Experience with manufacture of internal parts of WWER 440 reactor

The manufacture was studied of thick metal sheets from steel 08KH18N10T for reactor internals. The effect of carbon whose proportion in the chemical composition ranges optimally within 0.07 and 0.08% was found significant for obtaining optimal values of the yield point at a temperature of 325 degC and a pressure of 157, 167 or 177 MPa. The optimal working conditions include controlled rolling at low finishing temperatures of 850 to 950 degC, four-high mill rolling with material reduction of 5 to 15% from a heating temperature of 1220 degC, two-high mill rolling from a heating temperature of 1220 to 1240 degC at optimum working temperatures of 1060 to 1080 degC. The low reduction capacity of the mill in finishing at temperatures around 920 degC did not unfavourably affect the value of hot yield point but affected unfavourably the austenite grain size. Heat treatment was also tested comprising temper annealing, this possibly combined with stabilization annealing. Intercrystalline corrosion resistance tests were satisfactory in all cases. (J.B.)