Mechanical properties of steel pipe:
1. Yield point (σs)
Steel sample or stretching, when the stress exceeds the elastic limit, even if the stress is no longer increases, while the steel samples continue to occur or significant plastic deformation, this phenomenon is called the yield, and produce a minimum yield stress phenomena i.e. For the yield point. Let Ps be the external force at the yield point s, Fo is the area of the specimen, then the yield point σs = Ps / Fo (MPa), MPa called MPa equal to N (Newton) / mm2, (MPa = 106Pa, Pa: Pascal = N / m2)
2. Yield strength (σ0.2)
Some metallic material yield point very obvious, there are difficulties in measuring, and therefore to measure the yield characteristics of the material, a predetermined residual permanent plastic deformation is equal to a predetermined value (typically 0.2% of the original length) stress, known conditions Yield strength or yield strength σ0.2.
3. Tensile strength (σb)
The maximum stress value achieved by the material during the stretching process from the beginning to the occurrence of the breakage. It represents the ability of steel to resist fracture. And tensile strength corresponding to the compressive strength, bending strength and so on. Let Pb be the maximum tensile force before the material is pulled off, Fo is the cross-sectional area of the specimen, then the tensile strength σb = Pb / Fo (MPa).
4. Elongation (δs)
After the material is broken, the length of the plastic elongation is the elongation or elongation as the percentage of the original sample length.
5. Yield ratio (σs / σb)
The yield point (yield strength) of steel and the ratio of tensile strength, called the yield ratio. The higher the strength ratio, the higher the reliability of structural parts, the general carbon steel yield ratio of 0.6-0.65, low alloy structural steel 0.65-0.75 alloy structural steel 0.84-0.86.
Hardness means the ability of the material to withstand the hard objects into its surface. It is one of the important performance indicators of metal materials. The higher the hardness, the better the wear resistance. Commonly used hardness indicators are Brinell hardness, Rockwell hardness and Vickers hardness.
⑴ Brinell hardness (HB) at a constant load (typically 3000kg) to a certain size (diameter typically 10mm) hardened steel ball pressed into the surface of the material, for a time after removal of a load, the load ratio of its indentation area, Is the Brinell hardness (HB), in kilograms per square meter / mm2 (N / mm2).
⑵ Rockwell Hardness (HR) When HB> 450 or the sample is too small, can not use Brinell hardness test and use Rockwell hardness measurement. It is a vertex angle of 120 ° diamond cone or diameter of 1.59,3.18mm ball, under a certain load into the surface of the measured material, the depth of the indentation from the hardness of the material. According to the different hardness of the test material, divided into three different scales to represent:
HRA: is the use of 60kg load and diamond cone press the hardness obtained for high hardness materials (such as hard alloy, etc.).
HRB: is the use of 100kg load and 1.58mm diameter hardened steel ball, the hardness obtained for low hardness materials (such as annealing steel, cast iron, etc.).
HRC: is the use of 150kg load and diamond cone press device obtained hardness, for high hardness materials (such as hardened steel, etc.).
⑶ Vickers hardness (HV) to 120kg load and 136 ° angle of the diamond square cone press into the material surface, with the material indentation pits by the surface area of the load value, that is, Vickers hardness ( HV)