| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for manufacturing high carbon chromium bearing steel capable of re-carburizing a decarburized layer formed on a material surface by heating at a high temperature in a preceding step ( heating before blooming and hot rolling).SOLUTION: A spheroidizing heat treatment is applied to a high carbon chromium bearing steel in which a decarburized layer is formed on a surface thereof in a preceding step, and whose carbon activity aof a steel surface exceeds 0.7 in a temperature range of 700°C or less. The spheroidizing heat treatment includes a step of heating the steel to a temperature right above an Atransformation point and a step of annealing the steel. At that time, in the step of annealing, atmosphere control is carried out so that the carbon activity aof the steel surface and a carbon activity aof an atmosphere satisfies a following formula (1): 0≤a-a≤0.3, when the steel is in a temperature range of the Atransformation point or less, and, further, satisfies a following formula (2): a=1, when in a temperature range of 680°C or less. Here, maximum values of aand aare 1.0. A cooling rate in a temperature range below an Atransformation point is preferably set to 10 to 80°C/hr or less. |
