JP2017088975A - Cold rolled steel sheet for separate plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cold rolled steel sheet for a separate plate, enabling wear of a friction material to be suppressed.SOLUTION: The cold rolled steel sheet for a separate plate is constituted by a chemical component containing, by mass%, 0.03 to 0.08% of C, 0 to 1.0% of Si, 0.2 to 0.8% of Mn, 0.03% or less of P, 0.01% or less of S and 0.05% or less of Al, in amounts satisfying a relationship represented by 5×C%-Si%+Mn%-1.5×Al%<1, and at least one kind of 0.03 to 0.4% of Nb, 0.01 to 0.3% of V and 0.01 to 0.3% of Ti, in amounts satisfying a relationship represented by 0.04<(Nb%÷1.4)+(V%÷1.1)+Ti%<0.3, and the balance Fe with inevitable impurities. The cold rolled steel sheet for a separate plate has a cross section hardness of 200 HV to 350 HV and a difference of surface hardness to cross section hardness in a sheet thickness center part of 20 HV or more.SELECTED DRAWING: None

Description

  The present invention relates to a cold-rolled steel sheet for a separate plate used for, for example, a clutch plate.

  A wet multi-plate clutch of an automatic transmission has a plurality of friction plates with a friction material (wet friction material) formed of special paper attached to the surface, and separate plates that come into contact with the wet friction material. Has been placed. Then, the transmission of power is controlled by an operation of switching between opening and connection of the friction plate and the separate plate in an environment supplied with lubricating oil.

  Both the friction plate and the separate plate are ring-shaped steel plate members. In general, these friction plates and separate plates constituting the wet multi-plate clutch are collectively referred to as a clutch plate.

  When connected from the neutral state to the power transmission state in the operation of the wet multi-plate clutch, the friction material and the clutch plate of the friction plate are pressed with a high load at a high relative speed, and the friction material and the clutch plate The relative speed with the speed decreases rapidly. The frictional heat generated at this time is rapidly applied to the surface of the friction material serving as the sliding portion and the surface of the separate plate, thereby raising the surface temperature of both plates.

  Further, the friction material is worn due to frictional heat by repeatedly connecting to the separate plate as described above.

  When wear of such a friction material proceeds and a disappeared portion is generated, the steel plate surface under the friction material is exposed and comes into contact with a separate plate. For this reason, the friction coefficient is lowered, and the function as a transmission is deteriorated.

  Here, improving the fuel efficiency of automobiles is an extremely important issue in modern times, and the wet multi-plate clutch is also required to be smaller and lighter.

  In order to achieve a reduction in size and weight, it is necessary to improve the efficiency of the wet multi-plate clutch. In order to improve the efficiency of such a wet multi-plate clutch, measures such as a reduction in the size of the plate, a reduction in the number of plates, a reduction in the lubricating oil, and an improvement in the friction coefficient by changing the friction material can be considered. However, the above countermeasure causes a temperature increase due to frictional heat, and promotes wear of the friction material, thereby deteriorating the function of the transmission.

  Therefore, as a material performance of the separate plate, it is considered that if the temperature rise on the contact surface with the friction material is suppressed and the wear of the friction material can be suppressed, the efficiency of the transmission can be improved.

  As a technique for suppressing the surface temperature of the clutch plate due to frictional heat, a method described in Patent Document 1 is known.

  This Patent Document 1 describes a method of suppressing an increase in the temperature of a plate due to frictional heat by regulating the amount of alloying elements and improving the thermal conductivity of the steel sheet.

  Further, as a problem of the clutch plate, a heat spot derived from a temperature rise due to frictional heat is known. Since the heat spot causes local deformation on the plate surface, the frictional heat is increased when the clutch is engaged, and the wear of the friction material is promoted. Therefore, in order to suppress wear of the friction material, it is necessary not only to suppress the surface temperature of the clutch plate due to frictional heat but also to have heat spot resistance.

  As techniques for improving the heat spot resistance of a steel sheet used for a clutch plate, methods described in Patent Documents 2 to 5 are known.

  In Patent Document 2, by using low-carbon steel and increasing the phase transformation temperature from ferrite to austenite, the occurrence of phase transformation due to heating of the plate with frictional heat at the time of clutch connection is prevented, and Occurrence is suppressed.

  In patent document 3, generation | occurrence | production of a heat spot is suppressed by using the austenitic stainless steel which is hard to generate | occur | produce a phase transformation as a material for plates.

  In patent document 4, generation | occurrence | production of a heat spot is suppressed by utilizing Ti precipitate and Nb precipitate.

  In Patent Document 5, in addition to the use of Ti precipitates and Nb precipitates, the generation of heat spots is suppressed by adding Si or Al having an action of raising the transformation point.

  As methods for preventing wear of the friction material other than the improvement in heat spot resistance, methods of Patent Documents 6 and 7 are known. In these Patent Documents 6 and 7, by providing an oil groove on the separate plate, the lubricating oil flows into the oil groove and suppresses the temperature rise at the time of engagement to prevent the friction material from being worn.

  Further, in the manufacturing process of the separate plate, when the ratio of the primary shear surface generated in the cross section is small due to the punching of the cold-rolled steel sheet and the ratio of the secondary shear surface or the fracture surface is large, the fine powder derived from these ( The occurrence of contamination) increases and causes problems inside the transmission.

  Therefore, it is also important that the steel sheet used for the separate plate has good punchability so that a punched section with a high proportion of the primary shear plane can be obtained.

  Therefore, as a technique for improving punchability, the method of Patent Document 8 is known. In this patent document 8, the punching workability is improved by having a softened layer in the surface layer portion.

JP 2005-249051 A JP 2005-249050 A JP-A-2005-249106 JP 2008-266731 A JP 2010-132983 A JP 2004- 211728 A JP 2009-30663 A JP 2010-235965 A

  During the operation of the wet multi-plate clutch, frictional heat is generated on the entire connection surface when the clutch is connected, but there may be a region where the temperature rises locally compared to other portions. And the wear of a friction material will be accelerated | stimulated in the surface of the location where the temperature increased a lot locally.

  And in the said patent documents 1 thru | or 8, the influence on the abrasion of the friction material which is a contact partner is not considered as a performance of the steel plate for separate plates during the action | operation of a wet multi-plate clutch.

  This invention is made | formed in view of such a point, and it aims at providing the cold-rolled steel plate for separate plates which can suppress abrasion of a friction material.

  The cold-rolled steel sheet for a separate plate according to claim 1 is C: 0.03% by mass to 0.08% by mass, Si: 0% by mass to 1.0% by mass, Mn: 0.2% by mass More than 0.8 mass%, P: 0.03 mass% or less, S: 0.01 mass% or less, and Al: 0.05 mass% or less 5 × C% −Si% + Mn% −1.5 × Al % <1 so as to satisfy the formula (1), and Nb: 0.03% by mass to 0.4% by mass, V: 0.01% by mass to 0.3% by mass, and Ti: At least one of 0.01% by mass to 0.3% by mass is 0.04 <(Nb% ÷ 1.4) + (V% ÷ 1.1) + Ti% <0.3 (2 ) The chemical composition is contained so as to satisfy the formula, and the balance is Fe and inevitable impurities, and the cross-sectional hardness is 200 HV or more and 350 HV. Below, the relationship between the cross-sectional hardness and surface hardness in the sheet thickness center portion 20 HV ≦ (sectional hardness in the sheet thickness center) - satisfies the a (surface hardness) (3).

  The cold-rolled steel sheet for a separate plate according to claim 2 is the cold-rolled steel sheet for a separate plate according to claim 1, wherein Cr: 0.10% by mass to 2.0% by mass, Ni: 0.05% by mass Or more and 0.5 mass% or less, Mo: 0.05 mass% or more and 0.5 mass% or less, and B: 0.0002 mass% or more and 0.002 mass% or less. 5 × C% -Si % + Mn% + 1.6 × Cr% + 0.8 × Ni% −1.5 × Al% <1 The chemical component contained so as to satisfy the formula (4).

  According to the present invention, since ΔH, which is the difference in surface hardness with respect to the cross-sectional hardness at the center of the plate thickness, is 20 HV or more, it is possible to improve the heat transfer rate and suppress a local temperature rise during clutch operation. The wear of the friction material that is the contact partner can be suppressed.

It is a scatter diagram which shows the relationship between a cross-sectional hardness and the abrasion loss of the friction material in a SAE # 2 test.

  Hereinafter, the configuration of an embodiment of the present invention will be described in detail.

  The cold-rolled steel sheet for a separate plate according to the present invention is, for example, a separate plate that is brought into contact with and separated from a friction plate having a friction material (wet friction material) attached to the surface in a wet multi-plate clutch mechanism of an automatic transmission of an automobile. Used.

  To suppress wear of the friction material while the wet multi-plate clutch is operating, that is, when the separate plate and friction plate are connected, the local temperature rise at the contact surface is suppressed and the temperature rises unevenly. It is important to prevent this.

  That is, generally during operation of a wet multi-plate clutch, the friction plate and the separate plate are cooled with lubricating oil, so the temperature is normally 100 ° C. or less, but when the friction load due to connection is large In some cases, the frictional heat locally heats the connection surface to 800 ° C. or higher. Such local heating causes wear of the friction material unevenly.

  Therefore, by improving the thermal conductivity of the surface of the separate plate, the frictional heat can be diffused more quickly at the portion where the heat input amount is concentrated, and the local temperature rise can be suppressed. Therefore, it is important to improve the thermal conductivity of the surface of the cold-rolled steel sheet used as a separate plate in order to suppress wear of the friction material.

  Hereinafter, a configuration for suppressing wear of the friction material will be described.

  Since the surface of the cold-rolled steel sheet for a separate plate is decarburized, the thermal conductivity of the surface can be improved by reducing the carbon concentration.

  Here, even if the cold-rolled steel sheet for a separate plate is decarburized (softened), if the degree is low, the effect of suppressing wear of the friction material also decreases.

  The degree of decarburization of the cold-rolled steel sheet for separate plates can be confirmed by measuring the Vickers hardness of both the cross-sectional hardness and the surface hardness at the center of the plate thickness.

  In the Vickers hardness test for the softened surface, the hardness measurement value varies depending on the test load. Therefore, when examining the softening of the surface, the test load is fixed at, for example, 10 kgf.

  And when the difference in surface hardness (ΔH) with respect to the cross-sectional hardness at the central portion of the plate thickness is less than 20 HV, decarburization is insufficient and the effect of suppressing wear of the friction material cannot be obtained.

  Therefore, the cold-rolled steel sheet for a separate plate needs to satisfy the relationship expressed by the formula (3) where 20 HV ≦ (section hardness at the center of the sheet thickness) − (surface hardness). Further, ΔH is preferably 45 HV or less.

  Note that the difference in surface hardness (ΔH) with respect to the cross-sectional hardness at the center of the plate thickness is due to softening caused by decarburizing the vicinity of the plate surface in the hot-rolled steel plate. Since decarburization proceeds as the temperature during hot rolling increases, it is important to set the temperature of the heating furnace high in order to make ΔH 20 HV or higher.

  Further, in hot rolling, the scale is detached by rolling and descaling (water injection) performed before and after the rolling, and the growth rate of the decarburized layer is increased as compared with immediately after slab heating. Therefore, not only the temperature of the heating furnace but also the temperature and time during rolling affect the promotion of decarburization. Furthermore, raising the coiling temperature is also important for promoting decarburization.

  Therefore, it is important to set the temperature of the heating furnace, the temperature and time during hot rolling, and the coiling temperature so that ΔH does not become less than 20 HV.

  In addition, the carbon concentration in the vicinity of the decarburized plate surface is lower than the central portion of the plate thickness in the cross section even after cold working.

  When a hot-rolled steel sheet or a cold-rolled steel sheet is subjected to a surface polishing treatment, the softened layer on the surface is removed. Therefore, when performing the surface polishing treatment, it is necessary to set the polishing amount so that ΔH does not become less than 20 HV.

  Next, heat spot resistance will be described.

  If the friction load when the separate plate and the friction plate are connected is large, the frictional heat may locally heat the connection surface to 800 ° C. or higher. When such local heating occurs, the metal structure is transformed into austenite in the vicinity of the locally heated portion. After transformation to austenite, it is rapidly cooled by heat conduction and undergoes martensite transformation, resulting in volume expansion. And the convex part which protruded higher than the circumference | surroundings by volume expansion becomes a heat spot.

  Since the heat spot is a convex shape protruding from the surroundings, the frictional heat at the time of clutch engagement is remarkably increased, which is a factor that greatly promotes the wear of the friction material as a contact partner.

  In consideration of such factors, to improve heat spot resistance, it is effective to suppress the austenitization of the metal structure at the time of heat input, and it is an element that increases the A3 transformation point that is the α → γ transformation point. It is effective to add or reduce the amount of an element that lowers the A3 transformation point. It is also effective to delay the austenitization by making the solution of carbon difficult.

  On the other hand, reducing the hardenability to suppress martensite transformation after austenitization is also effective in improving the heat spot resistance. In order to lower the hardenability, it is effective to refine the γ crystal grain size or to add an element that lowers the hardenability.

  Next, punchability will be described.

  A cold rolled steel sheet for a separate plate used as a separate plate (product) is required to have a cross-sectional hardness of 200 HV to 350 HV and flatness from the viewpoint of punchability.

  That is, if the cold-rolled steel sheet for separate plates has a hardness of less than 200 HV, the sag and burrs of the punched product are increased, and the ratio of the secondary shear surface on the punched surface is increased, which deteriorates the punchability. On the other hand, if the hardness exceeds 350 HV, the punching die is likely to be worn or damaged, and the ratio of the shear surface on the punching surface is reduced, thereby deteriorating punchability.

  Therefore, the cross-sectional hardness of the cold-rolled steel sheet for separate plates is set to 200 HV or more and 350 HV or less in consideration of punchability. In addition, material hardness is calculated | required by measuring the Vickers hardness of the center part of the thickness direction in the cross section of a steel plate.

  Next, chemical components of the cold-rolled steel sheet for separate plates will be described.

  As described above, the chemical composition of the cold-rolled steel sheet for the separate plate is defined in consideration of the reduction in the amount of wear of the friction material that is the contact partner, heat resistance, and punchability.

  That is, the cold-rolled steel sheet for a separate plate is 0.03% to 0.08% C, 0% to 1.0% Si, 0.2% to 0.8% by mass. Mn, 0.03% by mass or less of P (not including additive), 0.01% by mass or less of S (not including additive) and 0.05% by mass or less of Al (including no additive) Is contained so as to satisfy the relationship represented by the formula (1) where 5 × C% −Si% + Mn% −1.5 × Al% <1, and 0.03% by mass or more and 0.0. At least one of 4 mass% or less of Nb, 0.01 mass% or more and 0.3 mass% or less of V and 0.01 mass% or more of 0.3 mass% or less of Ti is expressed as 0.04 <(Nb % ÷ 1.4) + (V% ÷ 1.1) + Ti% <0.3 so as to satisfy the relationship expressed by the formula (2), with the balance being F And configuring at chemical components consisting of unavoidable impurities. In the formula (1), C%, Si%, Mn%, and Al% are values of the content (% by mass) of each element. Further, Nb%, V% and Ti% in the formula (2) are values of the content (mass%) of each element.

  In addition to the above chemical components, 0.10% by mass to 2.0% by mass Cr, 0.05% by mass to 0.5% by mass Ni, 0.05% by mass to 0% as necessary. 0.5% by mass or less of Mo and 0.0002% by mass or more and 0.002% by mass or less of B at least one of 5 × C% −Si% + Mn% + 1.6 × Cr% + 0.8 × Ni You may contain so that the relationship shown by (4) Formula which is% -1.5xAl% <1 may be satisfy | filled. In the formula (4), C%, Si%, Mn%, Cr%, Ni% and Al% are values of the content (mass%) of each element.

C (carbon) is necessary for securing the hardness important for punchability, and considering the punchability, it is necessary to contain 0.03% by mass or more. On the other hand, as the C content increases, the A3 transformation point decreases, the hardness and the amount of expansion deformation when the martensite structure is formed in the heated portion by frictional heat, and the thermal conductivity decreases. End up. Further, as the C content increases, hard structures such as a ferrite structure in which pearlite structure, bainite structure, cementite phase (Fe ₃ C) and fine cementite are dispersed in the grains increase, and the punchability deteriorates. Therefore, the upper limit of the C content is set to 0.08% by mass in consideration of balance with other characteristics within a range satisfying the relationship of the formula (1) or the formula (4). Therefore, the C content is set to 0.03% by mass or more and 0.08% by mass or less.

  When Si (silicon) is contained for the purpose of normal deoxidation, a content of less than 0.4% by mass is sufficient. However, since Si has an effect of raising the A3 transformation point, Si may be contained in an amount exceeding 0.4% by mass. On the other hand, when Si is excessively contained exceeding 1.0 mass%, brittle fracture is likely to occur during rolling of a cold-rolled steel sheet. Therefore, the content of Si is set to 0% by mass (including no addition) to 1.0% by mass.

  Mn (manganese) is an element necessary for improving the strength of the material steel plate, and it is necessary to contain 0.2% by mass or more in order to improve the strength. On the other hand, Mn has an effect of lowering the A3 transformation point. Therefore, if the Mn content exceeds 0.8% by mass, the A3 transformation point is lowered. Therefore, the Mn content is set to 0.2% by mass or more and 0.8% by mass or less. As the Mn content increases, the hot-rolled steel sheet tends to have a band-like structure, and the properties of the punched section by punching processing are likely to deteriorate. Therefore, the Mn content is preferably 0.6% by mass.

  When P (phosphorus) is contained in an amount exceeding 0.03% by mass, the punchability is reduced. Therefore, the content of P is set to 0.03% by mass or less (excluding no addition).

  S (sulfur) forms MnS. And when S exceeding 0.01 mass% is contained, a fracture surface is likely to occur in the cross-sectional structure due to the soft MnS stretched by rolling. Therefore, the content of S is set to 0.01% by mass or less (excluding no addition).

  Al (aluminum) is an element having a deoxidizing effect. When it contains for the purpose of only a deoxidation effect, even if content is less than 0.01 mass%, it is enough. However, Al has an effect of increasing the A3 transformation point, so Al may be contained in an amount exceeding 0.01% by mass. Further, when Nb, V, or Ti is contained at a predetermined concentration, there is a possibility that the A3 transformation point cannot be effectively increased even if Al is contained in an amount exceeding 0.05 mass%. Therefore, the content of Al is set to 0.05% by mass or less (excluding no addition).

  Cr (chromium), Ni (nickel), Mo (molybdenum), and B (boron) are elements that improve wear resistance and toughness. Therefore, when wear resistance is required for the end face of the separate plate, it is preferable to contain these elements. However, since these elements may improve the hardenability and deteriorate the heat spot resistance, it is necessary to consider the content when they are contained.

  In consideration of both improvement in wear resistance and hardenability of the end face, Cr is contained in an amount of 0.10% by mass to 2.0% by mass.

  In consideration of both the wear resistance improvement and the hardenability improvement of the end face, the Ni content is set to 0.05 mass% or more and 0.5 mass% or less.

  In consideration of both improvement in wear resistance and hardenability of the end face, Mo is contained in an amount of 0.05 mass% to 0.5 mass%.

  In consideration of both improvement in wear resistance and hardenability of the end face, the content of B is 0.0002 mass% or more and 0.002 mass% or less.

The Fe ₃ C (cementite: θ) system, which is a carbide present in the steel sheet after cold rolling, tends to be a solid solution, but in the case of Cr-added steel, Cr tends to concentrate in Fe ₃ C. And Fe ₃ C is stabilized when Cr is concentrated. Therefore, the addition of Cr delays austenitization and is effective for heat spot resistance.

  When Cr or Ni is contained, the A3 transformation point and hardenability in the cold-rolled steel sheet are also affected by the action of Cr and Ni. Therefore, in order to raise the A3 transformation point and reduce the hardenability, the contents of C, Si, Mn and Al, and the contents of Cr and Ni contained as necessary are comprehensively considered. These elements need to satisfy the relationship represented by the formula (4) within the above-mentioned content range.

Nb (niobium), V (vanadium) and Ti (titanium) fix carbon in steel as NbC, VC and TiC with low solubility, and these carbides are very stable compared to Fe ₃ C, It has a low solubility in the γ phase. Therefore, there exists an effect | action which suppresses A3 transformation in the heating part by frictional heat. NbC, VC, and TiC also refine the γ crystal grain size by the pinning effect and reduce the hardenability even when A3 transformation is performed. That is, Nb, V and Ti are effective in improving the heat spot resistance.

  Further, NbC, VC and TiC effectively suppress the coarsening and softening of the ferrite crystal grain size and contribute to the improvement of wear resistance.

  In order to improve the heat spot resistance when containing at least one of Nb, V and Ti, Nb is 0.03% by mass or more, V is 0.01% by mass or more, or Ti is 0.01%. It is necessary to contain at least mass%. On the other hand, when Nb is contained more than 0.4 mass%, V is contained more than 0.3 mass%, and Ti is contained more than 0.3 mass%, the hardness of the hot rolled steel sheet increases. Thus, there is a possibility that a steel plate having a predetermined thickness and hardness as a product cannot be manufactured. Therefore, when at least one of Nb, V, and Ti is contained, the Nb content is 0.03% by mass or more and 0.4% by mass or less, and the V content is 0.01% by mass or more and 0.0. 3 mass% or less, and the Ti content is 0.01 mass% or more and 0.3 mass% or less.

  Moreover, since heat spot resistance is influenced by the effect | action of each element added among Nb, V, and Ti, it is necessary to consider comprehensively the content of these each element. Therefore, when at least one of Nb, V, and Ti is contained, it is necessary to make it contain so as to satisfy the relationship represented by the formula (2) within the above content range.

  Next, the operation and effect of the one embodiment will be described.

  According to the cold-rolled steel sheet for the separate plate, by decarburizing and softening the vicinity of the steel sheet surface so that ΔH, which is the difference in surface hardness with respect to the cross-sectional hardness at the center of the plate thickness, is 20 HV or more, Since the heat transfer rate can be improved and the local temperature rise during clutch operation can be suppressed, wear of the friction material that is the contact partner can be suppressed.

  Moreover, heat spot resistance and punchability can be improved by raising the A3 transformation point and lowering the hardenability and regulating the chemical components so that the cross-sectional hardness is 200 HV or more and 350 HV or less.

  Hereinafter, this example and a comparative example will be described.

  First, steel slabs having chemical components shown in Table 1 were melted. In Table 1, the steels satisfying the requirements of the chemical components in the present invention were designated as steels of the present invention, and those not satisfying the requirements of the chemical components in the present invention were designated as comparative steels. In Table 1, when Cr, Ni, Mo and B are not contained, the value on the left side of the formula (1) is shown as the Q value, and when at least one of Cr, Ni, Mo and B is contained Shows the value of the left side of the equation (4) as the Q value.

  Each steel slab having the chemical composition shown in Table 1 was hot-rolled. The hot conditions were a heating temperature of 1100 ° C. and 1250 ° C., and a winding temperature of 450 ° C., 470 ° C., 500 ° C., 550 ° C., 570 ° C., 600 ° C., 650 ° C. and 720 ° C.

  Each hot-rolled steel sheet was pickled with hydrochloric acid and then finished to a thickness of 1.8 mm at various cold rolling rates to prepare test materials. The cross-sectional hardness at the time after cold rolling was set to 250 HV. Moreover, about a part of example of this invention, the hot-rolled steel plate was annealed at 690 degreeC, or it cold-rolled after grind | polishing the surface. These processing conditions are shown in Table 2.

  Each test material was subjected to a punching test, surface hardness measurement, cross-sectional hardness measurement, and SAE # 2 test.

  In the punching test, each sample material was punched as a test piece having a plate thickness of 1.8 mm and a punching clearance of 8% of the plate thickness. Further, after punching, the burrs were removed with # 600 emery paper.

  In the punching process, a circular hole having a thickness of 1.8 mm and a diameter of 10 mm was punched from each test piece using a 300 kN universal testing machine. As the punching die, JIS standard SKD11 for cold die, which was tempered to 60HRC for both punch and die, was used. The test conditions were a punching speed of 1.7 mm / second and a clearance of 5%. And the punching processed goods whose punching shot number is 20-30 shots were collect | recovered, and the amount of sagging in a shear surface and a primary shear surface rate were evaluated. Specifically, each index was measured and the average value was calculated for the rolling direction of the material steel plate and the direction perpendicular thereto. These results are shown in Table 2. A primary shearing area ratio of 50% or more and a sag of less than 0.2 mm were evaluated as good evaluation, and in Table 2, it was rated as ◯, and the others were marked as x.

  In the surface hardness measurement, a part of each test material was cut out and the surface Vickers hardness was measured to obtain the surface hardness. Moreover, after embedding a part of each test material which measured surface hardness in resin and grinding | polishing, the Vickers hardness of plate thickness center part was measured and it was set as cross-sectional hardness. The test load for measuring the Vickers hardness was 10 kgf. These results are shown in Table 2.

  The SAE # 2 test was performed to evaluate the wear amount of the friction material and the heat spot resistance.

  When evaluating the wear amount of the friction material, each test material was processed into the shape of a separate plate to obtain a test piece. Using each test piece, the separation plate and the friction plate were repeatedly engaged 5000 times at a test rotation speed of 3600 rpm. Then, the thickness of the friction material on the friction plate was measured before and after the test to determine the thickness reduction amount. The thickness reduction amount was measured at 36 locations, and the maximum thickness reduction amount among the 36 locations was defined as the wear amount. These results are shown in Table 2.

  The heat spot resistance was obtained by processing a part of the sample materials of the invention examples and comparative examples into separate plates. Using each test piece, the separation plate and the friction plate were repeatedly engaged 5 times at a test rotation speed of 5000 rpm, and the presence or absence of a heat spot generated on the separation plate was visually confirmed. These results are shown in Table 2. In addition, the thing in which the heat spot was not confirmed was evaluated as being good in heat spot resistance and evaluated as “◯” in Table 2, and the case where the heat spot was confirmed as “x”.

  As shown in Table 2, all of the examples of the present invention had good punchability, and no heat spot was generated in the SAE # 2 test, and the heat spot resistance was good.

  Test No. which is a comparative example. 1-a, test no. 1-b and test no. Since 1-c has a C content of more than 0.08% by mass, it is considered that the punchability deteriorated due to an increase in the hard structure.

  Test No. which is a comparative example. No. 2 is considered that the punched surface properties deteriorated because the hard structure increases as the C content exceeds 0.08 mass% and the Si content exceeds 1.0 mass%.

  Test No. which is a comparative example. No. 3 has a Mn content of more than 0.8% by mass, so that the punched surface properties deteriorated, and since the Q value is larger than 1, it is considered that a heat spot was generated in the SAE # 2 test.

  Test No. which is a comparative example. In No. 4, the S content is more than 0.01% by mass, so that it is considered that the punched surface properties deteriorated.

  Test No. which is a comparative example. In No. 5, the Ti content was more than 0.3% by mass, and the value of the formula (2) was larger than 0.3. Therefore, it is considered that the material hardened and the punching surface properties deteriorated.

  Test No. which is a comparative example. 6 has a hard structure with a C content greater than 0.08% by mass, and the value of formula (2) is greater than 0.3, so the material hardens and the punching surface properties deteriorate. it is conceivable that.

  Test No. in the comparative example. In No. 7, since the Q value is larger than 1, it is considered that a heat spot was generated in the SAE # 2 test.

  Test No. which is a comparative example. In No. 8, since the value of the formula (2) is larger than 0.3, it is considered that the material is cured and the punching surface property is deteriorated.

  Test No. which is a comparative example. In No. 9, since the value of the formula (2) is smaller than 0.04, fine carbide hardly precipitates, and it is considered that a heat spot was generated in the SAE # 2 test.

  Test No. which is a comparative example. No. 10, since the C content is more than 0.08% by mass, the hard structure is increased, the Nb content is more than 0.4% by mass, and the value of the formula (2) is greater than 0.3. It is considered that the punched surface properties were deteriorated by curing.

  Test No. which is a comparative example. In 23-b, since the cross-sectional hardness, which is the material hardness, is lower than 200 HV, the punchability deteriorates, and it is considered that the sagging exceeded 0.2 mm in the punching process.

  Test No. which is a comparative example. 11-e and test no. 23-e has a low heating temperature in hot rolling, lack of promotion of decarburization, and ΔH becomes less than 20 HV. The amount is thought to have increased.

  Test No. which is a comparative example. 11-c, test no. 21-b and test no. 22-b has a short rolling time in hot rolling, lack of promotion of decarburization, and ΔH is less than 20HV. Seems to have increased.

  Test No. which is a comparative example. 11-b, test no. 12-a, test no. 13-a, test no. 14-d, test no. 15-a, test no. 19-a and test no. 20-b has a short rolling time in hot rolling, lack of promotion of decarburization, and ΔH becomes less than 20HV. Seems to have increased.

  Test No. which is a comparative example. 16-a, test no. 17-a and test no. Since 18-a has a short rolling time in hot rolling and a low coiling temperature, the promotion of decarburization is insufficient, and ΔH becomes less than 20 HV. It is considered that the wear amount of the friction material is increased as compared with.

  Test No. which is a comparative example. 14-b and test no. 23-d was obtained by removing the decarburized layer in the vicinity of the surface by performing surface polishing treatment on the hot-rolled steel sheet, and ΔH was less than 20 HV. It is considered that the wear amount of the friction material has increased.

  FIG. 1 is a scatter diagram showing the relationship between the cross-sectional hardness and the wear amount of the friction material in the SAE # 2 test. In FIG. 1, in each of the present invention examples and each of the comparative examples, a comparative example in which ΔH is less than 20 HV and a present invention example in which ΔH is 20 HV or more are plotted in different series.

  As shown in FIG. 1, the example of the present invention in which ΔH is 20 HV or more has a tendency that the wear amount of the friction material is lower than that of the comparative example, and the effect of reducing the wear amount of the friction material by surface decarburization could be confirmed. .

  Moreover, when the wear amount of the friction material of each invention example and each comparative example shown in Table 2 was compared in the same invention steel component, the wear amount of the invention example was smaller than that of the comparative example.

Claims (2)

C: 0.03 to 0.08% by mass, Si: 0 to 1.0% by mass, Mn: 0.2 to 0.8% by mass, P: 0.03% by mass Hereinafter, S: 0.01 mass% or less and Al: 0.05 mass% or less are contained so as to satisfy the formula (1), and Nb: 0.03 mass% or more and 0.4 mass% or less, V: Contains at least one of 0.01% by mass to 0.3% by mass and Ti: 0.01% by mass to 0.3% by mass so as to satisfy the formula (2), with the balance being Fe and inevitable Chemical component consisting of chemical impurities,
The cross-sectional hardness is 200 HV or more and 350 HV or less,
A cold rolled steel sheet for a separate plate, wherein the relationship between the cross-sectional hardness and the surface hardness at the center of the sheet thickness satisfies the formula (3).
(1) Formula: 5 × C% −Si% + Mn% −1.5 × Al% <1
(2) Formula: 0.04 <(Nb% ÷ 1.4) + (V% ÷ 1.1) + Ti% <0.3
(3) Formula: 20HV ≦ (section hardness at the center of the plate thickness) − (surface hardness) Cr: 0.10% by mass to 2.0% by mass, Ni: 0.05% by mass to 0.5% by mass, Mo: 0.05% by mass to 0.5% by mass and B: 0.0002 The cold-rolled steel sheet for a separate plate according to claim 1, wherein the cold-rolled steel sheet for a separate plate is a chemical component containing at least one of mass% or more and 0.002 mass% or less so as to satisfy the formula (4).
(4) Formula: 5 * C% -Si% + Mn% + 1.6 * Cr% + 0.8 * Ni% -1.5 * Al% <1

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