眼镜框架用316L不锈钢丝性能不均及模压缺陷

Inhomogeneity of properties and defects after die pressing of 316L stainless steel wire for glasses frame

对企业生产的眼镜框架用316L不锈钢丝试样的微观组织、表面缺陷及夹杂物进行观察,对试样力学性能进行测试,分析模压前钢丝的头尾部性能异常以及模压后产品的表面缺陷成因。结果表明:钢丝头部试样的抗拉强度在700 MPa左右,规定塑性延伸强度为300 MPa,伸长率接近50%,而尾部试样的抗拉强度达到了900 MPa,规定塑性延伸强度达到700 MPa,伸长率在20%左右。性能差异是由于,退火初期钢丝走线速度较慢,退火过程中提高了走线速度,因而尾部钢丝退火时间较短,同时退火温度变低,使得尾部钢丝的组织内应力未完全消除,导致其强度较高,塑性较差。对模压变形后缺陷钢丝的分析表明:不合格试样的组织分布不均匀,晶粒尺寸达到29.7μm,合格试样的晶粒尺寸为20.9μm;不合格试样表面存在暗灰色的夹杂物,EDS分析表明,夹杂物为钙基硅酸盐及硫化物,夹杂物处容易发生点蚀,从而形成凹坑、牙齿印等缺陷。

The abnormal properties from starting section to ending section before die pressing and the surface defects of 316 L stainless steel wire for glasses frame after die pressing was analyzed. The microstructure of the specimens,surface defects and inclusions were observed,and the mechanical properties were tested. The results show that the specimen of starting section possesses tensile strength of 700 MPa,yield strength of 300 MPa and the elongation of nearly 50%. In comparison,the specimen of ending section has tensile strength of 900 MPa,yield strength of 700 MPa and the elongation of 20%. This difference is owing to the increase of working speed in the process of annealing. For the ending section of steel wire,a rapid working speed shortens the annealing time and lowers its annealing temperature. As a result,the residual stress is retained in the ending section of steel wire,which results in a higher strength value as well as a lower elongation. Analysis of the defected steel wire after die pressing suggests the microstructure of the unqualified specimen is inhomogeneous. The grain size of unqualified specimen reaches 29. 7 μm,while that of qualified specimen is 20. 9 μm. Additionally,some dark-grey inclusions are found on the surface of unqualified specimen. Energy dispersive spectroscopy（ EDS） results show that these inclusions are composed of calcium silicate and sulfide. Pit corrosion is prone to take place around these inclusions,in which some eroded craters are formed.