Failure analysis of machining defects

2019-03-21 10:16:26 4

In the process of machining, there may be various defects. The following sections analyze some defects and determine what defects are based on their respective conditions. Let's take a look at them.

1.Forging and folding

        The metallographic sample of the defect section was observed under a microscope, and the defect tail was round and blunt, and the sides were smooth and there was obvious oxidation. No foreign matter distribution such as material inclusions was found in the defect. After cold metal corrosion corrosion of the metallographic specimens, the defects and their sides have serious decarbonization and oxidation. The surface morphology of the defect layer is observed. The plastic deformation marks are obvious, and there is no tearing fracture. appearance. After microhardness test and metallographic observation, there are different degrees of carburization and hardening on the surface of the defect layer. It indicates that the defect should exist before the heat treatment quenching and communicate with the outside world to determine that the defect is a forged folding.

2. Forged over burned

       The metallographic specimens taken along the defect section were observed under the microscope. It can be seen that the pores are distributed on the surface and the subsurface. The localities are sharp-angled, different in size, deep in the bottom, and there are fine cracks on the edges. Some areas have appeared. Grain boundary oxidation phenomenon, this defect is forged over-burning.

3. Quenching crack

       It is distributed in the circumferential direction, and the tail is tapered. After the crack is cut out, the metallographic sample is observed. It can be seen that the crack is very deep and is substantially perpendicular to the outer surface. No foreign matter such as material inclusions is found in the crack. After the fracture was made along the crack, the fracture was a brittle fracture, and the fracture surface had obvious tempering color. The defect was quenching crack.

4. Grinding cracks

       The magnetic traces are concentrated in the middle part, and are long-line or dendritic in the circumferential direction. The partial bifurcation and the magnetic traces converge. After the metallographic specimen of the crack section is prepared, the crack is fine and perpendicular to the surface. No foreign matter distribution such as material inclusions and scales were observed. After detecting the surface stress, the test results showed that the surface crack of the raceway was a grinding crack.

5. Raw material crack

       After the metallographic sample was taken along the crack section, it was observed that there was a large amount of alumina inclusions on the crack surface, and the crack was analyzed as a material crack.

       Materials should be able to grasp the defects that are easy to occur under various conditions during the machining process. Such as raw material materials, manufacturing methods, working media and other types of defects that may occur, in order to accurately analyze the cause when determining defects, and take improved process measures to prevent defects.