JPH09318515A - Deflection evaluating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable evaluating of the deflection of a member t6 be deformed under a bending stress by a method wherein one end of a test member made of a material of the same kind as that of a long-sized member in a heating furnace and a tensile stress is loaded on the other end thereof to measure a creep distortion. SOLUTION: A test member 15 is put into an oven 12 having a heater 11 and the lower end part thereof is fixed on a fixing device 13 while the upper end part thereof on a fixing device 14. A tensile stress 6 is applied so as to work upward. Then, a tensile test is performed, for example, under three kinds of temperature conditions to measure stress loading time and a distortion at a stationary creep stage and a creep distortion speed is calculated based on the stationary creep distortion of the test member 15 and the stress loading time. The rate of deflection converted from the stationary creep distortion speed at the tensile test is in a relationship of almost matching the rate of deflection at a three point bending test. So, the test member 15 comprising a material of the same kind as that of a long-sized member to be evaluated is produced and a handy tensile creep test is performed replacing a bending creep test to evaluate the deflective deformation of the long-sized member from the obtained stationary distortion speed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for evaluating flexure of a member which is deformed by bending stress at high temperature by utilizing creep strain generated by a tensile creep test.

[0002]

2. Description of the Related Art Referring to FIG. 7, a walking beam type heating furnace (1) is used, for example, in a hot rolling process of steel.
Skid beam (3) that is used for heating billets, slabs, etc. and supports and conveys heated materials (2) such as billets, slabs, etc.
Are provided in a plurality of rows along the longitudinal direction of the furnace. This skid beam has a structure in which a fixed beam and a moving beam are alternately arranged in the furnace width direction, and the material to be heated is conveyed in the furnace by periodically repeating the vertical movement and horizontal reciprocating operation of the moving beam. It

A skid beam is a hollow skid pipe.
(5) (See Fig. 8) A large number of skid buttons (6) are erected at a predetermined interval in the axial direction. From the outer peripheral surface of the skid pipe (5) and the base of the skid button (6) to the upper part. It has a refractory lining (7). Since the inside of the heating furnace (1) is usually kept at a high temperature of about 1000 ° C or higher, in order to prevent deformation such as bending due to the temperature rise of the skid pipe (5), cooling water flows through the hollow holes. Has been done. However, due to the influence of the cooling water flowing through the skid pipe (5), the skid button (6) will be lower than the temperature inside the furnace, so the material to be heated (2) will come into contact with the skid button (6). There is a problem that cold spots locally occur and the plate thickness of the rolled product becomes non-uniform in the next rolling step. Also, skid pipe
Circulating cooling water in (5) lowers the thermal efficiency, so there is a problem in effective utilization of thermal energy.

The above problems are solved by stopping the use of cooling water in the hollow holes of the skid pipe (5). For this reason, in order to shift from the water-cooled type to the non-water-cooled type skid pipe, as shown in FIG. 9, the outer surface of the skid pipe (5) is coated (8), and various studies have been conducted on pipe materials and pipe structures. Has been done. By the way, when the skid pipe is made non-water-cooled, the skid pipe is exposed to high temperature environment, so if the load of the material to be heated is repeatedly applied through the skid button due to long-term use, the skid pipe will bend and deform. . The typical size of the skid pipe is about 2000 mm in span length between support posts (9) and (9), outside diameter about 300 mm, inside diameter about 240 mm.
Therefore, it is difficult to evaluate the deflection of the skid pipe by simulating the actual operating conditions.

Even if the flexural deformation caused by the load intermittently applied to the skid pipe is evaluated by a bending test of a test member made of the same kind of material as the skid pipe, in the bending test, the span distance of the test member is increased. , Stress distribution,
Since it depends heavily on the shape, many tests are required and it is not very practical.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to prevent flexural deformation of a long member caused by repeated loading of a material to be heated in a heating furnace in a vertical direction from the same kind of material as the long member. It is an object of the present invention to provide a method for evaluating the created test member by utilizing a creep strain generated by performing a tensile creep test.

[0007]

In order to achieve the above object, the present invention is to prepare a test member from the same kind of material as a long member to be evaluated, fix one end of the test member and apply a tensile stress to the other end. Is applied to cause creep strain in the test member, the stress loading time and the strain at the steady creep stage are measured, and the creep calculated based on the measured strain at the steady creep stage and the stress load time is measured. Number 2 using strain rate
The coefficient A and the exponent n of are obtained, and the obtained A and n are substituted into Equation 3 to obtain the bending speed of the long member, and the bending speed of the long member is evaluated using the obtained bending speed. Is.

[0008]

[Equation 2]

[0009]

(Equation 3)

In the present invention, of the creep deformations, only the secondary creep, that is, the creep in the steady creep stage, is targeted because the creep deformation speed in the steady stage is substantially constant. In the creep process, as shown in FIG. 1, a transient creep that is a sum of elastic strain and plastic strain that does not depend on time occurs at the moment of load, and the strain rate decreases with time at the initial stage of creep. Appears,
Subsequently, steady creep showing a substantially constant strain rate is observed, and then accelerated creep in which the strain rate accelerates appears, leading to fracture.

The tensile creep test measures the stress loading time and the strain at the steady creep stage to calculate the creep strain rate. The relational expression between creep strain rate and stress is Equation 2
Is shown in Next, the stress and the creep strain rate are plotted on the logarithmic horizontal axis and the logarithmic vertical axis, respectively, and an approximate expression of a linear function is created. The coefficient A of the equation 2 is obtained as the vertical axis intercept of the obtained linear function equation, and the power exponent n of the equation 2 is obtained as the slope of the linear equation.

Substituting the obtained coefficient A and exponent n together with the values of L, W, b and h of the long member to be evaluated into the equation of the bending speed (see Eq. 3) in the bending creep test, The bending speed of the long member to be evaluated is calculated.

The relationship between equations 2 and 3 is as follows. When the radius of curvature when the beam is deflected is R and the position in the longitudinal direction of the beam is X, the deflection δ of the beam is given by equation 4.

[0014]

(Equation 4)

Assuming that the strain distribution in the thickness direction is a straight line, the height of the beam cross section is h, the strain of the outermost layer is ε ₀ , and the position in the height direction from the neutral axis is y, the strain ε of the beam cross section is several. Given by 5.

[0016]

(Equation 5)

When the equation 2 is definitely integrated at time t,
Equation 6 is obtained.

[0018]

(Equation 6)

From equations 5 and 6, the stress σ is represented by equation 7.

[0020]

(Equation 7)

Assuming that the width of the beam section is b, the moment M is expressed by the equation 8 from the balance of the moments of the beam section.

[0022]

(Equation 8)

Substituting the stress σ of the equation 7 into the equation 8, the moment M is expressed by the equation 9.

[0024]

[Equation 9]

When Equation 9 is rearranged, it is shown as Equation 10.

[0026]

(Equation 10)

By substituting equation 4 into equation 10, equation 11 is obtained.

[0028]

[Equation 11]

By the way, when the load is W, the moment M is expressed by Eq.

[0030]

(Equation 12)

By substituting the equation 12 into the equation 11, the equation 13 is obtained.

[0032]

(Equation 13)

In Expression 13, when X = L / 2, dδ
When / dX = 0 and X = 0, when X is integrated under the condition of δ = 0, Formula 14 is obtained.

[0034]

[Equation 14]

Since it is the bending of the center that is at issue, in the equation (14), X = L / 2 and the equation (15) is obtained.

[0036]

(Equation 15)

By dividing the deflection obtained by the equation 15 by the load time, the deflection speed shown by the equation 3 can be obtained.

[0038]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 2 shows a state in which a test member (15) is subjected to a tensile creep test in an oven (12) equipped with a heater (11). The test member (15) placed in the oven (12) has a lower end fixed to the fixture (13) and an upper end fixed by the fixture (14), and has a tensile stress σ directed upward.
Works.

The test member has an outer diameter of 8 mm and a gauge length 1
20 mm round bar, made of Cr, 25% by weight
%, Co: 12%, W: 9%, Nb: 2%, and the balance Ni. 817 ° C, 871 ° C and 92
Tensile tests were carried out under three temperature conditions of 6 ° C., and the stress load time and strain at the steady creep stage were measured. The creep strain rate was calculated based on the steady creep strain of the test member and the stress load time, and the coefficient A and the exponent n of the equation 2 were obtained in the above-described manner.

The values of the coefficient A and the exponent n at each temperature are shown in FIGS. 3 and 4. The horizontal axis is 1000 / (T + 27
3), expressed in units of 10 ³ / K, 817 ° C, 8
71 ° C. and 926 ° C. correspond to 0.92, 0.87 and 0.83, respectively. As shown in FIGS. 3 and 4, it can be seen that the coefficient A and the exponent n have a correlation with the temperature, respectively.

In order to examine the validity of Equation 3, a three-point bending test was conducted in the following manner. FIG. 5 shows a state in which the test member (15) is subjected to a three-point bending test in the oven (12) equipped with the heater (11). The test member (15) placed in the oven (12) is supported at its two ends by two supporting points (16) and (17), and the load P is approximately at the center between the supporting points (16) and (17). Is loaded vertically.

The dimension of the test member in the bending creep test is 5
(Height) × 10 (width) × 140 (length) mm, and the material is the same as that used in the tensile creep test. The test is conducted under three conditions of stress 98 MPa and temperature 926 ° C., stress 73.5 MPa and temperature 871 ° C., stress 49 MPa and temperature 817 ° C., and the test time is all 70 hours. After the transitional creep stage, the deflection generated in the steady creep stage, which shows a constant strain rate in the steady creep stage, was obtained. The bending speed measured by the bending creep test is shown on the horizontal axis of FIG.

Next, in the equation 3, regarding L (span), W (central concentrated load), b (width of beam section) and h (height of beam section), the condition values of the three-point bending test are As for the coefficient A and the exponent n, values corresponding to the respective temperatures shown in FIGS. 3 and 4 were substituted to obtain the converted value of the bending speed. The bending speed converted by the tensile test is shown on the vertical axis of FIG. As is clear from the results shown in FIG. 6, there is a substantial agreement between the bending speed converted from the steady creep strain speed in the tensile test and the bending speed actually obtained by the three-point bending test. The reason why there is a slight deviation in the matching relationship on the low stress side is that the bending test time was relatively short at 70 hours, and at low stress it took some time for steady creep to appear. It does not deny the relationship.

As described above, since the bending speed in the bending creep test is substantially in agreement with the bending speed converted from the steady creep speed in the tensile creep test, the same kind of material as the long member which needs to be evaluated for bending. A simple tensile creep test is carried out in place of the bending creep test by preparing a test member from the above, and using the obtained steady creep strain rate, it is possible to evaluate the flexural deformation of the desired long member. That is, the value of the coefficient A of Equation 2 and the exponent n obtained from the steady creep strain rate under a predetermined temperature condition is L (span), W (central concentrated load), b (beam cross section of the long member to be evaluated). By substituting the values of (width) and h (height of beam cross section) into Equation 3, the bending speed of the long member can be predicted and the bending can be evaluated. Although the long member is solid, it is needless to say that the bending evaluation method of the present invention can be similarly applied to a hollow long member such as a skid pipe.

The material of the test member is preferably the same as that of the member to be evaluated, but it does not have to be completely the same.
It is sufficient if at least the main components are the same.

The test temperature is preferably the same as the service temperature of the member to be evaluated, but may be any temperature at which creep occurs. When the temperature is different from the working temperature of the member to be evaluated, the coefficient A and the exponent n may be applied to the equation 3 according to the temperature.

[0047]

EFFECT OF THE INVENTION The bending of a member which is deformed by bending stress
Since the steady creep strain generated by the tensile creep test can be evaluated as a parameter, the measurement method can be simplified.

[Brief description of drawings]

FIG. 1 is a graph showing a creep curve in a tensile creep test.

FIG. 2 is an explanatory diagram of a tensile creep test in an oven.

FIG. 3 is a graph showing the relationship between coefficient A and absolute temperature.

FIG. 4 is a graph showing the relationship between power index n and absolute temperature.

FIG. 5 is an explanatory diagram of a three-point bending test in an oven.

FIG. 6 is a graph showing a relationship between a bending speed obtained by using a steady creep strain rate in a tensile creep test and an actually measured bending speed in a three-point bending test.

FIG. 7 is an explanatory diagram of a walking beam type heating furnace.

FIG. 8 is a cross-sectional view of a water-cooled skid pipe.

FIG. 9 is a cross-sectional view of a non-water cooled skid pipe.

[Explanation of symbols]

 (12) Oven (13) Fixture (14) Fixture (15) Test member

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Tohru Kawai 1-1-1, Nakamiya Oike, Hirakata-shi, Osaka Prefecture Kubota Hirakata Manufacturing Company (72) Inventor Shin Shinozaki 1-1-1, Nakamiya Oike, Hirakata-shi, Osaka Prefecture No. 1 stock company Kubota Hirakata Factory

Claims (1)

[Claims] 1. A method for evaluating flexural deformation of a long member caused by repeated vertical load application of a material to be heated in a high-temperature heating furnace, using a test member made of the same material as the long member. Then, a tensile stress is applied to the other end of the test member with one end fixed to cause creep strain in the test member, the stress loading time and the strain at the steady creep stage are measured, and the measured test member's Using the creep strain rate calculated based on the strain and the stress load time in the steady creep stage, the coefficient A and the exponent n of Equation 1 are obtained, and the obtained values of the coefficient A and exponent n are substituted into Equation 2. A flexure evaluation method comprising: calculating the flexure speed of a long member by using the obtained flexure speed and evaluating the flexure of the long member using the obtained flexure speed. [Equation 1]