CN115747674A - Low-cost hydrogen-embrittlement-resistant non-quenched and tempered steel for direct cutting of super-large cross section and preparation method and application thereof - Google Patents
Low-cost hydrogen-embrittlement-resistant non-quenched and tempered steel for direct cutting of super-large cross 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 directly cutting an oversized section and a preparation method and application thereof.A proper amount of Cu element is added, rolling and cooling are controlled, and on the premise of not obviously improving the alloy cost, more VCx precipitated phases with stronger hydrogen capturing capacity and copper-containing precipitated phases with a B2 structure are obtained as hydrogen traps, so that the hydrogen embrittlement hazard of endogenous hydrogen is reduced; by forming a passive film on the surface of the steel part, the self-healing trend of the steel part is improved, and 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 directly cutting the super-large section with the section diameter exceeding 160 mm.
Description
Technical Field
The invention relates to a low-cost hydrogen embrittlement-resistant non-quenched and tempered steel for directly cutting an oversized section, and a preparation method and application thereof, in particular to a ferrite-pearlite type low-cost hydrogen embrittlement-resistant non-quenched and tempered steel for directly cutting an oversized section, and a preparation method and application thereof, and belongs to the technical field of non-quenched and tempered steel.
Background
The non-quenched and tempered steel for direct cutting can obtain required mechanical properties after rolling, and then can be directly used after cutting, and is mainly used for producing parts such as push rods, hydraulic columns and the like. Compared with quenched and tempered steel, the quenched and tempered steel omits the quenching and tempering process, greatly saves energy consumption and production cost, and is more environment-friendly. As the cross section of the part is increased, the quenched and tempered steel has insufficient hardenability, and the microstructure from the surface to the core is gradually transformed from tempered sorbite to ferrite-pearlite. Not only has large tissue change, but also has obvious difference in section mechanical property. And the non-quenched and tempered steel for direct cutting is a ferrite-pearlite structure, has uniform mechanical property and higher use safety. However, as the cross section of the non-quenched and tempered steel bar increases, the risk of hydrogen embrittlement and fracture increases. Particularly, hydrogen embrittlement and breakage are more easily caused under the combined action of endogenous hydrogen and exogenous hydrogen of parts used in a weakly acidic environment.
Hydrogen embrittlement is a phenomenon that metal materials are brittle and broken under the combined action of hydrogen and stress, and has great harm to steel parts, particularly high-strength steel. The hydrogen in the steel is divided into an endogenous part and an exogenous part. A small amount of hydrogen element is inevitably brought when steel is smelted and solidified, the solubility of hydrogen is reduced along with the temperature reduction, and the hydrogen which cannot be diffused out can be accumulated in steel to become endogenous hydrogen. During the subsequent treatment and use process of the steel piece, in a hydrogen-rich environment, hydrogen ions and the like can also diffuse from the surface of the steel piece to the interior of the steel to become exogenous hydrogen, and the exogenous hydrogen and the endogenous hydrogen jointly cause hydrogen embrittlement. The non-quenched and tempered steel for directly cutting 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 distance and short time for outward diffusion of endogenous hydrogen and large risk of hydrogen embrittlement. The potential for hydrogen embrittlement is further increased if the steel article is subjected to a more acidic environment. Therefore, under the condition of reasonable cost control, reducing the risk of hydrogen embrittlement is the safety guarantee of further developing non-quenched and tempered steel with higher strength and larger sectional area for direct cutting.
In addition to strictly controlling hydrogen brought by the steel-making solidification process, adding carbo-nitrides of microalloy elements such as Nb, V, ti and the like into steel to increase the number of hydrogen traps is an important method for avoiding hydrogen embrittlement. The dislocation, the grain boundary, and the phase boundary of the second phase particle and the matrix are common hydrogen traps, and the hydrogen atoms can be captured and fixed by utilizing the lattice defects, so that the hydrogen atoms are prevented from being combined into hydrogen molecules to be gathered to cause steel cracking. The larger and the greater the number of lattice defects, the stronger the hydrogen trapping effect. The defect density brought by the second phase particles, particularly non-coherent precipitated phases with higher mismatching degree with the matrix is high, more hydrogen traps are provided, and the effect of avoiding hydrogen embrittlement is strongest. Chinese patent publication No. CN114645222A obtains high-density nano microalloy precipitates by adding microalloy elements with the mass ratio of less than or equal to 1.0 percent and controlling the proportion of Nb and V elements, and simultaneously improves the mechanical property and the hydrogen embrittlement resistance of 40CrNiMo quenched and tempered steel. The Chinese patent publication No. CN114908302A is characterized in that 1.3-2.0% of copper and 0.9-1.3% of aluminum are added to form 2-10nm NiAl with a B2 structure and Cu with a BCC structure so as to improve the strength and the hydrogen embrittlement resistance of the high-strength spring steel. The Chinese patent publication No. CN112522610A optimizes the hydrogen embrittlement resistance of bainite non-quenched and tempered steel by regulating and controlling the forging process to optimize the sizes of V and Ti precipitated phases. However, no report has been found on the improvement of the hydrogen embrittlement resistance of ferrite-pearlite type non-quenched and tempered steel. In addition, the above patents all add more than 0.4% of microalloy elements or 1% of impurity elements such as Cu, al and the like, which not only obviously improves the cost, but also makes the stability of the processing property and the mechanical property of the steel difficult to guarantee. Chinese patent ZL201410200432.7 discovered that nano-sized B2-structured Cu-containing precipitated phases can be precipitated in silicon steel with 0.1% -0.3% of Cu added, and the magnetic performance of non-oriented silicon steel is improved. It is shown that the addition of Cu element as an impurity to the steel is less likely to form a second phase to improve the hydrogen embrittlement resistance.
The surface of the steel part is oxidized to generate a compact protective film which can prevent exogenous hydrogen from entering to a certain degree. Stainless steel, i.e., stainless steel having a dense oxide film formed by adding at least 10.5% of Cr, has a rust-proof and hydrogen-proof function, but is too expensive. 0.15 to 0.25 percent of Cu is usually added into the weathering steel, a passive film is formed on the surface of a steel piece to further play a role in resisting common atmospheric corrosion, and the Cu is usually an impurity element in the steel, so that the cost is very low. However, it has not been found that Cu prevents hydrogen embrittlement by easily forming a weather-resistant passive film on the surface of a steel member.
Therefore, the invention provides a method for directly cutting the non-quenched and tempered steel by the ferrite-pearlite type with the oversized section, which not only saves the cost, but also can effectively avoid hydrogen embrittlement.
Disclosure of Invention
The invention aims to solve the technical problem that the extra-large section ferrite-pearlite type direct cutting non-quenched and tempered steel with hydrogen embrittlement resistance is obtained by optimizing the type and the number 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.
Meanwhile, the invention provides a preparation method of the low-cost hydrogen embrittlement-resistant non-quenched and tempered steel for directly cutting the oversized section, which is characterized in that by controlling the content and proportion of V, nb, ti and N, adding a proper amount of Cu element, and combining a controlled rolling and controlled cooling process, on the premise of not obviously improving the alloy cost, more VCx precipitated phases with stronger hydrogen capturing capacity and copper-containing precipitated phases with a B2 structure are obtained as hydrogen traps, so that the hydrogen embrittlement hazard of endogenous hydrogen is reduced; by forming a passive film on the surface of the steel piece and improving the self-healing trend of the steel piece, the hydrogen embrittlement hazard caused by the entering of exogenous hydrogen is prevented, so that the hydrogen embrittlement resistance of the non-quenched and tempered steel for directly cutting the ultra-large section with the diameter of 160-300mm is improved.
Meanwhile, the invention provides application of the low-cost hydrogen-embrittlement-resistant non-quenched and tempered steel for directly cutting the oversized section in a large-sized high-strength steel member.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows:
a preparation method of low-cost hydrogen embrittlement-resistant non-quenched and tempered steel for directly cutting super-large sections comprises the following steps:
s1: the smelting raw materials mainly comprise scrap steel, and fine copper wires with the diameter of 0.5-2.0 mm are uniformly fed after the Cu element content of the molten steel is measured at the final smelting stage so as to reach the target Cu content; the target Cu content was: the mass percent 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 to 0.03 percent of the total weight of the composition, and less than or equal to 0.02 percent of P; 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 billet is a rectangular billet with the section side length of 400 mm-1200 mm;
s3: after the continuous casting billet is discharged from the furnace, descaling by high-pressure water, removing surface oxide skin, and immediately rolling; the rolling reduction of each pass is 50-80mm in the first 8-10 passes, and from the second pass, the surface oxide skin of the billet is removed by using a high-pressure air gun before each pass of rolling; subsequent passes do not require until the blank is rolled into a square intermediate blank with the section side length of 200-500 mm;
s4: when the intermediate billet is heated to 920-980 ℃ on the surface, descaling by using high-pressure water again, and then rolling into round steel with the diameter of 160-300mm by using a finish continuous rolling mill at the finishing temperature of 850-880 ℃;
s5: cooling the round steel after final rolling by water, cooling the round steel to 650-700 ℃ by 2-3 groups of strong water, and alternately cooling the round steel by air for returning the temperature, wherein the surface temperature drop of each group of strong water-cooled round steel after returning the temperature is not more than 100 ℃;
s6: slowly cooling the round steel to 600-620 ℃ on the surface by using a heat-insulating cover, spraying and cooling the round steel to 520-550 ℃ by using water mist, and maintaining the surface of the round steel at 520-550 ℃ for 1-2 min;
s7: cooling the round steel on a stepping cooling bed with the straightening function to 300-350 ℃ of the surface, putting the round steel into a pit, and preserving heat for at least 48h to obtain a finished product.
Preferably, during the slow cooling of S6, a copper-containing precipitate phase of B2 structure is formed.
Preferably, the water pressure for 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 obtained by the preparation method of the low-cost hydrogen-brittleness-resistant non-quenched and tempered steel for directly cutting with the oversized cross section.
Preferably, the mass percent of Nb is less than or equal to 0.004 percent.
Preferably, the mass percent of Cu is 0.30-0.40%.
Preferably, the mass percent of S is 0.01-0.02%.
Preferably, the mass percent 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 fracture is 15-17%, and the impact energy KU 2 45～50J。
The non-quenched and tempered steel of the present invention is applied to large-sized 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 components of the steel billet are selected according to the following:
v: carbonitrides are formed, which produce a second phase that strengthens and may act as a hydrogen trap. The more the element V in the ferrite-pearlite type non-quenched and tempered steel, the higher the strength grade of the steel, generally about 0.1%. However, the cooling speed of the rolled non-quenched and tempered steel with the oversized section is slow, V carbonitrides are easy to gather and grow up, and the strength reduction needs to be avoided by properly increasing the V content. VN lattice constant of {111} plane and ferrite matrix {110} plane are both 0.204nm, easily forming coherent interface; and VCx (VCx is V) 2 C and/or V 4 C 3 ) Has a lattice constant different from that of ferrite, butA non-coherent interface is formed, and the hydrogen trapping effect is stronger. Meanwhile, the VCx precipitation temperature is lower than VN, the VCx precipitation temperature is finer and more dispersive, and the strengthening effect is stronger. Therefore, it is desirable that most of the V be precipitated in the form of finely dispersed VCx to ensure strength and hydrogen embrittlement resistance. Therefore, the content of the V element is 0.10-0.20%.
Nb: some non-quenched and tempered steels are added with about 0.02% of Nb, so that the recrystallization temperature of austenite is increased, and the room temperature structure is refined. However, the Nb has a large atomic weight, diffuses slowly in steel, is liable to form a large-sized precipitate phase, induces V to form composite carbonitride therewith, significantly reduces the precipitation amount of V (C, N) and the number of hydrogen traps, and requires strict control of the content of Nb element. In addition, the cost of the Nb element is obviously higher than that of other elements, and the reduction of the addition of the Nb element is also beneficial to reducing the raw material cost of the non-quenched and tempered steel. Therefore, the content of the Nb element is less than or equal to 0.01 percent. Preferably, the mass percent of Nb is less than or equal to 0.004 percent.
Ti: form stable austenite grains in the processes of carbonitride refined heating and rough rolling, further refine the room temperature structure and improve the toughness. The oversized-section non-quenched and tempered steel continuous casting blank needs Ti to ensure that crystal grains are not coarsened in the heating process due to the large section size, high temperature and long time required by heat penetration. In addition, ti can fix N element, and V with lower precipitation temperature is more precipitated in a VCx form. TiN itself is also a hydrogen trap and can also act to inhibit hydrogen embrittlement. Therefore, the content of Ti element in the invention is 0.010 percent to 0.050 percent. Preferably, the mass percent of Ti is 0.020-0.028%.
N: and combines with microalloy elements to form more stable nitride, wherein TiN and NbN are more used for refining grains, and VN is 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. Adding N element into non-quenched and tempered steel to convert TiC in the steel into TiN, improving the solid solution temperature of the TiN and ensuring the effect of refining grains when a continuous casting billet is heated. The atomic weight ratio of Ti and N elements is 3.4, in order to obtain more VCx, the N element needs to be ensured to be fixed by the Ti element as much as possible, and the mass percentage ratio of Ti to N is more than 3.4. Therefore, the content of the N element is 0.005-0.008%. Preferably, the mass percentage ratio of Ti/N is more than 3.4.
Cu: which are generally considered to be harmful elements in steel, are enriched in scrap steel since the steel making process cannot be oxidized. When the Cu element exceeds 0.25%, surface defects are likely to occur during hot working. Cu of less than 0.25 percent is often added into the weathering steel, and a passivation layer is formed on the surface of the steel piece, so that the corrosion resistance is improved. In some steel grades, the strength 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 desolvation sequential order of BCC → B2 → FCC, the BCC structure strengthens the best but the lowest mismatching degree, the FCC structure strengthens the weakest but the highest, and the B2 structure is centered. After the Cu element is added, a copper-containing precipitated phase of a B2 structure is precipitated when the austenite of the round steel is converted into the ferrite, so that the strength is improved, and a hydrogen trap is provided. Meanwhile, a thin passive 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 inside of the steel, and hydrogen embrittlement of the steel in the using process is avoided. The copper-containing precipitated phase with the B2 structure can also improve the driving force of the solid-solution Cu element precipitated on the surface, and once the passive film is damaged, the self-repairing speed of the passive film of the part is higher. Therefore, in order to improve the hydrogen embrittlement resistance and the 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 percent. In order to reduce the surface defects in the rolling process, the content of Cu is not too high, so that the content of the Cu element is 0.025-0.045%. Preferably, the mass percentage of Cu is 0.030% to 0.040%.
P, sn, sb: the impurity elements in the steel, which promote hydrogen embrittlement, need to be strictly controlled. Therefore, 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 hot processing of the steel billet is based on the following steps:
the smelting process comprises the following steps: the Cu element can be enriched in steel, so scrap steel smelting is mainly selected to improve the content of basic copper in molten steel, the addition of pure copper is reduced, and the cost is reduced. In addition, pure copper is added according to the Cu content gap after the Cu content of the molten steel is measured at the last stage of smelting. In order to ensure that the Cu element does not generate macrosegregation, fine copper wires with the diameter of 0.5-2.0 mm need to be fed uniformly.
And (3) heating the continuous casting blank: the section of a continuous casting billet used by the super-large section non-quenched and tempered steel is also very large, and the heat preservation time needs to be properly prolonged. In order to avoid surface cracking caused by segregation of Cu in grain boundaries due to overhigh heating temperature, the temperature of a soaking section of the continuous casting billet is slightly reduced to 1200-1220 ℃, and the heat preservation time is 5-7h.
Rough rolling process: since the Cu element content is high, defects are easily generated on the surface of the billet. Therefore, it is necessary to remove the scale continuously to prevent the scale from being broken and pressed into the surface of the slab during the rolling process, thereby further promoting the generation of surface defects. Therefore, the continuous casting billet water descaling needs to be cleaned and rolled quickly, and new scale formation is prevented. The single-pass deformation is properly controlled in the rolling process, and the surface defects caused by large deformation are reduced. Therefore, the reduction of each pass of 8-10 is 50-80mm before the invention. In order to avoid the scale produced in the rolling process from causing surface defects of the steel billet, a high-pressure air gun is used for removing the scale on the surface of the steel billet before each rolling from the second pass. And the subsequent pass does not need to be carried out due to small deformation.
A finish rolling process: and 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 finish rolling is carried out. In order to ensure the fine structure of the bar and improve the obdurability, the invention requires the initial rolling at 950 ℃ and the final rolling at 850-880 ℃.
Cooling after rolling: after the final rolling, VCx and copper-containing precipitated phases both begin to precipitate. The precipitation temperature is high, the size of the precipitated phase is large, and the precipitation strengthening and the hydrogen trap density improvement are not facilitated. And the interphase precipitation mode generated in the process of transforming from austenite to ferrite has larger precipitation power, and the precipitated phase is finer and is distributed uniformly. The interphase precipitation temperature range of the non-quenched and tempered steel of the components of the invention is 700-800 ℃, and the specific surface of the core of the bar is generally 100 ℃. Therefore, after finish rolling, the bar is rapidly cooled by water, so that the interior of the bar is reduced to 700-800 ℃, and the bar is slowly cooled in the temperature range, so that the sufficient generation of interphase precipitation is promoted. The steel bar is cooled through water after final rolling, 2-3 groups of strong water cooling are carried out until the surface temperature is 650-700 ℃, air cooling and temperature returning are carried out alternately, the temperature returning time is 5-10s each time, the temperature returning is carried out between every two groups of water tanks, and the surface temperature drop of each group of strong water cooling steel bar after temperature returning is not more than 100 ℃. The round steel is slowly cooled to 600-620 ℃ on the surface by using a heat-preserving cover. The process enables interphase precipitation to fully occur in the bar material within the temperature range of 700-800 ℃, so as to obtain uniformly distributed fine VCx and copper-containing precipitated phases and simultaneously avoid the supercooling transformation structures such as bainite and the like from appearing on the surface of the round steel. And then spraying and cooling the water mist to the surface of about 550 ℃, maintaining the surface of the round steel at 520-550 ℃ for about 1-2min, converting the unconverted austenite into non-equilibrium structures such as lamellar pearlite instead of coarse lamellar pearlite and bainite, and improving the structural uniformity and toughness of the section of the round steel.
The invention has the beneficial effects that:
(1) Strictly controlling the contents and proportions of the microalloy elements Ti, nb and N; n is completely combined with Ti element as much as possible, and composite precipitation of V and Nb is avoided, so that V is precipitated in a non-coherent VCx form; meanwhile, the precipitation temperature of VCx is lower, and the precipitated phase is more fine and dispersed (about 5nm of single particle), 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 (single particles are about 5nm, and a plurality of particles are agglomerated into a worm shape) with a B2 structure are precipitated in a phase-to-phase precipitation mode in the transformation process of austenite to ferrite (namely the process of slowly cooling from 650-700 ℃ to 600-620 ℃ on the surface of the steel by using a heat-insulating cover in S6), and the strengthening effect and the function of increasing hydrogen traps are achieved.
(3) The solid-dissolved Cu element can form a layer of extremely thin passive film on the surface of the round steel, so that the diffusion of external hydrogen elements into the steel is prevented when the steel is used, and the content of exogenous hydrogen is reduced. Meanwhile, the passive film layer also enables the steel part to have better weather resistance. Once the passivation film is damaged in the use process, 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 with the diameter of 160-300mm, which needs to be used in a weakly acidic environment, for direct cutting, the invention ensures sufficient grain refining effect and precipitation strengthening effect by regulating and controlling the content and proportion of Ti, nb, V and N elements on the premise of not obviously increasing the cost of alloy elements, improves the quantity of VCx with stronger capability of capturing and fixing hydrogen atoms as much as possible, and reduces the quantity of endogenous hydrogen. Thereby achieving the effect of simultaneously improving the strength and toughness and the hydrogen embrittlement resistance of the non-quenched and tempered steel for directly cutting the super-large section.
(5) According to the invention, a large amount of fine and dispersed copper-containing precipitated phases with B2 structures are formed in the steel by increasing the content of Cu, so that the hydrogen trap and precipitation strengthening effects are increased. Meanwhile, a layer of extremely thin passive film is formed on the surface of the steel piece in the use process of the steel piece, so that the diffusion of external hydrogen elements into the steel is prevented when the steel piece is used, and the content of exogenous hydrogen is reduced. Further reducing the possibility of hydrogen embrittlement of the steel piece in the using process. Meanwhile, the layer of passive film can also improve the weather resistance of the steel part.
The invention discloses a low-cost hydrogen embrittlement-resistant non-quenched and tempered steel for directly cutting an oversized section and a preparation process thereof, wherein more VCx precipitated phases with stronger hydrogen capturing capacity and copper-containing precipitated phases with a B2 structure are obtained as hydrogen traps on the premise of not obviously improving the alloy cost by controlling the content and proportion of V, nb, ti and N, adding a proper amount of Cu elements and combining a controlled rolling and controlled cooling process, so that the hydrogen embrittlement hazard of endogenous hydrogen is reduced; by forming a passive film on the surface of the steel part, the self-healing trend of the steel part is improved, and exogenous hydrogen is prevented from entering to form hydrogen embrittlement hazard. Thereby improving the hydrogen embrittlement resistance of the non-quenched and tempered steel with the diameter of 160-300mm for directly cutting the super-large section.
Drawings
FIG. 1 is a graph of austenite stable existence intervals obtained by computer simulation of the composition of a rolled material according to example 1;
FIG. 2 is a graph showing the pearlite interlamellar spacing at a 1/3 radial position of a rolled material of example 1;
FIG. 3 is a graph showing diffraction spots of a copper-containing precipitate phase and a precipitate phase in the structure at a radial position B2 of 1/3 of a rolled material in example 1;
FIG. 4 is a graph showing the radial position VCx of 1/3 of the rolled stock of example 1 and the composition thereof.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings, comparative examples and examples. The specific embodiments described herein are merely illustrative of the invention and do not delimit the invention.
A low-cost hydrogen embrittlement-resistant non-quenched and tempered steel for directly cutting with an oversized section has chemical components shown in a table 1.
TABLE 1 chemical composition (wt%) (balance Fe and incidental elements)
Wherein the rolling process of the comparative example 1 and the example 1 is as follows: soaking the continuous casting slab at 1210 ℃ for 6h, removing scale and surface oxide skin by high-pressure water after discharging, and then rolling. And (3) the reduction of each pass in the first 8 passes is 60mm, the second pass begins, and the oxide skin on the surface of the billet is removed by using a high-pressure air gun before each pass of rolling. And rolling the blank to a square billet of 320mm by a subsequent rough rolling process. And (3) descaling the intermediate blank by using high-pressure water again when the intermediate blank is heated to the surface of 950 ℃, then rolling the intermediate blank into round steel with the diameter of 200mm by using a finish continuous rolling mill, and finally rolling the round steel at the temperature of 850 ℃. And (3) cooling through water after final rolling, cooling to 680 ℃ on the surface through 2 groups of strong water cooling, returning temperature through air cooling in the period, returning temperature for 5s every time, returning temperature between every two groups of water tanks, and reducing the surface temperature of each group of strong water cooling round steel after returning temperature to be not more than 100 ℃. Slowly cooling the round steel to 600 ℃ on the surface by using a heat preservation cover, spraying and cooling water mist to 550 ℃ on the surface, and maintaining the temperature of the surface of the round steel to 540 ℃ for 2min. And then cooling the round steel on a stepping cooling bed with the straightening function to 330 ℃ on the surface, 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 interval obtained by computer simulation of the composition of the rolled material is shown in fig. 1, and the interphase precipitation temperature interval is: and at 700-770 ℃, VCx and copper-containing precipitated phases begin to precipitate after finish rolling, the precipitation temperature is high (850 ℃), and the size of the precipitated phases is large, so that precipitation strengthening is not facilitated and the density of a hydrogen trap is improved. And the interphase precipitation mode generated in the process of transforming from austenite to ferrite has larger precipitation power, and the precipitated phase is finer and is distributed uniformly. The interphase precipitation temperature range of the non-quenched and tempered steel of the components is 700-800 ℃, and the specific surface of the core of the bar is generally 100 ℃ higher. Therefore, after finish rolling, the bar is rapidly cooled by water, so that the interior of the bar is reduced to 700-800 ℃, and the bar is slowly cooled in the temperature range, so that the sufficient generation of interphase precipitation is promoted. The steel bar is cooled through water after final rolling, the steel bar is cooled to the surface of 680 ℃ through 2 groups of strong water, air cooling is alternately carried out for returning the temperature, the temperature of each two groups of water tanks can be returned within 5s each time, and the surface temperature drop of each group of strong water-cooled steel bar after returning the temperature is not more than 100 ℃; slowly cooling the round steel to 600 ℃ on the surface by using a heat-insulating cover; the process enables interphase precipitation to fully occur in the bar material within the temperature range of 700-800 ℃, as shown in fig. 3 and 4, uniformly distributed fine VCx and copper-containing precipitated phases are obtained, and meanwhile, supercooling transformation structures such as bainite and the like are prevented from appearing on the surface of the round steel. As shown in fig. 3, the copper-containing precipitates of the B2 structure are metastable phases with a composition close to Cu: fe =1 and a particle size of about 5nm, but often several phases are stuck together, and since the copper-containing precipitates of the B2 structure are not stable, the matrix solid-dissolved Cu can form a passivation film again after the surface passivation film is broken. The B2 phase releases Cu into a 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 passive film of the common weathering steel is damaged, the passive film is formed again by the solid-dissolved copper, but the content of the solid-dissolved copper around the common weathering steel is reduced, the driving force for forming the film is reduced, and the time for forming the passive film by subsequent damage is prolonged. The invention forms B2 precipitated phase, the B2 precipitated phase can be used as a copper reservoir, solid-dissolved copper element is continuously supplemented to the matrix, and the driving force for forming the passivation film is kept not to be reduced. The present invention can speed up the self-repair process. After slow cooling, the surface of the round steel is cooled to about 550 ℃ by water mist spraying, the surface of the round steel is maintained at 540 ℃ for about 2min, and the non-transformed austenite is transformed into non-equilibrium structures such as fine lamellar pearlite instead of coarse lamellar pearlite and bainite as shown in figure 2, so that the structural uniformity and the toughness of the section of the round steel are improved.
The rolling process of comparative example 2 was: soaking the continuous casting slab at 1210 ℃ for 6h, removing scale and surface oxide skin by high-pressure water after discharging, and then rolling. And (3) the reduction of each pass in the first 8 passes is 60mm, the second pass begins, and the oxide skin on the surface of the billet is removed by using a high-pressure air gun before each pass of rolling. And rolling the blank to 320mm square billet by a subsequent rough rolling process. And (3) descaling the intermediate blank by using high-pressure water again when the intermediate blank is heated to the surface of 950 ℃, then rolling the intermediate blank into round steel with the diameter of 200mm by using a finish continuous rolling mill, and finally rolling the round steel at the temperature of 850 ℃. And (3) cooling through water after final rolling, cooling to the surface of 550 ℃ through 6 groups of strong water cooling, returning the temperature through air cooling during the period, returning the temperature between every two groups of water tanks within 5s each time, and reducing the surface temperature of each group of strong water cooling round steel after returning the temperature to be not more than 100 ℃. And then cooling the round steel on a stepping cooling bed with the straightening function to 350 ℃ on the surface, putting the round steel into a pit, and preserving heat for 48 hours to obtain a finished product.
The rolling process of example 2 was: soaking the continuous casting slab at 1220 ℃ for 7h, removing scale and surface oxide skin by high-pressure water after discharging, and then rolling. And (3) the reduction of each pass of the first 10 passes is 80mm, the second pass begins, and the oxide skin on the surface of the billet is removed by using a high-pressure air gun before each pass of rolling. And rolling the blank to a square billet of 450mm by a subsequent rough rolling process. And (3) descaling the intermediate blank by using high-pressure water again when the intermediate blank is heated to the surface of 950 ℃, then rolling the intermediate blank into round steel with the diameter of 290mm by using a finish continuous rolling mill, and keeping the final rolling temperature at 880 ℃. And (3) cooling the steel by water after final rolling, cooling the steel to the surface of 690 ℃ by 3 groups of strong water cooling, returning the temperature by air cooling during the period, returning the temperature between every two groups of water tanks within 10s each time, and reducing the surface temperature of each group of strong water cooling round steel after returning the temperature to be not more than 100 ℃. Slowly cooling the round steel to the surface of 620 ℃ by using a heat preservation cover, spraying and cooling water mist to the surface of about 550 ℃, and maintaining the surface of the round steel at 520 ℃ for about 2min. And then cooling the round steel on a stepping cooling bed with the straightening function to 350 ℃ on the surface, putting the round steel into a pit, and preserving heat for 48 hours to obtain a finished product.
Examples 3 and 4 differ from example 1 only in the diameter of the final rolled round steel.
In order to characterize the mechanical property and the hydrogen embrittlement resistance of the material, a standard tensile sample is taken at the 1/3 radius position of the round steel for tensile test, a notch tensile sample is taken, a notch is placed in Walpole corrosion inhibition solution (hydrochloric acid, sodium acetate and deionized water) for constant load notch tensile test, and the notch tensile delayed 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 to the delayed fracture strength ratio for the comparative examples and examples. The mechanical properties of examples 1 to 4 were not much changed, but the hydrogen embrittlement resistance (DFSR) was remarkably improved, as compared with 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 directly cutting super-large sections comprises the following steps:
the smelting raw materials mainly comprise scrap steel, and fine copper wires with the diameter of 0.5mm are uniformly fed after the Cu element content of the molten steel is measured at the last stage of smelting so as to reach the target Cu content; the target Cu content was: the mass percent of Cu is 0.30%; soaking the continuous casting billet with the cross section side length of 800mm multiplied by 1200mm for 5h at 1200 ℃, removing scales and surface oxide skin by high-pressure water after discharging, and then rolling. And (3) the reduction of each pass of the first 9 passes is 50mm, the second pass begins, and the oxide skin on the surface of the billet is removed by using a high-pressure air gun before each pass of rolling. And rolling the blank to a square billet of 500mm by a subsequent rough rolling process. And (3) descaling the intermediate blank by using high-pressure water again when the temperature of the intermediate blank is up to 980 ℃ on the surface, then rolling the intermediate blank into round steel with the diameter of 300mm by using a finish continuous rolling mill, and finally rolling the round steel at the temperature of 860 ℃. And (3) cooling through water after final rolling, cooling to the surface of 650 ℃ through 2 groups of strong water cooling, cooling back to the temperature through alternate air cooling in the period, returning the temperature for 8s every time, returning the temperature between every two groups of water tanks, and reducing the surface temperature of each group of strong water cooling round steel after returning to the temperature to be not more than 100 ℃. Slowly cooling the round steel to the surface of 610 ℃ by using a heat preservation cover, spraying and cooling water mist to the surface of about 550 ℃, and maintaining the surface of the round steel at 550 ℃ for about 1min. And then cooling the round steel on a stepping cooling bed with the straightening function to the surface of 300 ℃, putting the round steel into a pit, and preserving heat for 50 hours to obtain a finished product.
A low-cost hydrogen embrittlement-resistant non-quenched and tempered steel for directly cutting super-large sections comprises the following elements in percentage by mass, C: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 percent, and the balance of Fe and inevitable impurities; the mass percentage ratio of Ti/N =10.
The non-quenched and tempered steel of the embodiment is applied to a large high-strength steel member.
The large high-strength steel member comprises a push rod or a hydraulic upright.
The non-heat treated steel of the present example can be used in a weakly acidic environment.
The 1/3 radius longitudinal tensile strength of the rolled round steel is 900MPa, the yield strength is 650MPa, the elongation after fracture is 15 percent, and the impact energy is 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 sections comprises the following steps:
the smelting raw material is mainly scrap steel, and after the Cu element content of molten steel is measured at the end of smelting, fine copper wires with the diameter of 2.0mm are uniformly fed to reach the target Cu content; the target Cu content was: the mass percent of Cu is 0.40%; soaking the continuous casting billet with the section side length of 400mm multiplied by 600mm at 1210 ℃ for 5.5h, removing scale and surface oxide skin by high-pressure water after discharging, and then rolling. And (3) the reduction of each pass in the first 8 passes is 70mm, 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 is rolled. And rolling the blank to a square billet of 200mm by a subsequent rough rolling process. And (3) descaling the intermediate blank by using high-pressure water again when the intermediate blank is heated to the surface of 920 ℃, then rolling the intermediate blank into round steel with the diameter of 160mm by using a finish continuous rolling mill, and finally rolling at the temperature of 870 ℃. And (3) cooling in water after final rolling, cooling to the surface of 700 ℃ through 3 groups of strong water cooling, returning the temperature in air cooling in the period, returning the temperature between every two groups of water tanks within 6s each time, and reducing the surface temperature of each group of strong water cooling round steel after returning the temperature to be not more than 100 ℃. Slowly cooling the round steel to 615 ℃ on the surface by using a heat preservation cover, spraying and cooling water mist to 520 ℃ on the surface, and maintaining the surface of the round steel at 520 ℃ for 1.5min. And then cooling the round steel on a stepping cooling bed with the straightening function to the surface of 310 ℃, putting the round steel into a pit, and preserving heat for 55 hours to obtain a finished product.
A low-cost hydrogen embrittlement-resistant non-quenched and tempered steel for directly cutting super-large sections comprises the following elements in percentage by mass, C: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; the mass percentage ratio of Ti/N =3.6.
The 1/3 radius longitudinal tensile strength of the rolled round steel is 1050MPa, the yield strength is 800MPa, and the elongation after fracturePercentage of 17%, impact energy KU 2 50J。
Example 7
This example only differs from example 6 in that:
the low-cost hydrogen-embrittlement-resistant non-quenched and tempered steel for directly cutting the super-large section comprises the following elements in percentage by mass, C: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; the mass percentage ratio of Ti/N =3.5.
The 1/3 radius longitudinal tensile strength of the rolled round steel is 1030MPa, the yield strength is 750MPa, the elongation after fracture is 16 percent, and the impact energy is KU 2 48J。
Example 8
This example differs from example 6 only in that:
the low-cost hydrogen-embrittlement-resistant non-quenched and tempered steel for directly cutting the super-large section comprises the following elements in percentage by mass, C: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; the mass percentage ratio of Ti/N =3.6.
After rolling, the 1/3 radius longitudinal tensile strength of the round steel is 1025MPa, the yield strength is 765MPa, the elongation after fracture is 16 percent, and the impact energy is KU 2 49J。
It should be appreciated that in the foregoing 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 interpreted as reflecting an intention that: that the invention as claimed 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 this description, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed 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 present invention has been disclosed in an illustrative rather than a restrictive sense, and the scope of the present invention is defined by the appended claims.
The above description is only of the preferred embodiments of the present invention, and it should be 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 invention and these are intended to be within the scope of the invention.
Claims (10)
1. The preparation method of the low-cost hydrogen embrittlement-resistant non-quenched and tempered steel for directly cutting the oversized section is characterized by comprising the following steps of:
s1: the smelting raw material is mainly waste 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 was: the mass percent 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 percent of P and less than or equal to 0.02 percent of P; 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 to 1220 ℃, and the heat preservation time is 5 to 7h; the continuous casting blank is a rectangular blank with the section side length of 400mm to 1200 mm;
s3: after the continuous casting billet is discharged from the furnace, descaling by high-pressure water, removing surface oxide skin, and immediately rolling; the rolling reduction of each pass is 50-80mm in the first 8-10 passes, and from the second pass, the surface oxide skin of the billet is removed by using a high-pressure air gun before each pass of rolling; the subsequent passes do not require until the blank is rolled into a square intermediate blank with the side length of the cross section of 200 to 500mm;
s4: when the intermediate blank is warmed to the surface of 920-980 ℃, descaling by using high-pressure water again, and then rolling into round steel with the diameter of 160-300mm by using a finish rolling mill, wherein the final rolling temperature is 850-880 ℃;
s5: after the round steel is finally rolled, cooling the round steel through water, cooling the round steel to the surface of 650-700 ℃ through 2-3 groups of strong water, and cooling the round steel through air in an alternating manner to return the temperature, wherein the surface temperature drop of each group of strong water-cooled round steel after returning the temperature is not more than 100 ℃;
s6: slowly cooling the round steel to the surface of 600-620 ℃ by using a heat insulation 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 1-2min;
s7: cooling the round steel on a stepping cooling bed with a straightening function to the surface of the round steel at 300-350 ℃, then putting the round steel into a pit, and preserving heat for at least 48 hours to obtain a finished product.
2. The method for preparing a low-cost hydrogen embrittlement-resistant non-quenched and tempered steel for direct cutting with an oversized cross section according to claim 1, wherein a copper-containing precipitated phase of a B2 structure is generated in the S6 slow cooling process.
3. The non-quenched and tempered steel obtained by the method for preparing the low-cost hydrogen-embrittlement-resistant non-quenched and tempered steel for super-large section direct cutting according to claim 1 or 2.
4. The non-quenched and tempered steel of claim 3, wherein the mass percentage of Nb is 0.004% or less.
5. The non-quenched and tempered steel of claim 3, wherein the mass percentage of Cu is 0.30% to 0.40%.
6. The non-quenched and tempered steel of claim 3, wherein the mass percentage of S is 0.01% to 0.02%.
7. The non quenched and tempered steel of claim 3, wherein the mass percentage of Ti is 0.020% to 0.028%.
8. The non-quenched and tempered steel as claimed in claim 3, wherein the 1/3 radius of the finished product has a longitudinal tensile strength of 900 to 1050MPa, a yield strength of 650 to 800MPa, an elongation at break of 15 to 17%, and a work of impact KU 2 45~50J。
9. Use of the non heat treated steel according to claim 3 in large high strength steel components.
10. The use according to claim 9, characterized in that the large high-strength steel member comprises a push rod, a hydraulic column, a single crystal furnace column, a shaft for wind power or a large-section power shaft.
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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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