机械加工零件表面烧伤的金相检验

Metallographic Testing for Surface Burning of Machined Parts

高碳钢淬硬件和渗碳淬硬件等在磨削时,会由于磨削工艺不当,如磨削余量过大、冷却不充分或砂轮选用不当等,产生烧伤,不仅降低零件的表面硬度,严重时还会产生裂纹,甚至导致零件报废。此外,线切割加工也会使零件发生烧伤。零件的烧伤实质上与过大的磨削热或线切割热使零件表层达到高温而发生相转变产生变质层有关,可根据这一点采取防止零件发生烧伤的措施。

The hardened parts of high-carbon steel or the parts carburized and hardened all are subjected to burning during grinding,owing to unsuitable grinding process,for example,excessive grinding allowance,unsufficient cooling,use of unallowable abrasive wheel and so on.The burning will cause part to exhibit lower surface hardness,more serious,will cause part to crack,even to be scrapped.In addition,wire-electrode cutting is likely to burn part,too.Substantially,the burning of part is concerned with that either grinding heat or wire-electrode cutting heat is large enough to permit part case to reach a higher temperature,thus transformation to occurs and to develop a case where nature is changed.In view of the above,the measures preventing part from burning may be adopted.