鍛鋼焼入れロールの早期破壊現象についての考察
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概要
- 論文の詳細を見る
Four high cold strip mill work rolls are fully hardened forged steel rolls which are made of high carbon chromium steel with an ordinary composition of 0.8-1.15 percent carbon and 0.8-2.6 percent chromium, subjected to water quenching and low temperature-stress relief at 100-250℃. They have residual stresses caused by the above mentioned heat treatment, so they are very liable to have troubles in rolling operations. Major troubles occurring in the early period of the life of these rolls are fracture taking with time lag after quenching in storage and fatigue fracture originating at the center bore surface in rolling operation. These troubles are, it seems, ascribable to their manufacturing conditions. However, as the occurrence of these fractures is not so frequent, the differences in properties between fractured rolls and sound rolls have not been clarified yet. Common understanding was that delayed fracture would most likely be the result of quench cracking due to heavy residual stresses developed during the quenching process of the roll, while the fatigue fracture might be caused by defects existing in the vicinity of the bore. A study on the manufacturing processes, properties and residual stresses of the roll has produced the following result which conflicts with the conventional understanding. 1) The phenomenon of a fracture occurring in the roll with time lag after quenching is a delayed failure caused by the hydrogen in the material under the influence of tensile residual stresses. It is not a simple quench cracking. And the occurrence of the fracture is very frequent in the winter time. This is not because the temperature was low, but because fractured rolls which had been cast in summer when humidity was high and hydrogen content in molten steel was increased accordingly, were subjected to quenching treatment in cold winter. The delayed failure is likely to happen in a roll whose steel contains 3.5 ppm or more of hydrogen at tapping. Some rolls of this steel may incur fracture, but others do not, possibly because of nonuniform distribution of hydrogen, excessive segregation and varied situation of micro defects from which fracture may originate. 2) Fatigue fracture at bore takes place even if there is no defect. The cause of fracture is that fatigue strength is lowered by tensile residual stress acting as a mean stress against working stress in rolling operation. And it is inferred that tensile residual stress at bore is caused through insufficient cooling in bore under quenching treatment.
- 社団法人日本鉄鋼協会の論文
- 1967-05-01