鋼の熱処理による残留応力

抄録

The residual stresses in quenched, tempered and isothermally treated steels were investigated by the X-ray method.
The materials used were plain carbon steels containing 0.08%∼1.03% carbon and Ni-Cr and Cr-Mo low alloy steels. Test specimens were 50×50×20(mm) plates and 25φ×100(mm) round bars. They were quenched in water or oil from 800°C∼1000°C and tempered at several temperatures between 100°C∼800°C. Ni-Cr low alloy steel specimens were martempered at 200°C or austempered at 400°C.
Residual stresses were determined by Sin²ψ method, using Cr-K_α radiation.
The experimental results are as follows;
(1) The surface residual stresses and residual stress distribution of these specimens were affected mainly by the hardenability of steels. The surface residual stresses of the plain carbon steel specimens quenched in water were compressive, while those of the low alloy steel specimens were tensile.
(2) The surface residual stresses of the specimens quenched in water or oil decrease with the increase in tempering temperature. Particularly, in case of tempering above 400°C, the surface residual stresses were very small.
(3) In the 0.85% carbon steel specimen quenched in water, large compressive stress was found just beneath the surface.
(4) At the surface of the Ni-Cr steel specimens quenched in water or oil, the residual stresses were 55∼58kg/mm² on tensile side, while those martempered at 200°C for 4 hours and those austempered at 400°C for 4 hours showed the residual stresses of 6.4kg/mm² on tensile side and 20.8kg/mm² on compressive side, respectively.
In the Ni-Cr steel with high hardenability, isothermal treatment was effective in lowering the residual stress.