Cold-drawn Seamless Steel Tubes Skin Cracking Reason Analysis

In the production and use of seamless steel tubes, cracking and skinning not only affect the quality of the product, but also may bring serious safety hazards.

Seamless steel tubes cracking and skin mainly from the material itself and the flaws in the production process, part of the reason is that the production process of steel tubes, improper heating, deformation pressure is too large and other process operations.

First, the material itself

1. Non-metallic inclusions in the steel billet in the cold drawing process will lead to stress concentration, becoming the starting point for warping or cracking. The presence of inclusions disrupts the continuity of the material, reducing the strength and toughness of the steel tubes.

2. Internal defects in the billet, pores within the billet may expand during the cold drawing process, forming surface defects. Uneven composition can lead to localized strength deficiency and increase the risk of cracking.

3. If the purity of the raw material is low and the impurity content is high, it will directly affect the cold drawing performance of the steel tubes and increase the possibility of cracking.

Zhangjiagang Huagang Industrial Co.,Ltd., the raw material selection of Baosteel, Huaigang Steel, Zhongtian and other high-quality mills round steel, to ensure that the steel composition is stable, high purity, reduce non-metallic inclusions and internal defects, to ensure the quality of materials from the source.

Second, the reasons for the production process

1. Too high or too low heating temperature will affect the plasticity and toughness of the material. Too high a temperature may lead to coarse grains, too low a temperature will make the material harden, easy to crack when cold drawing.

2. During cold drawing, if the deformation is too large, the material is subjected to stresses exceeding its yield strength, which may easily lead to surface cracking or buckling.

3. Insufficient lubrication will increase the friction between the steel tubes and the mould, resulting in local overheating and stress concentration, triggering warping or cracking.

4. Improper mould design can lead to uneven stress distribution, increasing the risk of cracking. Wear and tear of the mould can also lead to uneven deformation and formation of surface defects.

5. Too fast drawing speed will increase the material stress, leading to uneven local deformation and increasing the risk of cracking.

Zhangjiagang Huagang Industrial Co.,Ltd. in the production process to strictly control the drawing speed, reasonable control of deformation, strengthen the lubrication conditions and mould design, to ensure the stability of the cold drawing process.

Third, the impact of heat treatment process

1. Insufficient annealing will lead to high residual stress within the material, easy to crack when cold drawing.

2. Too fast cooling rate will lead to excessive tissue stress, increasing the tendency to crack.

3. Inaccurate control of normalising, annealing, tempering temperature will affect the organisational properties of the material, resulting in defects in cold drawing.

Zhangjiagang Huagang Industrial Co.,Ltd. in the heat treatment process, clearly marked normalising, annealing, tempering temperature, speed and other parameters to ensure that the annealing is sufficient to eliminate residual stress, control the cooling rate to avoid excessive tissue stress to ensure that the material properties to meet the requirements.