RU2614228C1 - Titanium-based cast alloy - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: casting titanium-based alloy contains, wt %: aluminium 3.5-5.0, carbon 0.02-0.14, oxygen 0.05-0.14, hydrogen 0.002-0.008, iron 0.02-0.20, silicon 0.02-0.10, vanadium 1.5-2.5, boriumn 0.001-0.003, titanium and impurities - the rest, if the following ratio is done Fe+Si≤0.25 wt %.

EFFECT: alloy is characterized by high fluidity and by the complex of mechanical properties, providing the quality and reliability of both cast and welded joints.

2 tbl

Description

The invention relates to non-ferrous metallurgy, in particular to the metallurgy of welded cast alloys based on titanium, and is intended for the manufacture of shaped castings of propellers, impellers of water-jet propulsors, pumps, etc., used in critical welded-cast structures of shipbuilding, chemical and other industries .

Titanium-based welded foundry alloys are known: VT1L grade, VT6L grade, the disadvantages of these alloys are reduced strength in one case, and insufficient ductility in the other (NF Anoshkin, AF Belov, B.I. Bondarev, etc. Production shaped castings from titanium alloys. M.: VILS, 1988).

Known casting alloy based on titanium, patent No. 2547371 from 03/11/2015, RU, which also has good casting properties, but its strength characteristics are insufficient.

The closest in technical essence and composition of the ingredients is the VT5L grade alloy, taken as a prototype, containing aluminum 4.1-6.2%, carbon 0.20%, oxygen 0.20%, hydrogen 0.015%, iron 0.35% , silicon 0.20%, zirconium 0, 80%, tungsten 0.20%, including other impurities 0.30% (N.F. Anoshkin, A.F. Belov, B.I. Bondarev, etc. Production shaped castings from titanium alloys. M.: VILS, 1988).

The disadvantages of the alloy are: poor fluidity when pouring molds from refractory oxides, low ductility and toughness, a tendency to crack in welded joints. The reason for these shortcomings is the high content in the composition of the alloy: carbon, hydrogen, iron, oxygen, silicon, tungsten.

The technical result of the invention is the creation of a casting alloy based on titanium, which has increased fluidity when filling casting molds from refractory oxides, high ductility and toughness while maintaining good welding properties.

The technical result is achieved due to the fact that the titanium-based alloy containing aluminum, carbon, oxygen, hydrogen, iron, silicon, additionally contains vanadium and boron in the following ratio of components, wt.%:

aluminum 3,5-5,0 carbon 0.02-0.14 oxygen 0.05-0.14 hydrogen 0.002-0.008 iron 0.02-0.20 silicon 0.02-0.10 vanadium 1.5-2.5 boron 0.001-0.003 titanium and impurities rest

under the following condition, Fe + Si≤0.25%.

The fulfillment of the condition Fe + Si≤0.25% prevents the coagulation of iron and silicon along grain boundaries, which leads to embrittlement of the alloy.

When the content in the alloy Fe + Si> 0.25% decreases the fluidity and ductility of the alloy.

Vanadium, an isomorphic β-stabilizing element, within the range of 1.5-2.5% lowers the temperature range of crystallization, which ensures good fluidity. Vanadium inhibits martensitic transformation and improves the quality of welded joints. Vanadium at a content of less than 1.5% does not affect the crystallization interval. When the content of vanadium is more than 2.5%, the number of β-stabilizing elements increases, which reduce fluidity.

When the aluminum content is more than 5.0%, a supersaturated α-solid solution is formed, which, upon slow cooling, is prone to decomposition with the formation of an α ₂ phase having a stoichiometric composition of the type Ti ₃ Al. The formation of this phase is accompanied by a loss of ductility and the formation of cracks in welded joints. When the aluminum content is less than 3.5%, the fluidity decreases.

With a carbon content of more than 0.12%, fluidity and ductility are reduced. A carbon content of less than 0.02% is technologically unfeasible when melting in a vacuum arc skull furnace.

When the oxygen content is more than 0.14%, there is a decrease in ductility and the formation of cracks in welded joints. When the oxygen content is less than 0.05%, the strength decreases.

When the hydrogen content is more than 0.008%, there is a decrease in ductility and the formation of cracks in welded joints. A hydrogen content of less than 0.002% is not technologically feasible when melting in a vacuum arc skull furnace.

When the iron content is more than 0.20%, the temperature range of crystallization increases, which leads to a decrease in fluidity.

When the silicon content is more than 0.10%, a brittle phase Ti ₂ Si _{3 is formed} , which reduces ductility and fluidity.

Boron in the specified limits of 0.001-0.003 introduced to refine the structure and increase ductility. When the boron content is less than 0.001%, the effect of grain refinement is absent; when the boron content is more than 0.003%, it forms borides, which reduce the plastic characteristics of the alloy.

Execution example

The compositions of the alloys of the proposed and known smelted in a vacuum arc garnissazh melting and casting furnace.

Cast billets of the “plate” type with a size of 20 × 300 × 400 mm were cast from the proposed and known alloy for the manufacture of samples. The metal was poured into magnesite molds. The mechanical properties were determined during tensile tests in accordance with GOST 1497-84 and impact samples in accordance with GOST 4697. To assess the quality of the welded joint, samples were prepared to determine the full work of fracture of the sample with the initial crack during impact bending - Atu.

The chemical composition of the proposed and known alloy are shown in table 1.

Fluid flow was determined on technological samples with a spiral measuring channel.

The channel with a triangle section 26 mm high and 8 mm base has a spiral shape and is located horizontally. The channel length is 700 mm.

Fluid flow was determined at the same pouring temperature of the metal. Forms were poured stationary.

An indicator of fluidity is the length of the flooded spiral sample.

The results of determining the ductility indicators, the work of the destruction of the weld metal and determining the fluidity are shown in table 2.

Compared with the known alloy, the proposed alloy has the following advantages.

The fluidity is higher by about 40%, the fracture work under shock bending of the welded joint and ductility are 3 times higher.

Claims (3)

A titanium-based casting alloy containing aluminum, carbon, oxygen, hydrogen, iron and silicon, characterized in that it additionally contains vanadium and boron in the following ratio, wt.%: aluminum  3,5-5,0 carbon  0.02-0.14 oxygen  0.05-0.14 hydrogen  0.002-0.008 iron  0.02-0.20 silicon  0.02-0.10 vanadium  1.5-2.5 boron  0.001-0.003 titanium and impurities  rest, when the condition Fe + Si≤0.25 wt.%.