JP6361279B2 - Medium and high carbon steel - Google Patents

Description

  The present invention relates to a medium-high carbon steel material, and more particularly to a medium-high carbon steel material subjected to induction hardening.

  The medium-high carbon steel material contains about 0.30 to 0.70 mass% of carbon (C). Medium and high carbon steel materials are used for Thomson blades, for example. The Thomson blade is a strip-shaped punching blade. The Thomson blade is used for punching plywood, cardboard, resin, paper, leather, etc. into a predetermined shape. The medium-high carbon steel material is used as a Thomson blade after being bent according to the punching shape.

  Medium and high carbon steel materials are also used in automotive machine parts. Such mechanical parts are, for example, chains, gears, clutches and the like.

  If the wear resistance of the Thomson blade edge is low, the edge tends to be rounded by use, the sharpness is deteriorated, and the durability as a blade is lowered. Therefore, the cutting edge of the Thomson blade is required to have durability (wear resistance). Similarly, wear resistance is also required for the mechanical parts. Therefore, induction hardening is performed on medium and high carbon steel materials used for these applications. Induction hardening increases the hardness of the steel. As a result, the wear resistance of the steel material is increased. Recently, further improvement in wear resistance of medium and high carbon steel materials that have been subjected to induction hardening has been demanded.

  Japanese Unexamined Patent Publication No. 2004-277801 (Patent Document 1) proposes a steel for a punching blade having excellent wear resistance. The steel disclosed in Patent Document 1 has a decarburized surface layer made of a ferrite single phase and having a thickness of 5 μm or more. The base part which is an area | region whose depth from the surface is 100 micrometers or more contains C: 0.40-0.80 mass%. The base portion further has a metal structure containing 1% by volume or more of spherical carbide in bainite or a metal structure containing 1% by volume or more of spherical carbide in tempered martensite. It is described that if a certain amount or more of spherical carbide is dispersed in the structure of bainite or tempered martensite, the wear resistance is improved.

  Japanese Patent Laying-Open No. 2005-336567 (Patent Document 2) proposes a steel for a punching blade excellent in durability. The steel sheet for punching blades disclosed in Patent Document 2 has a decarburized surface layer having a thickness of 1 to 10% of the thickness on both sides. Base parts not affected by decarburization are in mass% C: 0.4 to 1.0%, Si: 0.2 to 2.0%, Mn: 0.2 to 2.0%, P: 0.00. 05% or less, S: 0.05% or less, Cr: 0.3 to 1.6%, Mo: 0 to 1.0%, V: 0 to 0.5%, the balance being Fe and inevitable It has a chemical composition of impurities. The base portion is a structure made of ferrite having a hardness of 270 to 350 HV and a spherical carbide. It is described that the durability required as a punching blade can be achieved by controlling the hardness of the portion excluding the decarburized surface layer to a certain level of hardness or more while maintaining the ferrite structure.

Japanese Patent Application Laid-Open No. 2012-214887 (Patent Document 3) proposes a steel sheet for a strip-shaped punching blade having excellent durability. The steel sheet disclosed in Patent Document 3 includes a surface layer portion in a depth region from the surface to 200 μm, and a base portion inside the surface layer portion. The base portion has a chemical composition containing C: 0.40 to 0.80% and Nb: 0.10 to 0.50%. Further, the base portion further includes 1.0% by volume or more of spherical carbides composed of cementite in bainite or tempered martensite, and the existence density of Nb-containing carbides having an equivalent circle diameter of 1.0 μm or more is 10.0 per 900 μm ^2. It has the metal structure as described above, and the hardness is adjusted to 300 to 400 HV. It is described that the durability of the strip-shaped punching blade is improved by using a steel sheet having a metal structure in which Nb-containing carbides are dispersed.

  Japanese Unexamined Patent Publication No. 2000-348330 (Patent Document 4) and Japanese Unexamined Patent Publication No. 2000-348331 (Patent Document 5) propose steel sheets having excellent fatigue characteristics after rapid thermal processing. The steel sheets disclosed in these patent documents adjust the microstructure and surface roughness together with the definition of components in machine parts for automobiles. This describes that the rapid heat treatment property and the fatigue characteristics after heat treatment can be improved.

  Japanese Patent Application Laid-Open No. 2005-054204 (Patent Document 6) and Japanese Patent Application Laid-Open No. 2007-321190 (Patent Document 7) propose a steel material having excellent fatigue characteristics after induction hardening or induction hardening and tempering. In the steel material disclosed in Patent Document 6, the base material structure is a bainite structure and / or a martensite structure together with the component definition, and the total structure fraction of the bainite structure and the martensite structure is 10% or more. Furthermore, the prior austenite grain size of the hardened layer after induction hardening is 12 μm or less over the entire thickness of the hardened layer. Furthermore, an equation showing the particle size distribution of austenite is presented, and it is described that a steel material excellent in fatigue characteristics after induction hardening can be obtained by satisfying these.

  In Patent Document 7, the matrix structure is a bainite structure and / or a martensite structure together with the component definition, and the total structure fraction of the bainite structure and the martensite structure is 10% or more. Furthermore, the prior austenite grain size of the hardened layer after induction hardening is 12 μm or less over the entire thickness of the hardened layer, and the surface residual stress after induction hardening and tempering is −700 MPa or less. Thereby, it is described that a steel material having excellent fatigue characteristics after induction hardening and tempering can be obtained.

JP 2004-277801 A JP 2005-336567 A JP 2012-214877 A JP 2000-348330 A JP 2000-248331 A Japanese Patent Laying-Open No. 2005-054204 JP 2007-321190 A

  For applications such as Thomson blades, patents as described above are disclosed. However, in the steel for punching blades of Patent Documents 1 and 2, in order to improve the performance after quenching of the cutting edge, only the bending performance improvement by decarburization of the surface layer portion and the structure of the cutting edge before quenching are limited. Not reached. When the structure before the cutting edge is limited, it is obvious that if the edge is subjected to induction hardening, for example, the structure will change, clearly improving the durability of the cutting edge after hardening. Not connected.

  In Patent Document 3, as a measure for improving the durability of the cutting edge, Nb is added, and the particle diameter of the Nb-containing carbide generated thereby and the density thereof are defined. However, this is also the same, and it can be easily estimated that sufficient performance may not be ensured due to the difference in the heat treatment conditions after quenching the blade edge.

  On the other hand, high temperature and short time heat treatment such as induction hardening is mainly performed for other uses such as automobile parts. However, there is no patent document that mentions the wear resistance after heat treatment. In most cases, in order to cope with heat treatment at high temperature and short time, such as induction hardening, the structure of the material and the grain size of carbide are limited in order to perform the heat treatment without any problems. Patent Document 4, Patent Document 5, Patent Document 6, and Patent Document 7 have references to performance after rapid thermal processing or induction quenching, induction quenching and tempering. However, these are all intended to improve fatigue resistance, and are intended to achieve that purpose by defining the structure and surface roughness of the base material. Durability and wear resistance cannot be improved by using the methods as described.

  An object of the present invention is to provide a medium-high carbon steel material excellent in wear resistance after induction hardening.

The medium and high carbon steel materials according to the present invention are in mass%, C: 0.30 to 0.70%, Si: 1.0% or less, Mn: 0.3 to 1.5%, P: 0.03% or less, S: 0.03% or less, sol. Al: 0.1% or less, N: 0.01% or less, Ti: 0.1% or less, B: 0 to 0.005%, Cr: 0 to 0.5%, Ni; 0 to 0.5% , Mo: 0 to 0.5%, Cu: 0 to 0.5%, Ca: 0 to 0.0050%, and Nb: 0 to 0.05%, the balance being Fe and impurities, Equation (1) is satisfied.
(48/14) × [N] +10 ⁽ −7000 ^{/ T + 2.75) /} [C] + 0.001 ≦ [Ti] ≦ 0.1 (1)
Here, [N] is the N content (% by mass), [C] is the C content (% by mass), [Ti] is the Ti content, and T is the heating temperature (K) during induction hardening. Is substituted.

  The above medium and high carbon steel materials are B: 0.0001 to 0.005%, Cr: 0.01 to 0.5%, Ni; 0.01 to 0.5%, Mo: 0.01 to 0.5%, Cu: 0.01 to 0.5%, Ca: 0.005 to 0.0050%, and Nb: 0.015 to 0.05% containing one or more selected from the group May be.

  The medium and high carbon steel material according to the present invention is excellent in wear resistance after induction hardening.

FIG. 1 is a graph showing the relationship between the C content (mass%), the Ti content (mass%) that is not TiN, and the durability of medium- and high-carbon steel materials subjected to induction hardening at 1100 ° C. FIG. 2 is a graph showing the relationship between medium and high carbon C content (mass%) subjected to induction hardening at 950 ° C., Ti content (mass%) that is not TiN, and wear resistance. FIG. 3 is a diagram showing the relationship between medium and high carbon C content (mass%) subjected to induction hardening at 950 ° C., Ti content (mass%) which is not TiN, and wear resistance, which is different from FIG. is there. FIG. 4A is a side view of the Ogoshi type abrasion tester. FIG. 4B is a front view of the Ogoshi type abrasion tester.

  Hereinafter, embodiments of the present invention will be described in detail. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

  The present inventors investigated and examined the wear resistance after induction hardening of medium and high carbon steel materials, and obtained the following knowledge.

  By containing TiC in the steel material, the wear resistance after induction hardening is increased. In the steel manufacturing process, Ti combines with N in molten steel to form TiN. And the excess Ti which did not become TiN couple | bonds with C, and TiC which contributes to the abrasion resistance of steel materials is produced | generated. Therefore, it is preferable that the steel material contains a Ti amount more than that combined with N.

  Furthermore, if the heat treatment temperature of induction hardening is high, TiC is dissolved. In induction hardening, a steel material is heated to a heat treatment temperature and then rapidly cooled. Therefore, once dissolved TiC is difficult to reprecipitate. Therefore, in consideration of the solubility product of TiC, it is preferable that the TiC remains undissolved even when the steel is heated to the heat treatment temperature in the induction hardening process.

By the way, the Ti amount Ti1 other than Ti bonded to N is expressed by the following formula (A).
Ti1 = [Ti] − (48/14) × [N] (A)
Here, [Ti] and [N] are Ti content (% by mass) and N content (% by mass) in the steel material.

On the other hand, the solubility product of TiC is defined by the following formula (B).
log [Ti] [C] = − 7000 / T + 2.75 (B)
Here, T is a heat treatment temperature (K) in the induction hardening process. [Ti] and [C] are the Ti content (mass%) and C content (mass%) in the steel material.

Therefore, the Ti amount Ti2 for generating TiC is defined by the following formula (C).
Ti2 = 10 ^{(-7000 / T + 2.75)} / [C] (C)

In order to sufficiently deposit TiC that enhances the wear resistance, the Ti amount Ti1 defined by the formula (A) should be larger than the Ti amount Ti2 defined by the formula (C). Specifically, if Ti1 and Ti2 satisfy the following formula (D), sufficient TiC is precipitated and excellent wear resistance is obtained.
Ti1 ≧ Ti2 + 0.001 (D)

When formula (D) is developed, the Ti content [Ti] in the steel material is as follows.
[Ti] ≧ (48/14) × [N] +10 ⁽ −7000 ^{/ T + 2.75) /} [C] +0.001 (E)

Based on the equation (E), the Ti content [Ti] in the steel material is defined by the following equation (1).
(48/14) × [N] +10 ⁽ −7000 ^{/ T + 2.75) /} [C] + 0.001 ≦ [Ti] ≦ 0.1 (1)
Here, [N] is the N content (% by mass), [C] is the C content (% by mass), [Ti] is the Ti content, and T is the heating temperature (K) during induction hardening. Is substituted.

  If the Ti content of the medium and high carbon steel material satisfies the formula (1), TiC sufficiently remains in the medium and high carbon steel material after induction hardening. Therefore, the wear resistance of the medium and high carbon steel material is increased.

  FIG. 1 is a diagram showing the relationship between the C content (mass%) in medium and high carbon steel materials subjected to induction hardening at 1100 ° C., the Ti content (mass%) that is not TiN, and the durability due to wear of the blade edge. It is. 2 and 3 are diagrams showing the relationship between medium and high carbon C content (mass%) subjected to induction hardening at 950 ° C., Ti content (mass%) that is not TiN, and wear resistance.

  With reference to FIG.1 and FIG.2, a vertical axis | shaft is Ti content Ti1 defined by Formula (A). The solid curve in the figure is the Ti content Ti2 based on the solubility product represented by the formula (C), and the broken curve is a curve obtained by adding 0.001% to Ti2.

  A mark “◯” in FIG. 1 means that the durability was excellent in Example 1 described later. The “x” mark means that the durability was low in Example 1. The mark “◯” in FIG. 2 means excellent wear resistance in Example 2 described later. The “x” mark means that the abrasion resistance in Example 2 was low. A mark “◯” in FIG. 3 means excellent wear resistance in Example 3 described later. The “x” mark means that the abrasion resistance in Example 3 was low.

  In any of FIGS. 1 to 3, when Ti1 is more than the dashed curve obtained by adding 0.001% to Ti2, durability or wear resistance is excellent. Therefore, if the Ti content in the steel material satisfies the formula (1), the durability or wear resistance of the medium-high carbon steel material after induction hardening is increased.

Based on the above knowledge, the medium and high carbon steel materials according to the present embodiment are in mass%, C: 0.30 to 0.70%, Si: 1.0% or less, Mn: 0.3 to 1.5%, P : 0.03% or less, S: 0.03% or less, sol. Al: 0.1% or less, N: 0.01% or less, Ti: 0.1% or less, B: 0 to 0.005%, Cr: 0 to 0.5%, Ni; 0 to 0.5% , Mo: 0 to 0.5%, Cu: 0 to 0.5%, Ca: 0 to 0.0050%, and Nb: 0 to 0.05%, the balance being Fe and impurities, Equation (1) is satisfied.
(48/14) × [N] +10 ⁽ −7000 ^{/ T + 2.75) /} [C] + 0.001 ≦ [Ti] ≦ 0.1 (1)
Here, [N] is the N content (% by mass), [C] is the C content (% by mass), [Ti] is the Ti content, and T is the heating temperature (K) during induction hardening. Is substituted.

  The above medium and high carbon steel materials are B: 0.0001 to 0.005%, Cr: 0.01 to 0.5%, Ni; 0.01 to 0.5%, Mo: 0.01 to 0.5%, Cu: 0.01 to 0.5%, Ca: 0.005 to 0.0050%, and Nb: 0.015 to 0.05%, one or more selected from the group .

  Hereinafter, the medium and high carbon steel materials of this embodiment will be described in detail.

[Chemical composition]
The medium-high carbon steel material according to the present embodiment has the following chemical composition.

C: 0.30 to 0.70%
Carbon (C) increases the strength of the steel after quenching. If the C content is too low, this effect cannot be obtained effectively. On the other hand, if the C content is too high, the toughness after quenching decreases. If the C content is too high, the volume fraction of carbides in the steel further increases and the strength becomes excessively high. Therefore, the C content is 0.30 to 0.70%. The minimum with preferable C content is higher than 0.30%, More preferably, it is 0.32%. The upper limit with preferable C content is less than 0.70%, More preferably, it is 0.68%.

Si: 1.0% or less Silicon (Si) is inevitably contained. Si increases the hardenability of the steel. However, if the Si content is too high, the _Ac3 point will rise excessively. If the Si content is too high, it further becomes a cause of surface flaws during hot rolling. Therefore, the Si content is 1.0% or less. The upper limit with preferable Si content is less than 1.0%, More preferably, it is 0.5%, More preferably, it is 0.3%.

Mn: 0.3 to 1.5%
Manganese (Mn) lowers the A _c3 point and increases the hardenability of the steel. If the Mn content is too low, this effect cannot be obtained effectively. On the other hand, if the Mn content is too high, the strength of the steel becomes excessively high. If the Mn content is too high, Mn is further segregated. In this case, the steel easily forms a band-like structure, and the toughness of the steel decreases. Therefore, the Mn content is 0.3 to 1.5%. The minimum with preferable Mn content is higher than 0.3%, More preferably, it is 0.33%, More preferably, it is 0.35%. The upper limit with preferable Mn content is less than 1.5%, More preferably, it is 1.30%, More preferably, it is 1.0%.

P: 0.03% or less Phosphorus (P) is an impurity. P decreases the formability of the steel before quenching and the toughness of the steel after quenching. Therefore, the P content is 0.03% or less. A preferable P content is 0.015% or less. The P content is preferably as low as possible.

S: 0.03% or less Sulfur (S) is an impurity. S decreases the formability of the steel before quenching and the toughness of the steel after quenching. Therefore, the S content is 0.03% or less. A preferable S content is 0.005% or less. The S content is preferably as low as possible.

sol. Al: 0.1% or less Aluminum (Al) is inevitably contained. Al deoxidizes steel. However, if the Al content is too high, the _Ac3 point will rise excessively. If the Al content is too high, the production cost further increases. Therefore, sol. Al content is 0.1% or less. When further increasing the cleanliness, sol. A preferred lower limit of the Al content is 0.004%. sol. The upper limit with preferable Al content is less than 0.1%, More preferably, it is 0.07%, More preferably, it is 0.05%. sol. Al means so-called acid-soluble Al.

N: 0.01% or less Nitrogen (N) is an impurity. N decreases the formability of the steel before quenching. When N further contains B, BN is formed to reduce the amount of dissolved B. Therefore, the N content is 0.01% or less. A preferable N content is 0.005% or less. The N content is preferably as low as possible.

Ti: 0.1% or less Titanium (Ti) forms TiN and fixes N. Ti further combines with C to form fine TiC. When using medium and high carbon steel materials for blades or machine parts, induction hardening is performed on a part or the whole. In this case, in order to improve the wear resistance (durability) of the steel material after induction hardening, the lower limit of the Ti content is set so that TiC does not melt during induction hardening. This point will be described in the following [Equation (1)]. On the other hand, if the Ti content is too high, TiC is excessively precipitated and the strength after quenching is rather lowered. Therefore, the Ti content is 0.1% or less. The upper limit with preferable Ti content is less than 0.1%, More preferably, it is 0.07%, More preferably, it is 0.05%.

[Regarding Formula (1)]
As described above, the Ti content further satisfies the formula (1).
The medium-high carbon steel material of the present embodiment satisfies the formula (1).
(48/14) × [N] +10 ⁽ −7000 ^{/ T + 2.75) /} [C] + 0.001 ≦ [Ti] ≦ 0.1 (1)
Here, [N] is the N content (% by mass), [C] is the C content (% by mass), [Ti] is the Ti content, and T is the heating temperature (K) during induction hardening. Is substituted.

It is defined as F1 = (48/14) × [N] +10 ⁽ −7000 ^{/ T + 2.75) /} [C] +0.001. If the Ti content is F1 or more, Ti in the steel not only bonds with N to form TiN but also bonds with C to form a sufficient amount of TiC. As a result, the wear resistance of the medium and high carbon steel material is increased.

  The balance of the medium-high carbon steel material according to the present embodiment is Fe and impurities. Here, the impurities are mixed from ore as a raw material, scrap, or production environment, etc. when industrially producing steel materials, and do not adversely affect the medium-high carbon steel materials of this embodiment. Means what is allowed.

  The medium-high carbon steel material according to the present embodiment further contains one or more selected from the group consisting of B, Cr, Ni, Mo, and Nb instead of a part of Fe. These elements are arbitrary elements. All of these elements increase the hardenability of the steel.

B: 0 to 0.005%
Boron (B) is an optional element and may not be contained. When contained, B dissolves in the steel to enhance the hardenability and impact resistance of the steel. However, if the B content is too high, a B compound is produced and the above effect cannot be obtained. Therefore, the B content is 0 to 0.005%. The minimum with preferable B content is 0.0001%, More preferably, it is 0.0003%, More preferably, it is 0.0005%. The upper limit with preferable B content is less than 0.005%, More preferably, it is 0.004%, More preferably, it is 0.0035%.

Cr: 0 to 0.5%
Chromium (Cr) is an optional element and may not be contained. When contained, Cr increases the hardenability of the steel. However, if the Cr content is too high, the formability of the steel decreases. If the Cr content is too high, Cr is further concentrated in the carbide. In this case, the dissolution of the carbide is delayed and the hardenability is rather lowered. Therefore, the Cr content is 0 to 0.5%. A preferable lower limit of the Cr content is 0.01%. The upper limit with preferable Cr content is less than 0.5%, More preferably, it is 0.4%, More preferably, it is 0.3%.

Ni: 0 to 0.5%
Nickel (Ni) is an optional element and may not be contained. When contained, Ni increases the hardenability of the steel. However, if the Ni content is too high, the formability of the steel before quenching decreases. Therefore, the Ni content is 0 to 0.5%. A preferable lower limit of the Ni content is 0.01%. The upper limit with preferable Ni content is less than 0.5%, More preferably, it is 0.4%, More preferably, it is 0.3%.

Mo: 0 to 0.5%
Molybdenum (Mo) is an optional element and may not be contained. When contained, Mo increases the hardenability of the steel. However, if the Mo content is too high, the formability of the steel before quenching decreases. Therefore, the Mo content is 0 to 0.5%. A preferable lower limit of the Mo content is 0.01%. The upper limit with preferable Mo content is less than 0.5%, More preferably, it is 0.45%, More preferably, it is 0.4%.

Nb: 0 to 0.05%
Niobium (Nb) is an optional element and may not be contained. When Nb is contained, Nb forms a carbonitride similar to Ti, increases the wear resistance after the induction heat treatment, and increases the toughness of the steel after the heat treatment. However, if the Nb content is too high, the formability of the steel decreases. Therefore, the Nb content is 0 to 0.05%. The minimum with preferable Nb content is 0.015%, More preferably, it is 0.02%, More preferably, it is 0.025%. The upper limit with preferable Nb content is less than 0.05%, More preferably, it is 0.049%, More preferably, it is 0.048%.

  The medium-high carbon steel material according to the present embodiment may further contain Cu instead of a part of Fe.

Cu: 0 to 0.5%
Copper (Cu) is an optional element and may not be contained. When contained, Cu increases the surface cleanliness of the steel after pickling. However, if the Cu content is too high, the effect is saturated. Therefore, the Cu content is 0 to 0.5%. A preferable lower limit of the Cu content is 0.01%. The upper limit with preferable Cu content is less than 0.5%, More preferably, it is 0.4%, More preferably, it is 0.3%.

The medium-high carbon steel material according to the present embodiment may further contain Ca instead of a part of Fe.
Ca: 0 to 0.0050%
Calcium (Ca) is an optional element and may not be contained. When contained, Ca combines with S to form a sulfide. This increases the toughness of the steel in the direction perpendicular to the rolling. However, if the Ca content is too high, the cleanliness of the steel decreases. Therefore, the Ca content is 0 to 0.0050%. The minimum with preferable Ca content is 0.0005%, More preferably, it is 0.0010%, More preferably, it is 0.0015%. The upper limit with preferable Ca content is less than 0.0050%, More preferably, it is 0.0030%, More preferably, it is 0.0025%.

[Vickers hardness of steel]
When induction hardening is performed on only a part of the medium-high carbon steel material, the Vickers hardness of the portion where induction hardening is not performed is less than 400 HV. Vickers hardness is implemented in accordance with JIS Z2244. The test force is 49.03 N in Example 1 with a small plate thickness and 98.07 N in Examples 2 and 3 with a large plate thickness. If the Vickers hardness of the medium-high carbon steel material that has not been subjected to induction hardening treatment is in the above range, the bending workability when processing into a strip-shaped punching blade or the like is excellent. A preferable lower limit of the Vickers hardness of the above portion is 290 HV.

[Production method]
An example of the manufacturing method of the medium-high carbon steel material of this embodiment is demonstrated.

  A molten steel having the above chemical composition is produced. Slabs are manufactured by continuous casting using molten steel. You may manufacture an ingot by the ingot-making method using molten steel. You may manufacture a billet by hot-rolling an ingot and a slab.

  A hot-rolled steel sheet is produced by hot rolling using a slab, ingot or billet. Hot rolling conditions are not particularly limited. Preferably, the raw material temperature (rolling start temperature) at the start of rolling is 1000 to 1300 ° C. And preferable finishing temperature is 850 degreeC or more. In this case, pearlite is easily generated uniformly in the rolling process.

  A preferable winding temperature is 500 to 650 ° C. In this case, it can suppress that a yield falls by scale production | generation, maintaining a moldability. A descaling process is performed on the hot-rolled steel sheet. The descaling process is, for example, pickling.

  Spheroidizing annealing may be performed on the hot-rolled steel sheet after descaling. Spheroidizing annealing may be performed after descaling or after cold rolling described later. The execution timing of the spheroidizing annealing can be adjusted according to the plate thickness and hardness. The cold rolling and spheroidizing annealing described later may be repeated.

  Cold rolling is performed on the hot rolled steel sheet after descaling or spheroidizing annealing to produce a cold rolled steel sheet. If the cold pressure ratio is too high, the ferrite particle size after spheroidizing annealing becomes small, and the moldability of the product decreases. If the ferrite particle size is reduced, the induction hardenability is also affected. In order to obtain an appropriate ferrite grain size, it is preferable that recrystallization grain growth is promoted during finish annealing after cold rolling. If the cold pressure ratio is too high, it is difficult to promote grain growth. Therefore, the preferable upper limit of the cold pressure ratio is 50%. In order to improve the flatness of the steel material, the preferable lower limit of the cold pressure ratio is 10%. When the finish annealing is omitted, the cold pressure rate is not particularly limited. A cold-rolled steel sheet is manufactured by the above process.

  Induction hardening is performed on cold-rolled steel sheets. At this time, the heat treatment temperature of induction hardening is determined so as to satisfy the formula (1). The medium and high carbon steel material of this embodiment is manufactured by the above process. Prior to induction quenching, the cold-rolled steel sheet may be quenched and tempered one or more times.

  The molten steel which has the chemical composition of the test numbers 1-27 shown in Table 1 was manufactured.

  Slabs were produced from molten steel of each test number. Hot rolling was performed on the slab to produce a hot-rolled steel sheet having a thickness of 2.0 mm. The finish rolling temperature at this time was 830-860 degreeC, and the coiling temperature was 600-650 degreeC. After pickling the hot rolled steel sheet, cold rolling was performed to produce a cold rolled steel sheet having a thickness of 0.68 mm.

  Spheroidizing annealing was performed on the cold-rolled steel sheet. The heat treatment temperature was 690 ° C., and the annealing time was 24 hours. After spheroidizing annealing, cold rolling was further performed to produce a hardened steel sheet having a thickness of 0.44 mm.

[Preparation of test piece]
A plurality of test pieces having a length of 100 mm and a width of 25 mm were cut out from the hard-drawn steel sheet. The longitudinal direction of the test piece was made parallel to the rolling direction of the hard-drawn steel sheet. Cutting from both the front and back surfaces was performed on the longitudinal end portion of the test piece to perform cutting with a blade edge angle of 45 °.

  Quenching and tempering treatments were performed on the test pieces that had been bladed. The heat treatment temperature in the quenching process was 860 ° C., and the holding time was 20 minutes. The heat treatment temperature of the tempering treatment was 350 to 400 ° C., and the holding time was 40 minutes.

  After quenching and tempering treatment, induction hardening treatment was performed on the cutting edge portion of the test piece. The heat treatment temperature of the induction hardening treatment was 1100 ° C. After heating to the heat treatment temperature, rapid cooling was performed.

[Vickers hardness test]
The Vickers hardness test based on JIS Z2244 was implemented with respect to the blade edge | tip part and trunk | drum of the test piece obtained by said manufacturing process. Specifically, a Vickers hardness test was performed at a test force of 49.03 N on any three locations on the body of the test piece. The average of the obtained hardness was made into the hardness (HV) of the trunk | drum. The Vickers hardness test was implemented with respect to arbitrary 3 places of the blade edge | tip part in which induction hardening was implemented similarly to the trunk | drum. The average of the obtained hardness was made into the hardness (HV) of a blade edge | tip part.

[90 ° bending test]
A 90 ° bending test was performed on each test piece. Specifically, the test piece after induction hardening was subjected to bending with a punch having a tip radius of 0.25 mm and a tip angle of 90 °. After carrying out the butt bending, the body part of the test piece was visually observed. When no crack was found in the body part, it was judged that the bending workability was high, and when the crack was found, it was judged that the bending workability was low.

[Durability (Abrasion Resistance) Test]
In each test number, two test pieces bent by 90 ° were combined and embedded in a wooden mold to produce a punch mold. A corrugated cardboard was punched using a press testing machine incorporating a punch die. Punching was performed until the cardboard could not be punched, and the number of punchable sheets was determined.

  As a reference, a JIS standard S50C test piece was prepared, and a punch type was similarly prepared. Hereinafter, this punch type is referred to as a reference punch type. Punching was performed on a corrugated cardboard of the same size and material as described above with a standard punch type. Punching was performed until the cardboard could not be punched, and the number of cardboards that could be punched in the standard punch mold (hereinafter referred to as the standard number) was determined. When the number of punchable sheets for each test number was 10% or more than the reference number, it was judged that the durability (wear resistance) was high.

[Test results]
The test results are shown in Table 2. A “◯” mark in the “bending workability” column indicates that no cracks were observed by visual observation after bending. The “x” mark indicates that cracking was observed by visual observation after bending. A “◯” mark in “Durability Evaluation” indicates that the number of punchable sheets is 10% or more than the reference number. The “x” mark indicates that the number of punchable sheets is less than 10% compared to the reference number.

  Referring to Table 2, the chemical compositions of the steel materials of test numbers 2, 3, 7, 8, 10, 11, 13, 15, 18, 19, 21, 23, 25, and 26 are appropriate, and the formula (1) Met. Therefore, the hardness of the trunk was 290 HV or more and less than 400 HV, and the bending workability was also good. Furthermore, the durability of the blade edge portion was also excellent.

  On the other hand, the C content of Test No. 1 was too low. Therefore, the hardness of the trunk was as low as less than 290 HV. The C content of test number 4 was too high. Therefore, the hardness of the trunk portion exceeded 400 HV, and the bending workability was low. Although the chemical composition of Test No. 5 was appropriate, Formula (1) was not satisfied. Therefore, durability was low. It is thought that TiC was dissolved too much during induction hardening. The Mn content of test number 6 was too low. Therefore, the hardenability was low, and the hardness of the trunk was too low at less than 290 HV.

  The Mn content of test number 9 was too high. Therefore, the hardness of the barrel after quenching exceeded 400 HV, and the bending workability was low. Although the chemical composition of Test No. 12 was appropriate, Formula (1) was not satisfied. Therefore, durability was low. Although the chemical composition of the test number 14 was appropriate, the formula (1) was not satisfied. Therefore, durability was low.

  The Ti content of test number 16 was too high. Therefore, the hardness of the trunk after quenching was too low. It is considered that the hardness decreased because TiC precipitated excessively.

  In test number 17, Si was too high. Therefore, the hardness of the barrel after quenching exceeded 400 HV, and the bending workability was low.

  The Cr content of Test No. 20 was too high. Therefore, the hardness of the barrel after quenching was too hard and the bending workability was low.

  The chemical composition of Test No. 24 did not contain Ti and did not satisfy the formula (1). Therefore, the durability of the blade edge portion was low.

  Although each element content of the test number 27 was appropriate, the formula (1) was not satisfied. Therefore, durability was low.

  The molten steel which has the chemical composition of the test numbers 31-48 shown in Table 3 was manufactured.

  Slabs were produced from molten steel of each test number. Hot rolling was performed on the slab to produce a hot-rolled steel plate having a thickness of 2.6 mm. The finish rolling temperature was 830 to 860 ° C, and the winding temperature was 600 to 650 ° C. After performing pickling on the hot-rolled steel sheet, an annealing treatment was performed. The heat treatment temperature for the annealing treatment was 750 ° C., and the holding time was 5 hours. After annealing, temper rolling was performed to produce a steel plate.

[Preparation of test piece]
A plurality of test pieces having a length of 100 mm and a width of 25 mm were cut out from the steel plate. The longitudinal direction of the test piece was made parallel to the rolling direction of the steel plate. The test piece was subjected to induction hardening. The heat treatment temperature of the induction hardening treatment was 950 ° C. Furthermore, induction tempering was performed. The tempering temperature was 200 ° C. Induction tempering was performed, and the Vickers hardness of each test piece was set to 550 ± 5 HV (test force was 98.07 N).

[Ogoshi type wear tester]
Using the Ogoshi type abrasion tester shown in FIG. 4A and FIG. As shown in FIGS. 4A and 4B, the test piece 10 was disposed under the rotating plate 1. The radius R of the rotating plate 1 was 30 mm, and the width B was 3.0 mm.

  The test piece 10 was subjected to surface polishing with a puff before the test. After placing the test piece 10 under the rotating plate 1, while rotating the rotating plate 1, a load P of 67 N was applied to press the rotating plate 1 against the test piece 10. The wear rate V during the test was 0.76 m / s, and the wear distance was 400 m. The material of the rotating plate 1 as the counterpart material had a chemical composition corresponding to SCM415.

  The amount of wear after the test was measured. Furthermore, a test piece having a chemical composition corresponding to S35C was prepared as a reference test piece, and an Ogoshi-type wear test was performed under the same conditions as described above, and the amount of wear was measured. When the wear amount of each test number was smaller than the wear amount of the reference test piece, it was evaluated that the wear resistance was excellent.

[Test results]
The test results are shown in Table 4. “◯” mark in the “Abrasion Resistance Evaluation” column in Table 4 means that the wear amount of the test piece of the corresponding test number was smaller than the wear amount of the reference test piece. The “x” mark means that the wear amount of the test piece was equal to or greater than the wear amount of the reference test piece.

  Referring to Table 4, the chemical compositions of test numbers 33, 35-37, 39, 41, 44, 45 and 47 were appropriate and met formula (1). Therefore, it was excellent in wear resistance.

  On the other hand, although the chemical composition of the test numbers 31, 32, 34, 40, 42, 43, and 48 was appropriate, the formula (1) was not satisfied. Therefore, the wear resistance was low. The chemical compositions of test numbers 38 and 46 did not contain Ti and did not satisfy the formula (1). Therefore, the wear resistance was low.

  Molten steel having the chemical composition shown in Table 5 was produced.

  The chemical compositions of test numbers 51 to 54 in Table 5 corresponded to S45CM defined by JIS G3311. The chemical composition of test numbers 55-58 corresponded to S55CM. The chemical composition of test numbers 59-62 corresponded to S65CM.

  Slabs were produced from molten steel of each test number. Hot rolling was performed on the slab to produce a hot rolled steel sheet having a thickness of 4.5 mm. The finish rolling temperature was 830 to 860 ° C, and the winding temperature was 600 to 650 ° C. After performing pickling on the hot-rolled steel sheet, an annealing treatment was performed. The heat treatment temperature for the annealing treatment was 750 ° C., and the holding time was 5 hours. After annealing, cold rolling was performed to produce a cold rolled steel sheet having a thickness of 2.3 mm. Then, the annealing process was implemented with respect to the cold-rolled steel plate. The heat treatment temperature for the annealing treatment was 690 ° C., and the holding time was 24 hours. After annealing, temper rolling was performed to produce a steel plate.

[Preparation of test piece]
A plurality of test pieces having a length of 100 mm and a width of 25 mm were cut out from the steel plate. The longitudinal direction of the test piece was made parallel to the rolling direction of the steel plate. The test piece was subjected to induction hardening. The heat treatment temperature of the induction hardening treatment was 950 ° C. Furthermore, induction tempering was performed. The tempering temperature was 200 to 400 ° C. Induction tempering was performed, and the Vickers hardness of each test piece was set to 550 ± 5 HV (test force was 98.07 N).

[Ogoshi type wear tester]
Using the Ogoshi type abrasion tester shown in FIG. 4A and FIG. As shown in FIGS. 4A and 4B, the test piece 10 was disposed under the rotating plate 1. The radius R of the rotating plate 1 was 30 mm, and the width B was 3.0 mm.

  The test piece 10 was subjected to surface polishing with a puff before the test. After placing the test piece 10 under the rotating plate 1, while rotating the rotating plate 1, a load P of 67 N was applied to press the rotating plate 1 against the test piece 10. The wear rate V during the test was 0.76 m / s, and the wear distance was 400 m. The material of the rotating plate 1 as the counterpart material had a chemical composition corresponding to SCM415.

  The amount of wear after the test was measured. Furthermore, as a standard test piece, a standard test piece having a chemical composition corresponding to S45C is prepared for test numbers 51 to 54, and a standard having a chemical composition corresponding to S55C for test numbers 55 to 58. A test piece was prepared, and for test numbers 59 to 62, a reference test piece having a chemical composition corresponding to S65C was prepared. The Ogoshi type wear test was performed on each reference specimen under the same conditions as above, and the wear amount was measured. When the wear amount of each test number was smaller than the wear amount of the corresponding standard test piece, it was evaluated that the wear resistance was excellent.

[Test results]
The test results are shown in Table 6. “◯” mark in the “Abrasion resistance evaluation” column in Table 6 means that the wear amount of the test piece of the corresponding test number is smaller than the wear amount of the corresponding reference test piece. The “x” mark means that the wear amount of the test piece was equal to or greater than the wear amount of the corresponding reference test piece.

  Referring to Table 6, the chemical compositions of test numbers 54, 58 and 62 were appropriate and met formula (1). Therefore, it was excellent in wear resistance.

  On the other hand, the chemical compositions of the test numbers 51, 55 and 59 did not contain Ti and did not satisfy the formula (1). Therefore, the wear resistance was low. Although the chemical compositions of the test numbers 52, 53, 56, 57, 60 and 61 were appropriate, they did not satisfy the formula (1). Therefore, the wear resistance was low.

  The embodiment of the present invention has been described above. However, the above-described embodiment is merely an example for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiment, and can be implemented by appropriately changing the above-described embodiment without departing from the spirit thereof.

1 Rotating plate 100 Test piece

Claims (2)

% By mass
C: 0.30 to 0.70%,
Si: 1.0% or less,
Mn: 0.3 to 1.5%,
P: 0.03% or less,
S: 0.03% or less,
sol. Al: 0.1% or less,
N: 0.01% or less,
Ti: 0.1% or less,
B: 0 to 0.005%,
Cr: 0.01 to 0.5%,
Ni : 0 to 0.5%,
Mo: 0 to 0.5%,
Cu: 0 to 0.5%,
Ca: 0 to 0.0050%, and
Nb: 0 to 0.05% is contained, the balance consists of Fe and impurities,
Used in applications which are induction hardened at a heating temperature T satisfying the formula (1), medium and high carbon steel plate.
(48/14) × [N] +10 ⁽ −7000 ^{/ T + 2.75) /} [C] + 0.001 ≦ [Ti] ≦ 0.1 (1)
Here, [N] is the N content (% by mass), [C] is the C content (% by mass), [Ti] is the Ti content, and T is the heating temperature (K) during induction hardening. Is substituted. A medium and high carbon steel plate according to claim 1,
B: 0.0001~0.005%,
N i : 0.01 to 0.5%,
Mo: 0.01 to 0.5%,
Cu: 0.01 to 0.5%,
Ca: 0.0005 to 0.0050%, and
Nb: 1 kind selected from the group consisting of from 0.015 to 0.05 percent or containing two or more, middle and high carbon steel plate.

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