Cracking during flattening tests on seamless steel tubes is a common quality issue, often revealing certain defects in material, manufacturing process, or handling. Through years of production practice and quality analysis, Changzhou Tenjan Steel Tube Co., Ltd. has summarized a systematic set of cause analysis and solutions.

Material Quality Factors

Deviation in chemical composition is one of the most fundamental causes. When the content of elements such as carbon, sulfur, and phosphorus in the steel exceeds the standard range, it directly affects the material's plasticity and toughness. Changzhou Tenjan Steel Tube Co., Ltd. employs advanced spectrometers to conduct strict testing on each batch of raw materials, ensuring chemical composition is precisely controlled within the standard range. In particular, sulfur easily forms sulfide inclusions, which become stress concentration points during flattening, leading to crack initiation and propagation.

Analysis of Causes for Cracking During Flattening of Seamless Steel Tubes

Production Process Influences

Improper heat treatment process is a primary cause of flattening cracking. Changzhou Tenjan Steel Tube Co., Ltd. possesses fully automated heat treatment production lines, using computers to precisely control annealing temperature and holding time. If the annealing temperature is too low or the holding time is insufficient, the material cannot be fully softened, and its internal structure remains in a work-hardened state, failing to meet required plasticity indicators. Conversely, if the annealing temperature is too high, it may cause grain coarsening, which also impairs the material's plasticity.

Poor microstructure is directly related to flattening performance. Abnormal structures such as banded structure and Widmanstatten structure reduce the material's transverse plasticity. When the structure is non-uniform, differences in deformation capacity between different structures during flattening lead to stress concentration, thereby initiating cracks. The metallographic laboratory at Changzhou Tenjan Steel Tube Co., Ltd. regularly tests the microstructure of products to ensure a uniform and fine ferrite and pearlite structure is obtained.

Geometric Dimension Issues

Uneven wall thickness causes non-uniform deformation during flattening. Changzhou Tenjan Steel Tube Co., Ltd. utilizes advanced rolling equipment and process control systems to strictly control wall thickness deviation within the standard range. The thinner wall areas deform first and reach their plastic limit, while the thicker wall areas remain in an elastic state. This asynchronous deformation leads to stress concentration in the thin-walled regions, eventually causing cracking.

An unreasonable diameter-to-wall thickness ratio also affects flattening performance. When the ratio of outer diameter to wall thickness is too large, the bending stress borne by the tube wall during flattening increases significantly. The technical team at Changzhou Tenjan Steel Tube Co., Ltd. recommends the most suitable diameter-to-wall thickness ratio based on customer usage requirements, ensuring products exhibit good flattening performance.

Solutions to Cracking During Flattening of Seamless Steel Tubes

Inspection and Improvement Measures

To solve the flattening cracking problem, it is first necessary to strengthen raw material inspection. Changzhou Tenjan Steel Tube Co., Ltd. employs a comprehensive quality inspection system to conduct full-range testing and evaluation of raw materials. Chemical composition is ensured to be qualified through spectral analysis, and internal defects are detected using ultrasonic flaw detection, thereby controlling material quality from the source.

Optimizing the heat treatment process is crucial. Through extensive process testing, Changzhou Tenjan Steel Tube Co., Ltd. has established a comprehensive heat treatment process database. It is necessary to determine appropriate annealing temperature, holding time, and cooling rate based on the specific material and specifications of the steel tube, ensuring a uniform and fine ferrite and pearlite structure is obtained, granting the material good plasticity and toughness.

Through a perfected quality control system, Changzhou Tenjan Steel Tube Co., Ltd. has effectively addressed the flattening cracking issue. The company employs advanced heat treatment equipment to precisely control process parameters, ensuring uniform material structure and stable performance. Simultaneously, it is equipped with comprehensive inspection methods, conducting flattening test verification on each batch of products to guarantee that all outgoing products fully comply with standard requirements.