Processing method for small-size and high-strength niobium-hafnium alloy bar

Abstract

The invention provides a processing method for a small-size and high-strength niobium-hafnium alloy bar. The processing method comprises the following steps that 1, a niobium-hafnium alloy ingot blank is sawn, and after being heated, the sawn niobium-hafnium alloy ingot blank is coated with an anti-oxidative protective lubricant; 2, the niobium-hafnium alloy ingot blank coated with the anti-oxidative protective lubricant is forged through upsetting and stretching to obtain a bar billet; 3, the bar billet is sequentially turned, ground and vacuum-annealed for the first time; 4, the vacuum-annealed bar billet is heated, the heated bar billet is coated with an anti-oxidative protective lubricant, and the bar billet coated with the anti-oxidative protective lubricant is formed through die forging to obtain a forging stock; 5, the forging stock is sequentially turned, ground and vacuum-annealed for the second time; 6, the vacuum-annealed forged stock is rolled with grooved rolls to obtain a small-size bar billet; and 7, the small-size bar billet is sequentially straightened, scalped, polished, pickled and annealed to obtain the small-size and high-strength niobium-hafnium alloy bar. The diameter of the section of the bar obtained according to the processing method is 8-20 mm, the room temperature tensile strength of the bar is up to above 465 MPa, the yield strength of the bar is up to above 350 MPa, the elongation of the bar is above 47%, and the grain structure of the bar is fine and uniform.

Description

technical field [0001] The invention belongs to the technical field of niobium-based alloy processing, and in particular relates to a processing method for small-sized high-strength niobium-hafnium alloy rods. Background technique [0002] Nickel-based superalloys commonly used in high-temperature structural parts have a maximum service temperature of 1100 °C, which is close to the melting point of the material itself, which is far from meeting the technical requirements of aerospace structural parts. Therefore, alternative materials must be found. Refractory metals possess high melting points and low saturated vapor pressures and are able to withstand high stress levels at high temperatures, making them suitable for high temperature applications. For structural parts used in aerospace, weight reduction has always been the key to research, and the emergence of low-density niobium-based alloys just met the needs at that time. Niobium alloy is a promising high-temperature str...

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Problems solved by technology

However, after testing the mechanical properties of the small-sized bars prepared by these two processes, it was found that the bars obtained by the first process had poor mechanical properties, and the tensile strength and yield strength were only 415MPa and 304MPa, respectively, even lower than only Large-scale rods obtained by forging; although the mechanical properties of the second type of rods have been improved, up to 450MPa and 330MPa, there will be nearly two levels of grain size difference between the surface layer and the core structure, and it is also found that the rods The phenomenon that the mechanical properties of the front and rear ends of the material are not uniform

The analysis shows that the main reason for the poor mechanical properties of the rods in the first process is that the grain size of the structure is large and the grain size distribution is uneven, mainly in the surface grains of the rods are finer, while the core grains are smaller thick, the reason for this result is that its radial deformation is not enough

Niobium-hafnium alloy precision forging or rotary forging is a small deformation, high-frequency processing, the pass processing rate is very low, the radial processing amount is usually 1mm ~ 2mm, resulting in deformation mainly concentrated on the surface of the bar, plus the actual In production, it also shows that the forgeability of niobium-hafnium alloy is also poor, and the grains in the core of the bar are only deformed, which has the characteristics of large grains inherited to the finished product, thus affecting its mechanical properties

In addition, the tensile stress on the core of the billet continues to increase during the process of precision forging or rotary forging, which may easily cause cracks in the core of the bar.

Although the second process uses extrusion molding, due to the high viscosity of the niobium-hafnium alloy itself, and the metal flow is slow in the early stage of extrusion, the metal flow is fast in the later stage, often resulting in the fluidity of the middle metal and the end metal. There are differences, although subjected to three-dimensional stress, it will also cause differences in axial organization and mechanical properties

In addition, the production cost of extrusion in industrial production is slightly higher than that of forging, and the process is more cumbersome

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