The mechanical properties of metal refer to the characteristics of metal under external force, mainly including the following indicators.
① Ultimate Strength σb: the maximum stress point on the tensile stress-strain curve, unit
Is MPa.
② Yield Limit σs: when the tensile stress of the material exceeds the elastic range and plastic deformation begins to occur Stress. There is no obvious yield plateau in the tensile stress-strain curve of some materials, that is, its yield cannot be clearly determined Points. In this case, it is specified in engineering that the stress value of 0.2% residual deformation of the sample is taken as the conditional yield limit σ0.2 is expressed in MPa.
③ Endurance Limit : creep fracture of the sample after a certain time at a given temperature
Average stress at crack. In engineering, it is usually expressed by the average stress value of the sample when it breaks for 105h at the design temperature The bit is MPa.
④ Creep Limit: make the sample produce a certain amount of The stress value of creep. The stress value table of steel at design temperature for 105h and creep rate of 1% is usually used in engineering Is in MPa.
⑤ Percentage Elongation δ8: indicates that when the sample is damaged in tensile test Percentage of plastic elongation. It is an index to measure the plasticity of steel. The original length of the sample is generally selected as the straight length of the sample
5 times or 10 times the diameter, so the sample has δ5 and δ10, in%.
⑥ Reduction of Area ψ: indicates that when the sample is damaged in the tensile test
Raw plastic deformation rate. It is another indicator to measure the plasticity of materials, expressed in%.
⑦ Impact Value Ak: It is a measure of steel toughness and determines whether the steel has brittle failure Indicator, unit: J.
⑧ Hardness: reflects the resistance of the material to local plastic deformation and the wear resistance of the material. There are three types of hardness tables Indicating methods, i.e. Brinell hardness HB, Rockwell hardness HR and Vickers Vickers Diamond Hardness HV has different measuring methods and application ranges. According to experience There is an approximate relationship between hardness and tensile strength as follows: rolled and normalized low carbon steel σb=0.36HB; Rolled and normalized medium carbon Steel or low alloy steel σb =0.35HB; The hardness is 250 ～ 400HB, and the heat-treated alloy steel σb =0.33HB.
Due to the convenience of measurement, the hardness of the heat-affected zone is also commonly used to determine the degree of hardening of welded joints.
–本文内容摘抄自《压力管道设计及工程实例》
Post time: Feb-07-2023
