The neutron absorption cross section of hafnium (Hf) is up to 200 bar, which has excellent nuclear and corrosion properties. As a control rod, Hf has a much longer service life than B4C and AgInCd, and is the main control rod material for nuclear power. In recent years, with the maturity of zirconium hafnium separation technology, the global capacity of nuclear grade sponge zirconium has reached 10,000 tons/year, which means the capacity of Hf is close to 200 tons/year. Hf is being popularized and applied as control rod material in nuclear power, such as Hf in VVER and RBMK reactors.
Hafnium materials processing performance of deformation and deformation temperature sensitive, excessive deformation, deformation temperature is too low, prone to crack defects in the processing, the deformation is too small, inadequate core deformation, provides mechanical properties and corrosion resistance of hafnium is difficult to meet the requirements, which requires the machining process of hafnium plates, to reasonably control the key deformation parameters, improve the performance of hafnium plates.
A processing method for hafnium plate. By controlling the forging ratio, forging temperature, rolling deformation and rolling temperature of each hot rolling, the hafnium plate can fully break the coarse grain of the hafnium ingot and the core of the slab, so that the internal and external structures are consistent, thus ensuring the corrosion and mechanical properties of the finished plate.
Hafnium melting point is 2233℃, its α/β phase transformation temperature is as high as 1760℃, in the α phase area deformation slip system is less, and hafnium in the inevitable presence of oxygen, zirconium, iron and other impurities, causing hafnium plastic decline, especially the oxygen element, unless the oxygen content is very low level, its cold processing deformation capacity is generally not more than 25%; On the other hand, the grain size of hafnium ingot is coarse, the impurity elements between the dendrite are easy to enrich, there is a certain degree of segregation, grain boundary is easy to overburn; At the same time, hafnium is easy to oxidize, heating temperature higher than 1200℃ will lead to the formation of a large amount of oxidation on the surface of the forging, resulting in burning or even surface overburning.
The forging process will be set at 1000℃ ~ 1200℃ and heat preservation 1h ~ 3h, to ensure that the hafnium ingot has plastic processing ability in the forging process, reduce the hafnium ingot due to impurities caused by the hafnium plastic decline and not easy deformation processing adverse effects, eliminating the hafnium ingot solidification segregation, at the same time control the temperature does not exceed 1200℃, The surface oxidation, burning and overburning of forged slab are prevented.
