DD270139A1 - METHOD FOR PRODUCING AXIAL SYMMETRIC SAMPLES AND TESTING FOR WELDING SUITABILITY - Google Patents

Abstract

The invention relates to a method for the production of axially symmetric samples and for testing for welding suitability. The basic idea of the invention is to weld a plurality of sample series with the same defined temperature and deformation regime, the pattern in the weld seam region and the resulting mechanical-technological properties on a first sample series and the critical, external forces and / or shrinking forces on further sample series to determine the resulting tensile stress causing hot or cold cracks. On the basis of this experimental system analysis, the cause-and-effect relationship determining the hot or cold cracking tendency of a material - temperature and deformation regime in material processing - microstructures - mechanical-technological properties - tensile stress is recorded with greater accuracy and reproducibility than with the previous test methods. Fig. 2

Description

Field of application of the invention

The invention relates to a method of producing axially symmetric samples of metallic materials and to testing these samples for weldability, i. their tendency to hot and cold cracks.

Characteristic of the known state of the art

The weldability, defined in TGL14913, is a sub-concept of weldability. It is preferably determined by the material. Welding tests have the aim of determining the inclination of the material to cold and hot cracks. Cold cracks occur when a brittle, crack-sensitive, martensitic microstructure completes in the weld area and at the same time a mechanical stress, preferably a tensile stress, acts on the weld seam. The examination of the cold cracking tendency of a material takes place with self-stressing or externally stressed samples. The self-stressed test methods are most commonly used with the Controlled Thermal Severity (CTS) test and the Tekken test.

The criterion for cold cracking resistance in the CTS test is cracking in the control seams of the welded test specimen and in the Tekken specimen the lowest cooling rate at which the susceptibility to cracking in the seam root skyrockets.

The disadvantage of these samples is that only the welding temperature is approximately known. Unknown are the tempi w j gradient, the cooling rate, the structure and the height of the cold cracks causing tension. The CTS sample and the Tekken sample shown in detail and described in TGL1491 · "* 'therefore only allow a qualitatively 3' .smission. In the test methods with fre-, - 'claimed samples, the most frequently used is the implant test, the TRC test. Test (Tensile Restraint Cracking Test) and the RRC test (Rigid Res lint Cracking Test).

In the implant test, a cylindrical specimen with a circumferential thread notch is inserted as an implant in the bore of a steel plate and welded over with a bead. The circumferential thread notch is arranged so that it is in the critical region of the heat affected zone. Immediately after welding, the sample is loaded and the time to rupture is measured as a function of the applied stress. To assess the Kaltrißneigung serves recorded in this way voltage-life graph.

In the TRC test and the RRC test, two sheets are connected by a butt weld. Immediately after welding, the weld is loaded with a tensile stress acting perpendicular to it. The test criterion is the voltage at which cold cracks occur (critical TRC voltage).

In the RRC test, the applied stress is controlled in its time course so that the strain caused thereby compensates for the shrinkage that occurs during the cooling of the sample. The critical RRC stress is the lowest tension at which cold cracks occur.

When welding the samples for the implant, TRC and RRC test, the heat field changes constantly. There is thus no reproducible assignment of temperature-temperature gradient-cooling rate structure-mechanical properties possible. In addition, all three samples have an undefined multiaxial stress state.

Warm cracks occur in the weld and in the V region during cooling. Affected are all steel groups and non-ferrous metal alloys. Necessary condition for the occurrence of warm cracks are low? Jhmelzende grain boundary films whose effect is attenuated with increasing grain refinement. For this reason, determined in the previous test method not causal causal chain material temperature-forming degree-Umformgeschwindigkeit-Umformfestigkeit and resulting from the high temperatures Gefiiqe significantly the warm cracking tendency. The examination of the warm crack inclination is carried out with self-stressing and with foreign-claimed samples.

The self-stress is generated by the shrinkage caused during welding. These checks provide only yes-no decisions.

The test methods with externally stressed samples are of greater importance. The stress is applied reproducibly by bending (Varestraint test) or by train (test method according to Prochorow, after Wittke and Zwickert and after Kluge).

In these tests the load and the load speed are reproducible. The illustrated prior art shows that

- the three microstructures and the resulting mechanical-technological properties of causal chains a, b and c, which decisively determine metallic materials

a temperature-temperature gradient cooling rate,

b temperature-strain-forming rate, c atomic hydrogen recombination poison hydrogen diffusion recombination of atomic hydrogen in

Material inside, are not taken into account in welding suitability tests or only very imperfectly,

- Making the integral connection and checking the welded connection variously; and requires very expensive devices.

Object of the invention

The aim of the invention is a method by which the hot and Kaltrißneigung metallic materials can be determined with a lower cost of material, energy and working time but with greater accuracy and reproducibility than before.

Explanation of the essence of the invention

The invention has for its object to provide a method for producing axially symmetric samples and to check for welding suitability, with which it is possible due to the production due to the material acting, its structure and the resulting mechanical and technological properties significantly determining temperature and Determine deformation regime quantitatively and reproducibly.

According to the invention the object is achieved in that the facesplanged on a front side samples are arranged with rotationally symmetrical full or hollow cross section in alignment one behind the other and touch each other in the end faces.

The cohesive connection is made by the conversion of kinetic energy into heat on the elastic and plastic deformation and securing the near-surface material areas with the working values friction speed v _h . Friction pressure pi and friction time tj, ie by friction welding.

The working values, v _h , p _{l (} tj; 1 S h S 3; 2 S i, j S 5, with which the samples are welded, remain with all k sample series; 3 S k S 5; with a sample number Im; SIS 75; 3 S m S 10, each series unchanged The friction velocity ν is calculated for the solid section of diameter d = 2 r (r in m) according to the equation ν = 0,07 rn (n in min " ¹ ) and for the Hollow cross-section of average diameter d _m = 2rm according to the equation ν = 0.1 r _m η determined and set under consideration of the boundary condition 0.8m / s ä ν S 1.6 m / s.

For the friction pressure applies: 20MPa SpS 60MPa

The sample preparation after reaching the friction time t, the conditions

Otherwise <** 0 (D

= const Φ 0

dt (2)

has to suffice, finished.

The removal of the burr is done while rubbing.

The causal chains a and b determining the structure in the weld area, a temperature-temperature gradient-cooling rate,

b temperature-deformation-forming-forming resiliency, are set as defined during the sample preparation, in which the friction rate, the friction pressure and the friction time according to predetermined contexts, equations (1) to (16), varied and adjusted, and in addition control measurements of the axial temperature distribution and the P.'oberverkürzung be performed.

From Gi. (1) it follows that the differential equation Jer is heat conduction for the infinite homogeneous rod

dT d ² T ₍₃₎

dt ^{= a (}

in the shape

dT d ² T

^{β a} ?

can be written. By integrating the Eqs twice (4)

- = - C = degrees T ₍₅₎

dx

T = -C X + D (6)

results with the boundary conditions X = OT = Tm = D

_ | = X = +1, T = To

the temperature distribution in the abutting surface area during the quasi-stationary friction welding process

= - H x + Tm · (7)

dT, ^Tm "

From Eq. (2) it follows that the volume converted per revolution into the upsetting burr and thus also the weld part shortening I'je turn remains constant

_Δ 1ι _ £ i ₌ oonst.

nt O)

The following equations then apply: - Welded section shortening I

ΔΙ, = ntexo (p, / ö, -1) h (10)

Al ₂ = ntexp (p ₂ / öf -) h (11)

Al _n = ntexp (p "/ 6, -1) h (12)

h axial extent of the process zone - forming resistance Vt

Αίη-i

(13)

- degree of deformation φ

T =ln (i +~ ^ ~) (14)

- Forming speed φ

Shock temperature Tm

Λ = 270mol C = 2.5 x 10 ^"10 S- 'α = 0.013 ... 0,019mm ² N" ¹ η = 4.4

R = 8,314mor 'K' ¹ is the gas constant.

The testing of the sample is preferably carried out without disengagement from the clamping device in the device used for the preparation of the sample by the sample at standstill of the rotating part with a critical from the external forces and / or shrink forces resulting in hot or cold cracking tensile stress and if necessary still applied with a torsional moment.

The cause-and-effect relationship triggering the hot or cold cracks is determined by the experimental system analysis presented below.

On a first series of samples, the causal chains a and b are set in a defined manner and under the action of the causal chain b in the process zone at welding temperature adjusting microstructure and under the action of the causal chains a and b in the process zone and under the effect of the causal chain a in the adjoining areas at room temperature adjusting structure and the resulting mechanical-technological properties determined quantitatively. On a second series of samples, the process zone as well as the adjoining areas are visibly modeled by macro etching and loaded by df. draw from the cross-section A with a tensile force F ύ R _m A, the critical applied, the cold cracking tension applied \, it the experimental results of the first series of samples, the cause-effect relationship of Kaltrißneiyung closed.

On a third series of samples, the critical stress resulting from shrinkage forces and / or external forces resulting from hot cracks tensile stress RSR _m (T) is applied to all samples at standstill of the rotating part and closed with the test results of the first Probenserle the cause-effect relationship of Warmrißnotigung.

embodiment

The invention will be explained on a leadership example on. In the accompanying drawing ze Qt

Fig. 1: Unwelded sample

Fig. 2: device

Fig. 3: Axial temperature distribution and model of the deformation process Fig. 4: Time course of the impact surface temperature and the weld part shortening.

The unwelded samples (Fig. 1) consist of two parts. They are planed on a face, have a length of about 100mm and a diameter corresponding to the wall thickness of the component to be examined. The cohesive compounds are used in all three sample series with the working values

Pi = 20 MPa t, = 3s

n ₍ = 1000 min ^-1 p ₂ = 30 MPa t ₂ = 5 s

n ₂ = 1500rpm ^"1 p ₃ = 40MPa t ₃ = 7s

P ₄ = BOMPa t ₄ = 10s

manufactured. These are I = 32 different samples and therefore also 96 different microstructures per sample series. Since the average is formed from m = 3 samples, the number of lm = 96 samples per series is calculated. The two samples 1 and 2 are arranged in a respective clamping device 3 and 4 in alignment one behind the other (FIG. 2) so that they touch each other in the face-turned faces. In the region of the friction zone 5, a thermal imaging camera 6 is arranged to measure the axial temperature distribution. Further, the sample shortening is measured with a displacement transducer 7, the axial force with a load cell 8, the friction torque with a torque meter 9 and the speed with a tachometer 10.

The measured value processing and display is performed with the color monitor 11, the analog-to-digital converter 12, the electronic image data memory 13 and the microcomputer 14.

Under the effect of the working values friction pressure and friction speed, the two samples deform and heat up in the abutting surface area (FIG. 3). The causal chains a and b are determined during the sample preparation on the basis of the equations

(3) to (8) and (16) or (9) to (16) are set quantitatively and reproducibly.

The initial transient temporal course of the impact surface temperature and the shortening of the sample changes into the quasi-stationary course (FIG. 4). Sample preparation is done after reaching the t, which is the conditions

₌ oonat »0

dt

_{a const} μ ο

dt

has to suffice, finished.

On the samples of the first series, the two causal chains a and b are calculated for the area of the process zone and the adjoining areas, and the microstructure and the resulting mechanical-technological properties are determined.

On the samples of the second series, the upsetting burr is removed and the process zone and the adjacent Bore oak are visualized by a macro-etching. Subsequently, the samples are loaded by the cross section A in the device with a constantly increasing tensile force FSR _1n A. The experiment is aborted if at the tensile force F = R _m A no Kaitrisse have yet occurred.

On the samples of the third series, the upsetting burr is removed during the rubbing and the sample is loaded with a tensile force FSR _1n (T) A immediately after the braking of the rotating part. The test is aborted if at the tensile force F = R _m (T) A no hot cracks have yet occurred.

With the test results of the first sample series, the cause-effect relationship of the weldability is concluded for all subsequent sample series.

Claims (1)

Method for producing axially symmetrical specimens and for testing for weldability, in particular samples consisting of sections of different materials, characterized in that - Making the cohesive connection by the conversion of kinetic energy into heat on the elastic and plastic deformation and the shear d jr near-surface material areas with the working values friction rate Vh, friction pressure pi and friction time tj, d. H. by friction welding, takes place, The working values Vh, Pi, tj; 1 S h ^ 3; 2 ^ i, j ^ 5; with which the samples are welded, on all k sample series; 3 ^ k ^ 5; with a sample number Im; 9 ^ ^ 75; 3 ^ m ^ 10; each series remain unchanged, - the friction velocity ν for the solid section of diameter d = 2 r (r in m) according to the equation ν = 0,07 m (n in min " ¹ ) and for the hollow section of the mean diameter d _m = 2rm according to the equation ν = 0.1 rn is determined and adjusted in compliance with the boundary condition 0.8 m / s έν ^ 1.6 m / s, - the friction pressure is set in compliance with the limit range condition 20MPa ^ p = 60MPa, - The sample preparation after reaching the friction time t, dia the conditions dT / dt = const. --O and d [AI (t)] / dt = const. Φ 0 must be completed - the causal chains a and b a determining the structure in the weld area temperature-temperature gradient-cooling rate, b temperature-forming degree-forming resiliency, are set during the sample preparation defined in which the friction speed, the friction pressure, and the friction time according to predetermined contexts ΔΙ = ntexp (p / öf-1) h riι / 1 Τ (χ) β - χ + Tm
dx varied and adjusted and in addition Kontro'imessungen the axial temperature distribution and the Schweißteilverkürzung be performed the sample is preferably carried out without clamping out of the clamping device in the apparatus used for producing the sample by the sample at standstill of the rotating part with a resulting from external forces and / or shrinkage forces critical the hot or cold cracks causing tensile stress and optionally with a torsional moment is applied, the cause-and-effect relationship triggering hot or cold cracks is determined by experimental system analysis, on a first series of samples, the causal chains a and b defined set and under the action of the causal chain b in the process zone at welding temperature-adjusting structure and under the action of the causal chains a and b in the process zone and under the effect of the causal chain a in the adjoining areas at room temperature adjusting structure and the resulting mechanical-technological properties are quantified, on a second series of samples for all samples • the process zone as well as the adjoining areas are visualized by a macro-etching, By stressing the samples of the cross-section A with a tensile force F _z , F _z R _m A, the critical, the cold cracking tensile stress is determined • the cause-effect relationship of the cold cracking tendency is concluded with the test results of the first trial series; - on a third series of samples for all samples The critical stress resulting from shrinkage forces and / or external forces, which causes hot cracks R 1 R _m (T), is applied when the rotating part stops, • the cause of the hot crack inclination is deduced from the test results of the first series of samples. For this 4 pages drawings