Composition of Cementite during Various Heat-Treatment Processes on Ball-Bearing Steel

Abstract

As the fundamental concept to get the uniform martensite that was effective to the life of ball bearing, the author considered the behavior of cementite during various heat-treatment processes to arrive at the spherodizing annealed structure on the manufacturing process.
The primary-eutectoid net-work cementite was sharp and the Cr content in it decreased with the rise of cooling velocity. The diffusion constant was more important factor than the affinity of Cr for C.
When the specimen, of which the matrix was fine sorbitic pearlite, was heated at a temperature between A₁ and Acm transformation point, the non-dissolved cementite changed as follows. At the side of higher temperature of the range it was coarser somewhat and Cr% in it decreased with the rise of temperature and holding time. At the other side Cr% was increased with the holding time. The former the diffusion constant of cementite was effective, the latter the affinity of constructive elements in it.
In case of the specimen with globular cementite was heated at the same temperature, Cr content in the non-dissolved cementite was increased with the temperature, because the cementite with the poor Cr content was dissolved more rapidly.