Production of clad plates of extreme dimensions
This article analyses the crucial conditions for making the clad plates of maximum overall dimensions for different types of combinations of cladding and base metals.
Introduction
A problem of practical explosion welding of strong aluminium-magnesium and titanium alloys was considered In the reports [1] and [2] made at Symposiums EPNM-X and EPNM-XI. According to the results showed in those reports, the welded metals acquire different temperatures during their co-joint deformation. As a result, during the further post-welding heat-exchange the separation of the obtained composition takes place due to multi-directional thermal deformation. The most critical composition of such kind is one of AlMg6 and austenitic stainless steels, due to high thermal conductivity and low plasticity of the latter.
Special technological methods which are a know-how of Energometall Ltd. let us considerably reduce deformation of the welded composition during bonding process and thus reduce the temperature of bimetal measured by a pyrometer Scantemp 410 during the first 3-5 minutes after welding.
When welding with carbon steel the average temperature of stainless cladding surface of different grades through the above mentioned period of time is 35-40°C, for titanium cladding ASTM B265 Gr. 1 it is 50-60°C, for titanium alloys like ASTM B265 Gr.5 or Russian grade PT3V it is 65-70°C. It should be noted that these temperatures are true for the know-how technology of Energometall Ltd. Reducing of post-welding temperature of a composition due to new technology tested in 2009 let us weld and later include into our manufacturing program the bimetals which consist of strong aluminum-magnesium and titanium alloys.
As a parameter for evaluation of the relative heat dissipation, resulting primarily due to advancing deformation of the cladding layer, a factor of deformational heat generation khg was offered. This is the ratio of the tensile strength of cladding metal to its density Eq. (1).
It is easy to notice that bonding of metals and alloys with khg≤100 kJ/kg does not represent a big technological problem, whereas bonding of materials with the higher khg, and especially welding of bimetal plates of extreme large size represents a serious technological problem.
When using of a ductile interlayer like pure Aluminum for welding of AlMg6 with stainless steel, let us reduce the contact temperature and heat generation in a bonding zone and thus reduce the difference in temperatures of AlMg6 and steel up to the values, which allow to receive the size of clad plates of practical importance, e.g. 1500*3000 mm and over. [2]
The below experiment was implemented in order to study the possibility to obtain the large size clad plates made of structural steel and the most strong titanium alloys and evaluate the real physical limitations.
Description of the experiments
Bonding of high-strength Titanium alloy ASTM B265 Gr.5 with typical carbon steel
The strong titanium alloy ASTM B265 Gr5 and carbon steel 09G2S GOST5520-79 were taken for the experiment. Besides, one plate was made by direct welding of materials, while the second one was made using an intermediate layer of titanium ASTM B265 Gr1, thickness 1.5 mm. In order to provide maximal identity of properties of the components welded, they were obtained out of the same origin plate of titanium alloy ASTM B265 Gr5 and the same origin plate of steel plate 09G2S GOST5520-79.
The sizes of combinations were as: 1. (30+5)x500x2500mm (hereafter referred to as bi-clad); 2. (30+1.5+5)x500x2500mm (hereafter referred to as tri-clad).
Both plates were successfully welded on 2300 mm length from the point of detonation, behind this distance alloy ASTM B265 Gr5 cladding layer undergoes transverse ruptures, see the Photo 1 and Photo 2 (Fig.2).
In both cases the entire composition became 30 mm longer. Thus, the intermediate layer of titanium alloy ASTM B265 Gr.1 did not affect the length of bonding, as it could be expected. However, the bond strength of "tri-clad" is much higher. Groups of specimens were taken for tensile and shear strength tests every 500 mm, and the last group was taken in step of 300 mm, as shown on Fig. 3.
All specimens were heat treated with holding during 2 hours at the temperature 500˚С.
The test results are given in the Table 1.
TABLE 1
Mechanical properties of specimens sampled according to the sampling diagram 2.1 in Fig.3
Sample No. | Distance from detonation point, mm | Bi-clad | Tri-clad | ||
---|---|---|---|---|---|
ASTM B265 Gr.5 + 09G2S-13 (30+5) mm |
09G2S-13+ ASTM B265 Gr.1+ ASTM B265 Gr.5 (30+1.5+5) mm |
||||
Tensile strength (MPa) | Shear strength (MPa) | Tensile strength (MPa) | Shear strength (MPa) | ||
0, 1 | 100 | 223.76 | 258.11 | 540.08 | 299.02 |
2, 3, 4, 5 | 500 | 236.07 222.09 | 222.50 | 480.97 491.52 | 220.05 |
6, 7, 8 | 1000 | 189.60 175.24 | 259.54 | 464.70 438.07 | 198.84 |
9, 10, 11 | 1500 | 182.35 206.20 | 243.37 | 548.10 462.04 | 296.43 |
12, 13, 14 | 2000 | 173.33 169.04 | * | 439.39 379.50 | * |
15, 16, 17 | 2300 | 164.04 | 180.38 | 436.76 | 232.96 |
Specimens were destroyed while making tests.
The given data shows that the tensile strength of joint in both cases (bi-clad or tri-clad) has tended to decreased, while the shear strength was not obviously changed. This can be explained by the fact that when cladding, each next following element of a cladding layer undergoes the load in the form of tearing moment, relatively to its fragment newly welded, besides, the greater the load the more outstretch it undergoes, i.e. at the furthest distance from the point of initiation. As soon as the ability to outstretch of structural steel 09G2S is significantly higher than that of titanium alloy Gr5, then capacity to lengthen of cladding layer has been spent earlier, besides, the same happened either for bi-clad or tri-clad as the property of Gr5 cladding layer only. Active outstretch of the base and cladding layers is also confirmed by increase of a wave period at the boundary of a steel and titanium layer with distance from the point of initiation. We can assume that with increasing of the base metal thickness or with using the base metal of the greater strength (with the less outstretch), which excluded or limited outstretch of the base plate during cladding, we could manage to receive the longer length of cladding for titanium alloy ASTM B265 Gr5. Probably a slight increase of clad length could also be achieved by increasing of the cladding layer thickness. Also, attention should be paid on extremely high strength, as a result of using of "plastic" interlayer in the form of titanium B265 Gr1, which shows perspectiveness of using this combination.
Bonding of austenitic stainless steel with typical carbon steel
The preliminary conclusions received by the experiment described in Section 2.1 were confirmed in practice while manufacturing of an extra large plate (84+6)x2750x10800mm (09G2S GOST 5520-79 + ASTM A240 TP321). This clad plate was successfully welded without any discontinuities, but its main feature was that the dimensions of the plate for both components remained unchanged (see Photo 3 and Photo 4 in Fig.5), also the wave period remained unchanged at the boundary between cladding layer and backing steel, regardless the distance from the point of initiation.
Photo 3 – Edge of a clad plate as welded with no lengthening of a cladding layer; Photo 4 – Plate as welded
Values of bond strength between backing steel and cladding layer in the parts most distant from the point of initiation were kept extremely high, see the Resulting mechanical properties in Table 2, sampling diagram (Fig.6) and the photo of final product (Fig.7).
TABLE 2
Mechanical properties of specimens sampled according to the sampling diagram 2.2 in Fig.7
Specimen No. | Tensile strength, MPa | Shear strength, MPa |
---|---|---|
1 | 566.98 | 464.40 |
2 | 494.90 | 454.36 |
3 | 476.59 | 410.38 |
4 | 545.34 | 446.84 |
Remark: all specimens were taken after the final heat treatment of the end product:
t = (630÷660) °C, hold time 23÷24 hours; cooling with furnace up to 300°C; then in air.
Conclusions
There are several factors limiting the maximum possible size of plates for different combinations of metals welded:
- For a combination of metals of significantly different density, the maximum size is limited by value of tangential stresses caused by the difference in thermal deformation due to a difference in heating temperature of base and cladding plates.
- For a combination of metals, where one of the components features by high strength and low ductility, the maximum size is limited by ductility threshold of a high-strength component and resulting in a significant change in the size of the backing plate.
- For a combination of metals, when the base layer has a considerable inert mass and strength reserve that was not involved in the process of plastic deformation across all thickness, it is possible to achieve maximum dimensions, limited only by reserve of plasticity of a cladding layer.