抄録
The research was carried out in order to find the effect of preheat treatment, such process as annealing, quenching and tempering, on the effect of induction hardening of steel, and their difference in effects according to the kind of steel.
The steel used for the test is of four kinds; namely, carbon steel S40C, Mn steel SAE 1340, Cr steel SCr4 and CrMo steel SCM4.
As preheat treatment before induction hardening these steels were annealed at 880°C and 720°C, water quenched in case of carbon steel, oil quenched in case of other steels both from 850°C and after that tempered at 180°C, 400°C, 480°C, 540°C, 600°C, 650°C, 700°C and 730°C, respectively. Then they were all subjected to progressive and one shot heatings.
In those cases, all the test specimens were quenched under the same condition as that which yielded the thickness of hardened layer of 1.5mm (up to Micro Vickers 500), when S40C steel annealed at 880°C for two hours, was hardened by induction.
As the measure hardening effect, hardness, thickness of hardened layer, and residual stress by means of X-rays, were measured.
The effects of induction hardening are as follows:
(1) They vary with the conditions of carbide caused by the preheat treatment, reduced in proportion to the increase in the size of carbide particles.
(2) Steel not containing Cr and Mo such as S40C and SAE 1340 is subject to smaller influence than that containing those elements such as SCr4 and SCM4.
(3) As for S40C and SAE 1340, annealing at 880°C and tempering in the range from 180° to 400°C showed a good result.
As for SCr4 and SCM4, tempering in the range from 400° to 540°C showed a good result. Tempering done above this temperature resulted in a bad hardening effect.
(4) When the steel was annealed at 720°C, the result was least favorable.
