Abstract
This paper describes the technological process of manufacturing bimetallic billets, which are capable of operating at high pressures, high temperatures, and in corrosive environments, from VT-14 titanium alloy and 12KH18N10T stainless steel. To obtain a joint with a strength of at least 350 MPa, the diffusion welding method was used, which makes it possible to obtain equal-strength joints using dissimilar materials. The connection of VT-14 titanium alloy with 12KH18N10T stainless steel after obtaining bimetallic billets with the desired properties was investigated. We studied the welded VT-14 and 12KH18N10T joint obtained by diffusion welding through intermediate spacers of niobium Nb (NbStrip-1) and copper Cu (M1). On the basis of our investigations, the optimum welding modes are as follows: welding temperature: 1137 K; welding pressure: 18 MPa; welding time: 1200 s. Mechanical tests, tightness tests, and metallographic, factographic, and micro-X-ray structural studies were carried out, the results of which indicate the effectiveness of the proposed approach.
Highlights
In atomic power, space technology using pipelines, and other products made of titanium alloys, there is an urgent need to connect titanium pipes with steel ones.The high reactivity of titanium at high temperatures, the nature of its interaction with iron, including limited mutual solubility in the solid state, and the presence of a lowmelting eutectic and several intermetallic compounds [1,2,3] create significant technological difficulties in the manufacture of bimetallic titanium-steel compounds by welding methods.When obtaining brazed steel-titanium joints, there are several factors that negatively affect the manufacturability and the cost of their manufacture
Mutual diffusion between titanium and stainless steel is carried out by the migration of atoms of the same chemical type across the plane of the joint and causes the formation of intermetallic compounds based on Fe + Cr + Ti and Fe + Ti in the reaction zone; these brittle intermetallic compounds worsen the mechanical properties of the formed compound [1]
The purpose of this work is to study the possibilities of joining VT-14 titanium alloy with 12KH18N10T stainless steel by diffusion welding and to develop a technological process for producing billets of bimetallic adapters (Figure 1) with specified properties by diffusion welding instead of the currently used necks made of titanium bimetallic plates
Summary
When obtaining brazed steel-titanium joints, there are several factors that negatively affect the manufacturability and the cost of their manufacture. These factors include the use of silver as a solder, as well as the use of threads of an increased accuracy class. Direct diffusion welding of a titanium alloy with stainless steel leads to residual stresses in the solid-phase joint zone due to a mismatch in the thermal expansion coefficients of the materials being joined and the formation of brittle intermetallic phases in the diffusion zone [4,5,6]. The use of an intermediate material that prevents the formation of brittle intermetallic phases in the process of diffusion welding is of decisive importance for the quality of the welded joint
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