抄録
The boronized process is famous as one of the chemical methods to achieve case hardening of steels. There have been a number of studies concerning this treatment process and boronized layer. Consequently, it becomes well-known that the boronized layer has above 1400 Vickers hardness and a high resistance especially against wear. Also the present authors have reported the residual stress distribution by using X-ray method, the effects of thickness and compressive residual stress of boronized layer on bending fatigue strength properties and the results of fatigue crack observation.
On the other hand, few reports exist on the tensile mechanical properties. One of the characteristics in boronized steels is the formation of a carbon redistributed layer below the boronized layer. It is expected that this carbon redistributed layer contributes to the improvement of the total tensile and yield strength.
In the present study, tensile tests were conducted on mechanical and structural steel specimens of different diameters, which contained various amounts of carbon and had different thickness of boronized layers. The Effects of the thickness of boronized layer and the carbon redistributed layer on tensile strength were investigated.
The results obtained are summarized as follows;
(1) For SCM 420 and S50C, both the tensile and the yield strength were improved with increasing thickness of the carbon redistributed layer.
(2) Rupture elongation became less with increasing thickness of the boronized layer.
(3) As the carbon content became more, the ratio of boronized area to carbon redistributed area effective in improving tensile and yield strengths became smaller. The ratio was 45% in SCM 420, and 25% in S50C.
(4) When the carbon redistributed layer became thicker than the tensile residual stress distributed layer, both the tensile and yield strengths improved.
