クロムモリブデンおよびニッケルクロムモリブデン浸炭鋼の熱処理特性について
1971 年 57 巻 1 号 p. 37-46
詳細
1971 年 57 巻 1 号 p. 37-46
In order to establish an optimum heat-treatment condition of carburized parts to give an excellent combi-nation of high hardness and good toughness, the heat-treatment characteristics of some practical case-hardening steels have been studied by metallographic examination and hardness and static bending tests.
The results are summarized as follows;
(1) The transformation behavior of carburized layer and unaffected matrix of the steels SCM22, SNCM 21 and SNCM 23 during heating and cooling have been clarified with relation to the austenitizing temperatures, the conditions of heating to and cooling from that temperature and the carbon content.
(2) In order to obtain high hardness of the surface of these steels quenched directly after carburization, the optimum surface carbon contents of the steels are 0.80 percent for SCM 22 and SNCM 21, and 0.70 percent for SNCM 23 series. In these case, however, 5 to 10 percent of retained austenite was observed.
(3) The most important factor to obtain high hardness and toughness is the heating cycle after carburization, that is, the heating rate from A1transformation point to austenitizing temperature and the holding time at that temperature.
(4) When SNCM 23, containing 0.80 percent carbon with bainitic or pearlitic structure is quenched in oil immediately after rapid reheating up to 850°C. Rockwell C scale hardness 66 to 67 were obtained.
(5) It has been revealed by the static bending test that the absorbed energy of rapidly heated and quenched steels increases 30 to 60 percent compared with slowly heated ones.
