冷拉型钢在拉伸过程中会出现塑性变形,从而产生位错和局部的残余应力,由此可见,残余应力是由于工件在制备过程中,在构件内部产生的应力。在无外力作用下,以平衡状态存在于物体内部的应力。它不只存在压应力或拉应力,而是同时存在与之平衡的拉应力或压应力,理论上其数值不应该超过材料的屈服强度。
Cold-drawn section steel will undergo plastic deformation during the stretching process, which will cause dislocations and local residual stress. It can be seen that the residual stress is due to the stress generated in the component during the preparation of the workpiece. In the absence of external force, the stress existing in the object in a balanced state. It not only exists compressive or tensile stress, but also tensile or compressive stress that is balanced with it. Theoretically, its value should not exceed the yield strength of the material.
冷拉型钢之所以存在残余应力,原因是多方面的,一方面是不均匀变形引起的,塑性变形后,载荷去除后内部由于变形形成的应力;另一方面是热作用的结果,冷却过程中外部冷却快,内部冷却慢,因而外部呈现拉应力,内部呈现压应力状态;还有因为相变等等原因产生的热残余应力。还有一方面则是因为化学作用产生的应力。
There are many reasons for the residual stress of cold-drawn section steel. On the one hand, it is caused by uneven deformation. After plastic deformation, the internal stress caused by deformation after the load is removed; on the other hand, it is the result of thermal action and the cooling process. The internal and external cooling is fast, and the internal cooling is slow, so the tensile stress is present on the outside and the compressive stress is present on the inside; there is also thermal residual stress due to phase change and other reasons. On the other hand, it is due to the stress caused by chemical action.
为了能消除冷拉型钢中的残余应力,首先需要调整制备工艺参数,因为在冷拉型钢制备工艺过程中,大多阶段都可以引入残余应力,包括合金熔炼、锻造,轧制,焊接,切削等加工过程、热处理冷却等都会导致残余应力产生,因此首先要做的就是调整工艺参数。 然后是通过低温热处理,消除内部残余应力,也就是我们常说的去应力退火;或者是振动消除,用便携式强力激振器,使金属结构产生一个或多个振动状态,从而产生如同机械加载时的弹性变形,使零件内某些部位的残余应力与振动载荷叠加后,超过材料的屈服应力引起塑性应变,从而引起内应力的降低和重新分布。
In order to eliminate the residual stress in cold-drawn section steel, the preparation process parameters need to be adjusted first, because during the cold-drawn section steel preparation process, residual stress can be introduced in most stages, including alloy melting, forging, rolling, welding, cutting and other processing. Process, heat treatment and cooling will cause residual stress, so the first thing to do is to adjust the process parameters.Then, low-temperature heat treatment is used to eliminate internal residual stress, which is often referred to as stress relief annealing; or vibration elimination, using a portable powerful exciter, to make the metal structure generate one or more vibration states, so as to produce mechanical loading Due to the elastic deformation of the part, the residual stress in some parts of the part is superimposed with the vibration load, and the plastic strain is caused by the yield stress of the material, which causes the reduction and redistribution of the internal stress.