Case hardening steel excellent in coarse grain preventive property during carburizing, its manufacturing method, and material for carburized parts

摘要

The present invention relates to al: 0.015 to 0.04%, Nb: 0.005 to 0.04%, N: 0.006 to 0.020%, and other steels containing a specific range of specific components, heated at 1150 degrees Celsius for 10 minutes or more, and the finish temperature is hot rolled at 920 to 1000 u00b0 C. and then cooled at 800 to 500 degrees Celsius at less than 1 A method of producing a hardened steel capable of stably suppressing the occurrence of coarse grained grains, and the method described above, wherein the amount of precipitation of Nb (CN) after hot rolling is 0.005% or more, an amount of precipitation of AlN is 0.005% or less, and Nb (CN) having a diameter of 0.1. Mu. M or less in a matrix of steel is 20 / 100. Mu. M or more, bainite is set in the matrix of steel In the present invention, there is provided a raw material for carburizing parts using a hardened steel having a percent modulus of 30% or less, a ferrite crystal grain size of 8 to 11, and a carburized part using the hardened steel.