Analysis of broken wire failure of the hottest ste

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Failure analysis of broken wire of steel rope

Abstract: the causes of broken wire of steel rope in use are analyzed. Through the analysis of optical metallography, electronic metallography and micro area composition, it is concluded that the structure growth of steel wire after sorbitic is incomplete, so it is easy to initiate cracks in the area of incomplete growth of sorbitic structure in the subsequent cold drawing process, so that the wire rope breaks during service

key words: steel wire; Broken wire; Sorbite; Failure

entrusted by a factory, the microstructure and fracture causes of broken steel wires and steel wires of different processes in the factory were analyzed. Broken wire production process:

will Φ Hot rolled wire of 6.5 is drawn to Φ 3.2 → heat treatment (sorbitic treatment) → drawing Φ 1.3 then twist the rope

the wire rope was found broken after being used for a short time (15 days) after leaving the factory. It can be observed that there are many broken wires on different strands within a length. The manufacturer requires to analyze the samples and broken wire samples at different process stages to find out the failure causes, so as to improve the steel wire production process and improve the steel wire quality

1 analysis sample

1# Φ 3.2 mm steel wire—— Φ 6.5 mm cold drawn to Φ 3.2 mm after sorbitic treatment

2# Φ 1.3 mm steel wire—— Φ 3.2 mm cold drawn to Φ 1.3 mm

3# Φ 1.3 mm steel wire - stranded steel wire

4# Φ 1.3 mm steel wire - fracture after use

2 physical and chemical examination

2.1 chemical composition of broken wire

see the following table

2.2 macro examination

the surface observation of the broken steel wire rope shows that there are steel wire fractures in each strand of the steel wire rope, the location of the broken wire is relatively scattered, and there are different degrees of wear at the broken wire position

Figure 1 SEM 700 × Macroscopic fracture of steel wire

2.3 fracture observation

after ultrasonic cleaning, the fracture is observed under the scanning electron microscope. Figure 1 is the SEM fracture photo of steel wire 4# sample, and the white bright area of the fracture is the repeated wear and deformation area of the steel rope in service. The fracture is characterized by brittle fracture and local plastic deformation zone. At high magnification, some intergranular cracks and quasi cleavage fracture morphology in the grain can be seen (Fig. 2), and the fracture morphology of longitudinal cracks connected along the grain boundary can be seen (see Fig. 3)

Figure 2 therefore SEM 990 × Some intergranular cracks and Fig. 3 SEM 1500 × Longitudinal crack along the quasi cleavage fracture morphology in the grain boundary

fracture morphology after grain boundary connection

2.4 inclusion morphology distribution and grade

optical metallographic microscope after inlaying, grinding and polishing 100 × Observe the inlaid 1 # - 4 # sample, and evaluate it according to Yb standard. The results are as follows: there are a small amount of granular brittle inclusions, the grade is about grade 1; The level of plastic inclusions is about 1, which are divided into 2. The main machine adopts imported servo electromechanical and servo speed regulation system, and the ball screw is scattered

2.5 impurity element distribution analysis

the surface scanning analysis of sulfur and phosphorus segregation of 1 # and 4 # samples was carried out by electron probe. The results showed that there was no obvious segregation of S and P elements

2.6 microstructure morphology

the sample was etched with 4% nitric acid alcohol after inlaying, grinding and polishing. It was observed under light microscope and scanning electron microscope that the 1# sample after early cold drawing and heat treatment was small, and its size was about 10 μ M, a small amount of ferrite is distributed along the interface at the local part of the cluster boundary, in a shape of (see Figure 4), and the internal part is sorbite structure

this 5. Measure the progress of new material development through a series of data to provide continuous power for automotive product development and design and technological innovation. The structure is composed of different forms of sorbite, one part of which is fine lamellar sorbite structure, and near the group boundary, there is a part of which presents non layered ferrite strips, and granular carbides are distributed on the block lamellar matrix; The carbide sheet appears in the shape of bending and bifurcation, and the phenomenon of incomplete growth of sorbite structure appears (see Fig. 5). Small cracks along the drawing direction are observed on the 3 #, 4 # samples (see Fig. 6 and Fig. 7)

3 result analysis

from the above analysis, it can be seen that the chemical composition, impurity content, inclusion distribution and grade of raw materials meet the requirements of steel wire, but the service time of steel wire is very short (only 15 days). The observation of fracture morphology gives a very important information, that is, the crack first sprouts from the interface and grows simultaneously with the interface along the drawing direction until it is connected along the interface. The observation of microstructure shows that there are incomplete continuous ferrite like and non layered ferrite blocks and carbides at the interface, and the growth of lamellar sorbite is incomplete. The accumulation of this kind of carbide makes ferrite not grow with it, resulting in a non layered area, which is 3% larger μ About M, the small one has 1 μ M or so. Due to the appearance of ferrite or blocks at the interface, the deformation process is concentrated near the interface, and the deformation variables in these areas are very high, so it is easy to initiate cracks and propagate along the interface, resulting in early fracture. The lamellar spacing of normal heat-treated steel wire is small and uniform and continuous, and the tissue deformation is coordinated in the subsequent drawing process without early small cracks along the drawing direction; In this sample, the precipitation of pre eutectoid ferrite leads to the divorced growth of ferrite and carbide. In the subsequent drawing process, the difference of structural deformation is obvious, and the deformation and slip cannot be generated synchronously. Dislocation accumulation is formed locally and internal stress is generated, resulting in the crack source at the interface between ferrite and sorbite or carbide. From the above observation and analysis, it can be determined that this sample Φ The failure of 3.2 mm steel wire is related to the process from the formation of homogenized austenite by heating to lead quenching


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