2011246784A (en) * | 2010-05-28 | 2011-12-08 | Jfe Steel Corp | Rolled non-heat treated steel bar having excellent strength and toughness and method for producing the same |
| WO2017213166A1 (en) * | 2016-06-07 | 2017-12-14 | 新日鐵住金株式会社 | Rolled steel bar for hot forging |
| CN108246801A (en) * | 2017-12-29 | 2018-07-06 | 钢铁研究总院华东分院 | A kind of big specification non-hardened and tempered steel rolling equipment and its rolling production method |
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