CN114672723B - 46MnVS series steel for expansion connecting rod and manufacturing method thereof - Google Patents
46MnVS series steel for expansion connecting rod and manufacturing method thereof Download PDFInfo
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Abstract
The invention relates to 46MnVS series steel for a breaking connecting rod, which comprises the following chemical components in percentage by mass: 0.44 to 0.48 percent, si:0.60 to 0.75 percent, mn:1.10 to 1.20 percent, P: 0.015-0.045%, S0.06-0.070%, cr:0.20 to 0.28 percent, ni:0.10 to 0.18 percent, cu:0.08 to 0.15 percent, mo: less than or equal to 0.03 percent, al: less than or equal to 0.008 percent, nb: 0.020-0.040%, V:0.13 to 0.18 percent, N: 0.015-0.021%, ti:0.01 to 0.02 percent, and the balance of Fe and unavoidable impurity elements. The structure of the connecting rod is ferrite and pearlite, the content of ferrite is 5-15%, and the difference of the large-head expanded section grains of the connecting rod is 0.5-1 grade; the yield strength Rel of the connecting rod is more than or equal to 800MPa; the rejection rate in the swelling process is less than or equal to 0.1 per mill.
Description
Technical Field
The invention belongs to the technical field of iron-based alloys, and particularly relates to a manufacturing method of 46MnVS series steel for a broken connecting rod.
Background
46MnVS5 steel for the expansion connecting rod is introduced from Germany to China, and the material has the advantages of high strength and long fatigue life, and is used for replacing C70S6 series expansion connecting rod along with the development of automobiles to the energy-saving and light weight directions.
The 46MnVS5 steel is introduced into China, and the brand and standard requirements of each main machine factory are modified, such as 46MnVS6, 46MnVS5mod, 46MnVS6mod and the like; this application is collectively referred to as 46MnVS series steels.
Steel is smelted according to chemical components in foreign technical specifications, connecting rods are manufactured by domestic clients, abnormal structure of the connecting rods often occurs, small-batch testing is required before connecting rod processing, forging and cooling processes in the connecting rod processing process are adjusted according to test results, and therefore the required comprehensive performance of the connecting rods is met, and the production mode is not beneficial to mass production; meanwhile, as the process is adjusted and the same equipment of C70S6 series steel is still used for production, the rejection rate of the connecting rod produced by 46MnVS5 is too high in the expanding and breaking process, and the rejection rate reaches 2% -10%; causing serious waste.
Disclosure of Invention
The purpose of the invention is that: solving the problem of abnormal structure of the connecting rod, avoiding abnormal structure such as bainite or martensite, and enabling the connecting rod to obtain uniform ferrite and pearlite structure; the difference of the grains of the large head expansion section of the connecting rod is 0.5-1 grade; rel (yield strength) of the connecting rod is more than or equal to 800Mpa, ferrite content of the connecting rod is 5% -15% (the content refers to area percentage content of ferrite on a detection surface), and rejection rate in the expanding and breaking process is less than or equal to 0.1 per mill.
The more ferrite in the connecting rod structure, the better the toughness, and the less likely to swell, so it is necessary to suppress the ferrite content. The rejection rate investigation in the expanding and breaking process is that the connecting rod has the conditions of slag falling, edge tearing, deformation and the like in the expanding and breaking process.
In order to achieve the above object, the present inventors have made chemical composition improvements for steel for connecting rods in order to achieve the best balance of high strength, low plasticity and high fatigue properties on the basis of the published 46MnVS5 foreign standard and chinese standard: the 46MnVS series steel comprises the following chemical components in percentage by mass: 0.44 to 0.48 percent, si:0.60 to 0.75 percent, mn:1.10 to 1.20 percent, P: 0.015-0.045%, S0.06-0.070%, cr:0.20 to 0.28 percent, ni:0.10 to 0.18 percent, cu:0.08 to 0.15 percent, mo: less than or equal to 0.03 percent, al: less than or equal to 0.008 percent, nb: 0.020-0.040%, V:0.13 to 0.18 percent, N: 0.015-0.021%, ti:0.01 to 0.02 percent, and the balance of Fe and unavoidable impurity elements; the production form of the product steel is hot rolled round steel bar.
The design of the chemical components of the application is based on the following:
determination of C content
C is the most economical and basic strengthening element in steel, and is mainly used for obviously improving the strength of the steel, and as the carbon content in the steel increases, the yield and tensile strength increase, and the plasticity and impact property decrease. The content of C in the present invention is determined to be 0.44 to 0.48%. The invention relates to steel belonging to the category of medium carbon steel.
Determination of Si content
Si does not form carbide in the steel, can be dissolved in ferrite in a solid way to influence the strength performance of the steel, has strong effect of increasing the cold deformation hardening rate of the ferrite, and makes cold working of the steel difficult. However, si also promotes segregation of elements P and S at grain boundaries, and makes the grain boundaries properly embrittled; the Si content of the present invention is determined to be 0.6 to 0.75%
Determination of Mn content
Mn is an important alloying element that increases the strength and improves the toughness of steel. Mn is a weak carbide-forming element, is mainly present in the form of solid solution in steel, and is solid-dissolved in ferrite at room temperature, and the solid-dissolved Mn has a solid-solution strengthening effect. In ferrite, the solid solution strengthening effect of Mn is inferior to that of P and Si, but when the content is less than 0.80%, the strengthening effect is not obvious; mn can also enlarge a gamma region, increase Mn content in steel, reduce the content of eutectoid carbon in steel, increase pearlite content, improve steel strength, reduce phase transition temperature of steel, slow down transformation speed of austenite to pearlite, refine ferrite grains, pearlite groups and lamellar spacing of pearlite, improve steel strength, but when Mn content in steel exceeds 1.5%, the Mn content range of the invention is determined to be 1.10-1.20%.
Determination of P content
P can strengthen ferrite phase, so that the strength and the hardness of steel are increased, the effect of well inhibiting deformation capability is shown in the material processing process, the plasticity and the impact toughness are obviously reduced, a small amount of P is required to be added in order to improve the expansion effect, but the P content is not excessively high and exceeds 0.045%, the continuous casting blank produced by an arc continuous casting machine is extremely easy to crack, and only the production mode of casting steel ingots can be adopted; the range of the P content of the present invention is thus defined to be 0.015 to 0.045%.
Determination of S content
The addition of S element increases the machinability of steel by forming MnS inclusions in the steel, particularly by wrapping sulfide-coated oxide inclusions which are not easily deformed in the steel, and ferrite is precipitated at the prior austenite grain boundary, and ferrite is precipitated at the core, and the number of ferrite blocks is increased by increasing the ferrite-forming core, thereby refining the ferrite-pearlite structure, but the addition of excessive S not only results in deterioration of the mechanical properties of steel, but also causes serious segregation in the steel, thereby adversely affecting continuous casting and rolling of steel, and the S content range of the present invention is defined to be 0.06 to 0.07%.
Determination of Cr content
Cr is carbide forming element, cr dissolved in austenite during heating can obviously shift the C curve to the right, and can obviously improve the hardenability, so that the strength and hardness of steel are improved, but the content is not excessive, otherwise, a bainite structure is easy to generate, and the toughness is reduced. The Cr content of the present invention is determined to be 0.20 to 0.28%.
Determination of Ni content
Ni is a non-carbide forming element. Ni exists in steel in a solid solution form to exert a solid solution strengthening effect, but shows only a relatively weak strengthening effect; when Ni and Cr are used together, the hardenability can be obviously improved. More Ni more easily causes the occurrence of bainitic structure in steel. The range of Ni content in the present invention is determined to be 0.10 to 0.18%.
Determination of Cu content
Cu can improve the stability of austenite in steel, has the effect of strengthening ferrite, and is biased in grain boundaries, so that the grain boundary strength is reduced and the brittleness is improved; when the Cu content is high, the steel has hot brittleness, and hot forging and rolling are difficult, and the Cu content range of the invention is determined to be 0.08-0.15%.
Determination of Mo content
Mo exists in solid solution and carbide of steel, and has certain strengthening effect; however, mo can remarkably improve the hardenability of steel, has a remarkable deferral effect on pearlite transformation and has small influence on bainite transformation, so that the steel containing Mo can easily obtain a bainite structure and has adverse effect on the toughness of the steel; the steel of the present invention belongs to ferrite-pearlite type non-quenched and tempered steel, so that the steel of the present invention has a strict control of Mo content, and the Mo content range of the present invention is determined to be Mo not more than 0.03%.
Determination of Al content
Al is an effective element for deoxidization, and is easy to form in the molten steel smelting process 2 O 3 The brittle inclusions are equal, the purity of molten steel is reduced, and the content range of Al is less than or equal to 0.008 percent.
Determination of V content
V is used as the main added alloy element, which can reduce the phase transition temperature of gamma phase to alpha phase and form more dispersed pearlite. The solution temperature of vanadium in austenite is low, but the diffusion rate is quite high, the precipitate is dissolved during the heating and soaking stages, the dissolved state is maintained during hot working, and the strength of the steel increases due to the dispersion precipitation during subsequent cooling, the strength of the steel increases linearly with increasing vanadium content in the steel, but the further strengthening effect of more vanadium content on the steel is not great. The V content of the invention is determined to be 0.13-0.18%
Determination of Nb content
Adding Nb element, and making the Nb element exist in the form of Nb (CN) particles to play a role of refining austenite grains; when Nb-V is added in a compounding way, the strength is higher than that of Nb which is added singly, meanwhile, austenite grains can be further refined, the cooled ferrite grains are finer, a compound (NbV) CN is finer than that of Nb and V carbon nitrogen compounds, the precipitation temperature is wider, thereby more effectively preventing the growth and recrystallization process of the austenite grains, and the forging temperature can be increased to 1230-1270 ℃, so that the strength and hardness of the connecting rod are improved, and the plasticity is reduced; meanwhile, the crystal grains are not thickened due to the fact that the forging temperature is too high. The range of the Nb content of the present invention is determined to be 0.020 to 0.040%.
Determination of N content
N in steel has mainly reinforced precipitation strengthening effect and grain refining effect, and N and V have very strong affinity and may form very stable interstitial phase. The nitrides and carbides can be mutually dissolved to form carbonitrides, and the nitrides can also be mutually dissolved to form composite nitrides, and the compounds often exist in fine particles to generate dispersion strengthening effect and improve the strength of steel. VN in steel not only strengthens phases, but also can inhibit migration of austenite grain boundaries and refine austenite grains, thereby refining ferrite grains and pearlite clusters, and plays a core role in phase transformation to further refine ferrite grains. However, the excessively high N content in the steel is unfavorable for continuous casting production, and is easy to form continuous casting billet cracks, and the N content range of the invention is determined to be 0.015-0.021%.
Determination of Ti content
Ti is added to form tiny and dispersed TiN, tiN particles have high stability and low solubility, austenite grains are prevented from excessively growing when heating, and excessive Ti is added to generate a large amount of TiN, so that the strength of the connecting rod is not improved; ti is added in a small amount, f=S/Ti is more than or equal to 3, wherein element symbols represent the mass percentage of corresponding elements, composite sulfides such as TiS, ti-MnS, tiS-MnS and the like are generated in steel, the vulcanization denaturation rate exceeds 80 percent (the normal sulfides are long-strip-shaped as shown in figure 1, the length-width ratio of the denatured sulfides is less than or equal to 3, and the denatured sulfides are spindle-shaped and ellipsoid-shaped as shown in figure 2); the length of sulfide is reduced, sulfide with the length less than or equal to 50 mu m accounts for 60 percent of the total amount of sulfide, and the notch effect of sulfide is fully exerted when the material is swelled, so that the swellability and the machinability of the material are improved. The Ti content of the invention is determined to be 0.01-0.02%.
The invention realizes the optimal balance of high strength, low plasticity and high fatigue performance, the mechanical property of the connecting rod with too low carbon equivalent Ceq can not meet the requirement, and the excessive Ceq can cause abnormal structure of the connecting rod (abnormal structure such as martensite or bainite is generated), so that the Ceq is controlled to be 0.9-1.0 percent, the high strength and stable mechanical property of the connecting rod are ensured, and the structure is pearlite and ferrite.
Ceq＝[C]+0.07[Si]+0.16[Mn]+0.61[P]+0.19[Cu]+0.17[Ni]+0.20[Cr]+0.4[Mo]+[V]Wherein C, si, mn, P, cu, ni, cr, mo, V is the mass percent of the corresponding elements; further, the present inventors consider that: the P element affects plasticity and impact toughness, cu is easy to gather at a grain boundary, the grain boundary strength is reduced, the brittleness is improved,f influence S The shape of the sulfide is that,fully exert sulfide notch effect and obtain the product through production practice and regression equation50P+3Cu+(f/ 100 % control formula, satisfying 1% or less than 50P+3Cu+ (f/100)% -2% or less to ensure lower plasticity。
The method for manufacturing round steel of the MnVS series steel of the present application 46 is as follows:
the flow is as follows: primary refining (electric furnace or converter), external refining (VD or RH), vacuum degassing, continuous casting and continuous rolling;
the specific technological measures are as follows:
the chemical composition of the application accords with the design range of the table 1:
TABLE 1
Primary refining: the steel grade belongs to P-containing steel, thin slag is used during smelting, and the P content is controlled according to the proportion of P which is more than or equal to 0.010% and less than or equal to 0.045%; the tapping temperature is 1550-1580 ℃, the P content is 0.010-0.030% during tapping, and the C content is more than or equal to 0.20%; adding ferrotitanium, ferrosilicon, ferromanganese, ferrosulfur and lime after tapping, adding alloy according to the lower limit of the control component range, and then carrying out slag skimming treatment; lime and refining slag are added again for slagging.
Refining: the content range of the whole element components is adjusted, and the temperature of the hanging bag is 1590-1610 ℃.
Vacuum degassing: the steel grade belongs to high-N steel, nitrogen is used as lifting gas, the time proportion of low vacuum and high vacuum is controlled to be more than 3:1, wherein the high vacuum is kept for 5-10 minutes to ensure the N increasing level of molten steel, the soft argon blowing time is more than or equal to 10 minutes, and the inclusion floating is promoted.
Continuous casting: the casting superheat degree is 10-20 ℃, and the casting blank drawing speed is 0.6-0.9 m/min.
Tandem rolling: heating the steel billet in a furnace at the temperature: the heating time is more than or equal to 2.5 hours at 1200-1280 ℃, the steel is discharged from the furnace and is descaled by high-pressure water, the steel enters a continuous rolling mill to be rolled into round steel with required specification, the rolling compression ratio is more than or equal to 20, the final rolling temperature is more than 900 ℃, and the steel is air cooled after rolling is finished.
Preferably, the primary smelting adopts converter or electric furnace smelting, molten iron accounts for more than 85%, and the balance is scrap steel. The P removing process is special and is a production difficulty, slag operation is adopted for the difficulty, the lime content in the slag is reduced during smelting, and compared with the lime content of slag adopted in smelting molten steel without P, the alkalinity is reduced, and the oxidability is reduced; p is removed in place in the process of slag operation in smelting; al deoxidizer is not allowed to be used during tapping, and the oxidizing slag is not allowed to be discharged; the adding sequence of the alloy after tapping is ferrotitanium, ferrosilicon, ferromanganese, ferrosulfur and lime, and the adding amount of lime is 200kg/100 tons of molten steel.
Preferably, nitrogen stirring is adopted in the refining process, and the stirring strength of the nitrogen is better than that of the non-bare molten steel, so that silicon carbide particles and carbon powder are subjected to diffusion deoxidation, and the white slag time is ensured to be more than or equal to 20 minutes. The LF refining only needs to add a small amount of alloy for fine adjustment, so that the nonmetallic inclusion content in molten steel can be obviously reduced.
Preferably, in the continuous casting process, molten steel is recycled to a crystallizer from a ladle to a tundish, the molten steel is isolated from air by adopting sealed protection pouring, and the electromagnetic stirring M-EMS of the crystallizer and the electromagnetic stirring F-EMS of a solidification tail end are started.
Preferably, in the continuous rolling process, the billet is heated in a step-type heating furnace, the residual oxygen content in the furnace is less than or equal to 0.5%, the decarburization on the surface of the continuous casting billet is lightened, the continuous casting billet comprises a preheating section, a first heating section, a second heating section and a soaking section, wherein the temperature of the preheating section is controlled between 880 and 920 ℃, the temperature of the first heating section is controlled between 1070 and 1100 ℃, the temperature of the second heating section is controlled between 1021 and 1230 ℃, the temperature of the soaking section is controlled between 1230 and 1250 ℃, the total heating time is 2.5 to 3.5 hours, and the high-temperature heating is helpful for fully playing the roles of Nb and V, so that the steel obtains high-strength performance. The initial rolling temperature of continuous rolling is 1100-1135 ℃, the final rolling temperature is 920-950 ℃, the austenite is rolled in a single-phase region, and the single-pass maximum rolling reduction is controlled between 25-30 mm.
The manufacturing method of the 46MnVS series steel expansion connecting rod comprises the steps of sequentially carrying out blanking, heating, roll forging, pre-forging, final forging, trimming, correcting and cooling control, wherein the heating temperature before forging is as follows: the temperature of the upper cooling bed is controlled to be more than or equal to 900 ℃ when the upper cooling bed is cooled at 1230-1270 ℃.
The cooling process has a larger influence on ferrite content and the grain size of the connecting rod, the cooling speed after forging is less than or equal to 1 ℃/s, the connecting rod structure is ferrite and pearlite, the grain size difference of the big head part of the connecting rod is 5-6.5 grades, the grain size difference of the big head part is small, the grain size difference is 0.5-1 grade, the grain is uniform, the ferrite content is less than or equal to 15%, the larger the cooling speed is, the grain difference of the grain size of the big head part of the connecting rod is larger, particularly the grain size of the edge part of the connecting rod is finer, the toughness is improved, and the expansion is not facilitated.
Compared with the prior art, the invention has the advantages that:
the non-quenched and tempered steel is added with a certain content of Nb (0.020-0.040%) and Ti (0.01-0.02%), so that the forging temperature can be increased to 1230-1270 ℃, the strength and hardness of the connecting rod can be improved by high-temperature forging, and the plasticity is reduced; meanwhile, the grains are not thickened due to the too high forging temperature.
Compared with foreign standards, the method has the advantages that the Cu and the Ti with specific contents are added, the Ti can prevent austenite grains from growing excessively and promote sulfide to deform during heating, cu is concentrated at the grain boundary, the grain boundary strength is reduced, the brittleness is improved, and the expansion performance is improved.
The high strength and the stable mechanical property of the connecting rod are ensured by controlling Ceq to be more than or equal to 0.9 percent and less than or equal to 1.0 percent, and the structure is ferrite and pearlite.
By controlling the S/Ti to be more than or equal to 3, the vulcanization denaturation rate exceeds 80 percent; the size of sulfide is reduced, sulfide with the size less than or equal to 50 mu m accounts for more than 60 percent of the total amount of sulfide, nonmetallic inclusion inspection is carried out according to GB/T10561, the grade A of sulfide grade A is less than or equal to 2.0, the grade A of sulfide grade A is less than or equal to 1.5, and the notch effect of sulfide is fully exerted when the material is swelled, so that the swelled property of the material is improved.
The control of Ti, S, P, cu ensures that the reduction of area of the connecting rod is stabilized at 25% -35% and the connecting rod has higher expansion and breaking performances, and the reduction of area is ensured to be less than or equal to 1% -50 P+3Cu+ (f/100)% -2%.
After the raw materials are forged, cooling is controlled, the cooling speed is less than or equal to 1 ℃/s, the crystal grain at the large head part of the connecting rod is 5-6.5 grade, the grain size difference is small, the crystal grain is uniform, the ferrite content is less than or equal to 15%, the structure is pearlite and ferrite, and the expansion breaking performance is improved.
The invention realizes the optimal balance of high strength, low plasticity and high fatigue performance, and the connecting rod obtains uniform ferrite and pearlite; the expansion rejection rate of the connecting rod is less than or equal to 0.1 per mill.
Drawings
FIG. 1 is a view of the morphology of a rolled material without sulfide denaturation;
FIG. 2 is a view of the texture of the denatured sulfide of the present invention;
FIG. 3 shows the morphology of grains in the edge area of the large end of the connecting rod, and the grain size is 5.5 grade;
FIG. 4 shows the morphology of grains in the central region of the big end of the connecting rod, and the grain size is 5 grade.
Detailed Description
The invention is described in further detail below in connection with the following examples, which are exemplary and intended to illustrate the invention, but are not to be construed as limiting the invention.
Examples 1 to 4
The process flow comprises the following steps: primary refining (electric furnace or converter), refining, vacuum degassing, continuous casting blank cooling, continuous casting blank heating, rolling, cooling, finishing, inspection and finished product warehousing.
The primary smelting ingredients are selected from the blast furnace molten iron accounting for 85 percent, the rest is scrap steel, the steel grade belongs to P-containing steel, the P-removing process is special, and the production difficulty is also that the thin slag operation is adopted for the difficulty: the lime content of slag is reduced (compared with the lime content of slag adopted in smelting molten steel without P steel, the lime content is reduced by 10-35%), the alkalinity is reduced, the oxidability is reduced, P is removed in place once in the operation process of slag in smelting, and the P content is controlled according to 0.020% to 0.040%; the tapping temperature is 1560-1570 ℃, the tapping P is 0.015-0.030%, C is more than or equal to 0.20%, the tapping amount is about 100 tons; al-containing deoxidizer is not allowed to be added during tapping, and ferrotitanium, ferrosilicon, ferromanganese, ferrosulfur, 200kg of lime and the like are added in the steel ladle; adding alloy according to the lower limit of the control component, and then carrying out slag skimming treatment; lime, refining slag and the like are added again for slagging.
The refining process adopts nitrogen stirring, the stirring intensity of chemical nitrogen is adjusted to ensure that molten steel is not exposed, silicon carbide particles and carbon powder are subjected to diffusion deoxidation, the white slag time is ensured to be 20-25 minutes, all components are adjusted to enter the specified target value content requirement according to the analysis result, and the lower control limit is added due to tapping, and the ladle hanging temperature is about 1600 ℃.
The vacuum degassing uses nitrogen as lifting gas, strictly controls low vacuum for 18 minutes and high vacuum for 5 minutes, and carries out soft argon blowing for 12 minutes at the temperature of 1545 ℃ on an upper argon blowing table so as to promote the floating of inclusions.
The superheat degree of the tundish is controlled to be 10-20 ℃ by continuous casting. The continuous casting adopts a process of adopting a crystallizer electromagnetic stirring parameter of 3A/500HZ, adopting a terminal electromagnetic stirring parameter of 10A/250HA, adopting a tundish to perform induction heating and slightly pressing down by 10 mm. The molten steel transferring process is to isolate air to avoid oxidation.
Reheating: the blank is heated in a step-type heating furnace, and comprises a preheating section, a first heating section, a second heating section and a soaking section, wherein the temperature of the preheating section is controlled to 880-920 ℃, the temperature of the first heating section is controlled to 1070-1100 ℃, the temperature of the second heating section is controlled to 1021-1230 ℃, the temperature of the soaking section is controlled to 1230-1250 ℃, and the total heating time is 2.5-3.5 hours or longer.
The initial rolling temperature of continuous rolling is 1100-1135 ℃, the final rolling temperature is 920-950 ℃, rolling is carried out in a single-phase zone, the maximum rolling reduction of single pass is controlled between 25-30 mm, and slow cooling (air cooling) is carried out after rolling is finished. Table 2 shows the specific parameters of the continuous casting superheat degree and the rolling process.
TABLE 2 specific parameters of continuous casting superheat and rolling Process
The processing flow of the connecting rod comprises blanking, heating, roll forging, pre-forging, final forging, trimming, correcting and cooling, wherein induction heating is adopted, the heating temperature is 1250 ℃, the heat preservation is carried out for 10 seconds, forging is carried out, the connecting rod blank obtained by forging is cooled, the upper cooling line temperature is 920 ℃, the cooling line temperature is 580 ℃, and the cooling speed is lower than 0.8 ℃/s, so that the connecting rod blank is obtained.
The chemical compositions of the above examples are shown in Table 3.
TABLE 3 Table 3
In the table, the unit is wt.%, and the balance is Fe and other unavoidable impurity elements.
The nonmetallic inclusion of each of the above examples was examined according to GB/T10561 as shown in Table 4 below.
TABLE 4 Table 4
The connecting rod performance test of each of the above embodiments is shown in Table 5 below
TABLE 5
The "different positions" in the table refer to the big end, the small end, the rod part, etc. of the connecting rod.
The metallographic structure of the product is ferrite and pearlite balls, the ferrite content is less than or equal to 15%, the difference of the large-head-position grains of the connecting rod is 0.5-1 level, the expansion rejection rate of the connecting rod is less than or equal to 0.1 per mill, the expansion rejection rate is the proportion of 400000 connecting rods obtained by forging factories and machine processing factories.
In addition to the above embodiments, the present invention also includes other embodiments, and all technical solutions that are formed by equivalent transformation or equivalent substitution should fall within the protection scope of the claims of the present invention.
Claims (7)
1. A46 MnVS series steel for a breaking connecting rod is characterized in that: the steel comprises the following chemical components in percentage by mass: 0.44 to 0.48 percent, si:0.60 to 0.75 percent, mn:1.10 to 1.20 percent, P: 0.015-0.045%, S0.06-0.070%, cr:0.20 to 0.28 percent, ni:0.10 to 0.18 percent, cu:0.08 to 0.15 percent, mo: less than or equal to 0.03 percent, al: less than or equal to 0.008 percent, nb: 0.020-0.040%, V:0.13 to 0.18 percent, N: 0.015-0.021%, ti:0.01 to 0.02 percent, and the balance of Fe and unavoidable impurity elements;
controlling f=S/Ti to be more than or equal to 3, wherein element symbols represent the mass percentage of corresponding elements, so that composite sulfide mainly comprising TiS, ti-MnS and TiS-MnS is generated in steel, the vulcanization denaturation rate is more than 80%, the aspect ratio of the sulfide after denaturation is less than or equal to 3, the sulfide with the length less than or equal to 50 μm accounts for more than 60% of the total sulfide, nonmetallic inclusion inspection is carried out according to GB/T10561, the grade A of sulfide is less than or equal to 2.0 grade, and the grade A of A is less than or equal to 1.5 grade;
ceq= [ C ] +0.07[ Si ] +0.16[ Mn ] +0.61[ P ] +0.19[ Cu ] +0.17[ Ni ] +0.20[ Cr ] +0.4[ Mo ] + [ V ], wherein C, si, mn, P, cu, ni, cr, mo, V is the mass percentage of the corresponding element, and Ceq is controlled to be 0.9% -1.0%;
satisfying the conditions of 50P+3Cu+ (f/100)% -2%, wherein element symbols represent the mass percent of corresponding elements, and f=S/Ti, so that the reduction of area of the connecting rod is stabilized at 25% -35%;
the structure of the connecting rod is ferrite and pearlite, the content of ferrite is 5-15%, and the difference of the large-head expanded section grains of the connecting rod is 0.5-1 grade; the yield strength Rel of the connecting rod is more than or equal to 800MPa; the rejection rate in the swelling process is less than or equal to 0.1 per mill.
2. A method of manufacturing 46MnVS series steel for a expansion joint according to claim 1, characterized in that: comprising
Primary refining: the steel grade belongs to P-containing steel, thin slag is used during smelting, and the P content is controlled according to the proportion of P which is more than or equal to 0.010% and less than or equal to 0.045%; the tapping temperature is 1550-1580 ℃, the P content is 0.010-0.030% during tapping, and the C content is more than or equal to 0.20%; adding ferrotitanium, ferrosilicon, ferromanganese, ferrosulfur and lime after tapping, adding alloy according to the lower limit of the control component range, and then carrying out slag skimming treatment; lime and refining slag are added again to carry out slag formation;
refining: adjusting the total content of the element components to be within the designed content range, wherein the hanging temperature is 1590-1610 ℃;
vacuum degassing: the steel grade belongs to high-N steel, nitrogen is used as lifting gas, the time proportion of low vacuum to high vacuum is controlled to be more than 3:1, wherein the high vacuum is kept for 5-10 minutes to ensure the N increasing level of molten steel, and the soft argon blowing time is more than or equal to 10 minutes;
continuous casting: the casting superheat degree is 10-20 ℃, and the casting blank drawing speed is 0.6-0.9 m/min;
tandem rolling: heating the steel billet in a furnace at the temperature: the heating time is more than or equal to 2.5 hours at 1200-1280 ℃, the steel is discharged from the furnace and is descaled by high-pressure water, the steel enters a continuous rolling mill to be rolled into round steel with required specification, the rolling compression ratio is more than or equal to 20, the final rolling temperature is more than 900 ℃, and the steel is air cooled after rolling is finished.
3. The method according to claim 2, characterized in that: the primary smelting adopts converter or electric furnace smelting, molten iron accounts for more than 85%, the lime content in the thin slag is reduced by 10-35% compared with the lime content of slag adopted in the smelting of molten steel without P steel; p is removed in place in the process of slag operation in smelting; al deoxidizer is not allowed to be used during tapping; the adding sequence of the alloy after tapping is ferrotitanium, ferrosilicon, ferromanganese, ferrosulfur and lime, and the adding amount of lime is 200kg/100 tons of molten steel.
4. The method according to claim 2, characterized in that: the refining process adopts nitrogen stirring, and the stirring strength of the nitrogen is better than that of the non-bare molten steel, so that silicon carbide particles and carbon powder are subjected to diffusion deoxidation, and the white slag time is more than or equal to 20 minutes.
5. The method according to claim 2, characterized in that: in the continuous casting process, molten steel is recycled to a crystallizer from a ladle to a tundish, the molten steel is isolated from air by adopting sealing protection pouring, and the electromagnetic stirring M-EMS of the crystallizer and the electromagnetic stirring F-EMS of a solidification tail end are started.
6. The method according to claim 2, characterized in that: in the continuous rolling process, a billet is heated in a step-type heating furnace, the residual oxygen content in the furnace is less than or equal to 0.5 percent, the continuous rolling process comprises a preheating section, a first heating section, a second heating section and a soaking section, wherein the temperature of the preheating section is controlled between 880 and 920 ℃, the temperature of the first heating section is controlled between 1070 and 1100 ℃, the temperature of the second heating section is controlled between 1021 and 1230 ℃, and the temperature of the soaking section is controlled between 1230 and 1250 ℃ and the total heating time is 2.5 to 3.5 hours;
the initial rolling temperature of continuous rolling is 1100-1135 ℃, the final rolling temperature is 920-950 ℃, the rolling is carried out in a single-phase zone, and the maximum rolling reduction of single pass is controlled between 25-30 mm.
7. A method of making a blow-off link from 46MnVS series steel using a blow-off link as claimed in claim 1, wherein: the method comprises the steps of sequentially blanking, heating, roll forging, pre-forging, final forging, trimming, correcting and cooling control, wherein the heating temperature is as follows: the temperature of 1230-127O ℃ is controlled to be more than or equal to 900 ℃ and the cooling speed is controlled to be less than or equal to 1 ℃/s, the connecting rod structure is ferrite and pearlite, the crystal grains at the big head part of the connecting rod are 5-6.5 grades, and the crystal grain phase difference is 0.5-1 grade.
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