The healing of quenched crack in 1045 steel under electropulsing
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Specimens of 1045 steel with quenched crack were treated under electropulsing. Scanning electron microscopy was employed to examine the change of specimens before and after the treatment. The results showed that the crack can be healed under electropulsing without melting, and the healing could be produced within a very short time. The original microstructure of specimens was not changed during the healing. It is thought that the temperature and the transient thermal compressive stress caused by high-rate heating are the main factors causing the healing of the crack.
It is well known that cracks can be healed when the material with cracks is put into an environment with high temperature and high compressive stress for some time. However, the method is useless in many cases because the performances of material will be changed in this environment and the changes are not desirable. In the study of the reversing effect of electropulsing on the damage, we reported that the treatment of electropulsing can produce healing effects on the crack. Moreover, it has been shown that the method has two special characteristics: (i) The detection of the crack is automatic, and (ii) The effect of repair on the uninjured part is small.1 Therefore, the method has attractive prospects. A problem in our prior work was that we never compared the change in the same crack before and after the electropulsing treatment, so we never got direct proofs of healing. The aim of this paper is to solve this problem. The material used in the present investigation was 1045 steel, having a composition (in wt%) of 0.46 C, 0.62 Mn, 0.26 Si, 0.022 P, and 0.016 S. The specimens were heated to 1113 k for 10 min and then quenched in water to produce cracks. The surfaces of specimens were mechanically polished. The final size of specimens was 0.2 mm thick, 2.5 mm wide, and 45 mm long. The cracks penetrating the specimen were chosen for investigation. A JSM-6301F scanning electron microscope (JEOL Ltd., Tokyo, Japan) was employed to observe the change of specimens before and after the electropulsing treatment. Electropulsing was generated by capacitor discharging. The peak voltage of the pulse generator is 2000 V, and the pulse duration is 200 s. Here, the experimental volt-
a)
Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 16, No. 1, Jan 2001
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age was 1350 V, and the specimens were treated by a single pulse. The reasons for using 1045 steel are: (i) Cracks can be made easily by quenching, and (ii) it can be seen that the effect of repair on the uninjured part is small with the evidence of martensite being free from destruction during the treatment. Figure 1(a) shows the morphology of a crack before electropulsing. The morphology of the same crack after electropulsing is shown in Fig. 1(b). As a result of electropulsing treatment, there is a color change around the crack, the average width of the crack is decreased, and some parts of the crack are healed.
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