How to distinguish between hot-rolled and cold-drawn stainless steel seamless tubes

Hot rolling and cold rolling are both stainless steel seamless tube forming processes, they have a great impact on the organization and performance of stainless steel tubes, rolling of stainless steel tubes is mainly based on hot rolling, cold rolling is only used to produce small diameter stainless steel seamless tubes.


A.hot-rolled stainless steel seamless pipe
Advantages: can destroy the ingot casting organization, refining the stainless steel tube grain, and eliminate microstructural defects, so that the stainless steel tube organization is dense, mechanical properties are improved. This improvement is mainly reflected in the direction along the rolling, so that the stainless steel tube is no longer isotropic to a certain extent; bubbles, cracks and sparseness formed during casting, can also be welded together under the action of high temperature and pressure.
Disadvantages: 
1. After hot rolling, the non-metallic inclusions (mainly sulphides and oxides, and silicates) inside the stainless steel tube are pressed into thin sheets, and the phenomenon of delamination (sandwiching) occurs. Delamination makes the stainless steel tube along the thickness direction of the tensile properties greatly deteriorated, and there is the possibility of interlayer tearing when the weld shrinks. Weld shrinkage induced local strain often reaches the yield point strain of several times, much larger than the load-induced strain.
2. Residual stresses caused by uneven cooling. Residual stress is the internal self-phase equilibrium stress in the absence of external forces, a variety of cross-sectional hot-rolled stainless steel seamless pipe have such residual stress, the larger the general stainless steel seamless pipe cross-sectional size, the greater the residual stress. Although the residual stress is self-balancing, but the performance of the steel member under the action of external forces still has a certain impact. Such as deformation, stability, fatigue resistance and other aspects may have a negative effect.

B.cold rolled stainless steel seamless tube
Refers to the cold processing of steel plates or strips into various types of stainless steel tubes after cold drawing, cold bending, cold drawing, etc. at room temperature.
Advantages: fast forming, high yield, and no damage to the coating, can be made into a variety of cross-sectional forms to adapt to the needs of the conditions of use; cold rolling can make a large plastic deformation of stainless steel tubes, thereby improving the yield point of stainless steel tubes.
Disadvantages: 
1.although the forming process did not go through the hot state plastic compression, but there are still residual stresses within the cross-section, the overall and local yielding characteristics of the stainless steel tube is bound to have an impact;.
2.cold rolled stainless steel seamless tube style is generally open section, making the free torsional stiffness of the section is low. Easily twisted when bent, easily bent and torsionally buckled when compressed, with poor torsional resistance.
3.cold-rolled stainless steel seamless tube wall thickness is smaller, and not thickened at the corner of the plate articulation, the ability to withstand localized concentrated load is weak.

C.the main difference between hot-rolled and cold-rolled
1. cold rolled stainless steel seamless pipe allows the section to appear local buckling, so that you can make full use of the bearing capacity of the rod after buckling; while hot rolled stainless steel seamless pipe does not allow the section to occur local buckling.
2.hot rolled stainless steel seamless tube and cold rolled stainless steel seamless tube residual stress is generated for different reasons, so the distribution on the cross-section is also very different. The distribution of residual stress on the cross-section of cold-formed thin-walled stainless steel seamless pipe is bending type, while the distribution of residual stress on the cross-section of hot-rolled stainless steel seamless pipe or welded stainless steel seamless pipe is film type.
3. the free torsional stiffness of hot rolled stainless steel seamless pipe is higher than that of cold rolled stainless steel seamless pipe, so the torsional resistance of hot rolled stainless steel seamless pipe is better than that of cold rolled stainless steel seamless pipe.
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