JP6339284B1 - Steel products used in contact with steel - Google Patents

Abstract

An object of the present invention is to provide a steel product having excellent oxidation resistance on a contact surface with a steel material and excellent weldability. A steel product used in contact with a steel material according to the present invention is a steel product used in contact with a steel material, and has a centrifugal cast part, and the centrifugal cast part has a mass. %: C: 0.2% to 0.7%, Si: more than 0% to 2.0% or less, Mn: more than 0% to 3.0% or less, Cr: 15.0% to 40% 0.0%, Ni: 18.0% to 55.0%, Al: 1.0% to 5.5%, and Ti: 0.01% to 0.6%, and / or Nb: 0.0. It contains at least one selected from the group consisting of 1% to 1.8%, and consists of the balance Fe and inevitable impurities. [Selection] Figure 1

Description

  The present invention relates to steel products such as hearth rolls and coiler drums used in contact with steel materials such as steel slabs and steel plates.

  Steel products such as a hearth roll that transports the steel strip in an annealing furnace that continuously heat treats the steel strip and a coiler drum that winds the steel plate during rolling in a high-temperature furnace are used in steelworks.

  Since these steel products are used in direct contact with steel materials such as steel slabs and steel plates in a high temperature environment in the atmosphere, the metal in the base material is oxidized and Cr (including Fe and Ni) on the surface. A Cr oxide mainly composed of is formed. Cr oxide is easy to peel off by contact with a steel material, and the steel material may be damaged by the peeling. Then, peeling of the Cr oxide or polishing for removing the Cr oxide to suppress this may cause the steel product itself to be thinned quickly.

  Therefore, a product in which a sprayed layer is formed by spraying a CoCrAlY alloy or the like on the outer periphery of a hearth roll has been proposed (see, for example, Patent Document 1).

JP 2008-240072 A

  However, since the sprayed layer is also oxidized, the oxide film formed on the sprayed layer is peeled off, the oxidation resistance is lowered, and the steel material may be damaged by the peeled oxide film. Furthermore, since the amount of Al (about 10% by mass) added to the sprayed layer is large, mechanical properties such as tensile ductility of the sprayed layer may be deteriorated, and further, weldability may be deteriorated.

  An object of the present invention is to provide a steel product having excellent oxidation resistance on a contact surface with a steel material and excellent weldability.

Steel products used in contact with the steel material according to the present invention are:
Steel products used in contact with steel materials,
A centrifugal casting part,
The centrifugal casting part is in mass%,
C: 0.2% to 0.7%
Si: more than 0% and 2.0% or less,
Mn: more than 0% and 3.0% or less,
Cr: 15.0% to 40.0%,
Ni: 18.0% to 55.0%,
Al: 1.0% to 5.5%, and
Containing at least one selected from the group consisting of Ti: 0.01% to 0.6% and / or Nb: 0.1% to 1.8%;
It consists of the balance Fe and inevitable impurities.

The centrifugal casting part is in mass%,
Rare earth element (REM): more than 0% and 0.4% can be contained.

The centrifugal casting part is in mass%,
W: more than 0% and 5.0% or less, and / or Mo: more than 0% and 2.0% or less.

The centrifugal casting part is
Pa = −11.1 + 28.1 × C + 29.2 × Si−0.25 × Ni−45.6 × Ti + 18.0 × REM−16.6 × Nb
Ya = -13.75 × Al + 63.75
And when
Pa <Ya
It is desirable that

  The centrifugal force casting portion is formed by centrifugal casting, and can be welded to a stationary casting portion formed by stationary casting.

  The stationary cast part preferably does not contain Al.

  The centrifugal force casting part may be formed on a surface that contacts the steel material.

  A ceramic sprayed layer may be provided on the surface of the centrifugal force casting part.

  The steel product may be a hearth roll or a coiler drum.

  According to the present invention, by setting the centrifugal cast part formed on the steel product to the above composition, Al can preferentially form Al oxide over Cr, and formation of Cr oxide can be suppressed. , Problems such as Cr oxide peeling can be suppressed. Moreover, since the addition amount of Al is as low as 1.0% to 5.5%, it is possible to suppress a decrease in mechanical properties.

  Moreover, since the centrifugal force cast part can secure weldability since the addition amount of Al is low, the centrifugal force cast part can be favorably welded to the stationary cast part.

FIG. 1 is a graph showing the results of regression analysis of a test centrifugal force cast part based on weldability with the Pa value as the vertical axis and the Al content as the horizontal axis. FIG. 2 is an enlarged graph showing the range of the present invention in which the Al oxide layer is formed satisfactorily in the graph of FIG.

  Hereinafter, embodiments of the present invention will be described in detail. Unless otherwise specified, “%” means mass%.

  The steel product of the present invention is preferably applied to products such as hearth rolls and coiler drums that are used in direct contact with steel materials such as steel slabs and steel plates in a high temperature environment in the atmosphere.

Steel products
C: 0.2% to 0.7%
Si: more than 0% and 2.0% or less,
Mn: more than 0% and 3.0% or less,
Cr: 15.0% to 40.0%,
Ni: 18.0% to 55.0%,
Al: 1.0% to 5.5%, and
Containing at least one selected from the group consisting of Ti: 0.01% to 0.6% and / or Nb: 0.1% to 1.8%;
Consisting of the balance Fe and inevitable impurities,
It has a centrifugal casting part.

  The centrifugal casting part can be produced by centrifugal casting, and the reasons for limiting the components are as follows.

C: 0.2% to 0.7%
C has the effect of improving castability and increasing the high temperature creep rupture strength. Moreover, it combines with Ti, Nb, Cr, etc., forms a carbide | carbonized_material, and there exists an effect which raises high temperature strength. For this reason, at least 0.2% is contained. However, if the content is too large, primary carbides of Cr ₇ C ₃ are likely to be formed widely, the transfer of Al to the surface of the centrifugal cast part is hindered, and an insufficient supply of Al occurs, resulting in Al ₂ O ₃ Thus, the formation of Al oxide is suppressed. Moreover, since secondary carbide precipitates excessively, it causes a reduction in ductility and toughness. For this reason, the upper limit is set to 0.7%. The C content is more preferably 0.35% to 0.6%.

Si: more than 0% and not more than 2.0% Si is contained as a deoxidizer for the molten alloy, and for improving the fluidity of the molten alloy and improving the oxidation resistance. However, excessive addition of Si causes a decrease in ductility, a decrease in high-temperature creep rupture strength, a deterioration in surface quality after casting, and a decrease in weldability. For this reason, the upper limit of the Si content is set to 2.0%. The Si content is desirably 1.5% or less, and more desirably 1.0% or less.

Mn: More than 0% and 3.0% or less Mn is a deoxidizer for the molten metal alloy, and it is contained for fixing S in the molten metal to improve weldability and improve ductility. However, excessive addition of Mn causes a decrease in high-temperature creep rupture strength and decreases oxidation resistance, so the upper limit is made 3.0%. The Mn content is more preferably 1.0% or less.

Cr: 15.0% to 40.0%
Cr contributes to improvement in high-temperature strength and repeated oxidation resistance. Further, Cr exhibits excellent heat resistance in a high temperature range exceeding 1000 ° C. together with Ni and Fe, generates C and N and primary carbides, and improves high temperature creep rupture strength. And an oxide layer is formed with Al, and the characteristic which was excellent in oxidation resistance and corrosion resistance is brought to a centrifugal cast part. Therefore, it is contained at least 15.0% or more. On the other hand, excessive generation of Cr carbide or Cr nitride causes a decrease in ductility, so the upper limit of the content is 40.0%. The Cr content is more preferably 22.0% to 35.0%.

Ni: 18.0% to 55.0%
Ni is an element necessary for ensuring repeated oxidation resistance and stability of the metal structure, ensuring high-temperature creep strength, and stabilizing the austenitization of the centrifugal cast part. Moreover, it contributes to improvement of high temperature strength and oxidation resistance together with Cr. Further, when the Ni content is low, the Fe content is relatively high and the production of Al oxide is inhibited. For this reason, it contains at least 18.0% or more. On the other hand, even if Ni is added excessively, the effect is saturated and also disadvantageous economically, so the upper limit is made 55.0%. The Ni content is more preferably 29.0% to 46.0%.

Al: 1.0% to 5.5%
Al is an indispensable element for forming Al oxide in the centrifugal cast part. The formation of the Al oxide improves the carburization resistance of the centrifugal cast part together with the Cr oxide. Further, Al forms a γ 'phase together with Ni, strengthening the austenite phase of the centrifugal cast part. For this reason, Al is contained 1.5% or more. However, excessive addition of Al causes a decrease in ductility, and the γ ′ phase becomes unstable, leading to the formation of an embrittled phase. Furthermore, excessive addition of Al leads to deterioration of castability and lowers the cleanliness of the centrifugal cast part. Therefore, the upper limit is set to 5.5%. The Al content is more preferably 2.0% to 4.5%.

At least one selected from the group consisting of Ti: 0.01% to 0.6% and / or Nb: 0.1% to 1.8% Ti and Nb are elements that easily form carbides. , Contributes to improvement of creep rupture strength and high temperature tensile strength. Nb also contributes to the improvement of aging ductility. Therefore, at least one of Ti: 0.01% or more and Nb: 0.1% or more is contained. On the other hand, excessive addition of these elements causes a reduction in ductility. Nb causes a decrease in the peel resistance of the Al oxide layer and also reduces the oxidation resistance. Moreover, excessive addition of Ti accelerates | stimulates the production | generation of Ti oxide and reduces the cleanliness of a centrifugal-force casting part. Therefore, the upper limits are set to Ti: 0.6% and Nb: 1.8%. The Ti content is more preferably 0.05% to 0.30%, and the Nb content is more preferably 0.1% to 1.3%.

  In addition, the centrifugal casting part can contain the following elements.

Rare earth element (REM): more than 0% to 0.4%
REM means 18 kinds of elements obtained by adding Y, Hf and Sc to 15 kinds of lanthanum series from La to Lu in the periodic table. Nd is the main component, and it is preferable that these three elements occupy about 80% or more, more preferably about 90% or more of the total amount of rare earth elements. Since REM contributes to the stabilization of the Al oxide layer and is an active metal, the adhesion of the oxide film can be improved. Further, REM is desirably contained because it prevents spoke ring breakage of the oxide layer due to temperature changes in the furnace, and further contributes to improvement in oxidation resistance by solid solution in the base material. On the other hand, REM forms oxides preferentially and causes a decrease in the cleanliness and ductility of the base material, so the upper limit is made 0.4%. The REM content is more preferably 0.01% to 0.30%.

W: more than 0% to 5.0% or less, and / or Mo: more than 0% to 2.0% or less W and Mo are dissolved in the base material to strengthen the austenite phase of the base material and creep. In order to improve the breaking strength, it is desirable to contain either one or both. However, excessive inclusion of W and Mo causes a drop in ductility and carburization resistance, and inhibits the formation of Al oxide, particularly when an Al oxide is produced at a temperature of 1050 ° C. or lower. Moreover, excessive inclusion of W and Mo causes a reduction in the oxidation resistance of the base material. Therefore, the upper limit of W is 5.0% and the upper limit of Mo is 2.0%. The upper limit of the W content is more preferably 3.0%, and Mo is more preferably 1.0%.

In addition, as shown in FIG.
Pa = −11.1 + 28.1 × C + 29.2 × Si−0.25 × Ni−45.6 × Ti + 18.0 × REM−16.6 × Nb,
When Ya = −13.75 × Al + 63.75,
It is desirable that Pa <Ya. In addition, when the element displayed above is not included as Pa value, the value of the said element is handled as zero.
When the Pa value and the Ya value satisfy the above formula, the weldability and oxidation resistance (formation of an Al oxide layer) of the centrifugal cast part can be ensured.

  The Pa value is related to the content of each element of C, Si, Ni, Ti, REM, and Nb, and a sample centrifugal force cast part in which the content of each of these elements and the content of Al are variously produced is produced. did. And the bead-placement test in the Example mentioned later was implemented with respect to each test centrifugal force cast part, and the data regarding the weldability of a test centrifugal force cast part were acquired. From the obtained data, the influence coefficient of the element affecting the weldability was obtained by regression analysis.

  When the Pa value is referred to for its influence coefficient, positive C, Si, and REM are elements that adversely affect weldability, and the larger the numerical value (absolute value), the greater the negative effect. Ni, Ti, and Nb, which have negative influence coefficients, are elements that improve weldability, and the larger the numerical value (absolute value), the better the influence.

  FIG. 1 is a plot of the sample centrifugal force cast portion with the Pa value as the vertical axis and the Al content as the horizontal axis, with the diamond having a good weldability and the weldability being insufficient. Things are plotted as squares.

  In order for the Al oxide layer to be satisfactorily formed in the test centrifugal force casting part and to have oxidation resistance, the Al content range (Al: 1.0% to 5.5%) is set. There is a need. The graph which expanded the range of this Al content is shown in FIG. Referring to FIG. 2, the group having excellent weldability and the group having insufficient weldability are clearly divided in terms of the Pa value and the Al content in which the Al oxide layer is well formed. I understand. From this graph, it can be seen that the correlation between the Ya value including the Al content was clearly analyzed based on the weldability.

  And the linear Ya value based on the content of Al dividing these groups could be determined as Ya = −13.75 × Al + 63.75. In other words, it can be seen that when Pa <Ya is satisfied in the range of Al: 1.0% to 5.0%, a centrifugal cast part having excellent oxidation resistance and excellent weldability can be obtained.

  The centrifugal casting part is formed, for example, in a cylindrical shape by centrifugal casting, and a steel product can be produced by welding with a base material such as an axle or a shaft part constituting the steel product. Since the centrifugal cast part is excellent in weldability, it can be well welded to the base material, and a sufficient bonding strength can be ensured.

  The base material can be produced, for example, by static casting, and the static casting part is preferably made of a material that does not contain Al in order to suppress deterioration in mechanical properties and weldability.

  In steel products, the centrifugal cast part can be formed on the surface in contact with the steel material. In this case, an Al oxide layer forming process for forming an Al oxide layer on the surface of the centrifugal cast part is required. The Al oxide layer formation process can be performed by heat-treating the steel product in an oxidizing atmosphere as an independent process, or in a high temperature atmosphere when the steel product is installed and used in a heating furnace. You can also

The Al oxide layer forming treatment is performed at 900 ° C., desirably 1000 ° C., more desirably 1050 ° C. or more in a steel product in an oxidizing atmosphere mixed with an oxidizing gas containing 1% by volume of oxygen, steam or CO ₂ . Heat treatment at a temperature is preferred. The heat treatment time is preferably 1 hour or longer.

By applying an Al oxide layer forming process to steel products, the centrifugal casting part comes into contact with oxygen, and Al, Cr, Ni, Si, Fe, etc. diffused on the surface of the base material are oxidized to form an oxide layer. Form. At this time, by forming the heat treatment in the above temperature range, Al forms an oxide in preference to Cr, Ni, Si, and Fe. In addition, Al in the base material is also transferred to the surface to form an oxide, and an Al oxide layer mainly composed of Al ₂ O ₃ is formed.

  Since the obtained steel product has excellent weldability in the centrifugal cast part, it is firmly bonded to the base material without causing weld cracking and the like, and has excellent mechanical characteristics. In addition, the mechanical properties of the centrifugal cast part are excellent, and the Al oxide layer formed on the surface can exhibit excellent oxidation resistance when used in a high temperature atmosphere. Therefore, steel products can be favorably used for hearth rolls and coiler drums that come into contact with steel in a high temperature atmosphere.

  If necessary, ceramic spraying may be performed on the surface of the centrifugal force casting portion to form a ceramic sprayed layer on the surface of the centrifugal force casting portion.

  Specimen specimens (centrifugal resistance test specimens: 25 mm x 3 pieces) welded by centrifugal casting with the alloy composition (unit: mass%, balance Fe and inevitable impurities) listed in Table 1 by centrifugal casting Specimens for bead placement tests for confirming the properties (invention examples only): thicknesses of 25 mm or less and 25 mm or more) were prepared. The invention example is a test no. 101-110, the comparative example is test No. 201-206. In Table 1, REM indicates the total amount of Ce, La, and Y. The invention examples are all within the range of the composition of the present invention. 201-204 are Al zero, sample No. 205 and 206 are comparative examples in which Al is insufficient, and “*” is given to the corresponding part.

  Moreover, Pa and Ya were calculated about each test piece of Table 1, and these magnitude relationships were compared. In Table 1, for the specimens satisfying Pa <Ya, a check mark is entered in the column “Pa <Ya”. Referring to Table 1, test no. It can be seen that 103, 109, 110, 205 and 206 are specimens that do not satisfy Pa <Ya.

<Oxidation resistance test>
After measuring the weight of the specimen, it was kept in a heating furnace (atmosphere) at 1000 ° C. for 100 hours, the scale on the surface of the specimen after heating was removed with an acid solution, and the weight was measured again. And the oxidation loss was computed from the weight change amount before and behind heating of each test piece, and the average of the oxidation loss (mg / cm ² · h) per hour was determined. The results are shown in “Oxidation resistance” in Table 1. As for oxidation resistance, as shown in “Evaluation” in Table 1, an oxidation weight loss of 0.1 mg / cm ² · h or less was evaluated as “A”, and 0.3 mg / cm ² · h or less was evaluated as “B”. 1 mg / cm ² · h or less was evaluated as “C”, and 1 mg / cm ² · h or more was evaluated as “D”.

  Referring to Table 1, all of the inventive examples are evaluated “A” or “B”, and the oxidation weight loss is small compared with the comparative examples having the evaluation “C” or “D”, and the oxidation resistance is excellent. Recognize. This is because Al oxide was generated on the surface of the test piece of the inventive example, and further oxidation was suppressed. On the other hand, the test piece of the comparative example produced Cr oxide and Si oxide on the surface, which are less dense than the Al oxide, have insufficient oxygen intrusion prevention function, and suppress oxidation. It was because it was not possible.

  When comparing the inventive examples, the test No. 102, 103, 106, and 108 to 110 have an evaluation of “A”, and it can be seen that they are particularly excellent in oxidation resistance. This is presumably because a particularly excellent Al oxide layer was formed because the Al concentration was high and the Cr concentration at which an oxide layer was easily formed was relatively low.

<Bead placement test>
About the test piece of the invention example shown in Table 1 (thickness: 25 mm or less and two types of 25 mm or more), the bead-placement test was implemented in the following way, and the cracking property by welding was determined.

  Prior to the bead placement test, the test surface of the specimen was machined with a grinder to smooth the surface. The test surface is a portion that becomes a welding groove and a portion that is affected by heat due to welding.

  In addition, a liquid penetration test was performed on the test surface of each specimen, and it was confirmed that there was no crack on the test surface.

  Conditioned bead placement tests shown in Table 2 were performed by TIG welding on the specimens whose test surface was confirmed to be healthy. The bead is a straight bead and the bead length is 50 to 100 mm.

  In addition, as for the execution sequence of this test, the test of B method was implemented when the defect was found in the liquid penetration test after the test by A method.

  FIG. 2 and Table 3 show the bead judgment criteria according to method A (filler metal (welding rod): none) and method B (filler metal: present). In the method B, the determination is “OUT” even for a minute crack.

  As a result of the above test, the test piece in which no defect was found in any of the test pieces having a thickness of 25 mm or less by the A method and a thickness of 25 mm or more was evaluated as “A” for crackability, and a defect was found by the A method. However, the test piece in which no defect was found by the B method was evaluated as a crackability evaluation “B”, and the test piece in which a defect was also found by the B method was evaluated as a crackability evaluation “C”. The results are shown in “Crackability” in Table 1.

  Referring to Table 1, the test piece which is an example of the invention is the test No. Nos. 101, 102, 104 to 108 are evaluated as “A”. 103, 109 and 110 were evaluated as “B”.

  Examining the inventive examples, it can be seen that all specimens having a crackability evaluation of “A” had a larger Ya than Pa and Pa <Ya.

<Comprehensive judgment>
For each test piece, the overall evaluation “A” is evaluated as “A” for both the oxidation resistance test and the bead placement test, and the comprehensive determination “B” for one “A” and the other “B”. ”, Evaluation including“ C ”or“ D ”was determined as a comprehensive determination“ C ”. The results are shown in “Overall judgment” in Table 1. Referring to Table 1, all of the test pieces of the invention example were judged as “A” or “B”, and all of the test pieces of the comparative examples were judged as “C”. That is, it can be seen that the specimen of the inventive example is less likely to crack during welding, and has superior oxidation resistance as compared to the specimen of the comparative example. Therefore, the steel product of the present invention is extremely suitable for application to a hearth roll, a coiler drum, or the like used in contact with a steel material such as a steel piece or a steel plate.

  The above description is for explaining the present invention, and should not be construed as limiting the invention described in the claims or limiting the scope thereof. Further, the configuration of each part of the present invention is not limited to the above-described embodiment, and various modifications can be made within the technical scope described in the claims.

10 Bead 12 Crater 14 Crack 16 Point-like defect

Claims (6)

Steel products used in contact with steel materials,
The centrifugal force casting part formed on the surface in contact with the steel material and manufactured by centrifugal casting is welded to and mounted on a stationary casting part formed by stationary casting.
Before SL centrifugal casting unit, at mass%,
C: 0.2% to 0.7%
Si: more than 0% and 2.0% or less,
Mn: more than 0% and 3.0% or less,
Cr: 15.0% to 40.0%,
Ni: 18.0% to 55.0%,
Al: 1.0% to 5.5%, and
Containing at least one selected from the group consisting of Ti: 0.01% to 0.6% and / or Nb: 0.1% to 1.8%;
Ri Do the balance Fe and unavoidable impurities,
The stationary casting part does not contain Al,
Steel products. The centrifugal casting part is in mass%,
Rare earth element (REM): more than 0% containing 0.4%,
The steel product according to claim 1. The centrifugal casting part is in mass%,
W: more than 0% to 5.0% or less, and / or Mo: more than 0% to 2.0% or less,
The steel product according to claim 1 or 2. The centrifugal casting part is
Pa = −11.1 + 28.1 × C + 29.2 × Si−0.25 × Ni−45.6 × Ti + 18.0 × REM−16.6 × Nb
Ya = -13.75 × Al + 63.75
And when
Pa <Ya
Is,
The steel product according to any one of claims 1 to 3. The surface of the centrifugal cast part has a ceramic sprayed layer,
The steel product according to any one of claims 1 to 4 . The steel product is a hearth roll or a coiler drum,
The steel product according to any one of claims 1 to 5 .

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