1. Definition of cold drawn seamless tube tensile test
Tensile test can determine a series of strength and plasticity indexes of cold drawn seamless pipe. Strength usually refers to the ability of cold drawn seamless pipes to resist elastic deformation, plastic deformation and fracture under the action of external force. When the cold-drawn seamless pipe is subjected to a tensile load, the phenomenon that the load does not increase but continues to undergo obvious plastic deformation is called yielding;The stress when yielding is called the yield point or the physical yield strength, and is expressed by σS (Pa). In many cases, the cold-drawn seamless pipe does not have an obvious yield point. Usually, the stress value when the residual plastic deformation of the cold-drawn seamless pipe is 0.2% is used as the yield strength, which is called the conditional yield limit or the conditional yield strength, which is expressed by σ0.2 ; The maximum stress value of the cold-drawn seamless pipe before fracture is called tensile strength or strength limit, expressed by σb (Pa).
Plasticity refers to the ability of cold drawn seamless pipes to plastically deform under load without damage. The commonly used plasticity indicators are elongation and section shrinkage. Elongation, also known as elongation, refers to the percentage of the ratio of the total elongation to the original length after the cold-drawn seamless pipe sample is broken by tensile load, expressed by δ; the section shrinkage refers to the cold-drawn seamless pipe sample. After being broken by tensile load, the percentage of the ratio of the area reduced by the section to the original section area is expressed by ψ.
2. Test method
Tensile tests are carried out on a material testing machine. There are mechanical, hydraulic, electro-hydraulic or electronic servo-type testing machines. The sample type can be the full section of the cold drawn seamless pipe, or it can be processed into a round or rectangular standard sample. Some physical samples such as steel bars and wires generally do not need to be processed and keep their full cross-sections for testing. During the preparation of the sample, the structure of the cold-drawn seamless tube should be avoided from being affected by cold and hot processing, and a certain smoothness should be guaranteed.
During the test, the testing machine uniformly stretches the sample at a specified rate, and the testing machine can automatically draw a tensile curve. For materials with good plasticity such as low carbon steel, when the sample is stretched to the yield point, the force measuring pointer has obvious jitter, and the upper and lower yield points (and) can be separated.In the calculation, the δ and ψ of the material are often taken, which can be calculated by splicing the specimens after the test fracture, and measuring their elongation and section shrinkage.