球化退火可消除过共析钢中的网状二次渗碳体.对 错

In this research GCr15 of the grains will be refined ball annealing and process.
GCr15 steel,prepare for heat treatment using spheroidizing annealing,is to make the steel spheroidization,improve carbide steel processing performance,and for the quenching organize well prepared.Finally,by grain refinement process heat to improve the performance of GCr15 steel,especially the fatigue life of improved,there are evident effects.
This topic with resistance furnace,microscope,hardness tester etc equipment,through general spheroidizing annealing,isothermal spheroidizing annealing,rapid spheroidizing annealing (namely piece.modified) prepare comparative experiments,discussion of the spheroidizing treatment heat best effect.In the final heat treatment,through conventional quenching + cryogenic tempering and circulation quenching process is compared,and get the best fine grains process.
Experiments show that the rapid prepare heat treatment spheroidization annealing (conditioning) get good results of spheroidal graphite.In the final heat treatment using circular quenching grain refinement effect is good,three times quenching refinement of grain can achieve 10 levels.
Keywords:GCr15 steel spheroidizing annealing grain refinement heat treatment

球化退火是使钢中碳化物球化而进行的退火工艺.将钢加热到Ac1以上20～30℃,保温一段时间,然后缓慢冷却,得到在铁素体基体上均匀分布的球状或颗粒状碳化物的组织.
球化退火主要适用于共析钢和过共析钢,如碳素工具钢、合金工具钢、轴承钢等.这些钢经轧制、锻造后空冷,所得组织是片层状珠光体与网状渗碳体,这种组织硬而脆,不仅难以切削加工,且在以后淬火过程中也容易变形和开裂.而经球化退火得到的是球状珠光体组织,其中的渗碳体呈球状颗粒,弥散分布在铁素体基体上,和片状珠光体相比,不但硬度低,便于切削加工,而且在淬火加热时,奥氏体晶粒不易长大,冷却时工件变形和开裂倾向小.另外对于一些需要改善冷塑性变形（如冲压、冷镦等）的亚共析钢有时也可采用球化退火.
球化退火加热温度为Ac1+(20～40)℃或Acm-(20～30)℃,保温后等温冷却或直接缓慢冷却.在球化退火时奥氏化是“不完全”的,只是片状珠光体转变成奥氏体,及少量过剩碳化物溶解.因此,它不可能消除网状碳化物,如过共析钢有网状碳化物存在,则在球化退火前须先进行正火,将其消除,才能保证球化退火正常进行.
球化退火工艺方法很多,最常用的两种工艺是普通球化退火和等温球化退火.普通球化退火是将钢加热到Ac1以上20～30℃,保温适当时间,然后随炉缓慢冷却,冷到500℃左右出炉空冷.等温球化退火是与普通球化退火工艺同样的加热保温后,随炉冷却到略低于Ar1的温度进行等温,等温时间为其加热保温时间的1.5倍.等温后随炉冷至500℃左右出炉空冷.和普通球化退火相比,球化退火不仅可缩短周期,而且可使球化组织均匀,并能严格地控制退火后的硬度.