TWI555859B - Stainless steel with mattress iron and its manufacturing method - Google Patents

Description

Ma Tian scattered iron series stainless steel and its manufacturing method Technical field of the invention

The present invention relates to a stainless steel plate for a brake disc for a two-wheeled vehicle and a method for manufacturing the same, and relates to a 麻田散铁-based stainless steel plate for a two-wheeled brake disc having excellent surface and end face properties.

Background technique

The brake discs of the two-wheeled vehicle are required to have characteristics such as wear resistance, rust resistance and toughness. The abrasion resistance system generally becomes larger as the hardness becomes higher. On the other hand, since the hardness is too high, a so-called brake sound is generated between the brake device and the pad, so the hardness of the brake device is required to be 32 to 38 HRC (Rockwell hardness C rating). Because of these required characteristics, the brake discs of the two-wheeled vehicle use the Ma Tian loose iron stainless steel plate.

Previously, SUS420J2 was quenched and tempered to adjust the required hardness to be used as a brake disc. However, there are two heat treatment steps requiring quenching and tempering. In contrast, Patent Document 1 (Japanese Laid-Open Patent Publication No. SHO 57-198249) discloses an invention relating to a steel composition which is stably obtained in a quenching temperature range wider than that of the prior steel of SUS420J2 steel. Hardness required, and capable of quenching Use directly below. In the same manner as SUS410, SUS403, and SUS410S steels, the C is reduced in the same manner as the SUS410, SUS403, and SUS410S steels, and the Mn of the Vostian iron stabilizer element is added to supplement the reduction of the single-phase temperature region of the Worthite iron due to the low C, that is, the quenching. The heating temperature region is narrowed.

In the patent document 2 (Japanese Laid-Open Patent Publication No. Hei 8-60309), the invention relates to a steel sheet for a locomotive disc brake which can be used directly in a quenched state. This steel sheet is formed by reducing Mn and simultaneously adding Ni and Cu having the same effects as the elements forming the Worth iron.

Moreover, in recent years, the two-wheeled vehicle has also been expected to reduce the weight of the vehicle body and has studied the weight reduction of the two-wheel brake disc. At this time, the deformation of the disk caused by the softening of the disk material due to the heat generated during braking is a problem, and in order to solve this problem, it is necessary to improve the heat resistance of the disk material. As one of the solutions, there is an invention for improving the heat resistance by adding Nb and Mo, as disclosed in Japanese Laid-Open Patent Publication No. 2001-220654. . Patent Document 4 (Japanese Laid-Open Patent Publication No. 2005-133204) discloses an invention of a disk material having excellent heat resistance by performing a quenching treatment at a temperature of more than 1000 °C. As a brake disc having an excellent temper softening resistance, the patent document 5 (Japanese Patent Laid-Open Publication No. Hei. No. 2006-322071) discloses a granulated iron structure having an average particle diameter of the old Worthfield iron particles of 8 μm or more. In the invention of the present invention, Patent Document 6 (Japanese Patent Laid-Open Publication No. 2011-12343) discloses a structure after quenching, in which the area ratio is 75% or more of 麻田散铁, and Nb is set to 0.10% or more. The invention of 0.60% or less.

Such a low-C ramie-dispersed iron-based stainless steel has a low hot workability, and is liable to cause cracking at the end of the width during hot rolling, so-called edge cracking. Patent Document 7 (Japanese Patent Laid-Open Publication No. 2008-285692) It is revealed that the composition can be controlled and limited to a range in which cracks are not easily generated.

Patent Document 8 (Japanese Laid-Open Patent Publication No. 2000-61524) relates to a method for producing a ferrite-based iron-based stainless steel belt. This patent document relates to a method for producing a ferrite-grained stainless steel hot-rolled steel strip which can be produced with good productivity, particularly excellent in formability and material uniformity, and which discloses sheet bar heating. Optimal conditions.

With this technology, the low-C Ma Tian loose-iron stainless steel system is widely used as a material for a disc brake device for a two-wheeled vehicle. On the other hand, in recent years, there has been a gradual demand for improved productivity in the manufacture of disc brakes. For example, it is required to shorten the heating time during heating quenching and to shorten the polishing time after heating quenching. Further, it is also required to improve the yield by using the width end portion of the steel strip.

In order to shorten the polishing time and increase the amount of polishing per unit time, the friction of the processing friction causes an increase in the wear of the jig, and the material is tempered and softened, which is not preferable. Therefore, in order to shorten the polishing time without generating machining friction heat, the polishing thickness is usually reduced. Therefore, the edge seam at the edge of the width of the steel strip is gradually becoming a problem.

1A shows the appearance of the linear crack 边缘 at the edge of the actual product, and FIG. 1B shows a micrograph of the cross section of the linear crack 边缘 at the edge of the actual product. The step of manufacturing a hot-rolled steel strip is to heat a steel embryo having a thickness of 150 to 250 mm to 1100 to 1300 ° C, using coarse heat. The rolling mill rolls into a thick steel strip having a thickness of 20 to 40 mm, and then it is usually rolled up by a finishing hot rolling mill to a thickness of 3 to 6 mm. Since the tension is not applied during the rough hot rolling, the width is enlarged and a part of the end face of the steel is formed into the surface of the thick steel strip. Since the end face of the steel blank does not contact the roll at the beginning of the rough hot rolling, the roughness is large, and then it is a cause of flaws when it comes into contact with the roll.

In many hot-rolled steel strips of iron and steel materials, edge linear cracks can be observed. Various stainless steel 80 mm thick steel blocks were hot rolled to 20 mm in the laboratory, and a photograph of the observed end faces is shown in Fig. 2, and it was found that the surface roughness at each steel end face was greatly different. Moreover, in SUS410 steel, it was found that the surface roughness of the end surface greatly changed in accordance with the hot rolling heating temperature. Since the surface of the steel embryo end face is rough at the time of rough hot rolling, which is caused by the difference in the deformation pattern due to the crystal orientation difference of each crystal grain of the steel blank, the case where the crystal grain size is coarse is remarkable. For example, when the ordinary steel system is cooled to room temperature after solidification, the δ/γ and γ/α are transformed to a 2 degree state and the structure is made fine. Here, the δ system represents δ ferrite iron, the γ system represents Worth iron, and the α system represents α ferrite iron, but when it is described as fertilized iron, it generally means α ferrite iron. The ferrite iron precipitated from the δ ferrite iron system above the A4 metamorphic point, and the alpha ferrite iron system precipitated the ferrite iron below the A3 metamorphic point.

Ordinary steel is made fine by α/γ metamorphism again during hot rolling heating, and since coarse hot rolling is performed in a γ single-phase region which is easy to recrystallize, crystal grains obtained by recrystallization are also added. The effect of miniaturization becomes fine particles, and it is not easy to produce edge-line cracks. On the other hand, if the ferrite is made of iron-based stainless steel, the ferrite particles at the time of solidification are also The deformation is not carried out, and it is maintained until the hot rolling is heated. Since it is coarse particles, edge linear cracks are likely to occur. If the ferrite-based iron-based stainless steel does not become a γ single-phase steel after solidification, it is usually not distinguished from the δ ferrite iron and the alpha ferrite iron.

The Matian iron-based stainless steel is also SUS420J1, and its composition is 13%Cr-0.2%C. When hot-rolled, it is a single phase of Worthite iron. By metamorphosis, the microstructure is refined and the Worstian iron is re-used. Crystallization causes the microstructure to be finer, and it is less prone to edge edge cracks.

However, when the low-C 麻田散铁-based stainless steel is used, the temperature range of the single phase of the Worthite iron is narrow, and it becomes a two-phase structure of the δ ferrite iron and the Worthite iron during hot rolling heating. At this time, it is easy to cause the edge linear crack 瑕疵 due to the δ ferrite iron, and in the grinding step after the disk brake is quenched, the polishing thickness must be larger than the edge linear crack 瑕疵 depth to impede productivity.

When the hot rolling heating temperature is lowered to increase the Worthite iron ratio, the hot workability is lowered due to an increase in deformation resistance, and there is a problem that edge cracking occurs during hot rolling. When the amount of C is increased and the γ phase fraction is increased, the quenching hardness becomes too high. When the Worstian iron stabilizer element such as Mn, Ni or Cu is further added, the raw material cost increases, and the annealing cooling time in the hot-rolled sheet annealing step is prolonged and the productivity is impaired. When the amount of Cr is lowered and the iron fraction of Worth is increased, there is a problem that the corrosion resistance is impaired.

In order to control the iron fraction of δ fertilizer, it is necessary to know the change of the δ fertilizer iron fraction in hot rolling, but it is impossible to determine the δ fertilizer iron fraction of the hot rolled sheet. The δ fat fraction of the steel embryo during hot rolling heating can be measured by a state diagram calculation method and a heat treatment test in a laboratory. From Worthfield Iron and Hemp When the two-phase structure of the field iron is quenched, the Worthite iron phase system becomes the Matian loose iron structure, and the δ fat grain iron phase system can be easily distinguished by the less strained δ fat grain iron phase. However, in the actual hot rolling step, after the steel blank is discharged from the hot rolling furnace, it is impossible to know how the δ ferrite iron amount changes during the hot rolling. The hot-rolled steel strip after the hot rolling is finished, and the hot-rolled steel strip which is wound with the Worth iron is a low-toughness and is difficult to directly unwind. Although it is possible to anneal the hot-rolled sheet in a box annealing furnace and temper the granulated iron into a ferrite iron and a carbide, the hot-rolled sheet structure before annealing cannot be investigated. After hot rolling annealing, as shown in Fig. 3, it is impossible to determine the δ fertilizer iron fraction by the structure of ferrite iron and carbide.

Summary of invention

The inventors of the present invention have studied the method of investigating the iron fraction of the delta-fertilizer in the ferrite-grained iron-phase phase in the hot-rolled annealed steel sheet of the low-C Matian iron-based stainless steel. In order to test the results of various etching liquids by the structure analysis and optical microscope observation of Electron Backscatter Diffraction (EBSD), it was found that the δ fat iron system can be colored using Murakami reagent. The Murakami reagent is an aqueous solution of potassium ferricyanide, which is etched by heating the aqueous solution and immersing the sample therein. Usually, it is used in the solidification structure of the iron-based stainless steel such as Vostian, by coloring the δ ferrite iron doped in the Vostian iron matrix to distinguish the Worthite iron from the δ fat iron phase. In the hot-rolled annealed steel sheet of the granulated iron and the granulated iron of the granulated iron, the δ ferrite iron was initially unimaginable, but as shown in Fig. 4, it can be clearly identified. The gray contrast portion of Figure 4 is the δ fat iron portion. The mechanism for coloring and identifying the δ ferrite iron using the Murakami test is not clear, but the results of the investigation by the inventors can be presumed to be due to the δ ferrite iron phase and the Worthite iron phase (in the room) during hot rolling heating. The Cr concentration of Wenwei Matian bulk iron phase is about 1.5%, and the high-Cr δ ferrite iron phase system can be colored and identified by Murakami test. This kind of δ ferrite iron in the low-Cr Matian iron-based stainless steel is an example in which the Murakami test is not used, and it is a novel insight that the difference in the amount of Cr can be recognized by a little 1.5%. By using this technique, the behavior of the δ fat iron that was not known in the past has become clear. For example, it is found that the amount of ferrite in the hot rolled sheet is greatly reduced as compared with the amount of δ ferrite in the hot rolling heating temperature. Further, it is considered that the amount of ferrite in the width end portion is larger than that in the central portion of the width of the steel strip; there is a possibility of a temperature difference between the width end portion and the width center portion of the steel blank; There is a possibility that the amount of carbon and δ fat iron will increase. For the hot-rolled steel sheet which is not subjected to hot rolling annealing, the δ ferrite iron can be identified by evaluating the steel sheet sample as described above.

The relationship between the edge linear crack 瑕疵 and the δ ferrite iron amount is shown in Fig. 5, and the edge linear crack 无法 cannot be observed in the Worthfield iron-based stainless steel system in which the δ fertilizer iron fraction is 0%. As the iron fraction of δ fertilizer increases, the depth of the linear crack 逐渐 gradually increases, and the increase of the linear crack 瑕疵 depth to the δ fertilizer iron fraction of 30% is small. However, when the iron fraction of the δ fertilizer is more than 30%, the depth of the linear crack 遽 is rapidly increased.

On the other hand, the edge cracking of the end portion of the steel sheet is likely to occur when the iron fraction of the granules is less than 5%.

Figure 6 shows the end morphology of the iron fraction of the fertilizer after hot rolling of 4%, 20% (11% Cr, 12% Cr) - 0.04% C - 1.4% Mn - 0.03% N steel. When the iron fraction of the δ fertilizer is low, a significant edge rupture occurs.

Thus, any of the hot-rolled annealed steel sheets and the hot-rolled steel sheets is strongly correlated with the δ-fertilizer iron fraction and the edge-line crack 瑕疵 depth and edge rupture at the edge end of the steel sheet width, because as long as the δ is controlled The granulated stainless steel of the Ma Tian, which is made of iron and iron, has no edge cracking and the edge line crack is shallow. Therefore, it is possible to sharpen the grinding depth in the manufacturing step of the brake disc, and to improve the brake disc. Productive. Moreover, since it is possible to use the end limit of the steel sheet, the yield is also improved.

Thus, as a method of controlling the iron fraction of the δ fat particles which largely dominates the surface quality, it is considered that the control (1) chemical composition and (2) hot rolling heating temperature are effective. However, in the chemical composition of (1), since the amount of C and N is controlled, the quenching hardness necessary for the disc brake is not obtained, which is not preferable. In addition, Si, Mn, Cr, Ni, Cu, etc., in addition to the influence on the thickness of hot-rolled rust, and also on temper softening resistance and corrosion resistance, and at the same time a large amount of addition, there is a problem of an increase in alloy cost. , so that the range of control can be limited. (2) When the amount of iron in the δ ferrite is adjusted by the hot rolling heating temperature, in order to reduce the amount of δ ferrite and the heating temperature is 1150 ° C or less, the iron phase of the Worthfield and a little residual fertilizer The strength of the iron phase is poor and edge cracking is liable to occur, so that it is not easy to improve the surface quality by controlling the δ ferrite iron.

The inventors of the present invention have conducted detailed studies on the amount of δ ferrite grains, hot rolling operation conditions, and chemical compositions of hot-rolled annealed steel sheets, and found that both surface quality and edge cracking are satisfied and the hardness and corrosion resistance necessary as a disc brake are satisfied. An effective method. That is, to satisfy (1) the amount of δ ferrite in hot rolling heating And (2) adjusting the composition in various ways, and at the same time, in order to prevent the δ fat iron amount from being lowered due to the temperature decrease during rough rolling from the (3) hot rolling furnace, in the rough hot rolling and The hot steel strip must be heated and heated by means of induction heating or the like between the finishing hot rolling.

Based on these findings, it is possible to provide a hot-rolled steel sheet and a hot-rolled annealed steel sheet for the brake disc for the brake disc with the edge line crack and the edge of the width of the hot-rolled steel strip from being broken at the same time as the tissue control method.

The present invention has been achieved based on such findings, and the means for solving the problems of the present invention, that is, the granulated stainless steel (including hot-rolled steel sheet (not subjected to hot rolling annealing)) and hot rolling of the two-wheeled brake disc of the present invention. The annealed steel sheet and its manufacturing method are as follows.

(1) A maitian iron-based stainless steel for a two-wheeled brake disc, characterized by containing C: 0.025 to 0.080%, Si: 0.05% to 0.8%, and Mn: 0.5 to 1.5% by mass%, P: 0.035% or less, S: 0.015% or less, Cr: 11.0 to 13.5%, Ni: 0.01 to 0.50%, Cu: 0.01 to 0.08%, Mo: 0.01 to 0.30%, V: 0.01 to 0.10%, and Al: 0.05% or less , N: 0.015~0.060%, and the remaining part is Fe and unavoidable impurities; and the DFE value specified by the formula (1) is 5 or more and 30 or less, and the δ fertilizer iron fraction observed in the cross-sectional structure is The area ratio is 5% or more and 30% or less.

DFE=12(Cr+Si)-430C-460N-20Ni-7Mn-89‧‧‧(1)

Further, Cr, Si, C, N, Ni, and Mn in the formula (1) mean the content (% by mass) of each element.

(2) The Ma Tian scattered iron type stainless steel for the two-wheeled brake disc of the present invention, In terms of % by mass, one or two types of Ti: 0.03% or less and B: 0.0050% or less are further contained.

(3) The granulated iron-based stainless steel for the two-wheeled brake disc of the present invention further contains Nb: 0.30% or less in mass%.

(4) In the mass%, the mass of the two-wheeled brake disc of the present invention further contains one or two types of Sn: 0.1% or less and Bi: 0.2% or less.

(5) A method for manufacturing a granulated iron-based stainless steel for a two-wheeled brake disc of the present invention, wherein the two-wheeled brake disc uses a maiden iron-based stainless steel, and the two-wheeled brake disc uses a maiden iron-based stainless steel, the method It is characterized in that between the rough hot rolling and the finishing hot rolling, the crude steel strip is heated at 10 ° C or more and 50 ° C or less.

(6) The method for producing a granulated stainless steel for use in a two-wheeled brake disc according to the present invention, wherein the two-wheeled brake disc is made of a hot-rolled steel sheet which is not subjected to hot-rolled sheet annealing.

(7) A method for producing a granulated iron-based stainless steel for a two-wheeled brake disc according to the present invention, wherein the rammed iron-based stainless steel for the two-wheeled brake disc is a hot-rolled annealed steel sheet.

According to the structure and composition control technique of the present invention, it is possible to obtain a hot-rolled steel sheet and heat of the granulated iron-based stainless steel sheet for the brake disc which has been reduced in the edge of the width of the hot-rolled steel strip and which prevents the edge of the width end from being broken. Roll annealed steel sheets. The quality is better from the viewpoint of productivity and productivity improvement of the brake disc.

Fig. 1A is a view showing the appearance of a linear crack ridge at the edge of the width end of a hot rolled annealed steel strip with a granulated iron steel for a brake disc.

Fig. 1B is a microscopic image showing a section of a linear crack 边缘 at the edge of the width of the hot-rolled annealed steel strip from the brake disc with the granulated iron.

Fig. 2 is a photograph showing the width end face of a 300 L × 180 w × 80 t (mm) steel block cast by a laboratory by rolling it into a thickness of 20 mm by an experimental hot rolling mill in order to show the generation process of the edge linear crack.

Figure 3 shows the microstructure of the hot-rolled annealed sheet (mainly grain boundary and carbide), showing the normal cross-sectional structure of the hot rolled annealed sheet of 11%Cr-1%Mn-0.04%C-0.04%N steel. . It is used for a short time etching using aqua regia.

Fig. 4 shows the δ section of the TD section of the 11%Cr-1%Mn-0.04%C-0.04%N Ma Tian scattered iron stainless steel hot rolled annealed sheet steel strip with no edge line cracks and edge cracks observed. Photograph of iron distribution (edge line crack 瑕疵, edge rupture quality is good δ ferrite iron structure of hot rolled annealed sheet).

Fig. 5 shows a hot-rolled steel after the hot-rolling heating temperature is changed from 1100 to 1280 °C in a two-wheeled disc brake device after hot rolling to a thickness of 3.8 mm. The roll was unrolled and a sample was taken, and the relationship between the depth of the edge linear crack and the amount of δ ferrite was investigated.

Figure 6 is a 50mm thick steel block of 11~12%Cr-0.04%C-0.5~1.4%Mn-0.03%N steel. After heating to 1250 °C in the laboratory, hot rolling A sheet thickness of 3 mm was used to investigate the relationship between the amount of δ ferrite and iron which would affect the edge crack of the end face.

Form for implementing the invention

Hereinafter, embodiments of the present invention will be described. First, the reason for limiting the steel composition of the stainless steel sheet of the present embodiment will be described. Further, the description of the % of the composition means the mass % unless it is notified in advance.

C: 0.025~0.080%

C is an element necessary for obtaining a predetermined hardness after quenching, and is added in combination with N so as to have a predetermined hardness level. In order to avoid the excessive addition of C and to maximize the effect of N, in the present invention, 0.080% is set as the upper limit. When it is added more than this amount, the hardness is too hard to cause a defect such as a brake sound or a low toughness. The upper limit of the C content is preferably 0.060% from the viewpoint of hardness control and improvement in corrosion resistance. On the other hand, when the C content is less than 0.025%, since N must be excessively added to obtain hardness, 0.025% is made the lower limit of the C content. The stability of the quenching hardness is preferably set to 0.040% or more.

Si: 0.05%~0.8%

In addition to the necessity of deoxidation during the refining and refining, the Si system is also useful for suppressing the formation of oxidized scale during the quenching heat treatment. Since the effect is exhibited at 0.05% or more, the Si content is set to 0.05% or more. However, since Si is mixed from a raw material such as a molten iron furnace, excessive reduction causes an increase in cost, and therefore it is preferably 0.20% or more. Moreover, since the Si system narrows the single-phase temperature region of the Worthite iron and impairs the quenching stability, the Si content is set. It is 0.8% or less. Further, in order to reduce the amount of addition of the Worthite iron stabilizer element and reduce it, it is preferably 0.6% or less.

Mn: 0.5~1.5%

Mn is added as an element of the deoxidizer, and at the same time contributes to the expansion of the single phase of the Worthite iron and improves the hardenability. Since the effect is clearly exhibited at 0.5% or more, the Mn content is set to 0.5% or more. In order to stably ensure the hardenability, it is preferably set to 1.1% or more. However, since Mn promotes generation of oxidized scale at the time of quenching heating and increases the subsequent polishing load, the upper limit of the Mn content is made 1.5% or less. When it is considered that the corrosion resistance due to the granules of MnS or the like is low, it is preferably 1.3% or less.

P: 0.035% or less

Among the main raw materials such as a molten iron furnace of a raw material and a ferro-chrome, P is an element contained in the form of an impurity. Since the element is harmful to the toughness after quenching of the hot rolled annealed sheet, the P content is set to 0.035% or less. Further, it is preferably 0.030% or less. Since the excessive reduction requires the use of a high-purity raw material or the like to cause an increase in cost, the lower limit of P is preferably 0.010%.

S: 0.015% or less

S forms sulfide inclusions and deteriorates the general corrosion resistance (total corrosion and pitting corrosion) of steel materials. Moreover, since S system lowers hot workability and improves edge cracking sensitivity of hot rolled steel sheets, the content of S The upper limit is preferably less and the upper limit of the S content is set to 0.015%. A preferred upper limit is 0.008%. Further, the smaller the content of S, the better the corrosion resistance is. However, since the desulfurization load with a low S is increased and the production cost is increased, the lower limit is preferably 0.001%.

Cr: 11.0~13.5%

Cr is an essential element for ensuring oxidation resistance and corrosion resistance in the present invention. When the Cr content is less than 11.0%, these effects are not exhibited. On the other hand, when the Cr content is more than 13.5%, the single phase region of the Worthite iron shrinks and the hardenability is impaired, so the Cr content range is set to be 11.0 to 13.5%. Further, in consideration of the stability of the corrosion resistance, the Cr content is preferably 12.0% or more. Further, in consideration of press formability, the Cr content is preferably 13.0% or less.

Ni: 0.01~0.50%

In the alloy raw material of the ferrite-based stainless steel, Ni is inevitably mixed with impurities, and is usually contained in the range of 0.01 to 0.10%. In addition, since it is effective to suppress the progress of pitting corrosion, since the effect of adding 0.03% or more can be stably exhibited, it is preferable to set the lower limit of Ni content to 0.03%. On the other hand, in the hot-rolled annealed steel sheet, since the addition of a large amount is likely to cause a decrease in press formability due to solid solution strengthening, the upper limit of the Ni content is made 0.50%. Further, in consideration of the alloy cost, the Ni content is preferably 0.15% or less.

Cu: 0.01~0.08%

The effect of improving the corrosion resistance of the granulated iron structure of the granulated iron containing δ ferrite is more than 0.01%. In addition, in order to improve the hardenability as a stable element of the Worthite iron, there is also a case where it is actively added. However, since excessive addition causes a decrease in hot workability and an increase in raw material cost, 0.08% or less is made the upper limit of the Cu content. It is preferable to set the lower limit of the Cu content to 0.02% or more in consideration of rust or the like due to acidic rain. Further, in consideration of the press formability of the hot-rolled sheet-fired steel sheet, it is preferably 0.08% or less.

Mo: 0.01~0.30%

In order to improve the corrosion resistance of the granulated iron structure of the granulated iron containing δ ferrite, the Mo system is effective because the effect is exhibited at 0.01% or more, so the lower limit of the Mo content is set to 0.01%. Since it is effective for improving the hardenability and improving the heat resistance after quenching, it is preferably 0.02% or more. Due to the heating after quenching, the steel is tempered and there is a case where the hardness is lowered. Here, the improvement of the heat resistance after quenching means that the degree of hardness reduction is small. Also known as tempering softening resistance. The disc brakes are used for quenching, and the discs are heated by the heat generated by the brakes during use. This feature is therefore important.

The stability factor of the iron phase of the Mo-based ferrite is because the excessive addition system makes the single-phase temperature region of the Vostian iron narrow and impairs the quenching property, so the upper limit of the Mo content is set to 0.30% or less.

In order to improve the heat resistance after quenching, it is preferable to add Nb in combination, and when added, Mo: 0.05 to 0.20%, and Nb: 0.05 to 0.20% is a particularly preferable range.

V: 0.01~0.10%

In the alloy raw material of the ferrite-based iron-based stainless steel, the V-series is mixed as an unavoidable impurity, and since it is difficult to remove in the refining step, it is usually contained in the range of 0.01 to 0.10%. Further, in addition to the fine carbonitride and the improved wear resistance of the brake disc, the V-based system also has an effect of improving the corrosion resistance, so that the element can be deliberately added as necessary. Since the effect is stably exhibited by adding 0.02% or more, it is preferable to set the lower limit of the V content to 0.02%. It is preferably 0.03% or more. on the other hand, When it is excessively added, there is a possibility that the precipitate is coarsened. As a result, the toughness after quenching is lowered, so the upper limit of the V content is made 0.10%. Further, in consideration of the production cost and the manufacturability, the V content is preferably 0.08% or less.

Al: 0.05% or less

In addition to being added as a deoxidizing element, the Al system is also an element which improves oxidation resistance. Since the effect is obtained by 0.001% or more, the lower limit of the Al content is preferably 0.001% or more. On the other hand, since the solid solution strengthening and the formation of large oxide-based inclusions impair the toughness of the brake disk, the upper limit of the Al content is set to 0.05%. It is preferably set to 0.03% or less. Al may not be included.

N: 0.015~0.060%

In the present invention, N is one of the most important elements. Similarly to C, in order to obtain a necessary element of a predetermined hardness after quenching, it is added in combination with C so as to have a predetermined hardness level. Further, when quenching is performed by quenching the two-phase structure of the Worthite iron and the ferrite iron, the Cr carbide precipitates, that is, the sharp sensitization phenomenon is likely to occur, and the corrosion resistance is lowered, and the nitrogen system exhibits suppression of Cr. The effect of carbide precipitation and improved corrosion resistance. Since the effect is exhibited by 0.015% or more, the N content is made 0.015% or more. On the other hand, since the effect is saturated at 0.060% and it is feared that bubble formation defects are caused, the yield is lowered, so 0.060% is made the upper limit of the N content. When the effect of improving the corrosion resistance by strengthening the passive film is also considered, it is preferable to set the N content to 0.030% or more. Further, it is preferably in a range of 0.050% or less.

δ fertilizers observed in hot rolled steel sheets or hot rolled annealed steel sheets The amount of iron (δ ferrite iron fraction) is 5% or more and 30% or less in terms of area ratio.

The amount of δ ferrite in the steel is affected by the edge linear cracks and hot-rolled edge cracking during hot rolling. When the δ fertilizer particle fraction is less than 5%, the hot workability is low and edge cracking is likely to occur, so it is set to 5% or more. On the other hand, when the iron fraction of the δ fertilizer is more than 30%, the edge linear crack 容易 is likely to occur due to the coarsening of the crystal grain size, and the grinding step after quenching of the brake disc requires a large amount of grinding thickness. Since the edge linear crack is removed by grinding, the ferrite iron fraction is set to 30% or less. In addition, the δ ferrite iron during hot rolling was observed in the cross section of the hot-rolled annealed steel sheet and the hot-rolled steel sheet, and was evaluated by a normal microscope observation. The etch of the δ ferrite iron was performed by immersing the sample in the village. It is preferred that the reagent (the aqueous solution of potassium ferricyanide) is heated to carry out the solution.

The DFE value defined by the above formula (1) (DFE=12(Cr+Si)-430C-460N-20Ni-7Mn-89) is 5 or more and 20 or less.

When the DFE value is low, the amount of δ ferrite is less, and the frequency of edge cracking during hot rolling is increased, so it is set to 5 or more. Further, when the DFE value is high, the δ ferrite is increased, and the edge linear crack is likely to occur, so that it is 20 or less. Further, each of Cr, Si, C, N, Ni, and Mn in the formula (1) means the content (% by mass) of the element.

Further, in the present invention, in addition to the above elements, the following elements may be added in order to improve rust resistance, heat resistance, hot workability and the like.

Ti: 0.03% or less

Ti is suppressed from being formed in stainless steel by forming carbonitride Chromium carbonitride causes elements of sharp sensitization and low corrosion resistance. The Ti content is preferably 0.001% or more. However, in the brake disc, since a large TiN is formed and the toughness is lowered and sound is generated, the upper limit of the Ti content is set to 0.03% or less. When considering the toughness in winter, it is preferably set to 0.01% or less. Ti may not be included.

B: 0.0050% or less

B is an effective element for improving hot workability, and since the effect is exhibited at 0.0002% or more, B of 0.0002% or more can be added. In order to improve hot workability in a wider temperature range, it is preferably set to 0.0010% or more. On the other hand, since the excessive addition is impaired by the composite precipitation of the boride and the carbide, 0.0050% is made the upper limit of the B content. When corrosion resistance is also considered, it is preferably 0.0025% or less.

Nb: 0.3% or less

Nb is an element which suppresses sharpening and corrosion resistance caused by folding of chromium carbonitride in stainless steel by forming carbonitride. The Nb content is preferably 0.001% or more. Moreover, it is an element which greatly improves the heat resistance after quenching. Here, the term "heat resistance" refers to the extent to which softening is not easily obtained when heat is received after quenching, that is, also referred to as temper softening resistance.

However, when Nb is excessively added, it is not preferable because the NbN is formed to cause low toughness and cause sound, so 0.3% is made the upper limit of the Nb content.

It is preferable to increase the heat resistance after quenching in combination with Mo, and when added, Mo: 0.05 to 0.20%, and Nb: 0.05 to 0.20% is a particularly preferable range.

Sn: 0.1% or less

The Sn-based element which is effective for improving the corrosion resistance after quenching is preferably 0.001% or more, and more preferably 0.02% or more is added as necessary. However, since excessive addition promotes edge cracking during hot rolling, it is preferably 0.10% or less.

Bi: 0.2% or less

Bi is an element that enhances corrosion resistance. Although the mechanism is not clear, it is considered that the effect of making MnS which is likely to become a rust starting point is reduced by the addition of Bi, so that the probability of becoming a rust starting point is lowered. The effect is exerted by adding 0.01% or more of Bi. Even if it is added more than 0.2%, since the effect is saturated, the upper limit of the Bi content is set to 0.2%.

In addition to the elements described above, impurities may be contained in a range that does not impair the effects of the present invention. It is preferable to reduce the aforementioned P, S, and Zn, Pb, Se, Sb, H, Ga, Ta, Ca, Mg, Zr, and the like of the usual impurity element as much as possible. On the other hand, in order to solve the problem of the present invention, the content ratio of these elements is controlled, and the content thereof is Zn ≦ 100 ppm, Pb ≦ 100 ppm, Se ≦ 100 ppm, Sb ≦ 500 ppm, H ≦ 100 ppm, Ga ≦ 500 ppm, Ta ≦ 500 ppm, Ca ≦ 120 ppm, Mg ≦ 120 ppm, Zr ≦ 120 ppm.

In the hot rolling step, it is preferable to use an induction heating device (rod heater) between the rough rolling and the finishing rolling to heat the steel strip having a thickness of 20 to 40 mm at 10 ° C or more and 50 ° C or less. When the heating temperature of the thick steel strip is less than 10 ° C, the amount of δ ferrite iron is small, and edge cracking is likely to occur due to low hot workability. On the other hand, because the heating temperature is greater than 50 ° C, δ The amount of ferrite grains will become too much, so the crystal grains will become coarse and the surface roughness of the end faces of the thick steel strips will become large, resulting in the formation of deep edge line cracks. Without the use of a thick rod heater, even if the previous steel billet heating temperature is increased, the temperature of the crude steel strip becomes higher, but since the heating temperature is greater than 1250 ° C, the crystal grain size becomes coarse and the rough rolling process, the thick steel strip end face The surface roughness becomes large, which causes the edge linear crack to become deep, so the hot rolling heating temperature is preferably 1250 ° C or less. Moreover, since the hot rolling heating temperature is less than 1150 ° C and the deformation resistance of the Wostian iron matrix phase is increased, the deformation will concentrate on a small amount of the δ fat iron phase due to the low amount of the δ fertilizer grain iron, resulting in a low thermal deformation ability. The edge cracking causes the yield to be low, so the hot rolling heating temperature is preferably 1150 ° C or higher.

The quality specified in each request item can be achieved by having the composition of each request item and the δ fertilizer grain iron fraction. In the two-wheeled brake disc of the present invention, the use of the granulated stainless steel, the hot-rolled steel sheet which is not subjected to the hot-rolling annealing, and the hot-rolled annealed steel sheet can exhibit an effect.

Example

Hereinafter, the effects of the present invention will be described by way of examples, but the present invention is not limited by the conditions used in the following examples.

In the present embodiment, steel having a composition shown in Table 1-1 and Table 1-2 was first melted to cast a 200 mm thick steel blank. After heating the steel bristles to 1,150 to 1,250 ° C, the hot-rolled steel sheets having a thickness of 4 mm were subjected to rough hot rolling and finishing hot rolling, and coiled at a temperature of 750 to 900 ° C. Between the rough hot rolling and the finishing rolling, a thick rod heater by induction heating is used, and the temperature rise condition is set to a range of 10 to 50 ° C to perform heating. Box type The annealing furnace heats the hot rolled steel coil by hot rolling the steel sheet. The maximum heating temperature is set to a temperature range of 800 ° C or more and 900 ° C or less. After the rust on the surface of the hot-rolled annealed steel sheet was removed by a shot blast and pickled, the edge line crack and edge cracking were evaluated. When the depth of the edge linear crack 小于 is less than 150 μm, it is judged to be acceptable, and the edge linear crack cannot be confirmed by visual observation as S, and it can be judged as A by visual observation. The edge linear crack system was judged to be unacceptable (determined as C) when the depth was 150 μm or more.

In addition, the case where the depth is 10 mm or more is not judged as a pass (decision is A), and the case where it is generated is judged as unacceptable (determined as B). Further, the person who continues to generate the edge breakage is judged to be unacceptable (determined as C).

Further, the cross-sectional structure was observed using an optical microscope, and the amount of δ fertilized iron was measured by image analysis. The appearance of δ fat iron is the use of Murakami test drugs.

Next, the hot-rolled annealing- pickling plate was quenched and the surface was subjected to #80 polishing finishing, and then the JIS surface hardness (quenching hardness) was evaluated by a Rockwell hardness meter C grade, and 32 to 38 were judged as pass, and In addition, it was judged as unqualified. The quenching condition of the disc brake was set to an average heating rate of about 50 ° C / s, and after the temperature was raised to 1000 ° C, it was kept for 1 second and cooled to a normal temperature at an average cooling rate of about 70 ° C / s.

Further, as evaluation of heat resistance after quenching, tempering was performed at 500 ° C for 1 h, and the surface was subjected to #80 polishing finishing, and then JIS surface hardness (quenching hardness) was evaluated by a Rockwell hardness meter C grade. Less than 32 is judged as a failure (B), and 32 or more is judged as a pass (A). Further, in the same manner, a test was performed in which the tempering temperature was 530 ° C, and 32 or more was judged as pass (S) and Enter the “temper softening resistance” column in Table 2-1, Table 2-2, and Table 2-3.

The corrosion resistance was evaluated by performing a #600 polishing finish on the surface of the hot-rolled annealed pickled sheet, and then performing a salt spray test for 4 hours (JIS Z 2371 "Salt Spray Test Method"), and measuring the rust area ratio, and the rust area. A rate of 10% or more was judged as unacceptable (B), and less than 10% was judged as pass (A). In particular, if the rust area ratio is zero, it is judged as pass (S).

For the polishing property, the depth of the edge linear crack 为 was 150 μm or less, and it was judged as pass (A), and the thickness of more than 150 μm was judged as unacceptable (B).

As a comparative example, the composition other than the present invention, the hot rolling heating conditions, and the area ratio of the δ ferrite iron in the hot-rolled annealed sheet to the outside of the present invention were also evaluated in the same manner.

It can be clearly seen from Table 1-1, Table 1-2, Table 2-1, Table 2-2, and Table 2-3 that the composition of the composition of the present invention is applied and the area ratio of the δ fertilizer iron is 5% or more and 30%. In the following examples of the present invention, the quality of the edge-line crack 瑕疵 was acceptable, the edge rupture quality was also acceptable, and the quenching hardness, heat resistance, and corrosion resistance were also good. Further, when the heating temperature of the thick steel bar using the thick rod heater is within the range of the present invention, the depth of the edge linear crack 变为 becomes lower and the grinding time of the disk after quenching can be shortened. Moreover, the edge rupture quality was further improved and became unobservable. On the other hand, when the composition of the detached component of the present invention is composed, it is difficult to control the amount of δ ferrite of the hot-rolled annealed sheet, and the quality of the edge linear crack, the quality of the edge crack, the hardness of the quenching, and the corrosion resistance after quenching. Any one of the above is unqualified. Thereby, it can be seen that the characteristics of the brake disc in the comparative example are inferior.

Specifically, in Test Nos. 38 and 56, C and N were high, and Nos. 42 and 55 were low in C and N, so the quenching hardness was outside the target range. Since NO. 40 is low in Si, No. 54 is high in V, so the polishing property in the polishing step after quenching is poor. No. 41, 42, 45, 46, 57, 58, 59, 60, 61, 62 is because the amount of δ ferrite of the hot-rolled annealed sheet is more than 30% or less than 5%, so the quality of the edge-line crack is Edge rupture was assessed as poor. No. 43 is because P is high, No. 44 is because S is high, and No. 50 is because Cu is high, so the edge fracture is evaluated as defective.

No. 45, 47, 49, 51, and 53 are low in corrosion resistance because Cr, Ni, Cu, Mo, and V are low. In No. 48 and 50, a large amount of Ni and Cu were added, and the press formability was poor. No. 46 and 60 to 62 were due to a large amount of Cr, and No. 39 and 52 were each quenched by Si and Mo. The fire is low and the quenching hardness is low. Further, No. 48, 50, 52, and 54 were judged to have high raw material costs and were economically disadvantageous. Further, since the No. 57 system has a low DFE value, the δ fertilizer has a low iron fraction and a poor edge crack.

From these results, the above findings can be confirmed, and the basis for defining the above-described respective steel compositions and configurations can be demonstrated.

As can be clearly understood from the above description, the optimum amount of the δ fertilizer iron amount observed in the hot-rolled annealed steel sheet and the hot-rolled steel sheet by the 麻田散铁-based stainless steel sheet for the brake disc of the present invention is designed by the composition and By controlling the hot rolling conditions, it is possible to obtain a good quality of the edge line crack and the edge cracking quality, and at the same time, it is a high quality brake disc which does not deteriorate in hardness and corrosion resistance after quenching. Further, by heating the crude steel strip under the optimum conditions between the rough hot rolling and the finishing hot rolling, the quality of the edge linear crack and the quality of the edge crack can be further improved. By applying the material of the present invention to a two-wheel brake disc, the productivity can be improved and the inspection load can be reduced, and the productivity can be improved by shortening the grinding time and the contribution to society can be improved. . That is, the present invention is sufficiently advantageous in industrial use.

Claims (14)

The utility model relates to a Ma Tian scattered iron-based stainless steel for a two-wheeled brake disc, which is characterized by: C: 0.025 to 0.080%, Si: 0.05% to 0.8%, Mn: 0.5 to 1.5%, and P: 0.035% or less by mass%. , S: 0.015% or less, Cr: 11.0 to 13.5%, Ni: 0.01 to 0.50%, Cu: 0.01 to 0.08%, Mo: 0.01 to 0.30%, V: 0.01 to 0.10%, Al: 0.05% or less, N: 0.015~0.060%, and the remainder is Fe and unavoidable impurities; and the DFE value specified in the formula (1) is 5 or more and 30 or less, and the δ fertilizer iron fraction observed in the cross-sectional structure is calculated as the area ratio. 5% or more and 30% or less, DFE=12(Cr+Si)-430C-460N-20Ni-7Mn-89 (1) Further, in the formula (1), Cr, Si, C, N, Ni, Mn means the content (% by mass) of each element. In the case of the two-wheeled brake disc of the claim 1, the granulated iron-based stainless steel is further contained in one or two of Ti: 0.03% or less and B: 0.0050% or less in mass%. In the case of the two-wheeled brake disc of claim 1 or 2, the granulated stainless steel is made of Nb: 0.30% or less by mass%. In the case of the two-wheeled brake disc of the claim 1 or 2, the granulated iron-based stainless steel is further contained in one or two of Sn: 0.1% or less and Bi: 0.2% or less in mass%. In the case of the two-wheeled brake disc of claim 3, the Ma Tiansan iron-based stainless steel is further contained in a mass%, and further contains Sn: 0.1% or less and Bi: 0.2% or less. 1 or 2 types. A method for manufacturing a Ma Tiansan iron-based stainless steel for a two-wheeled vehicle brake disc, wherein the two-wheel brake disc uses a Matian iron-based stainless steel system, such as the aforementioned two-wheel brake disc for any one of the items 1 to 5, Ma Tiansan In the iron-based stainless steel, the method of the present invention is characterized in that the rough steel strip is heated between 10° C. and 50° C. between the rough hot rolling and the finishing hot rolling in the two-wheel brake disc. For the two-wheeled brake disc of claim 1 or 2, the Ma Tiansan iron-based stainless steel is used, and the above-mentioned two-wheeled brake disc is made of a hot-rolled steel sheet which is not subjected to hot-rolled sheet annealing. For example, the two-wheeled brake disc of claim 3 uses the Ma Tian scattered iron-based stainless steel, and the two-wheel brake disc uses the Ma Tian scattered iron-based stainless steel which is a hot-rolled steel sheet which is not subjected to hot-rolled sheet annealing. For the two-wheeled brake disc of claim 4, the Ma Tiansan iron-based stainless steel is used, and the two-wheel brake disc uses the Ma Tian-distributed iron-based stainless steel which is a hot-rolled steel sheet which is not subjected to hot-rolled sheet annealing. For example, the two-wheeled brake disc of claim 5 uses the Ma Tian scattered iron-based stainless steel, wherein the two-wheel brake disc uses the Ma Tian loose iron-based stainless steel which is a hot-rolled steel sheet which is not subjected to hot-rolled sheet annealing. For example, the two-wheeled brake disc of claim 1 or 2 uses the Ma Tian scattered iron-based stainless steel, wherein the two-wheel brake disc uses the Ma Tian scattered iron-based stainless steel as the hot-rolled annealed steel sheet. For example, the two-wheeled brake disc of claim 3 is made of Ma Tian loose iron stainless steel, among which The above-mentioned two-wheel brake disc uses the Ma Tian scattered iron-based stainless steel as a hot-rolled annealed steel sheet. For example, the two-wheeled brake disc of claim 4 uses the Ma Tian scattered iron-based stainless steel, wherein the two-wheel brake disc uses the Ma Tian scattered iron-based stainless steel as the hot-rolled annealed steel sheet. For example, the two-wheeled brake disc of claim 5 uses the Ma Tian scattered iron-based stainless steel, wherein the two-wheel brake disc uses the Ma Tian scattered iron-based stainless steel as the hot-rolled annealed steel sheet.