JP2013007084A - Thin steel strip plate and endless steel strip of high strength and high fatigue strength, and method for manufacturing the same - Google Patents

Abstract

An object of the present invention relates to a power transmission metal band applied to a steel belt or the like of a mechanism for transmitting a driving force or the like in an electrophotographic printer, a copying machine, a printer of a personal computer or the like. In addition to increasing the C content to the hypereutectoid level, a thin steel strip with high strength and high fatigue strength characterized by controlling the surface hardness, pearlite structure, and residual stress, and its endless steel strip provide.
SOLUTION: In mass%, C: 0.6 to 1.3%, Si: 0.1 to 1.50%, Mn: 0.1 to 1.5%, Al: 0.01% or less, Ti A thin steel strip having a high strength and a high fatigue strength, each of which is regulated to 0.01% or less, and consists of the balance Fe and inevitable impurities, a tensile strength of 1500 MPa or more, an elongation of 2% or more, and a surface hardness of 400 HV0.3 or more. That endless steel strip.
[Selection figure] None

Description

  An object of the present invention is to provide a thin steel strip plate and an endless steel strip used for a power transmission metal strip applied to a steel belt or the like of a mechanism for transmitting a driving force in a copying machine, an electrophotographic printer, a personal computer printer, etc. It relates to the manufacturing method.

  Steel belts are used for the power transmission parts of copiers, electrophotographic printers, personal computer printers, etc., but these devices are rapidly becoming smaller and faster, and accordingly, the drive parts The need for downsizing and thinning is increasing. Therefore, it is necessary to make the thickness of the steel belt used for the drive unit thinner than before, and high strength is required.

  When a steel belt is used for the power transmission unit, tension is applied to the belt to prevent the steel belt from slipping. As the tension applying mechanism, for example, a structure in which the tension between the driving pre and non-driving pres is slightly widened to apply tension, or one of the driving pre and non-driving pres is held in both hands, and a spring force or the like. A structure in which a pulley held by both hands is stretched in a direction in which tension is applied to the belt, or the shafts of the drive pulley and the driven pulley are fixed and a third separate pulley is provided. There is a structure in which tension is applied to the belt by pressing it against the inner and outer surfaces of the belt.

  In order to increase the printing efficiency of copying machines, electrophotographic printers, personal computer printers, etc., the power is increasing at higher speeds, and the tension applied to the steel belt is increasing to prevent slipping. Therefore, in addition to increasing the strength, steel belts are also required to have an improved bending fatigue life.

  Against this background, steel belts have high needs for high fatigue life in addition to high strength. Conventionally, stainless steel strips for springs specified by JIS have been applied. For example, SUS304, which is a work hardening type austenitic stainless steel, SUS632J1, which is a precipitation hardening type stainless steel, and the like are used (Non-Patent Documents 1, 2, and Patent Document 1).

  Furthermore, steel which adds about 0.7 to 1.2% of Mo to SUS632J1 and has higher strength and higher fatigue life is also applied (Non-patent Document 2). Further, there is a case where NSSHT-2000 is applied to a steel belt as a high-strength stainless steel that achieves a tensile strength of 1700 to 2400 MPa (Non-patent Document 2).

Japanese Patent Laid-Open No. 11-080906

JISG4313 Nisshin Seisaku Co., Ltd. Product Catalog CC01-080107-J

  However, in the above-described stainless steel, it is difficult to drastically reduce the cost because alloy elements are added in a total amount of 20 to 40% in any component system.

  An object of the present invention relates to a power transmission metal band applied to a steel belt or the like used in a mechanism for transmitting a motor driving force or the like in an electrophotographic printer, a copier, a personal computer printer, or the like.

  A steel strip with high strength and high fatigue strength, characterized by controlling the surface layer hardness, pearlite structure and residual stress in addition to increasing the C content to the hypereutectoid level and adding a small amount of alloying elements A plate and its endless steel strip are provided.

  The present inventor has excessively shared the C content in a power transmission metal band applied to a steel belt or the like used in a mechanism for transmitting a motor driving force in an electrophotographic printer, a copying machine, a personal computer printer, or the like. In addition to adding a small amount of alloying elements to increase the precipitation level, the strength of the thin steel strip and its endless steel strip is increased and fatigued by controlling the surface hardness, pearlite structure, residual stress, etc. It was found that strength could be achieved.

  That is, the present invention is, by mass%, C: 0.6 to 1.3%, Si: 0.1 to 1.50%, Mn: 0.1 to 2.0%, Al: 0.01% or less, Ti: 0.01% or less, nitrogen (N) and oxygen (O) content are both regulated to 20 to 40 ppm (mass basis), the balance is Fe and inevitable impurities, tensile strength is 1500 MPa or more, elongation is 2% As described above, a high strength and high fatigue strength thin steel strip having a surface hardness of 400 HV 0.3 or more and its endless steel strip.

  In the present invention, in addition to the above-mentioned composition, it is possible to further contain 3 ppm or more of solid solution boron (B) with a mass ppm, a boron (B) content of 4 to 30 ppm, and a solid solution boron (B).

  In the present invention, in addition to the above two compositions, Cr: 0.01 to 1.0%, Nb: 0.01 to 0.20%, Co: 0.01 to 1.0 %, V: 0.01 to 0.50%, Cu: 0.01 to 0.20%, Mo: 0.01 to 0.50%, Ni: 0.01 to 0.50%, W: 0.0. At least one selected from the group consisting of 01 to 0.20% can be contained.

  Further, in the present invention, the pearlite fraction is 80% or more, and the balance is bainite, pseudo-pearlite, grain boundary ferrite, proeutectoid cementite, spherical cementite, characterized by high strength and high fatigue strength Thin steel strip and its endless steel strip.

  In the present invention, the mass (%), the nitrogen (N) and oxygen (O) contents are both defined as 20 to 40 ppm, and the pearlite block size (referred to as PBS) is 20 μm or less. A high carbon steel strip having high strength and high fatigue strength and its endless steel strip.

  Further, the present invention is a thin steel strip having high strength and high fatigue strength, and an endless steel strip thereof, characterized in that compressive residual stress is applied to the surface.

  Further, the endless steel strip manufacturing process of the present invention includes a step of welding ends of thin steel strips to form a ring-shaped drum, a step of heat-treating the drum after welding, and a heat-treated drum. Is cut to a predetermined width to form a ring, and the ring is rolled. As a heat treatment for the post-weld drum, while the welded part temperature after welding is in the range of 720 ° C. to Ms point, 720 After heating to ℃ -1500 ℃ and performing the melt treatment, after cooling to a nose temperature ± 30 ℃ temperature range of TTT diagram at a cooling rate of 10 ℃ / s or more, isothermal transformation treatment is performed at that temperature And

  In the endless steel strip manufacturing process of the present invention, after the ring rolling process, at least one kind of nitriding treatment, skin pass rolling, straightening processing, and shot pinning treatment is performed.

  The high carbon steel strip with high strength and high fatigue strength of the present invention has a tensile cost, ductility, and fatigue characteristics equivalent to or higher than that of high strength stainless steel, etc. to which conventional steel belts have been applied. This can be achieved with a reduction, and is expected to have a significant industrial and economic effect.

  The present invention is a method for producing a high strength, high fatigue strength endless steel strip having a welded portion, a high strength, high fatigue strength thin steel strip, or an endless steel strip.

  In the endless steel strip having the welded portion of the present invention, the base metal portion and the welded portion, and the thin steel strip have a tensile strength of 1500 MPa or more, an elongation of 2% or more, and a surface layer hardness of 400 HV 0.3 or more. By containing tensile strength and elongation within the scope of the present invention as well as containing the following components, conventional high-strength stainless steel (Mo-added SUS632J1) for both the base metal part and the welded part in the endless steel strip 0.042% C-1.53% Si-0.30% Mn-7.2% Ni-14.7% Cr-0.39% Ti-0.70% Cu-0.72% Mo steel It is possible to achieve a fatigue strength equal to or greater than. Endless steel strips and thin steel strips are mainly applied to steel belts used to transmit driving force by belt / pulley mechanism, but the pulley surface layer improves wear resistance. Therefore, carburization and nitriding are often performed, and the surface hardness is 400HV0.3 or more. For this reason, the surface hardness of the steel belt needs to be 400HV0.3 or more from the viewpoint of durability and wear resistance of the steel belt.

  The action of each element in the present invention will be described below. Unless otherwise specified, it is expressed as mass%.

C: 0.6 to 1.3%
If it is less than 0.6%, the desired tensile strength cannot be stably obtained. If it exceeds 1.3%, pro-eutectoid cementite is generated and the workability deteriorates, causing not only a cause of breakage during steel strip processing, but also the ductility and fatigue life of the steel strip.

Si: 0.1 to 1.5%
Si is an effective element for strengthening ferrite in pearlite and for deoxidizing steel. However, if the Si content is less than 0.1%, the above effect cannot be expected. On the other hand, if the Si content exceeds 1.5%, harmful hard SiO ₂ inclusions that deteriorate the fatigue strength of the steel strip are likely to be generated. Become. For this reason, Si was limited to the range of 0.1 to 1.50%.

Mn: 0.1 to 2.0%
Mn is an element effective not only for deoxidation and desulfurization, but also for improving the hardenability of the steel and increasing the tensile strength of the steel strip after heat treatment. However, if Mn is less than 0.1%, the above effects cannot be obtained. On the other hand, if Mn exceeds 2.0%, Mn segregation is likely to occur, and the workability of the steel strip deteriorates, causing breakage during steel strip processing. In addition, the ductility and fatigue life of the steel strip are deteriorated. For this reason, Mn was limited to 0.1 to 2.0% of range.

Al: 0.01% or less Al content tends to generate hard non-deformable alumina-based nonmetallic inclusions that deteriorate the fatigue strength of the steel strip. For this reason, it limited to 0.01% or less. Al less than 0.01% contributes as a deoxidizer. The lower limit is 0.001%, which is inevitably mixed.

Ti: 0.01% or less The Ti content tends to generate hard non-deformation Ti oxides, Ti carbonitrides, and Ti carbides non-metallic inclusions that degrade the fatigue strength of the steel strip. For this reason, it limited to 0.01% or less. Ti less than 0.01% contributes as a deoxidizer. The lower limit is 0.001%, which is inevitably mixed.

  The impurities P and S are not particularly defined, but are preferably 0.02% or less from the viewpoint of securing ductility as in the case of conventional steel.

  The steel strip used in the present invention contains the above-mentioned elements as basic components, but for the purpose of further improving mechanical properties such as strength, ductility, fatigue life, etc., one kind of the following selectively permissible additive elements is used. Alternatively, two or more kinds may be positively contained.

B: 4 to 30 ppm
B has a content of 4 to 30 ppm, of which the solid solution B content is 3 ppm or more. If B exists in a solid solution state before heat treatment, it suppresses the precipitation of a non-pearlite structure. If the solute B content is less than 3 ppm, this effect is insufficient. If the B content is 4 ppm or more, 3 ppm can be secured as the solid solution B. Conversely, if the content is less than 4 ppm, it is difficult to make the solid solution B content 3 ppm or more. On the other hand, when the content of B exceeds 30 ppm, coarse Fe ₃ (CB) ₆ carbide is generated and the fatigue life of the steel strip is deteriorated. When B contains 4 to 30 ppm and N contains 20 to 40 ppm, it is also preferable to produce the nitrides moderately.

Cr: 0.01-1.00%
Cr is an effective element that refines the lamellar spacing of pearlite, increases the tensile strength after heat treatment, and particularly improves the cold work hardening rate. However, if the Cr content is less than 0.01%, the effect is small. On the other hand, if the Cr content exceeds 1.00%, the pearlite transformation finish time during the heat treatment becomes long and the productivity is lowered. For this reason, it is preferable to make Cr into the range of 0.01 to 1.00%.

Nb: 0.01-0.200%
Nb has the effect of refining the lamellar spacing of pearlite and increasing the tensile strength after the patenting treatment, and further has the effect of refining austenite grains during heat treatment. However, if Nb is less than 0.01%, the effect is small. On the other hand, even if Nb exceeds 0.200%, the effect is saturated. For this reason, it is preferable to make Nb into the range of 0.01 to 0.200%.

Co: 0.01-1.00%
Co has the effect of improving the cold workability of the hot rolled material and the steel strip after the heat treatment. However, if Co is less than 0.01%, the effect is small. On the other hand, even if Co exceeds 1.00%, an effect commensurate with the amount of addition cannot be exhibited. For this reason, it is preferable to make Co into the range of 0.01 to 1.00%.

V: 0.01 to 0.50%
V has an effect of reducing the lamellar spacing of pearlite and increasing the tensile strength after heat treatment. However, this effect is small when V is less than 0.01%, whereas the effect is saturated when V exceeds 0.50%. For this reason, it is preferable to make V into the range of 0.01 to 0.50%.

Cu: 0.01 to 0.2%
Cu has the effect of increasing the corrosion resistance of the steel strip. Addition of 0.01% or more is preferable for effectively exhibiting such an effect. However, if excessively added, it reacts with S to segregate CuS in the grain boundaries, so that flaws are generated in the steel ingot, steel strip, etc. during the steel strip manufacturing process. In order to prevent such adverse effects, the upper limit was made 0.2%.

Mo: 0.01 to 0.50%
Mo has the effect of increasing the strength during heat treatment due to the effect of improving hardenability. However, if the Mo content is less than 0.01%, the effect is small. On the other hand, even if the Mo content exceeds 0.50%, bainite is easily generated in the structure after hot rolling, which deteriorates the cold workability. For this reason, it is preferable to make Mo into the range of 0.01 to 0.50%.

Ni: 0.01 to 0.5%
Ni does not contribute much to increasing the strength of the steel strip, but is an element that increases the toughness of the steel strip. Addition of 0.01% or more is preferable for effectively exhibiting such an effect. On the other hand, if Ni is added excessively, the transformation end time becomes longer, so the upper limit was made 0.5%.

W: 0.01-0.2%
W has the effect of increasing the corrosion resistance of the steel strip. Addition of 0.01% or more is preferable for effectively exhibiting such an effect. On the other hand, if W is added excessively, the transformation end time becomes longer, so the upper limit was made 0.2%.

  In the endless steel strip having the thin steel strip of the present invention and the welded portion, both the base metal portion and the welded portion have a pearlite fraction of 80% or more, and the balance is bainite, pseudo-pearlite, grain boundary ferrite, proeutectoid Cementite and spherical cementite are preferred. By adjusting the structure of the steel strip to a pearlite fraction of 80 area% or more and the remainder to be bainite, pseudo-pearlite, grain boundary ferrite, proeutectoid cementite, and spherical cementite, the tensile strength, ductility, and fatigue life of the welded part are adjusted. And so on, the hypereutectoid component system can be applied to the steel belt.

  The pearlite fraction was measured by dividing the endless steel strip for steel belt into 10 equal parts, embedding the C cross section of each of the 10 samples in a resin, cutting the ground, and polishing the cut surface. Can be observed by SEM analysis at a magnification of 5000 times, and the area ratio of pearlite can be obtained as an average of 10 samples.

  In the endless steel strip having the thin steel strip of the present invention and the welded portion, the fatigue strength of the endless steel strip is reduced by reducing the pearlite block size (PBS) to 20 μm or less for both the base metal portion and the welded portion. Further improvement is possible. By defining the N and O contents as follows and adjusting the solution treatment temperature as described later, PBS can be reduced to 20 ppm or less.

N: 20 to 40 ppm
If the content of nitrogen (N) is less than 20 ppm, the effect of preventing the coarsening of PBS through the prevention of coarsening of austenite grains by forming Al, B or Ti and nitride present in a trace amount is insufficient. In particular, it becomes difficult to achieve 20 μm or less with PBS. On the other hand, if it exceeds 40 ppm, aging during steel strip processing is promoted and ductility deterioration and the like are caused.

O: 20 to 40 ppm
If the oxygen (O) content is less than 20 ppm, the effect of preventing the coarsening of PBS through the prevention of coarsening of austenite grains by forming oxides with Al, Ti, Si, Mn, etc. is insufficient. In particular, it becomes difficult to achieve 20 μm or less with PBS. If it exceeds 40 ppm, the fatigue life of the steel strip decreases due to oxide formation.

  The measurement of PBS is divided into 10 equal parts in the length direction of the endless steel strip for steel belt, and the C section of each of the 10 samples is embedded in a resin and cut, the cut surface is polished, and the central part is polished. By the EBSP analysis, the region surrounded by the interface having a magnification of 500 times and an orientation difference of 9 degrees was analyzed as one block grain, and obtained from the average volume of 10 samples.

  As a result of controlling PBS to 20 μm or less, the endless steel strip is effective in suppressing surface flaws in addition to stabilization by suppressing variations in mechanical properties such as tensile strength, ductility and fatigue life.

  A high strength, high fatigue strength endless steel strip for steel belts utilizing the steel strip of the present invention is manufactured, for example, by the following steps.

  That is, after the steel from the converter is subjected to secondary refining treatment and the molten steel composition is adjusted to the component range of the present invention, for example, a continuous casting method is performed to produce a slab having a width of 250 × length of 1500 mm. Further, the slab is repeatedly subjected to continuous hot rolling, further cold rolling and annealing, and a steel strip having a thickness of 0.5 mm is formed as an example.

  Thereafter, a steel strip having a thickness of 0.5 mm is cut into a predetermined length and width, and both ends thereof are joined by Tig welding, plasma welding, laser welding, or the like to form a drum shape. After welding to the drum, the drum is reheated to 720 ° C. to 1500 ° C. while the welded part temperature is in the range of 720 ° C. to Ms point, and a solution treatment is performed. After performing the melt treatment, after cooling to a nose temperature ± 30 ° C. temperature range of the TTT diagram at a cooling rate of 10 ° C./s or more, a constant temperature transformation treatment is performed at that temperature. The Ms point temperature is determined by the general formula of Ms (k) = 823-350C% -40Mn% -35V% -20Cr% -17Ni% -10Cu% -10Mo% -10W% + 15Co% + 30Al% based on the component content. Can be estimated. The nose temperature in the TTT diagram can be determined experimentally by a formaster.

  If the welded part temperature after welding is too low, cracks will occur in the welded part, the tensile strength will decrease and the fatigue life will deteriorate, and if the welded part temperature is too high, when setting the strip to the next heat treatment step However, since the dimensions such as the width and thickness of the welded portion are softened so as to fluctuate, there is a problem that a large variation occurs in the dimension after cold rolling, but the temperature of the welded part is in the range of 720 ° C. to Ms point. If so, these problems do not occur. If the melt treatment temperature is too low, undissolved carbides remain and the elongation decreases and the fatigue life deteriorates. If the melt treatment temperature is too high, the γ grain size becomes coarse and the elongation decreases and the fatigue life decreases. However, these problems do not occur if the melting temperature is 720 ° C to 1500 ° C. If the cooling rate after the solution treatment is too slow, the tensile strength is reduced and the fatigue life is deteriorated. Elongation and ductility decrease and fatigue life deteriorates. However, after cooling to a nose temperature ± 30 ° C temperature range of the TTT diagram at a cooling rate of 10 ° C / s or higher, isothermal transformation treatment is performed at that temperature. These problems do not occur.

  After the heat-treated drum is cut into a predetermined width, surface scale removal, surface coating treatment or the like is performed as necessary, and cold rolling is further performed to a thickness of 0.2 mm as an example. Thereby, both the base metal part and the welded part are endless steel strips having a tensile strength of 1500 MPa or more, an elongation of 2% or more, and a surface layer hardness of 400 HV0.3. In addition, surface layer hardness measured the hardness of five places each including the welding part of the front and back in the endless steel strip length direction, and made it the average value.

  While applying the production method of the present invention and setting the C content in the steel to 0.77% by mass or more, the structure of the steel strip has a pearlite fraction of 80% or more and the balance is bainite, pseudo. It is possible to adjust to pearlite, grain boundary ferrite, pro-eutectoid cementite, and spherical cementite, and the tensile strength, ductility, fatigue life, etc. of the welded part are not significantly different from the base metal part. Can be applied.

  In the endless steel strip having the thin steel strip and the welded portion of the present invention, in order to refine the pearlite block size (PBS) to 20 μm or less in both the base metal portion and the welded portion, the N and O contents are set. While adjusting to 20-40 mass ppm, the solution treatment temperature is set to 1000 ° C. or lower. As a result, when the structure is observed with the central part of the longitudinal section of the endless steel strip as a representative part, the components are appropriately adjusted within the scope of the present invention, and the PBS is finely reduced to 20 μm or less by the heat treatment after welding described above. Thus, the fatigue strength of the endless steel strip can be further improved.

  In order to improve the fatigue life of the endless steel strip, it is effective to increase the compressive residual stress of the surface layer. The ring after cold rolling is subjected to nitriding treatment, skin pass cold rolling, straightening processing, shot pinning. By performing at least one kind of treatment or the like, it is possible to reduce the tensile residual stress of the surface layer and to introduce the compressive residual stress. In the nitriding treatment, it is a condition that the tensile strength of the endless steel strip is not lowered after cold rolling, and it is preferable to apply a general ion nitriding treatment.

  Moreover, when manufacturing a slab by continuous casting, it casts to a cross section of 400 * 500 mm, for example, and after that, after heating to about 1000 degreeC with a heating furnace, it is set as a steel piece of a 165 square section by hot continuous rolling. . The steel slab is further heated to about 1000 ° C. in a heating furnace, and then rolled into a wire having a wire diameter of, for example, 5.5 mm by hot continuous rolling.

  After removing the scale on the surface of the wire with a wire diameter of 5.5 mm by pickling or the like, if necessary, it is treated with a lubricating coating, for example, cold-rolled with a die and finished into a wire with a wire diameter of 3.0 mm, Then, after repeatedly carrying out heat treatment and cold working with deformed dies, roller mills, cassette roller dies, etc. to finish a steel strip with a thickness of 0.5 mm, a steel strip with a thickness of 0.2 mm is processed in the same manner as described above. It is also possible to produce a ring.

  Since the high carbon steel specified in the present invention is adjusted to a pearlite structure excellent in cold workability, a steel strip from a wire can be manufactured as a cheaper manufacturing process.

  Since the endless steel strip of the present invention has high tensile strength and high fatigue life, and can be easily made into an endless steel strip by optimizing the welding method, for example, an electrophotographic printer, It is effective to apply to a steel belt used for a mechanism for transmitting a driving force in a copying machine, a printer of a personal computer or the like.

  The manufacturing method of the thin steel strip of this invention is demonstrated. A thin plate coil produced by hot and cold rolling a thin steel strip containing the components within the scope of the present invention is cut and further cold worked to produce a thin plate having a specified width and thickness. If the specified strength and elongation cannot be ensured in the above process, heat treatment is applied during the processing. The heat treatment is carried out by heating from room temperature to 720 ° C. to 1500 ° C. and carrying out a melt treatment, and then cooling to a temperature range of 30 ° C./TTT diagram at a cooling rate of 10 ° C./s or more. Perform isothermal transformation treatment at temperature. About the manufacturing method which makes the structure of a steel strip 80% or more of pearlite, and the manufacturing method which refine | miniaturizes PBS to 20 micrometers or less, it is the same as that of the manufacturing method of the said endless steel strip.

  The following examples illustrate the details of the present invention. As described above, a 0.35 mm thick steel strip manufactured by hot working from a thin plate or wire was prepared. Further, this steel strip is welded, reheated when the temperature of the welded portion is lowered to the temperature of the welded portion before heat treatment, melted, cooled at a predetermined cold speed, and then subjected to a constant temperature transformation treatment. The endless steel strip was rolled and adjusted to a thickness of 0.2 mm. The endless steel strip was examined for tensile strength, elongation, pearlite fraction, PBS, surface hardness, residual stress and fatigue life. The results are shown in Tables 1 and 2.

  The fatigue test is evaluated by repeated bending fatigue tests of test pieces including welded parts, taking into account that bending stress is applied to the endless steel strip under the condition where a steel belt is used. did. The fatigue life was measured when a bending stress was repeatedly applied with an average stress of 540 MPa and a maximum stress of 1020 MPa.

  In order to evaluate that the endless steel strip of the present invention has high strength and high fatigue life, 0.042% C-1 which is the conventional high strength stainless steel (Mo-added SUS632J1) shown in Comparative Example 14 .53% Si-0.30% Mn-7.2% Ni-14.7% Cr-0.39% Ti-0.70% Cu-0.72% Mo steel with an average stress of 540 MPa and maximum stress Was evaluated by the fatigue life when bending stress was repeatedly applied at 1020 MPa.

  Invention Examples 1 to 7 and Comparative Examples 8 to 13 in Table 1 are 1.02% C-0.20% Si-0.30Mn-0.2Cr steel (Al, no Ti addition, O = 32 ppm, N = 28 ppm). The nose temperature in the TTT diagram is 575 ° C. Along with Comparative Example 14, the heat treatment conditions after welding and the tensile strength, elongation, pearlite fraction, PBS, surface hardness, and fatigue test results of the 0.2 mm endless steel strip are shown. Numerical values that fall outside the scope of the present invention are underlined. The same applies to Tables 3 and 4.

  If the heat treatment after welding is within the scope of the present invention, the characteristics and structure of the endless steel strip including the welded portion are controlled within the scope of the invention, and 0.086% C-2. Fatigue life exceeding 63% Si-0.31% Mn-8.25% Ni-13.73% C-2.24% Mo-0.17% Cu steel is developed. In particular, Examples 4 to 7 of the present invention show that the fatigue life is further improved by controlling the PBS to 20 μm or less by setting the melting treatment temperature to 1000 ° C. or less.

  In Comparative Example 8, the temperature of the welded part is too low, cracking occurs in the welded portion, TS is less than 1500 MPa, and the fatigue life is also deteriorated. In Comparative Example 9, the melting temperature is too high, the γ grain size becomes coarse, the pearlite fraction is lowered, the elongation is less than 2%, and the fatigue life is deteriorated. In Comparative Example 10, the melting temperature is too low, undissolved carbide remains, the pearlite fraction also decreases, TS is less than 1500 MPa, and the fatigue life is deteriorated. In Comparative Example 11, the cooling rate after the solution treatment is too slow, the pearlite becomes coarse, TS is less than 1500 MPa, and the fatigue life is also deteriorated. In Comparative Example 12, the isothermal transformation temperature is too high, the pearlite becomes coarse, TS is less than 1500 MPa, and the fatigue life is also deteriorated. In Comparative Example 13, the isothermal transformation temperature is too low, the pearlite fraction is decreased, the elongation is less than 2%, and the fatigue life is deteriorated.

  Further, in Table 2, in order to confirm the effect of controlling the residual stress of the surface layer, No. In the endless steel strip of No. 4, nitriding, skin pass rolling, straightening, and shot peening were performed after the ring rolling process, and the results were shown. For comparison, the characteristics of Comparative Example 14 in Table 1 are also shown. It can be seen that the fatigue life is greatly improved by reducing the tensile residual stress or controlling the compression to compression. In addition, the number provided to each process in Table 2 has shown the order of the process implemented after a rolling process.

  Table 3 shows that a steel strip with a thickness of 0.5 mm manufactured with various chemical compositions is joined at both ends by Tig welding to form a drum, and after welding to the drum, the welding part temperature is kept at 500 ° C. and the drum is used as a heating furnace. After charging, reheating to 1000 ° C., and performing a melt treatment, the solution was cooled to a nose temperature in a TTT diagram at a cooling rate of 50 ° C./s, and then subjected to a constant temperature transformation treatment at that temperature. Then, the result of investigating the tensile strength, elongation, pearlite fraction, PBS, surface layer hardness, and fatigue life of the endless steel strip rolled to a thickness of 0.20 mm is shown. No. 25 to 54 are steels of the present invention, No. 55 to 66 are comparative steels.

  The fatigue test is evaluated by repeated bending fatigue tests of test pieces including welded parts, taking into account that bending stress is applied to the endless steel strip under the condition where a steel belt is used. did.

  In order to evaluate that the thin steel strip of the present invention and its endless steel strip have high strength and high fatigue life, it is the conventional high strength stainless steel (NSSHT-2000) shown in Comparative Example 66. 0.06% C-2.63% Si-0.31% Mn-8.25% Ni-13.73% Cr-0.17% Cu-0.39% Ti-2.24% Mo-0.70 % Cu steel was subjected to comparative evaluation by fatigue life when bending stress was repeatedly applied at an average stress of 540 MPa and a maximum stress of 1020 MPa.

  If the contained component is within the range of the present invention, combined with the application of the production method of the present invention, the tensile strength is 1500 MPa or more, and the fatigue is higher than that of the conventional high strength stainless steel (NSSHT-2000). It can be seen that lifetime can be achieved.

Comparative Example No. 55 is too high at C = 1.36%, proeutectoid cementite is generated, the elongation is less than 2%, and the ductility is low. Therefore, fatigue characteristics are also poor, and when the bending stress is repeatedly applied, it breaks early. Comparative Example No. 56 is too low at C = 0.52%, and the tensile strength does not reach 1500 MPa. Therefore, fatigue characteristics are also poor, and when the bending stress is repeatedly applied, it breaks early. Comparative Example No. 57 is too low at C = 0.48%, the tensile strength is 1500 MPa, and the hardness does not reach 400 HV0.3. Therefore, fatigue characteristics are also poor, and when the bending stress is repeatedly applied, it breaks early. Comparative Example No. 58 is too high with Si = 1.7%, and a large amount of SiO ₂ oxide is generated. Therefore, fatigue characteristics are also poor, and when the bending stress is repeatedly applied, it breaks early. Comparative Example No. No. 59 is too high at Mn = 1.65%, and the ductility and fatigue properties are lowered due to center segregation. When repeated bending stress is applied, it breaks early. Comparative Example No. 60 is too high with Al = 0.020% and Ti = 0.013%, and a large amount of inclusions such as alumina and titania are generated. Therefore, fatigue characteristics are also poor, and when the bending stress is repeatedly applied, it breaks early. Comparative Example No. No. 61 is too much as N = 48 ppm, the ductility decreases due to aging, and the elongation decreases from 2%. Therefore, fatigue characteristics are also poor, and when the bending stress is repeatedly applied, it breaks early. Comparative Example No. 62 is too high at O = 46 ppm, and a large amount of oxide inclusions are generated. Therefore, fatigue characteristics are also poor, and when the bending stress is repeatedly applied, it breaks early. Comparative Example No. 63 is too high with B = 35 ppm, and produces coarse Fe ₃ (CB) ₆ carbide. Therefore, fatigue characteristics are also poor, and when the bending stress is repeatedly applied, it breaks early. Comparative Example No. 64 is too high, Cu = 0.3%, and surface defects occur. Therefore, fatigue characteristics are also poor, and when the bending stress is repeatedly applied, it breaks early. Comparative Example No. In No. 65, Mo was too high, cold workability deteriorated, and surface defects occurred. Therefore, fatigue characteristics are also poor, and when the bending stress is repeatedly applied, it breaks early.

  Next, examples of the thin steel strip will be described.

  Table 4 shows 0.5 mm-thick steel strips manufactured with various chemical compositions, reheated to 1000 ° C., melted, and then brought to the nose temperature of the TTT diagram at a cooling rate of 50 ° C./s. After cooling, a constant temperature transformation treatment was performed at that temperature. Thereafter, the results of investigating the tensile strength, elongation, pearlite fraction, PBS, surface layer hardness, and fatigue life of the thin steel strip rolled to a thickness of 0.20 mm are shown. No. Nos. 67 to 96 are steels of the present invention, No. Reference numerals 97 to 108 are comparative steels.

  In order to evaluate that the thin steel strip of the present invention has high strength and high fatigue life, 0.086% C-2 which is the conventional high strength stainless steel (NSSHT-2000) shown in Comparative Example 108. .63% Si-0.31% Mn-8.25% Ni-13.73% Cr-0.17% Cu-0.39% Ti-2.24% Mo-0.70% Average stress on steel Was evaluated by the fatigue life when repeatedly bending stress was applied at a maximum stress of 1020 MPa.

  If the contained component is within the range of the present invention, the tensile strength is 1500 MPa or more, and it can be seen that a high fatigue life can be achieved as compared with the conventional high-strength stainless steel (NSSHT-2000).

Comparative Example No. In No. 97, C was too high, and pro-eutectoid cementite was produced, and the ductility was low at EL <2%, and the fatigue life was also reduced. Comparative Example No. In 98, C was too low, TS <1500 MPa, the tensile strength was low, and the fatigue life was reduced. Comparative Example No. No. 99 was too low in C, and had a low tensile strength <1500 MPa and a hardness <400, resulting in a reduced fatigue life. Comparative Example No. In No. 100, Si was too high, a large amount of SiO ₂ oxide was generated, and the fatigue life was reduced. Comparative Example No. In No. 101, Mn was too high, and ductility and fatigue life decreased due to center segregation. Comparative Example No. In No. 102, Al and Ti were too high, and a large amount of inclusions such as alumina and titania were generated, resulting in a decrease in fatigue life. Comparative Example No. No. 103 had too much N, and the ductility decreased due to aging, the elongation decreased from 2%, and the fatigue life also decreased. Comparative Example No. In 104, O was too high, a large amount of oxide inclusions were generated, and the fatigue life decreased. Comparative Example No. In No. 105, B was too high, and coarse Fe ₃ (CB) ₆ carbide was produced, and the fatigue life decreased. Comparative Example No. In No. 106, Cu was too high, surface defects were generated, and the fatigue life was reduced. Comparative Example No. In No. 107, Mo was too high, the cold workability deteriorated, surface flaws occurred, and the fatigue life decreased.

  The thin steel strip of the present invention and its endless steel strip have a high strength in addition to being able to significantly reduce additive alloys by increasing the C content to 0.6 to 1.3%. Since it can achieve a long fatigue life, it is most suitable for application to a power transmission metal strip used in a mechanism for transmitting a driving force of an electrophotographic printer, a copying machine, a printer of a personal computer, and the like.

Claims (14)

  An endless steel strip having a welded portion, in mass%, C: 0.6 to 1.3%, Si: 0.1 to 1.50%, Mn: 0.1 to 2.0%, Al : Ti, 0.01% or less, Ti: 0.01% or less, each of which consists of the remaining Fe and inevitable impurities. Both the base metal part and the welded part have a tensile strength of 1500 MPa or more, an elongation of 2% or more, and a surface hardness of 400 HV0. An endless steel strip with high strength and high fatigue strength having 3 or more.   The endless steel strip having a high strength and a high fatigue strength according to claim 1, further having a mass ppm and a B content of 4 to 30 ppm.   Further, in mass%, Cr: 0.01 to 1.0%, Nb: 0.01 to 0.20%, Co: 0.01 to 1.0%, V: 0.01 to 0.50%, Cu : At least selected from the group consisting of 0.01 to 0.20%, Mo: 0.01 to 0.50%, Ni: 0.01 to 0.50%, W: 0.01 to 0.20% The endless steel strip having high strength and high fatigue strength according to claim 1, comprising at least one kind.   The pearlite fraction is 80% or more in both the base metal part and the welded part, and the balance is bainite, pseudo pearlite, grain boundary ferrite, proeutectoid cementite, and spherical cementite. An endless steel strip with high strength and high fatigue strength described in 1.   5. The high strength according to claim 1, wherein the N and O contents are specified to 20 to 40 ppm in mass ppm, and the pearlite block size (referred to as PBS) is 20 μm or less. Endless steel strip with high fatigue strength, high fatigue strength.   The endless steel strip having high strength and high fatigue strength according to any one of claims 1 to 5, wherein a compressive residual stress is applied to the surface.   A process for forming a ring-shaped drum by welding ends of thin steel strips having the components of claims 1 to 3; a process for heat-treating the drum after welding; and a heat-treated drum having a predetermined width. In the method for producing an endless steel strip comprising the steps of forming a ring by cutting and rolling the ring, the temperature of the welded part after welding is in the range of 720 ° C. to Ms as the heat treatment for the drum after welding. In the meantime, after heating to 720 ° C to 1500 ° C and performing the melt treatment, cooling to the nose temperature ± 30 ° C temperature range of the TTT diagram at a cooling rate of 10 ° C / s or more, and then isothermal transformation treatment at that temperature The method for producing an endless steel strip according to any one of claims 1 to 6, wherein the method is performed.   The method for producing an endless steel strip according to claim 7, wherein at least one kind of nitriding treatment, skin pass rolling, straightening processing, and shot peening treatment is performed after the ring rolling step.   In mass%, C: 0.6 to 1.3%, Si: 0.1 to 1.50%, Mn: 0.1 to 1.5%, Al: 0.01% or less, Ti: 0.01 %, A balance of Fe and inevitable impurities, a tensile strength of 1500 MPa or more, an elongation of 2% or more, and a surface strength of 400 HV 0.3 or more.   The thin steel strip having high strength and high fatigue strength according to claim 9, further having a mass ppm and a B content of 4 to 30 ppm.   Further, in mass%, Cr: 0.01 to 1.0%, Nb: 0.01 to 0.20%, Co: 0.01 to 1.0%, V: 0.01 to 0.50%, Cu : At least selected from the group consisting of 0.01 to 0.20%, Mo: 0.01 to 0.50%, Ni: 0.01 to 0.50%, W: 0.01 to 0.20% The high-strength and high-fatigue strength thin steel strip according to claim 9 or 10, characterized by containing at least one kind.   The pearlite fraction is 80% or more, and the balance is bainite, pseudo pearlite, grain boundary ferrite, pro-eutectoid cementite, spherical cementite, high strength, high strength according to any one of claims 9 to 11 Thin steel strip with fatigue strength.   13. The high content according to claim 9, wherein the N and O contents are specified to 20 to 40 ppm in mass ppm, and the pearlite block size (referred to as PBS) is 20 μm or less. Thin steel strip with high strength and high fatigue strength.   The thin steel strip having high strength and high fatigue strength according to any one of claims 9 to 13, wherein a compressive residual stress is applied to the surface.