Studies on Peening Operation (Part 2)

Effects on Stress Relieving and Notch Toughness

Abstract

Some experiments were made to determine the effects of peeping on the residual stress relieving and the properties of the peened weld metal for the low-temperature brittleness in the butt weld joints, , which were prepared from two plates of 1200×500×19mm. by manual welds. Details of the specimens and the conditions of welding and peening are shown in Fig. 1, 2 and Table 1-5, respectively.
The residual stresses as welded and after peened were mesured by three methods successibly, for the purpose of increasing the reliability of the measured data.
Electric resistance strain gauges were fastened on the plates, as shown in Fig. 4, which then was drilled as follows:
1. One Hole Relaxation
2. Two Hole Relaxation
3. Plug Relaxation
4. Slit Relaxation
Austrian tests were conducted as the extensive experiments to research the effects of peening on the low temperature brittleness of the weld metal.
Measured residual stresses are shown in Fig. 5-8, and the results of Austrian Tests conducted at the range of -650°C... -70°C are shown in Table 6, respectively.
Summary results of measured longitudinal residual stresses are shown in Table 7.
Fig. 8 represents the summary of longitudinal mean stress resulted from the various peeping conditions. Except for the specimen No. 2, in Fig. 8, longitudinal stresses were considerably reduced by peeping compared with the as-welded specimen, namely in the specimen No. 3, peening lowered the longitudinal stress of 28 kg/mm² tension.
The following conclusions appear to be warranted:
1. The first laver shall not be peened.
2. Peening of the last layer should be considered a dangerous practice which greatly increases the hazard of low temperature brittleness.
3. Hot peening confers the undesirable effects on the properties of weld metal.
4. The welds shall not be over peened.
5. As the stress relieving procedur, peening only the last layer by 2-in. stroke is even effective.
6. Transverse stresses were lowerd to some extent by peening.