titanium/stainless steel clad plate manufacturing process and properties

Titanium clad stainless steel plate development

With the development of industrial modernization, a variety of new materials are emerging in endlessly. Pure titanium / steel composite plates can no longer meet the needs of customers. Titanium cladding stainless steel materials have shown broad application prospects in aerospace, national defense and chemical industries with their superior properties. It is difficult to obtain ideal bonding strength of welding interface through ordinary welding methods. At present, it is commonly used to add transition metal (bronze or Monel alloy, etc.) for welding bonding. The process is complex and the cost is high, and there will be melting, delamination and other defects. In this paper, titanium and stainless steel are welded by explosive welding without adding transition metal to achieve the desired bonding strength.

Process Plan:

Material: gr2/S30408

Size:3/16*1630*3080mm  2pcs

The clad plate is placed in parallel, and the detonator distribution method of equal thickness is selected.

The expanded explosive with high detonation velocity and high sensitivity shall be used as the explosive. The detonation velocity shall be between 1800 and 1900, and the height of the support shall be 6mm (Greater than theoretical height 4mm)

The bonding surface of the clad plate is polished by 120# 1000 leaf wheel to ensure that the bonding surface of the base and clad plate is smooth and free of oxidation inclusions or other defects. Sandy soil foundation shall be selected as the foundation, which shall be flat and the ground matrix shall be uniform.

Explosion result

interface metallography

As shown in Figure 2, the metallographic structure photos of two composite plates after explosion are shown respectively. In this image, the joint surface is wavy, the waveform is stable and uniform, and there is no obvious brittle phase such as melting block.

After explosive welding, the surface quality is good without tearing and edge melting, and the UT detection bonding rate is more than 98%.

After explosion, the finished product is sampled for shear test to test its bonding strength, as shown in Table 1.

Table 1 The shear strength

The data in Table 1 shows that the shear strength of two composite plates with the same explosive welding method is taken for data analysis. The results show that the bonding strength of the middle part of the composite plate is higher than that of the end part of the composite plate. The shear data meet and are higher than the standard nb/t47002.3-2009. The shear strength ≥ 140MPa, which fully meets the manufacturing requirements of industrial equipment.

Discuss and analysis

1. surface quality of material joint surface affects welding joint

  This time, the surface treatment of the clad plate was carried out by using the 120# thousand impellers of the automatic polishing machine for many times. The polishing quality was good, eliminating the problem of local uneven quality caused by manual polishing. The sampling length of the roughness test was 1=2.50mm, and the measured longitudinal roughness was about 10~1.3, and the transverse roughness was 1.5~1.85. The size of the concave and convex part of the surface determines the retention degree of the jet, that is, the degree of additional melting on the welding interface when the kinetic energy of the jet is transformed into heat energy.

  After the surface is well polished, the pollution layer formed by the oil, grease and water attached to the surface is easy to be taken away. Using the theory of foreign literature for reference, if the sum of the roughness of the base plate and the clad plate is less than one tenth of the normal wave amplitude, generally between 2~3um, a qualified weld can be obtained. If it is greater than this data, there may be a periodic melting layer. After polishing, the roughness of the base plate used this time can reach 1~2um, so it can meet the material bonding requirements.

2. interface melting affects the bonding of titanium / stainless steel

  It is easy to see a phenomenon during the explosion of titanium stainless steel that the interface melts. This is because titanium and iron are easy to form intermetallic compounds such as TiFe、TiFe2、Ti2Fe, etc., and multiple composite brittle intermetallic compounds may also be formed between titanium, iron, chromium and nickel. Excessive heat accumulation at the welding interface will lead to excessive melting of the composite interface. Due to the brittleness of intermetallics, the joint is brittle, which is easy to cause cracks at the welding interface under the action of welding stress. The defects on the interface due to crack propagation have a great impact on the bonding strength of the explosive welding interface. Therefore, the occurrence of interface melting should be minimized or even avoided. Therefore, the upper limit of dynamic parameters of explosive welding should be avoided for explosive welding of titanium / stainless steel, Do not adopt too high detonation velocity, so that the interface can produce thermal softening and jet, and rapidly cool and solidify to have sufficient tensile strength.

  Two titanium / stainless steel explosive welding tests show that it is feasible to carry out explosive welding of titanium / stainless steel without transition layer within a certain range. Direct explosive welding of titanium / stainless steel is carried out by controlling its surface quality, improving the collision angle and increasing the amount of jet flow. This process solves the problems of insufficient melting and bonding strength caused by no transition layer of titanium / stainless steel, simplifies the process and reduces the cost, And the product quality is stable, meeting the equipment manufacturing needs of the industry.