WO2009157661A2 - 표면특성 및 내2차 가공취성이 우수한 소부경화강 및 그 제조방법 - Google Patents
표면특성 및 내2차 가공취성이 우수한 소부경화강 및 그 제조방법 Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
- C21D8/0421—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the working steps
- C21D8/0426—Hot rolling
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
- C21D8/0447—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment
- C21D8/0463—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment following hot rolling
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
- C21D9/48—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals deep-drawing sheets
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
- C21D8/0447—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment
- C21D8/0473—Final recrystallisation annealing
Definitions
- the present invention relates to a bake hardened steel having both high strength properties and excellent secondary work brittleness properties, and a method of manufacturing the same. More specifically, the bake hardened steel has a high amount of bake hardening and a low bake hardening and aging index (AI) value.
- the present invention relates to a hardened hardened steel excellent in secondary workability and excellent in secondary work brittleness and a method of manufacturing the same.
- Steels capable of satisfying the above-described conditions include a composite structured cold rolled steel sheet and a hardened hardened steel.
- Relatively easy to manufacture composite tissue steel has a tensile strength of more than 390MPa class as a material used in automobiles has the advantage of high elongation compared to high tensile strength.
- the average r value indicating the press formability of the automobile is low, and expensive alloying elements such as Mn and Cr are often added excessively, which may lead to an increase in manufacturing cost.
- the hardened hardened steel has a yield strength close to that of soft steel with a tensile strength of 390 MPa or less during press molding, and thus has excellent ductility.
- Increasing is attracting attention as a very ideal steel compared to the conventional cold rolled steel sheet is deteriorated formability.
- Baking hardening is a kind of strain aging that occurs when carbon or nitrogen, an invasive element solid solution dissolved in steel, adheres to the potential generated during the deformation process. Due to the deterioration of moldability with room temperature aging is a process of controlling the appropriate employment element is very important.
- hardened hardenable steel In general, known as a method for producing hardened hardenable steel is a low-carbon P-added Al-killed steel simply by winding at low temperatures, that is, by cold winding at a hot rolled winding temperature of 400-500 °C temperature range, here Hardening amount of about 40-50 MPa steel was mainly used. It is known that such a manufacturing method can improve both moldability and baking hardenability by annealing.
- the complex oxides of the Al and P main streams formed within several micrometers of the pole surface layer of the steel sheet form a selective oxide along the grain boundary or the amorphous grain interface. This is usually the case.
- Japanese Laid-Open Patent Publication No. 61-026757 discloses a technique related to ultra low carbon cold rolled steel with a Ti and Ti-Nb composite having a C: 0.0005-0.015% and an S + N content ⁇ 005%, and Japanese Laid-Open Patent No. 57-089437 No. introduces a method for producing steel having a hardening hardening amount of about 40 MPa or more using Ti-added steel of less than C: 0.010%.
- This method is to control the addition amount of Ti and Nb or the cooling rate at the time of annealing to appropriately adjust the amount of solid solution in the steel to prevent material deterioration and to give the hardening hardening, but in the case of Ti or Ti-Nb composite additive steel
- a strict control such as Ti, N, S, etc. is required during the steelmaking process, resulting in a cost increase.
- the Nb-added steel of the prior arts may exhibit problems of deterioration of workability due to high temperature annealing and an increase in manufacturing cost due to the addition of special elements.
- DBTT can be very deteriorated as 0 ⁇ 10 °C. This corresponds to the steel containing B added to about 5ppm, because the P content is excessively high, it seems that there was a problem in improving DBTT by B.
- C 0.0016 to 0.0025%
- Si 0.02% or less
- Mn 0.2 to 1.2%
- P 0.01 to 0.05%
- S 0.01% or less
- Al 0.08 to 0.12%
- N 0.0025% or less
- Ti 0.003% or less
- Nb 0.003 ⁇ 0.011%
- Mo 0.01 ⁇ 0.1%
- B 0.0005 ⁇ 0.0015% balance Fe and other unavoidable impurities
- the grain size of the hardened hardened steel is preferably ASTM No. 9 or higher.
- this invention is C: 0.0016 to 0.0025%, Si: 0.02% or less, Mn: 0.2 to 1.2%, P: 0.01 to 0.05%, S: 0.01% or less, Al: 0.08 to 0.12%, N in weight% : 0.0025% or less, Ti: 0.003% or less (excluding 0), Nb: 0.003 ⁇ 0.011%, Mo: 0.01 ⁇ 0.1%, B: 0.0005 ⁇ 0.0015% balance Fe and other unavoidable impurities
- It provides a method for producing a hardened hardened steel comprising a cold rolling step of rolling, an annealing step of continuous annealing at 750-830 ° C., and a temper rolling step of temper rolling at a reduction ratio of 1.2-1.5%.
- the winding step is the following relationship between the Al and P at a coiling temperature of 600 ⁇ 650 °C
- the winding temperature can be made without the above P-Al conditions at 600 °C.
- this invention is C: 0.0016 to 0.0025%, Si: 0.02% or less, Mn: 0.2 to 1.2%, P: 0.01 to 0.05%, S: 0.01% or less, Al: 0.08 to 0.12%, N in weight% : 0.0025% or less, Ti: 0.003% or less, Nb: 0.003% to 0.011%, Mo: 0.01% to 0.1%, B: 0.0005% to 0.0015%, and remainder Fe and other unavoidable impurities.
- the heating step of heating to a temperature of 1200 °C or more, the hot rolling step of hot finishing rolling at 900 ⁇ 950 °C, the winding step to be wound at 600 ⁇ 650 °C, after cooling the water within 30 minutes after removing the scale, 70-80% of Cold rolling step of cold rolling at a rolling reduction rate, annealing step of continuous annealing at 750 ⁇ 830 °C and a temper rolling step of temper rolling at a rolling rate of 1.2 ⁇ 1.5% provides a method for producing a small hardened steel. .
- the hardened hardened steel according to the present invention has excellent aging resistance at room temperature, and at the same time, the hardened hardened steel has a high strength of 30 MPa or more and a tensile strength of 340 to 390 MPa, which is suitable for use in various automotive parts.
- 1 is a graph showing the effect of grain size on the hardening hardening and aging index.
- FIG 3 is a view showing the results of analysis of the fine oxide and EDS formed on the grain boundary surface of the metal surface of the 750 ° C winding material.
- Figure 4 is a photograph showing the fine oxide distribution of the metal surface layer according to the coiling temperature.
- 5 is a graph showing defect generation and non-occurrence zones according to P and Al contents.
- Figure 6 is a graph showing the change in secondary work brittleness characteristics according to the content of P and Mn.
- the slab of the composition provides a method for producing a hardened hardened steel comprising the step of homogenizing heat treatment at 1200 ° C or higher, finishing hot rolling at a temperature range of 900 to 950 ° C, and winding after winding.
- the winding temperature 600 ⁇ 650 °C to control the content of P and Al through a relationship such as the following equation 1 to prevent surface defects by the selective oxidation of the hot-rolled steel sheet surface.
- the present invention provides a method of winding at 600 to 650 ° C. and cooling in water within 30 minutes or winding at or below 600 ° C. as a means of controlling the surface defect as much as possible without satisfying the condition of Equation 1 above. do.
- the hot rolled coil is then scaled off by hydrochloric acid solution, and then cold rolled at a reduction ratio of 70 to 80%, and tempered at a temperature range of 750 to 830 ° C. with a continuous annealing and a reduction ratio of 1.2 to 1.5%. It is made into a steel sheet.
- the steel sheet produced by the above-described method is finely managed so that the crystal grain size after annealing is 9 or more ASTM number (hereinafter simply referred to as ASTM No.) so that the hardening hardening amount (BH) is 30 MPa or more, and AI (Aging Index) The value has a characteristic of 30 MPa or less. Furthermore, in order to secure excellent DBTT characteristics, Mn and P contents are adjusted to satisfy the following Equation 2, and the tensile strength of the 340MPa grade high strength hardened hardened steel with excellent surface properties and secondary work embrittlement resistance and cold rolled steel sheet or hot dip plating using the same Steel sheet can be provided.
- carbonitrides such as TiN, AlN, TiC, Ti 4 C 2 S 2 , and NbC are formed by combining with precipitate forming elements such as Al, Ti, or Nb in the hot rolling step.
- carbon or nitrogen which cannot be combined with these carbonitride-forming elements, is present in solid solution in the steel, which affects the hardenability or age.
- nitrogen since nitrogen has a much higher diffusion rate than carbon, deterioration of aging resistance is very fatal compared to an increase in BH. Therefore, in general, it is often desirable to remove nitrogen from steel.
- Al or Ti precipitates first with nitrogen at higher temperature than carbon, even if it is judged that there is little BH property or ageability by nitrogen in steel, there is no big problem.
- C is an element that is indispensable to steel and its properties are determined by its content.
- the role of carbon is very important in the field of hard hardened steel, and the hard hardenability and aging resistance may change due to the presence of a small amount of solid solution C present in the steel.
- the effects on the hardening hardening and aging may vary depending on the location of the solid solution Cs present in the steel, that is, at the grain boundaries or within the grains.
- solid solution C which can often be measured by internal friction tests, is mainly present in grains and is relatively free to move, affecting aging characteristics in combination with operational potential.
- Aging index or AI (Aging Index) is an item that evaluates the aging characteristics. In general, if the AI value is 30 MPa or more, aging defects may occur before the six months of normal temperature, and may cause serious defects in press working.
- the solid solution Cs present in the grain boundaries are difficult to detect by vibration test methods such as internal friction because they exist in grain boundaries, which are relatively stable regions, and have little effect on low-temperature aging characteristics such as AI in stable regions.
- high temperature baking conditions such as baking hardening are affected.
- employment C in grains affects both aging and hardening at the same time, while employment C in grains only affects hardening of grains.
- the grain boundary is a relatively stable region, all the solid solution Cs present in the grain boundary do not affect the hard hardenability, and it is known that a part of solid solution C in the grain boundary, about 50%, affects the hard hardenability. If the presence state of such solid solution C can be properly controlled, that is, the added solid solution C can be controlled to exist in a grain boundary rather than in grains, it will be possible to secure both aging resistance and baking hardening.
- Figure 1 shows the relationship between the bake hardening amount (BH) value and the aging index (AI value) according to the grain size change.
- the grain size number (No) increases, so that the grain size becomes finer, the decrease in AI value against the BH value is remarkable.
- the BH-AI value gradually increases, and thus the aging resistance is excellent.
- the present inventors attempted to refine the annealing grain size below an appropriate level in order to control so as to distribute the solid solution C present in the steel as much as possible within the grain boundaries.
- ASTM No the grain size for maximizing the aging resistance while minimizing the degradation of the baking hardenability was determined by ASTM No. It was found that controlling to 9 or more is preferable.
- the component system (% of the component system is the weight% or less) constituting the steel material in detail.
- Carbon (C) is an element showing solid solution hardening and baking hardening. If the carbon content is less than 0.0016%, the tensile strength is insufficient due to the very low carbon content, and even if the grain refining effect by the Nb is added, the absolute carbon content in the steel is low, so that sufficient baking hardening property is not obtained. In addition, there is no site competition effect between employment C-Ps, which is very deteriorating in terms of secondary processing brittleness. On the other hand, if the amount of carbon is more than 0.0025%, even if the carbon content is excessively increased and the grain size becomes fine, the solid solution C present in the grain increases in proportion to the total amount of carbon added. May deteriorate. The total amount of carbon added to satisfy these conditions was limited to 0.0016% to 0.0025%.
- Si is an element which increases the strength, but the strength increases as the amount added increases, but ductility deterioration is remarkable.
- excessive addition of Si may degrade the hot-plating property, so it is advantageous to add it as low as possible. Therefore, in order to prevent such material deterioration and plating property deterioration, the amount of Si added is limited to 0.02% or less.
- Manganese (Mn) is an element that refines particles without damaging ductility, and precipitates S in steel completely with MnS to prevent hot brittleness due to the formation of FeS and to strengthen the steel. If the Mn content is less than 0.2%, it is difficult to secure proper tensile strength.However, if the Mn content exceeds 1.2%, strength increases rapidly due to solid solution strengthening and moldability deteriorates. Since a large amount of oxide is formed on the surface, there is a concern that a large amount of plating defects such as deterioration of plating adhesiveness and streaks are generated, which is not good for the quality of the final product, so the amount of addition is limited to 0.2 to 1.2%.
- Phosphorus (P) is a substitution-type alloy element having a high solid solution strengthening effect, and serves to improve in-plane anisotropy and strength.
- P refines the hot-rolled sheet grains and promotes the development of the (111) aggregate structure, which is advantageous for the improvement of the average r value in the future annealing step.
- the baking hardenability tends to increase.
- P has two problems as follows. First, since P promotes selective oxidation along the grain boundaries of the steel sheet at high temperatures such as hot rolling, the surface is dropped during rolling when the selective oxidation is intensified. May cause defects. In addition, the selective oxidation phenomenon may increase more rapidly in the presence of Al in the steel components may cause more danger.
- the content of P is limited by the following equation according to the Al content.
- P has a problem in that the secondary work brittleness deteriorates due to the weakening of the binding force of the grain boundary when the amount of addition increases more than a certain level.
- the molding of the parts performed in the automobile company goes through several times of repeated press processing, and the second cracking occurs in the processing cracks after the first press processing. .
- These cracks occur due to the presence of phosphorus (P) in the grain as a grain boundary, which weakens the binding force of the grains.
- P phosphorus
- the least decrease in elongation is the employment element P, and above all, the cost is low.
- S Sulfur
- S is an element that must be precipitated as a sulfide of MnS at high temperature in order to prevent hot brittleness due to FeS. If the content of S is excessive, the precipitated MnS and the remaining S may embrittle the grain boundary, causing hot brittleness. In addition, even if the amount of S added can sufficiently precipitate the MnS precipitate, if the amount is large, material degradation due to excessive precipitate may occur, so the amount is limited to 0.01% or less.
- Aluminum meaning soluble Al (sol. Al) in the present invention.
- Aluminum is usually added for deoxidation of steel, but it is also possible to obtain grain refining effect and Al hardenability improvement by AlN precipitation.
- nitrogen precipitates mostly coarse with TiN at a high temperature of 1300 ° C. or higher.
- AlN precipitation by Sol. Al occurs in steel in which Ti is added in a small amount of 30 ppm or less.
- Sol.Al when Sol.Al is present in the usual range of 0.02 ⁇ 0.06%, it simply plays a role of fixing nitrogen solution. However, when 0.08% or more is added, the precipitate of AlN is very fine.
- Nitrogen (N) deteriorates the formability of steel by being in solid solution before or after annealing.
- the aging deterioration is very large compared to other invasive elements, so it is necessary to fix with Ti or Al.
- Nb is appropriately added along with a small amount of Ti addition
- excessive addition of nitrogen generates solid solution nitrogen in the steel.
- nitrogen has a very fast diffusion rate compared to carbon, so when present as solid nitrogen, the deterioration of room temperature aging resistance is very serious compared to solid solution C.
- the yield strength increases and elongation and r value deteriorate due to the remaining of solid solution nitrogen, the content thereof needs to be limited to 0.0025% or less as in the present invention.
- Ti is a carbonitride forming element and forms nitrides such as TiN, sulfides such as TiS or Ti 4 C 2 S 2 and carbides such as TiC in the steel.
- Ti is added to 0.003% or less, and only a small amount of nitrogen is fixed.
- the reason for suggesting such a small amount of Ti content is that a very small amount of various components are added to satisfy the material characteristics of steelmaking during production. This is because Ti may be contained, and when the tapping is performed several times at the same time due to the performance characteristics of steel making, the present Ti may be contained in the tapping material of the present invention steel. Therefore, in the case of controlling Nb as a main element to improve the aging resistance as in the present invention, it may not be necessary to add Ti, and further, BH may occur when Ti is added. The content of Ti was limited below.
- Nb is a strong carbonitride-forming element that fixes carbon present in steel with NbC precipitates, and especially NbC precipitates produced are very fine compared to precipitates in other steels and can act as a strong barrier to grain growth during recrystallization annealing. . Therefore, the grain refining effect by Nb is due to the effect of such NbC precipitates, which can achieve the hardening hardening by solid solution C by remaining solid solution C in steel. To this end, it is necessary to properly control the amount of NbC precipitates in the steel and to maintain solid solution C in a range that minimizes material degradation. Therefore, Nb is limited to 0.003 ⁇ 0.011% by considering the carbon content (16-25ppm) in order to achieve grain refining effect by NbC precipitates and to secure baking hardening through proper solid solution C residual.
- Mo is dissolved in steel to improve strength or to form Mo-based carbides. In particular, it increases the binding force of the grain boundary when in the solid state, and serves to improve the grain breakage problem caused by phosphorus (P), that is, the secondary work brittleness. In addition, the diffusion of carbon is suppressed by the affinity with solid solution C, and the aging resistance is also improved. Therefore, Mo is added at least 0.01%. However, when the Mo content is excessively excessively exceeding 0.1%, the improvement effect of the secondary work brittleness and the aging resistance is saturated and the economical efficiency is low. Therefore, Mo content is limited to the range of 0.01 to 0.1%.
- B exists as an invasive element in steel and is dissolved in grain boundaries or combines with nitrogen to form nitrides of BN.
- B is an element having a great influence of the material compared to the added amount, and it is necessary to strictly limit the added amount. In other words, even if a small amount of B is added to the steel, segregation at grain boundaries can improve secondary work brittleness, but if it is added above a certain amount, material degradation occurs due to an increase in strength and a significant decrease in ductility. Add to limit 0.0005 to 0.0015%.
- the slab having the above composition is heated to a temperature of 1200 ° C. or higher at which austenite structure can be sufficiently homogenized before hot rolling, and finishes hot rolling at 900 to 950 ° C., which is directly in the Ar 3 temperature range.
- the slab temperature is less than 1200 °C, the structure of the steel does not become uniform austenite grains, and the mixing occurs, which may cause deterioration of the material.
- the hot rolling finish temperature is less than 900 °C, the top of the hot rolled coil may be The tail and edges become single-phase regions, which may increase the in-plane anisotropy and deteriorate the moldability. When it exceeds 950 ° C, remarkable coarse grains occur, such as orange peel or the like on the surface after processing. Defects can occur.
- the present invention performs a winding step while controlling the relationship of Al-P by preventing the deterioration of formability due to excessive grain refinement as well as an appropriate grain refinement effect of 9 or more as ASTM No.
- winding is performed at 600 to 650 ° C. If the coiling temperature exceeds 650 ° C, the grain size increases after annealing and sufficient grain refining effect cannot be obtained even if other conditions are satisfied, and grain boundary segregation of P increases and Al-P as shown in FIG. Internal oxides may increase to deteriorate secondary work brittleness.
- FIG. 5 shows X when the embrittlement of the surface of the hot-rolled steel sheet was observed at a coiling temperature of 620 ° C. for the specimens in which P and Al components were variously changed. It was. Referring to FIG. 5, it can be seen that the composition of Al and P must be properly managed to control surface embrittlement.
- the process can be performed by setting the coiling temperature to 600 ° C or lower.
- the third aspect also does not have to satisfy the relational expression of Al-P, and it is possible to prevent embrittlement of the surface by adjusting only the winding temperature.
- the third aspect may be advantageous because the coiling temperature is lower than the first aspect and is not limited to the Al-P relation, but the lower coiling temperature is not always preferable for the process. Therefore, the hardened hardened steel can be manufactured under appropriate winding conditions.
- the distribution of each of the fine oxides according to the coiling temperature conditions is shown in the micrograph of FIG. 4.
- the steel After hot rolling, the steel is pickled in the usual manner and then cold rolled at a high cold rolling rate of 70 to 80%.
- the reason why the cold rolling rate is higher than 70% is to improve moldability, in particular, r value as well as improving aging resistance due to grain refinement effect.
- the cold rolling rate exceeds 80%, the grain refining effect is large, but the grain size becomes too large due to excessive rolling rate, which causes hardening of the material, and the r value may gradually decrease due to excessive cold rolling rate increase. have.
- Cold-rolled steel is continuously annealed by conventional methods in the temperature range of 750 ⁇ 830 °C. Since the Nb additive steel has a higher recrystallization temperature than the Ti additive steel, it is annealed at a temperature of 750 ° C, preferably 770 ° C or higher. This is because when the annealing temperature is lower than 750 ° C, the yield strength increases and the elongation and r value may deteriorate due to the presence of unrecrystallized grains. However, if the annealing temperature exceeds 830 °C formability can be improved, but the grain size of the ASTM No. It becomes smaller than 9, AI value is 30 MPa or less, and aging resistance deteriorates.
- the temper rolling is carried out at a reduction ratio of 1.2 to 1.5%, which is somewhat higher than the usual temper rolling ratio, for the purpose of securing appropriate bake hardening resistance and room temperature aging resistance using the calcined hardened steel manufactured by the above-described manufacturing method.
- the reason why the temper rolling ratio is set higher than 1.2% is to prevent the deterioration of room temperature aging due to solid solution C in steel.
- the temper rolling rate exceeds 1.5%, even though the room temperature aging resistance can be improved, the temper rolling rate is high, resulting in work hardening, resulting in deterioration of the material, and especially in the case of manufacturing a hot-dip galvanized sheet, deterioration of plating adhesion due to excessive temper rolling. Since the peeling of the plating layer may occur, it is limited to the temper rolling ratio of 1.2 ⁇ 1.5%.
- Table 1 below shows the chemical composition of the inventive steels and comparative steels in which the amounts of C, P, Ti, Nb, Sol.Al, and Mo are strictly controlled in order to simultaneously satisfy the surface and material properties.
- the grain size of the invention steel exhibited through the above conditions was ASTM No. as 9.8 to 11.5 (average grain size 6.7-12.0 ⁇ m) as ASTM No. It turns out that all the conditions which are nine or more are satisfied.
- the invention steels are excellent in hardening hardening resistance and aging resistance in the range of 38.1 to 50.2 MPa of BH and 8.0 to 29.1 MPa of AI, and DBTT of -45 ° C or lower, and fully satisfying DBTT conditions of -30 ° C or lower. I was satisfied.
- the plating defects of the hot-dip plated material had a surface defect per 10 km per coil within 10 km.
- the C content was 0.0054%, which satisfies the process conditions such as the hot rolling temperature and the annealing temperature.
- the recrystallized grain size was also very fine as 11.2 as ASTM No., but due to the high carbon content, BH The value is very high and the AI value is 51.2 MPa, which is outside the proper range.
- Comparative steel 4 had a low C content, resulting in coarse grains and no BH or AI properties.
- Comparative steel 5 could not obtain the effect of improving the grain size and BH value due to the deviation of Sol.Al content and Nb content, and because the high Nb content, all solid solution C in the steel was formed as NbC precipitates, resulting in no BH value. I didn't lose.
- Comparative steel 5 had a high P content and did not add Mo and B at all, and did not improve the secondary work brittleness improvement effect by Mo and B.
- P content was increased to 0.062%, and P and Al interaction occurred, thereby increasing the surface oxide from the hot rolling step. Therefore, a large amount of surface defects, such as linear defects, are generated during the production of a hot dip plating material due to the increase of the oxide.
- Comparative steel 6 had an inadequate P content of 0.059%, a low addition of Slo.Al and no Mo at all. Therefore, as shown in Table 2, the BH and AI properties were satisfactory, but the DBTT characteristics deteriorated due to the decrease in the bonding strength between grains due to the high content of P and no addition of Mo, and surface defects also exceeded 10 or less per coil.
- Comparative steel 7 had a low content of Sol.Al and no Mo and B were added. Therefore, there is no room for further improvement of grain refining effect and hardening hardenability due to the low content of Sol.Al, and the DBTT characteristic is deteriorated due to the addition of Mo and B.
- Comparative steel 8 is 0.12% of P, much more than 0.01 to 0.05%, and B is not added. Although small amount of DBTT property is improved by Mo, the addition amount of P is very high, and the improvement effect is limited. In particular, the addition of B has lost the effect of improving DBTT property. Due to this effect, the DBTT was very high as 15 ° C., and the surface defects of the molten plating material were greatly increased due to the excessive addition of P.
Abstract
Description
강종 | 화학성분(wt%) | |||||||||
C | Mn | P | S | Sol.Al | Ti | Nb | N | Mo | B | |
발명강 1 | 0.0021 | 0.58 | 0.032 | 0.0082 | 0.087 | 0 | 0.008 | 0.0016 | 0.034 | 0.0005 |
발명강 2 | 0.0022 | 0.73 | 0.012 | 0.0081 | 0.098 | 0 | 0.01 | 0.0024 | 0.048 | 0.0005 |
발명강 3 | 0.0023 | 0.75 | 0.022 | 0.0058 | 0.105 | 0.0025 | 0.0082 | 0.0019 | 0.061 | 0.0007 |
발명강 4 | 0.002 | 0.61 | 0.031 | 0.0083 | 0.118 | 0.0015 | 0.0073 | 0.0015 | 0.059 | 0.0005 |
발명강 5 | 0.0017 | 0.98 | 0.036 | 0.0070 | 0.105 | 0 | 0.004 | 0.0017 | 0.051 | 0.0008 |
발명강 6 | 0.0019 | 1.01 | 0.04 | 0.0063 | 0.089 | 0 | 0.005 | 0.0020 | 0.062 | 0.0009 |
비교강 1 | 0.0054 | 0.64 | 0.039 | 0.0071 | 0.082 | 0.001 | 0.011 | 0.0017 | 0.021 | 0.0007 |
비교강 2 | 0.0022 | 0.63 | 0.036 | 0.0085 | 0.04 | 0.025 | 0.009 | 0.0015 | 0.015 | 0.0005 |
비교강 3 | 0.0012 | 0.65 | 0.04 | 0.0072 | 0.075 | 0.001 | 0.0105 | 0.0019 | 0.059 | 0.0008 |
비교강 4 | 0.0021 | 0.93 | 0.036 | 0.0089 | 0.043 | 0 | 0.022 | 0.0017 | 0.021 | 0.0006 |
비교강 5 | 0.0022 | 0.049 | 0.062 | 0.0066 | 0.071 | 0.002 | 0.009 | 0.0022 | 0 | 0.0007 |
비교강 6 | 0.0019 | 0.99 | 0.059 | 0.0078 | 0.041 | 0.001 | 0.008 | 0.0021 | 0 | 0 |
비교강 7 | 0.0021 | 0.62 | 0.047 | 0.0085 | 0.061 | 0 | 0.008 | 0.0019 | 0 | 0 |
비교강 8 | 0.0023 | 0.98 | 0.12 | 0.0078 | 0.098 | 0.001 | 0.009 | 0.0023 | 0.031 | 0 |
강종 | CT | 소둔온도 | TS | BH(MPa) | AI(MPa) | Grain size No. | DBTT(℃) | 도금결함 |
발명강 1 | 620℃ | 800℃ | 355.8 | 42.7 | 22.8 | 10.5 | -45 | ⊙ |
발명강 2 | 620℃ | 810℃ | 357.3 | 40.2 | 16.8 | 9.8 | -65 | ⊙ |
발명강 3 | 620℃ | 780℃ | 361.4 | 41.3 | 17.9 | 9.9 | -60 | ⊙ |
발명강 4 | 610℃ | 800℃ | 365.7 | 44.4 | 20.5 | 10.5 | -50 | ⊙ |
발명강 5 | 640℃ | 790℃ | 357.9 | 50.2 | 29.1 | 10.0 | -50 | ⊙ |
발명강 6 | 620℃ | 820℃ | 367.8 | 47.6 | 25.7 | 11.1 | -50 | ⊙ |
비교강 1 | 620℃ | 810℃ | 370.0 | 62.7 | 51.2 | 11.2 | -40 | ⊙ |
비교강 2 | 640℃ | 800℃ | 346.2 | 16.1 | 12.5 | 8.1 | -40 | ⊙ |
비교강 3 | 620℃ | 810℃ | 368.9 | 0.0 | 0.0 | 8.2 | -40 | ⊙ |
비교강 4 | 630℃ | 800℃ | 391.4 | 0.0 | 0.0 | 9.1 | -50 | ⊙ |
비교강 5 | 620℃ | 810℃ | 349.3 | 38.3 | 24.1 | 10.9 | 0 | × |
비교강 6 | 630℃ | 790℃ | 363.6 | 38.9 | 26.6 | 9.2 | -10 | △ |
비교강 7 | 620℃ | 810℃ | 353.8 | 41.1 | 27.0 | 9.5 | -15 | ⊙ |
비교강 8 | 640℃ | 820℃ | 407.2 | 40.9 | 20.6 | 9.8 | 15 | × |
Claims (6)
- 중량%로, C:0.0016~0.0025%, Si:0.02% 이하, Mn:0.2~1.2%, P:0.01~0.05%, S:0.01% 이하, Al:0.08~0.12%, N:0.0025% 이하, Ti:0.003% 이하, Nb:0.003~0.011%, Mo:0.01~0.1%, B:0.0005~0.0015% 잔부 Fe 및 기타 불가피한 불순물을 포함하며,상기 Mn과 P는DBTT = 803P - 24.4Mn - 58 ≤ -30(℃)의 관계를 만족하며,상기 Al 및 P는P ≤ -0.048*loge (Al) - 0.07의 관계를 만족하는 소부경화강.
- 제1항에 있어서, 상기 소부경화강의 결정립 크기는 ASTM No.9 이상인 소부경화강.
- 중량%로, C:0.0016~0.0025%, Si:0.02% 이하, Mn:0.2~1.2%, P:0.01~0.05%, S:0.01% 이하, Al:0.08~0.12%, N:0.0025% 이하, Ti:0.003% 이하(0을 제외), Nb:0.003~0.011%, Mo:0.01~0.1%, B:0.0005~0.0015% 잔부 Fe 및 기타 불가피한 불순물을 포함하며상기 Mn 및 P사이에는 다음의 관계DBTT = 803P - 24.4Mn - 58 ≤ -30(℃)를 만족하는 강 슬라브에 대하여,1200℃ 이상의 온도로 가열하는 가열 단계;900~950℃에서 열간 마무리 압연하는 열간압연 단계;상기 열간압연된 강판을 권취하는 권취단계;공냉 후 스케일을 제거한 후, 70~80%의 압하율로 냉간압연하는 냉간압연 단계;750~830℃에서 연속소둔하는 소둔 단계; 및1.2~1.5%의 압하율로 조질압연하는 조질압연 단계를 포함하는 소부경화강의 제조방법.
- 제3항에 있어서, 상기 권취단계는 권취온도가 600~650℃에서 상기 Al 및 P 사이에 다음의 관계P ≤ -0.048*loge (Al) - 0.07를 만족하며 이루어지는 소부경화강의 제조방법.
- 제3항에 있어서, 상기 권취단계는 권취온도가 600℃ 이하에서 이루어지는 소부경화강의 제조방법.
- 중량%로, C:0.0016~0.0025%, Si:0.02% 이하, Mn:0.2~1.2%, P:0.01~0.05%, S:0.01% 이하, Al:0.08~0.12%, N:0.0025% 이하, Ti:0.003% 이하, Nb:0.003~0.011%, Mo:0.01~0.1%, B:0.0005~0.0015% 잔부 Fe 및 기타 불가피한 불순물을 포함하며,상기 Mn과 P는DBTT = 803P - 24.4Mn - 58 ≤ -30(℃)의 관계를 만족하는 강 슬라브에 대하여,1200℃ 이상의 온도로 가열하는 가열 단계;900~950℃에서 열간 마무리 압연하는 열간압연 단계;600~650℃에서 권취하는 권취단계;권취 후 30분 이내에 수냉 후 스케일을 제거하고, 70~80%의 압하율로 냉간압연하는 냉간압연 단계;750~830℃에서 연속소둔하는 소둔 단계; 및1.2~1.5%의 압하율로 조질압연하는 조질압연 단계를 포함하는 소부경화강의 제조방법.
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CN115627414A (zh) * | 2022-09-23 | 2023-01-20 | 马鞍山钢铁股份有限公司 | 一种抗二次加工脆性及优良表面质量的含磷if钢板及其生产方法 |
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CN115627414A (zh) * | 2022-09-23 | 2023-01-20 | 马鞍山钢铁股份有限公司 | 一种抗二次加工脆性及优良表面质量的含磷if钢板及其生产方法 |
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