JP2004100027A - Steel for liquid-phase diffusion bonding having excellent resistance to low-temperature transformation crack - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide steel for liquid-phase diffusion bonding by which the hardening crack or reheat crack sensitivity of a joint to which refining heat treatment is applied after liquid-phase diffusion bonding can be reduced. <P>SOLUTION: The steel for liquid-phase diffusion bonding has a composition containing, by mass, 0.05 to 1.0% C, 0.01 to 1.0% Si, 0.05 to 3.0% Mn, 0.005 to 0.1% Ti and 0.01 to 0.2% Al, also containing P, S and O in the amounts limited to ≤0.01%, ≤0.003% and ≤0.01%, respectively, further containing As, Sn, Sb, Pb and Zn in the amounts each limited to ≤0.005% and satisfying the relation of inequality (As%+Sn%+Sb%+Pb%+Zn%)≤0.015%, and having the balance Fe with inevitable impurities. When liquid-phase diffusion bonded joints using the steel are reheated to a temperature not lower than the Ac<SB>3</SB>point and subjected to accelerated cooling at a rate of ≥0.1 °C/s or are tempered, after the accelerated cooling, to a temperature not higher than the Ac<SB>1</SB>transformation point, Charpy absorption energy at 0°C is ≥47J. <P>COPYRIGHT: (C)2004,JPO

Description

【００４１】
【表２】

【００４２】
【表３】

【００４３】
【表４】

【００４４】
これに対して表５、６には従来技術のみを用いて製造した鋼材による液相拡散接合継手の化学成分と評価結果の例を示してある。表５、６のうち、第８１番鋼はＰが０．０１％を超えたため、継手の靱性が接合部のみならず全体的に低下し、確保できなかった例、第８２番鋼は母材Ｓが高かったため、接合部継手の粒界に原子状Ｓが偏析して継手靱性が低下した例、第８３番から第８７番鋼は、それぞれＡｓ，Ｓｎ，Ｓｂ，Ｐｂ，Ｚｎの含有量が各個に０．００５％を超えたため、（Ａｓ％＋Ｓｎ％＋Ｓｂ％＋Ｐｂ％＋Ｚｎ％）の質量％総和は０．０１５％以下であったが、継手靱性が低下した例、第８８番鋼はＡｓ，Ｓｎ，Ｓｂ，Ｐｂ，Ｚｎの含有量は各個には０．００５％以下であったものの、総和が０．０１５％を超えたため、継手の靱性が低下した例、第８９番鋼はＴｉが過剰となり、Ｔｉの炭化物が多量に析出し、継手靱性が低下した例、第９０番鋼はＡｌ含有量が不足し、Ｔｉとともに鋼中に存在して接合中の結晶粒径制御に作用しなければならない窒化物の量が低下し、継手の靱性が低下した例、第９１番鋼はＣの量が不足し、継手の接合後の熱処理にもかかわらず、継手の強度が不足した例である。
【００４５】
【表５】

【００４６】
【表６】

【００４７】
【発明の効果】
本発明は液相拡散接合を用いて継手を形成し、構造体を製造する際に、構造体に６００ＭＰａを超える高い強度、場合によっては１０００ＭＰａを超える超高強度と継手における熱処理時の焼き戻し割れの発生がないことを求められる場合に好適な液相拡散接合用鋼を提供するものであり、液相拡散接合の技術適用および難接合材の組立、さらには省工程による安価な部品の製造など、液相拡散接合の適用によって達成されうる構造体の機能向上に大きく寄与する。
【図面の簡単な説明】
【図１】焼き戻し割れ感受性を高める不純物元素の総和（Ａｓ％＋Ｓｎ％＋Ｓｂ％＋Ｐｂ％＋Ｚｎ％）と液相拡散接合継手の０℃における靱性、すなわち焼き戻し割れ感受性指標との関係を示す図である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a steel material that enables a joint structure such as a part or an apparatus using liquid phase diffusion bonding, and more specifically, a strength produced by applying liquid phase diffusion bonding to a part or all of the steel has a strength of 600 MPa or more, particularly The present invention relates to a steel material for liquid phase diffusion bonding that can constitute a high-strength structure or a pressure vessel of 1000 MPa or more.
[0002]
[Prior art]
[Patent Document 1] Japanese Patent Application Laid-Open No. 2001-164332 [Patent Document 2] Japanese Patent Application Laid-Open No. 2001-131682 [0003]
Liquid phase diffusion bonding is becoming widespread as an industrial new bonding technology between metal materials. In liquid phase diffusion bonding, an element having the ability to form a joint through a diffusion-controlled isothermal solidification process, such as B or P, and these are interposed between the grooves, between the bonding surfaces or grooves of the materials to be bonded. In order to intervene a multi-element alloy consisting of Ni or Fe to be a base material and heat and maintain it at a temperature equal to or higher than the melting point of the low-melting alloy into which the joint has been inserted, this is a technique for forming a joint, unlike a normal welding technique, It has features such as almost no welding residual stress, and the ability to form a smooth and precise joint that does not generate extra welding as in welding. In particular, since it is a surface joining, the joining time is constant and the joining is completed in a relatively short time regardless of the area of the joining surface, which is completely different from the conventional welding. Therefore, if the temperature can be maintained for a predetermined time at a temperature equal to or higher than the low melting point metal into which the groove is inserted, there is a feature that joining between surfaces can be realized regardless of the shape of the groove.
[0004]
However, the melting point of the low melting point alloy (hereinafter referred to as “insert metal”) interposed between the grooves is 900 ° C. to 1300 ° C. because the diffusing element is B or P, and particularly a steel having a ferrite structure. A temperature above the transformation point, Ac ₁ or Ac ₃ , must be achieved in the groove. At this time, in order to end the diffusion-controlled isothermal solidification early in the industry, the joining temperature will substantially exceed 1000 ° C., and naturally, the steel material is heated to the transformation point or higher, so after the joining is completed, cooling is performed. Sometimes retransformation occurs, and the properties of the material are determined by the transformation structure at this time. Therefore, there is a case where the heat treatment is added later to perform the tempering treatment.
[0005]
However, when isothermal solidification of the joint is achieved by liquid phase diffusion bonding, diffusion-limited solidification of B or P occurs, and these elements tend to concentrate at the grain boundaries of the joint structure, and in some cases precipitate as compounds. There is also. Furthermore, the isothermal solidification portion involves melting and fusion of the base material, and the impurities present in the matrix also re-melt once and tend to segregate at the grain boundaries during formation of the joint structure. Their detailed study revealed this.
[0006]
In particular, when obtaining a low-temperature transformed structure, that is, a martensite structure or a bainite structure, by tempering treatment such as quenching or normalizing to increase the strength, avoid enrichment of the impurity element and B or P in the former γ grain boundary. However, the grain boundaries are easily embrittled, and in some cases, quenching cracks occur due to transformation expansion during cooling. Alternatively, the time difference of the transformation caused by the temperature difference between the inside and the outside surface of the structure that occurs during accelerated cooling using a refrigerant.If tensile stress remains on the surface of the structure, in the subsequent tempering process, carbide Under the conditions that precipitates and nitrides at the grain boundaries by embrittlement occur, cracks along the grain boundaries, ie, tempering cracks (also referred to as reheat cracks or SR cracks) occur, or even if not cracked, the brittleness has an extremely low impact value. It may become a joint. Joints with such brittle properties are subject to cracking after a certain period of time or aging when shocking stress is applied to structural members at low temperatures below room temperature, or when hydrogen enters steel. There was a problem.
[0007]
All of these exhibit the appearance of grain boundary fracture, and are particularly remarkable in a high-strength steel composed of a low-temperature transformation structure and a tempered structure requiring a strength of 600 MPa or more, and sometimes 1000 MPa or more, and embrittlement of grain boundaries. Has led to embrittlement of the material, and therefore, it has been required for the material to be joined to improve the properties of the grain boundaries.
This phenomenon is characteristic of liquid-phase diffusion bonding in which B or P is diffused in a large amount. Unlike tempering embrittlement that occurs in ordinary low-alloy steel, embrittlement that assumes B and P grain boundary segregation is assumed. Since it is a phenomenon, there is almost no similar technology for countermeasures.
[0008]
Japanese Patent Application Laid-Open No. 2001-164332 and Japanese Patent Application Laid-Open No. 2001-131682 disclose the latest technology for improving the reheat cracking resistance of alloy steel. No knowledge of liquid phase diffusion joints is found. Therefore, at the present time, there is no disclosure of a technology capable of effectively preventing the characteristic temper embrittlement occurring in the liquid phase diffusion bonded joint.
[0009]
[Problems to be solved by the invention]
The present invention solves the above-mentioned problems of the prior art, and after performing liquid phase diffusion bonding using B as a diffusion atom, a high-strength joint of 600 MPa or more, and in some cases, 1000 MPa or more, is subjected to heat treatment heat treatment. It is an object of the present invention to obtain a steel material having resistance to grain boundary embrittlement such as quenching cracking or tempering cracking occurring when the steel material is to be obtained, mainly by limiting steel material impurity components.
[0010]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention limits the chemical components that contribute to the grain boundary embrittlement of steel, and particularly the individual and total contents of As, Sn, Sb, Pb, and Zn, which have a large effect as an embrittlement factor. Is a steel material designed so that embrittlement of the grain boundary does not occur in the liquid phase diffusion bonded joint, and is specifically as follows.
{Circle around (1)} The invention according to claim 1 is, by mass%, C: 0.05 to 1.0%, Si: 0.01 to 1.0%, Mn: 0.05 to 3.0%, Ti : 0.005 to 0.1%, Al: 0.01 to 0.2%, and P: 0.01% or less, S: 0.003% or less, O: limited to 0.01% or less In addition, all of As, Sn, Sb, Pb, and Zn are limited to 0.005% or less, and the value of (As% + Sn% + Sb% + Pb% + Zn%) is 0.015% or less, and the remainder is inevitable. For liquid-phase diffusion bonding consisting of chemical impurities and Fe, the joint obtained by liquid-phase diffusion bonding of this steel is reheated to the Ac ₃ transformation point or higher, and then accelerated cooling at a cooling rate of 0.1 ° C./s or higher. or, the Charpy absorbed energy at 0 ℃ when tempered below the accelerated cooling after Ac ₁ transformation point as more 47J A liquid-phase diffusion bonding steel material excellent in low-temperature transformation cracking resistance, characterized in that the lower quench cracking or reheat cracking susceptibility.
[0011]
{Circle over (2)} The invention according to claim 2 is the steel according to claim 1, further comprising B: 0.0003 to 0.005% and N: 0.01% or less. Liquid phase diffusion bonding steel with excellent transformation cracking properties.
[0012]
{Circle around (3)} The invention according to claim 3 is the steel according to claim 1 or 2, further comprising 0.0005 to 0.01% of Ca, 0.0005 to 0.005% of Mg, and 0. 0005 to 0.02%, Ce: 0.0005 to 0.02%, La: 0.0005 to 0.02%, and Zr: 0.001 to 0.02%. This is a steel material for liquid phase diffusion bonding that has excellent low-temperature transformation cracking resistance.
[0013]
{Circle around (4)} The invention according to claim 4 is the steel according to any one of claims 1 to 3, wherein Ni: 0.01 to 5.0%, Co: 0.01 to 5.0%, Cu : 0.01 to 5.0%, Cr: 0.01 to 13.0%, Mo: 0.01 to 5.0%, W: 0.01 to 5.0%. Further, the present invention provides a liquid phase diffusion bonding steel excellent in low-temperature transformation cracking resistance, wherein the strength of the joint after accelerated cooling or after accelerated cooling and tempering is 1000 MPa or more.
[0014]
(5) The invention according to claim 5 is the steel according to any one of claims 1 to 4, further comprising: Nb: 0.005 to 0.5%, V: 0.005 to 1.0%, Ta : 0.005 to 0.5%, Hf: 0.005 to 0.5%, Re: 0.005 to 0.5%, baking after accelerated cooling or accelerated cooling A liquid phase diffusion bonding steel excellent in low-temperature transformation cracking resistance, wherein the strength of the joint after returning is 1000 MPa or more.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
First, the reason for limiting the chemical components of the steel material for liquid phase diffusion bonding according to the present invention will be described below.
C is the most basic element that controls the hardenability and strength of steel. If it is less than 0.01%, the strength cannot be ensured, and if it exceeds 1.0%, the strength is improved, but the toughness of the joint cannot be ensured even after tempering, so that the strength is 0.01 to 1.0%. Limited to.
[0016]
Si is a deoxidizing element of steel material and is usually added together with Mn for the purpose of reducing the oxygen concentration of steel. At the same time, it is an element necessary for intragranular strengthening, and its deficiency causes a decrease in strength. Similarly, in the present invention, the main purpose is to add deoxidation and intragranular strengthening, and the effect is exhibited at 0.01% or more, and when added in excess of 1.0%, the steel may become brittle. For this reason, the addition range is limited to 0.01 to 1.0%.
[0017]
Mn is effective for deoxidation together with Si, but is present in steel to enhance the hardenability of the material and contribute to the improvement of strength. The effect is manifested from 0.05%, and if it exceeds 3.0%, a coarse MnO-based oxide is crystallized, and on the contrary, the toughness may be reduced. Therefore, the addition range is 0.05 to 3.0%. Limited to
[0018]
Ti precipitates fine carbides, refines crystal grains, and increases the toughness of steel. For this purpose, 0.005% or more must be added. However, if it exceeds 0.1%, carbides are coarsened to cause a decrease in toughness. Therefore, the range of Ti is limited to 0.005 to 0.1%.
[0019]
Al combines with N and precipitates as AlN, does not dissolve even in the temperature range of liquid phase diffusion bonding, and has the effect of suppressing the movement of γ grains. Even if added in a large amount, carbides are not formed, so that the behavior is fundamentally different from nitride forming elements such as Ti and Zr, and the toughness of steel does not decrease. Therefore, it is necessary to add 0.01% as a minimum amount for exhibiting the effect, and if it exceeds 0.2%, AlN itself becomes coarse and affects toughness. In the range of 0.01 to 0.2%.
[0020]
In order to increase the toughness of a high-strength steel such as the present steel, it is necessary to avoid impurity enrichment at the grain boundaries as much as possible. It was limited to 0.003% or less. O must be limited to 0.01% or less in order to efficiently combine Al with N.
[0021]
In the present invention, As, Sn, Sb, Pb, and Zn are all classified as impurities. All of these tend to segregate at the grain boundaries of the liquid phase diffusion bonded joints and cause tempering cracks, so it is necessary to reduce them, but the upper limit is 0.005% for each. Even if an element is added in excess of this, tempering cracks are induced. At the same time, it has been clarified in the study of the present inventors that the sum of these elements exceeding 0.015% also promotes tempering cracks. That is, in mass%,
(As% + Sn% + Sb% + Pb% + Zn%) ≦ 0.015%
Must be achieved at the joint. In addition, this must also be achieved simultaneously with steel materials that limit S, which is harmful to temper brittleness, to 0.003% or less.
[0022]
The limiting ranges of these impurity elements were determined by the following experiments.
Laboratory scale vacuum melting or vacuum melting of 100 kg, 300 kg, 2 ton, 10 ton, 100 ton, 300 ton, or ordinary blast furnace-converter-out-of-furnace refining-degassing / trace element addition-continuous casting- Various carbon steels, low alloy steels, and alloy steels including the chemical composition range steel materials according to claims 1 to 5 manufactured by hot rolling, and a length of 10 mmΦ or 20 mm square and 50 mm in length from a direction parallel to the rolling direction. It was processed into a simple small test piece. The end face of the test piece was ground to Rmax <100 μm, degreased and washed, and the two end faces were joined to form a pair of bonded test pieces, using a tensile / compression testing machine equipped with a high-frequency induction heating device having an output of 150 kW. And a substantially volume fraction of Ni-base-B system, Fe-base-B system, Ni-base-P system, and Fe-base-P system which can realize liquid phase diffusion bonding at 1000 to 1300 ° C. between the bonding surfaces. The entire test piece is heated to the required joining temperature by interposing an amorphous foil having a thickness of 20 to 50 μm, which is amorphous by 50% or more, and is subjected to a liquid phase under a stress of 1 to 20 MPa for 30 seconds to 60 minutes. Diffusion bonding was performed, and after the bonding, it was allowed to cool.
[0023]
Subsequently, the entire joint obtained is reheated to 900 to 1000 ° C. (substantially at a temperature not lower than the Ac ₃ transformation point of the base material), held for 10 to 200 minutes, and then cooled at 0.1 ° C./s or more. After accelerated cooling at a speed to form a low-temperature transformed structure of bainite to martensite, and after confirming this by observing with an optical microscope, if necessary, the temperature is appropriately set at 200 to 700 ° C. for 0.1 to 500 hours. Tempered in the range to give a tempered structure. A tensile test piece having a diameter of 6 mm was collected from the obtained round bar joint test piece pair and subjected to strength evaluation, and a Charpy impact test piece with a JIS 4 2 mm V notch was sampled from the square bar test piece pair, and the notch position was measured. Was used as a joint to evaluate the toughness of the joint, and this was used as an index of susceptibility to tempering cracking of the joint.
[0024]
The impurity components were analyzed by a conventional wet chemical analysis on the base material before joining, and were evaluated based on the content in steel regardless of the presence or absence of precipitation. FIG. 1 shows the relationship between the value of (As% + Sn% + Sb% + Pb% + Zn%) in mass% and the Charpy absorbed energy of the joint at 0 ° C. as an index of tempering crack. When the value of (As% + Sn% + Sb% + Pb% + Zn%) is 0.015% or less, the Charpy absorbed energy of the joint at 0 ° C. always exceeds 47 J, but conversely (As% + Sn% + Sb%). When the value of (+ Pb% + Zn%) exceeds 0.015%, the Charpy absorbed energy of the joint at 0 ° C. does not reach 47 J.
[0025]
Also, as described in Examples, when each element exceeds 0.005%, similarly, the toughness of the joint does not reach 47 J at 0 ° C. Furthermore, it was experimentally determined that the joint toughness could not be ensured even when S exceeds 0.003%.
These values are characteristic of liquid phase diffusion bonding using B and P as diffusion elements, and are different from tempering embrittlement parameters or evaluation indices found in heat treatment of continuous welded joints and alloy steels. It is both a limit and an indicator. If these indices and restrictions are not satisfied, it is difficult to completely suppress temper embrittlement.
[0026]
The steel material has the chemical components described above, and the balance consists of unavoidable impurities and Fe. When such a steel material is subjected to liquid phase diffusion bonding, a heat-affected zone is formed in the vicinity of the bonded portion, but in this portion, the crystal grains are coarsened and the toughness is low. If the heat-affected zone having low toughness is subjected to heat treatment, toughness is restored. For this purpose, the joint is heated to an Ac ₃ transformation point or higher and then accelerated and cooled at a cooling rate of 0.1 ° C./s or more. If the heating temperature is lower than the Ac ₃ transformation point, transformation to austenite is insufficient and toughness is not sufficiently restored. If the cooling rate is less than 0.1 ° C./s, it is difficult to obtain a high-temperature, low-temperature transformed structure such as martensite or bainite. The accelerated cooling is performed by quenching or normalizing.
[0027]
After the accelerated cooling, it can be tempered to an Ac ₁ transformation point or lower as needed to further recover toughness. If the tempering temperature exceeds the Ac ₁ transformation point, the steel is partially transformed into austenite, so the tempering temperature is set to the Ac ₁ transformation point or lower. It is necessary that the toughness of the joint subjected to the heat treatment as described above has a Charpy absorbed energy at 0 ° C. of 47 J or more. That is, if the absorbed energy is less than 47 J when the Charpy impact test is performed at 0 ° C. using a test piece with a 2 mm V notch, the steel material does not have sufficient toughness. By making the steel have the above-mentioned chemical composition and toughness, it is possible to obtain a steel material for liquid phase diffusion bonding excellent in low-temperature transformation cracking resistance that does not cause sintering cracks or reheat cracking.
[0028]
In the present invention, if it is the steel described in claim 1, as described in claims 2 to 5, B: 0.0003 to 0.005%, N: 0.01% or less, or Ca: 0. 0005 to 0.01%, Mg: 0.0005 to 0.005%, Y: 0.0005 to 0.02%, Ce: 0.0005 to 0.02%, La: 0.0005 to 0.02% , Zr: one or more of 0.001 to 0.02%, or Ni: 0.01 to 5.0%, Co: 0.01 to 5.0%, Cu: 0.01 to 5.0. %, Cr: 0.01 to 13.0%, Mo: 0.01 to 5.0%, W: 0.01 to 5.0%, Nb: 0.005 to 0.5%. 5%, V: 0.005 to 1.0%, Ta: 0.005 to 0.5%, Hf: 0.005 to 0.5%, Re: 0.005 to 0.5% Species or two or more species may be contained.
[0029]
The range of addition of the above alloy components is limited for the following reasons.
A small amount of B greatly enhances the hardenability of steel, but the effect of improving hardenability is small when the addition amount is less than 0.0003%. On the other hand, if it is added in excess of 0.005%, a boride is formed, which rather reduces the hardenability. Therefore, it is desirable to set the addition range of B to 0.0003 to 0.005%.
[0030]
N combines with Al and precipitates fine AlN to refine crystal grains. However, N combines with B to reduce the amount of solid solution B effective for hardenability. If N exceeds 0.01%, it is difficult to secure solid solution B and a large amount of Ti is required for fixing N, resulting in high cost. Therefore, N is desirably 0.01% or less. .
[0031]
Ca, Mg, Y, Ce, La, and Zr are all elements having a sulfide form controllability. In order to exhibit this effect, Ca: 0.0005% or more and Mg: 0.0005% or more. , Y: 0.0005% or more, Ce: 0.0005% or more, La: 0.0005% or more, and Zr: 0.001% or more. However, when the content exceeds Ca: 0.01%, Mg: 0.005%, Y: 0.02%, Ce: 0.02%, La: 0.02%, and Zr: 0.02%, a coarse oxide is formed. It is formed and the toughness of the steel decreases. Accordingly, Ca: 0.0005 to 0.01%, Mg: 0.0005 to 0.005%, Y: 0.0005 to 0.02%, Ce: 0.0005 to 0.02%, La: 0. [0005] It is desirable to set the range of 0005 to 0.02% and Zr: 0.001 to 0.02%.
[0032]
Ni, Co, and Cu are all γ-stabilizing elements, and are elements that improve the hardenability by lowering the transformation point of the steel material and promoting low-temperature transformation. can get. On the other hand, if the addition exceeds 5.0%, the residual γ increases and affects the toughness of the steel material. Therefore, the addition ranges of Ni: 0.01 to 5.0% and Co: 0.01 to 5. 0%, Cu: desirably 0.01 to 5.0.
[0033]
Cr, Mo, and W are all α-stabilizing elements, but Cr is also useful for improving corrosion resistance. In any case, the effect is recognized when 0.01% is added. However, when Cr exceeds 13.0%, δ ferrite is formed, and it becomes difficult to form a low-temperature transformation structure, and instead, strength toughness may be reduced. The upper limit was limited to 13.0%. Mo and W exhibit remarkable solid solution strengthening. However, if both of them are added in excess of 5.0%, borides or phosphides are formed with B and P, which are diffusion atoms of the liquid phase diffusion bonding, and the toughness of the joint is increased. May deteriorate. Therefore, it is desirable that the respective addition amounts are Cr: 0.01 to 13.0%, Mo: 0.01 to 5.0%, and W: 0.01 to 5.0%.
[0034]
Further, Nb, V, Ta, Hf, and Re precipitate fine carbides to increase the strength of steel. In any case, the addition of 0.005% or more is effective. However, Nb, Ta, Hf, and Re are 0.5%, and when V exceeds 1.0%, carbides are coarsened and the toughness is reduced, so that Nb: 0.005 to 0.5% , V: 0.005 to 1.0%, Ta: 0.005 to 0.5%, Hf: 0.005 to 0.5%, and Re: 0.005 to 0.5%.
[0035]
One or more of the elements of each group described above may be appropriately combined and added in combination, or each element may be added alone, and imparts various properties to the steel material without hindering the effects of the present invention. can do.
[0036]
In addition, in the manufacturing process of the steel material of the present invention, not only an integrated process of pig steel using a normal blast furnace and a converter, but also an electric furnace manufacturing method and a converter manufacturing method using a cold iron source can be applied. Even if it is not available, it can be manufactured through normal casting and forging processes. Further, the shape of the manufactured steel material is completely free, and a molding technique necessary for the shape of the member to be applied can be applied. That is, it can be applied to a wide range such as a steel plate, a steel pipe, a steel bar, a wire rod, and a shaped steel. In addition, since this steel has excellent weldability and is suitable for liquid phase diffusion bonding, if it is a structure that includes a liquid phase diffusion bonding joint, it is possible to apply welding to a part of the structure or use it together. The body can be manufactured and does not hinder the effects of the present invention.
[0037]
【Example】
In a laboratory scale vacuum melting, or vacuum melting of 100 kg to 300 ton weight in a real steel plate manufacturing facility, or manufactured by ordinary blast furnace-converter-outside furnace refining-degassing / trace element addition-continuous casting-hot rolling, The chemical composition range steel material according to claims 1 to 4 was processed into a simple small test piece of 10 mmΦ or 20 mm square and 50 mm long from a direction parallel to the rolling direction. The end face of the test piece was ground to Rmax <100 μm, degreased and washed, and the two end faces were joined to form a bonded test piece pair, using a tensile / compression testing machine equipped with a high-frequency induction heating device having an output of 150 kW. And a substantially volume fraction of Ni-base-B system, Fe-base-B system, Ni-base-P system, and Fe-base-P system which can realize liquid phase diffusion bonding at 1000 to 1300 ° C. between the bonding surfaces. The entire test piece is heated to the required joining temperature by interposing an amorphous foil having a thickness of 20 to 50 μm, which is amorphous by 50% or more, and is subjected to a liquid phase under a stress of 1 to 20 MPa for 30 seconds to 60 minutes. Diffusion bonding was performed, and after the bonding, it was allowed to cool.
[0038]
Subsequently, the entire joint obtained is reheated to 900 to 1000 ° C. (substantially at a temperature not lower than the Ac ₃ transformation point of the base material), held for 10 to 200 minutes, and then cooled at 0.1 ° C./s or more. After accelerated cooling at a speed to form a low-temperature transformed structure of bainite to martensite, and after confirming this by observing with an optical microscope, if necessary, the temperature is appropriately set at 200 to 700 ° C. for 0.1 to 500 hours. Tempered in the range to give a tempered structure. A tensile test piece having a diameter of 6 mm was collected from the obtained round bar joint test piece pair and subjected to strength evaluation, and a Charpy impact test piece with a JIS 4 2 mm V notch was sampled from the square bar test piece pair, and the notch position was measured. Was used as a joint to evaluate the toughness of the joint, and this was used as an index of susceptibility to tempering cracking of the joint.
The impurity components were analyzed by a conventional wet chemical analysis on the base material before joining, and were evaluated based on the content in steel regardless of the presence or absence of precipitation.
[0039]
Tables 1 to 4 show examples of the chemical composition of the steel of the present invention, the impact absorption energy (J) of the joint, the tensile strength (MPa) of the joint, and the mass% sum of (As% + Sn% + Sb% + Pb% + Zn%). And the heat treatment conditions after the joining are shown. In the steel of the present invention, the toughness of the joint after the heat treatment is 47 J or more, and it is considered that the tempering crack sensitivity is low. Further, tempering cracks and tempering cracks did not actually occur in the joint. The left end of Table 2 is connected to the right end of Table 1, and so on.
[0040]
[Table 1]

[0041]
[Table 2]

[0042]
[Table 3]

[0043]
[Table 4]

[0044]
On the other hand, Tables 5 and 6 show examples of chemical components and evaluation results of liquid phase diffusion bonded joints made of steel materials manufactured using only the conventional technology. In Tables 5 and 6, No. 81 steel had a P exceeding 0.01%, so that the toughness of the joint was reduced not only at the joint but also as a whole and could not be secured. In the case where atomic S was segregated at the grain boundary of the joint due to high S and the toughness of the joint decreased, the 83rd to 87th steels had As, Sn, Sb, Pb and Zn contents respectively. Since the content exceeded 0.005% for each piece, the total mass% of (As% + Sn% + Sb% + Pb% + Zn%) was 0.015% or less. , Sn, Sb, Pb, and Zn contents were 0.005% or less for each piece, but the sum exceeded 0.015%, and the toughness of the joint was reduced. Excessive, a large amount of Ti carbides precipitated, and joint toughness was reduced. In the case where the amount is insufficient, the amount of nitride which must be present in the steel together with Ti and act to control the crystal grain size during joining decreases, and the toughness of the joint decreases, the 91st steel is the amount of C This is an example in which the strength of the joint was insufficient despite the heat treatment after joining the joint.
[0045]
[Table 5]

[0046]
[Table 6]

[0047]
【The invention's effect】
The present invention forms a joint by using liquid phase diffusion bonding, and when manufacturing a structure, the structure has a high strength exceeding 600 MPa, and in some cases, an ultra-high strength exceeding 1000 MPa and a tempering crack during heat treatment in the joint. The purpose of the present invention is to provide a liquid phase diffusion bonding steel suitable for the case where it is required that there is no occurrence of liquid phase diffusion, apply liquid phase diffusion bonding technology, assemble difficult-to-bond materials, and manufacture inexpensive parts by saving steps. In addition, it greatly contributes to improving the function of the structure that can be achieved by applying liquid phase diffusion bonding.
[Brief description of the drawings]
FIG. 1 is a diagram showing the relationship between the sum total of impurity elements (As% + Sn% + Sb% + Pb% + Zn%) that enhances tempering crack susceptibility and the toughness of a liquid phase diffusion bonded joint at 0 ° C., that is, the tempering crack susceptibility index. It is.

Claims (5)

In mass%, C: 0.05 to 1.0%, Si: 0.01 to 1.0%, Mn: 0.05 to 3.0%, Ti: 0.005 to 0.1%, Al: 0.01 to 0.2%, P: 0.01% or less, S: 0.003% or less, O: 0.01% or less, in addition to As, Sn, Sb, Pb, All of Zn are limited to 0.005% or less, and the value of (As% + Sn% + Sb% + Pb% + Zn%) is 0.015% or less, and the balance is unavoidable impurities and steel for liquid phase diffusion bonding made of Fe. The joint obtained by subjecting the steel material to liquid phase diffusion bonding is reheated to an Ac ₃ transformation point or more and then accelerated cooling at a cooling rate of 0.1 ° C./s or more, or is cooled to an Ac ₁ transformation point or less after the accelerated cooling. The Charpy absorbed energy at 0 ° C when tempered is set to 47 J or more, and the susceptibility to quenching or reheat cracking is increased. Low temperature transformation cracking resistance excellent liquid phase diffusion bonding steel material, characterized in that there was a comb. 2. The liquid phase diffusion bonding excellent in low temperature transformation cracking resistance according to claim 1, further comprising B: 0.0003 to 0.005% and N: 0.01% or less. For steel. The steel according to claim 1 or 2, further comprising: Ca: 0.0005 to 0.01%, Mg: 0.0005 to 0.005%, Y: 0.0005 to 0.02%, Ce: 0. 0.0005 to 0.02%, La: 0.0005 to 0.02%, and Zr: 0.001 to 0.02%. Steel for liquid phase diffusion bonding. The steel according to any one of claims 1 to 3, further comprising: Ni: 0.01 to 5.0%, Co: 0.01 to 5.0%, Cu: 0.01 to 5.0%, Cr: 0.01 to 13.0%, Mo: 0.01 to 5.0%, W: 0.01 to 5.0%, and after or after accelerated cooling. A liquid phase diffusion bonding steel excellent in low-temperature transformation cracking resistance, wherein the strength of the joint after tempering is 1000 MPa or more. The steel according to any one of claims 1 to 4, wherein Nb: 0.005 to 0.5%, V: 0.005 to 1.0%, Ta: 0.005 to 0.5%, One or two or more of Hf: 0.005 to 0.5% and Re: 0.005 to 0.5%, and the joint strength after accelerated cooling or accelerated cooling and tempering is 1000 MPa or more. A liquid phase diffusion bonding steel excellent in low temperature transformation cracking resistance.

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