Pull Rail Investigation Report

920 Words4 Pages
Pull rod made of 30CrNiMo8 steel in the ATOX grinding mill are used to exert grinding pressure on the rollers. The grinding forces are transmitted vertically by the 3 pull rod which is placed at 1200C apart directly into the hydraulic cylinder. This paper describes the metallurgical investigation that was carried on a failed pull rod to understand the cause of failure. Fracture surface of the failed pull rod showed multiple ratchet mark indicated that the crack was initiated at multiple regions. Higher fatigue zone (55%) with low over load region (45%) indicated that the load was light, but there were high stress concentration zone on the pull rod. Macro etch test and microstructure analysis clearly indicated the presence of a non- homogeneous…show more content…
Multiple ratchets marking indicates that crack was initiated from several location of pull rod. This might have resulted due to high stress or high stress concentration. 2. The measured overload zone was 45% which is less than the fatigue zone (55%). 3. The presence of ratchet marks indicates a multiple origin of crack. 4. Several ratchet marks and low over load region indicates that the load was light, but there were high stress concentration. 5. Morphology of fracture surface indicates the failure was due to one side bending load from the crack initiation region. 6. The side of ratchet mark was perpendicular to the fracture surface which indicates that the plane bending or tension caused the failure. 7. The sharp corners are visible on the fracture surface which indicates the presence of stress concentration at that area. 8. Stress concentration are arise due to several reason such as poor radius of curvature, weld repair on the pull rod, slag inclusions, corrosion etc. 9. The material removal was in a flaky manner. At some location cracks were present at the core region, not at the surface. 10. It was informed that no other related failure such as bolt, nuts was taken place along with the pull…show more content…
Small overload region and large fatigue region associated with multiple ratchet marks on the fracture surface indicates that the load was light but there were high stress concentration at the crack initiated region. 2. Chemical Analysis revealed that the pull rod material conformed to EN 10083-2 grade 30CrNiMo8, as specified by the customer. 3. Unbroken dendritic structure resulted in segregation at inter- dendritic region and other anomalies such as blow holes, inclusions resulted in hardness difference across the cross section of pull rod. 4. In the SEM-EDX analysis, presence of exogenous type inclusion was noticed at one of the crack initiated region. The exogenous type of inclusion created a stress concentration and generated cracks during the operation. 5. Mechanical properties of the material conform to the specification except the tensile strength. A low value of tensile strength resulted in reduction of fatigue property of the pull rod. 6. The failure was caused by low cycle fatigue, which was initiated due the presence of exogenous type of inclusions in the pull rod. The de-cohesion of inclusions creates the development of micro cracks at the surface and caused the local stress concentration and of crack initiation and propagation along the inter dendritic region by fatigue mode (refer fig

More about Pull Rail Investigation Report

Open Document