Pass design process of niobium-hafnium alloy bar

In the middle of the 20th century, due to the need for the development of new engines, superalloy materials appeared. Among them, high-temperature niobium alloys represented by niobium-hafnium alloys (grades: C-103, Nb-10%-Hf-1%Ti) have found important applications in the aerospace field. The alloy has excellent comprehensive properties, and the ductile brittle transition temperature can be Up to -180℃, the maximum operating temperature can reach 1250℃. Niobium-hafnium alloy is mainly used in the combustion chamber of aerospace engines and is one of the most mature key materials for aerospace engines. At present, the commonly used processing method for niobium-hafnium alloy bars is swaging after extrusion. Due to the small deformation in a single pass, the surface of the blank is severely deformed and cracks are prone to appear. At the same time, the uniformity and mechanical properties of the finished product of rotary forging bars are poor, which is not conducive to the improvement of product quality.

The pass rolling is introduced into the processing of niobium-hafnium alloy bars. Through pass design and rolling experiments, good results have been obtained, and the surface quality, uniformity of the structure, mechanical properties and quality stability of the product have been greatly improved.

Through searching the literature, there is no report about the pass rolling of niobium-hafnium alloy bars. According to the mature experience of round steel and titanium rod rolling, the pass design is carried out.

The design process includes:
(1) Select the pass system.
(2) Determine the rolling pass.
(3) Reasonably distribute the elongation coefficient of each pass type.
(4) Calculation of isometric section size.
(5) Calculate the width expansion and fullness of the rolling piece in the non-equaxial cross-section elliptical pass, check the accuracy of the set value, and finally determine the elliptical pass size.
(6) Calculate the size of the round hole of the finished product.
(7) Determine the value of each parameter of the hole pattern, and draw the hole pattern diagram for each pass.
(8) Carry out the pass rolling experiment of niobium-hafnium alloy bar to test the rationality of pass design.

Through the pass design and rolling experiments, it can be known that the Z·Usatowski relative widening coefficient formula is used to calculate the pass (the parameters in the formula refer to the existing experience of titanium), and the designed pass is suitable for niobium-hafnium alloy Bars, the rolled bars have no serious underfilling and ear defects, which meet the quality control requirements; Compared with rotary forging, pass hot rolling has sufficient deformation and good microstructure uniformity, which is beneficial to improve the mechanical properties and corrosion properties of niobium and hafnium bars.