SU1420035A1 - Method of treating welded metal structures - Google Patents

Abstract

The invention relates to the treatment of steel by vibration and can be used in mechanical engineering, construction, transport and other areas in the manufacture of large cost-effective welded structures that experience variable and alternating loads during operation: cranes, bridges, ship hulls etc. The purpose of the invention is to increase the cyclic durability of welded metal structures by creating a normalized value and distribution pattern of residual stresses in the heat-affected zone. The area adjacent to the weld is machined using an ultrasonic percussion instrument, and the amplitude of oscillation of the output end A of the transducer is set from the ratio 2.24 i A4ff -m / io R 3.36, where 6 ,,, the yield strength of steel ; f is the frequency of shock pulses; m is the mass of the drummer; R is the striker radius. 2 hp f-ly, -4 Il. and sl

Description

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The invention relates to the processing of hoists by vibration and can be used in mechanical engineering, construction, transport and other areas in the manufacture of large expensive welded structures, testing and alternating loads: lifting wounds, bridges, ship hulls etc. I The purpose of the invention is to increase the cyclic durability of welded metal | Lokonstruktsiy by creating normalized in magnitude and pattern of distribution of residual stresses in the heat-affected zone,

I FIG. Given the dependence of the depth | of the deformed layer on the amplitude of the Oscillations of the output end of the 1KOVA ultrasound transducer (medium strength steel case) 2 -, the distribution of residual compressive stresses over the depth of the deformed layer with an ultrasonic impact treatment I with a different amplitude | (medium strength steel body); I in FIG. 3 shows the test results of butt joints of low carbon steel j 1 in the initial state, 2 - after ultrasonic treatment; Figure 4 shows the results of fatigue tests of T-joints, high-strength steel: 1 - in the initial state of the scientific research institute, 2 after ultrasonic treatment.

The advantage of the invention lies in the fact that the treatment is carried out at the amplitude of the oscillations of the output end of the ultrasonic transducer, which is assigned taking into account the yield strength of the material being processed, as well as the frequency of shock impulses, the mass and the cross-sectional area of the impactor:

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where A is the oscillation amplitude of the output end of the ultrasonic transducer; 6 yield strength of the material being processed;

f is the frequency of shock pulses; m is the mass of the drummer; R is the striker radius.

It was established experimentally that the implementation of this ratio ensures the receipt of residual compressive stresses at a level of 1.2-1.5

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flowability of the treated material in the surface layer with a thickness of 0.1 0.2 mm with a total depth of the deposit; accurate compressive stresses of 1.0-1.2 mm for steels of medium strength.

The area of welding heating limited by the isotherm of structural transformations is subjected to treatment, which completely eliminates their adverse effect on the cyclic durability of the welded joint.

In welded joints of low-carbon steels, the welding heating area limited by the primary recrystallization isotherm is subjected to processing.

In welded joints of low-alloyed and high-strength steels, the welding heating area bounded by a low tempering isotherm is subjected to treatment.

Example. In practice, the displacement amplitude is determined from the condition that the depth of deformation is maximized for this material. In this case, for each material, the dependence of the depth of the deformed layer on the amplitude of oscillations of the output end of the ultrasonic transducer is experimentally constructed. It can be seen that the increase in amplitude is accompanied by a proportional increase in the depth of the deformed layer. The curve has a saturation region, starting with amplitudes approximately equal to 20-25 microns. An increase in the amplitude above the specified values causes only a slight increase in the depth of the layer. The maximum depth of deformation, in particular, is achieved by machining with an amplitude of 35, is 1.2 mm. The treatment is subjected to the area adjacent to the weld for the width of the zone of action of residual stresses. An example of the variation of residual stresses along the depth of a deformed layer with an increase in amplitude to the limiting values is shown in Fig. 2. It can be seen that the maximum residual compressive stresses on the metal surface are reached at an amplitude of 25 microns. Increasing the amplitude to a value that provides the maximum depth of deformation (for a given material, 35 µm), leads to a decrease in

residual compressive stresses at the surface at 40% of the maximum value. Processing with an amplitude of 45 µm creates tensile stresses in a thin surface layer, the cause of which is metal over-hardening and local temperature effects in the zone of contact between the indenter and the surface to be treated. The increase in cyclic durability compared with the initial state is respectively: 95% for treatment with an amplitude of 25 µm, 60% for processing with an amplitude of 35 µm. Samples treated with an amplitude of 45 μm have a cyclic durability at the level of the original. Consequently, the optimum in the example described is a processing with an amplitude of 25 µm, i.e. approximately 25-30% less amplitude, providing the maximum depth of deformation.

As studies have shown, the ultrasonic treatment according to the proposed method increased the cyclic durability of the butt joints of low carbon steel in the medium and high cycle region by 4-5 times and increased the fatigue limit by 54% (FIG. 3).

Fatigue testing of welded specimens of high-strength steel with a T-joint showed that, under conditions of alternating symmetrical loading cycle, ultrasonic: 0 processing by the proposed method provides a threefold increase in yield strength (Fig. 4) and no less than 1 5-fold increase in cyclic durability.

When conducting fatigue tests of specimens with T-joints, the foci of fatigue crack formation were located far from the joint and the treated area of the metal surface with a rolling crust. This circumstance indicates that ultrasonic treatment provides an increase in fatigue resistance of the welded joint to the level of the base metal,

The technical and economic efficiency of the method is determined by increasing the cyclic durability and increasing the guaranteed service life of welded steel structures, with the exception of losses due to interruptions in operation, responsible welded metal structures such as bridges, cranes, and so on. in cases when a break is necessary for carrying out repair work to eliminate fatigue damage, as well as reducing the labor capacity of repairing structures by preventing fatigue damage by the proposed method.

Claims (3)

Invention Formula  The method of treating welded metal structures of structures mainly of steel, including the impact of an ultrasonic shock HHCTpi MeHTOM with a given displacement amplitude the end face of the converter in the zone adjacent to the weld, which is designed to increase the cyclic durability of the welded metal structures by creating normalized in size and pattern of distribution of residual compressive stresses in the heat-affected zone, the action is carried out with an offset amplitude A determined from the ratio 2.24 BUT 5 3.36, 0.1 where o l is the yield strength of steel welded construction; f is the frequency of shock pulses; m is the mass of the percussion instrument; R is the radius of the tip of the shock tool in the area limited by the fusion line a weld with a main mechanism and a line through which structural transformations have taken place. .2, The method according to claim 1, which differs from the fact that in welded metal structures from low-carbon steels, the impact is carried out in the zone bounded by the line ,, which was primary recrystallk- 0 3 ace. 3. The method according to claim 1, characterized in that in welded metal structures from low-alloyed and high-strength steels, the impact is carried out in the zone bounded by the line through which the low tempering has passed. ten 15 b оС / 77 V. from 6;) J ABOUT 20 fiu 60 80 100 120 t t 180 A 35mnm A-25pkp 0.2 Ojf 20 25 fie.-f 30 3S  um D 5 microns 0, b 1.0 7.2 //, l // bd.mpa