Failure Analysis of Roller squeezed _734

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Failure Analysis of Roller squeezed

Table 1 Physical and OOCrl9Nil0 squeezed roller tube between the composition of steel (mass fraction,%) casing material CSiMnCrNiCuMo kind 0.0770.425.62911.803.141.090.12l8. O08. O000Crl9Nil0 ≤ O. 030 ≤ 1.00 ≤ 2.00-20.00-12.001.3 microscopic observation of the crack will be squeezed source roller tube placed in the fracture scanning electron microscopy and found that the wall is thin (about 6 .20 ram) machined at the inner wall of the line near the source region for the crack (see Figure 4), and its morphology shows oxidation features high power, end-off area on the wall near the outer wall of the casing, low power features of shape show scratches (see Figure 5), the fatigue crack propagation area striation characteristic morphology (see Figure 6). Figure 4 Morphology of crack source of low-fold Figure 5, the casing end wall off areas of low topography 6 times high magnification morphology of the crack extension sleeve fracture of 1.4 Metallographic examination roll sleeve fracture in squeezed two samples taken near test for metallographic examination, was found near the fracture for the welding of the organization, No. 5, Li et al: Failure Analysis of Roller squeezed hold 511 samples the phenomenon of lack of penetration exists, see Figure 7.2 # base metal specimen cracks and weld fusion area, the crack extended to the base metal as shown in Figure 8. Weld metal ferrite, austenite, austenitic base metal organizations. Figure # 71 Figure 82 Fracture morphology sample sample sample fracture surface morphology of 1.5 times the test will fail squeezed low roller casing near the outer wall of polished fracture surface, with ferric chloride aqueous solution of hydrochloric acid etching method of cold low-fold test and found there in the fracture near the welding characteristics of low magnification, shown in Figure 9. Figure 9 near the outer wall of the fracture morphology of low-1.6 times the tube squeezed roll hardness testing hardness of the casing 187,197,185,197,200,190 HBW. 2 results of a comprehensive discussion of 2.1 results from the above experimental results, the failure squeezed roller casing materials and design requirements 00Crl9Nil0 steel does not match; metallographic examination found that there is welded casing features in the fracture site, indicating that The casing is the use of circumferential butt welding method of splicing, the casing wall of the local area with the phenomenon of lack of penetration, the casing of the parent organization for the austenitic material, weld metal ferrite + austenite; sets The hardness of base metal tube :185-200HBW. Roll squeezed macroscopic morphology of the casing shows off I21, thin tube wall thickness is about 6.2 area / / 1 / / 1, the existence of the near wall region is similar to the traces of machining lines, and its maximum depth on the wall about 21/l/lq, this is when the two casing ring butt weld end near the wall in the local area due to lack of penetration, a sleeve fracture of the source of defects, the crack from there extended to the outer wall, and gradually extended to both sides of the casing off the entire cross-section area in the split end opposite the location of the source area, morphology displayed in the presence of fatigue crack propagation area striation. 2.2 Fracture Analysis squeezed squeezed roll roll in the service process, the entire roll body loads are cyclical, the cyclical loading on the surface of the roller body for the stress, but it was pulled for the casing wall stress. Existence of welding defects as the casing wall, under the effect of tensile stress in the formation of fatigue source easy to crack the casing along the radial and circumferential expansion, eventually leading to squeezed roll body fracture. Although the general squeezed roller sleeve forces suffered less, but because of the thinnest wall of the inner wall of the casing there deeper defects, where more than the actual thickness of only 4mm, and the design drawings the original wall thickness of casing 10mill, so the crack in a short period of time through the wall, leading to early failure occurred squeezed roll. In addition, the casing material is not used in the design requirements 00Crl9Nil0 austenitic stainless steel, the mechanical properties of steel with 00Crl9Nil0 different sources is also easy to produce and accelerate the corrosion fatigue fracture of the factors. 3 Conclusions and recommendations of the failure of the tube is not squeezed roll 00Crl9Nil0 steel design requirements, and the method is the use of circumferential butt splicing, welding serious uneven wall thickness and the thinnest wall thickness is less than the design requirements 10InlTl 50% of the thinnest in the inner wall of the wall near the welding defects also exist, resulting in squeezed roll in the formation of cyclic fatigue crack under stress source, and rapid expansion, resulting in early failure. According to the testing and conclusions, the following recommendations. (1) the use of the casing material should meet the design requirements, the use of 00Crl9Nil0 steel. (2) squeezed is best not to roll the sleeves welded splicing process. (3) If the squeezed tube roll splicing by welding, the welding quality of the casing should be strictly checked. Revised manuscript received date :2009-05-06
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