GB2233259A - Armoured wall consisting of multi-layer steel - Google Patents

Abstract

In a process for the manufacture of an armoured wall consisting of multi-layer steel with at least one hard outer layer providing ballistic protection and with at least one softer inner layer suitable for welding with ferritic electrodes; a) the armoured wall is heated to 870 to 940 DEG C; b) the temperature reached according to a) is maintained for about one minute for each millimetre of total thickness of the armoured wall, but at least for 20 minutes; c) the armoured wall heated according to a) and b) is quenched to room temperature; d) whereupon the armoured wall quenched according to c) is tempered at less than 200 DEG C the tempering temperature reached being maintained for at least 2 minutes for each millimetre of total thickness of the armoured wall, but for at least 20 minutes; e) whereupon the armoured wall treated according to d) is cooled to room temperature in still air; f) and in that the softer ductile inner layer of the multi-layer steel has the following composition: C less than 0.15%, Si 0.15 to 0.35%, Mn 0.85 to 1.60%, P and S each less than 0.020%, Ni 0.50 to 0.80%, and Al 0.020 to 0.040% (all percentages being percentages by weight), the remainder being Fe.

Description

Process for the manufacture of an armoured wall consisting of multi-layer steel and application to armour-plating of the multi-layer steel manufactured according to this process This invention relates to a process for the manufacture of an armoured wall consisting of multilayer steel and application to armour-plating of the multilayer steel manufactured according to this process.

In the construction of objects protected against ballistic missiles, especially in the construction of armour-plating, the use of armoured sheets of extremely high hardness has hitherto been limited since such steel becomes more and more difficult to weld as the hardness increases and, as a rule, has to be processed by the use of expensive austenitic electrodes. When sheets from about HB 30 of 450 kg/mm2 are used, welding difficulties arise which can lead in various regions of construction to considerable crack formation even during manufacture, especially in regions of welding seams.

The use of armour plates with these hardnesses is the state of the art especially with bulkhead armouring for armoured combat vehicles. Also, after the equipment has been commissioned, crack formation can arise and can consequently cast doubt on functions such as ABC tightness, submersion tightness or the like. The crack formation, which is mainly caused by the application of welding heat in the welding processes conventionally used, increases with increasing hardness of the armour steel used, said hardness being, however, favourable for the ballistic protection of the protected object. During bombardment of the equipment, crack formation-arising in the welding seam regions may.manifest itself so strongly that, especially with bulkhead armouring, cracks allowing the passage of light can occur over an entire length of the armoured wall.

The following counter-measures have hitherto been taken to remedy this: a) grinding out, jointing and welding up the cracks; b) filling the cracks with materials of a different type; c) changing the armour plates, especially reducing the hardness of the armour steel used, the sheet thickness being increased correspondingly to maintain the ballistic protection.

The counter-measures listed under b) have mainly been employed on ready-assembled equipment.

On the contrary, the counter-measures listed under c) have been adopted where no known measure in production was able to effect reduction in crack formation.

The above-described crack formation arises especially strongly when the parts are welded to high-hardness special heat-treated steels which must be provided with an all-round welding seam for reasons of strength. Here, also, the local application of considerable heat, the shrinkage stresses associated therewith and changes in structure are substantially the causes of crack formation.

Accordingly, it is known that the manufacture of, as a rule, three-dimensionally curved parts of bombardmentproof metal housings of armour steel presents difficulties which considerably restrict the technological possibilities which exist. At the present time, such bombardmentproof or bombardment-protected structures are made by the following processes: 1. casting 2. forging 3. hot-pressing and 4. extrusion.

A disadvantage common to all these known processes is that after the shaping operation, the parts have to be heat-treated and generally complicated technological measures have to be taken in order to exclude the distortion of the parts during quenching and tempering.

These generally complicated manufacturing processes are also necessitated due to the fact that the threedimensionally curved parts of ballistically protected objects, especially armoured housings of armoured combat vehicles, are connected to the remaining part of the ballistically protected housing our the like predominantly by welding. However, such welded constructions of high-strength heat-treated steels have, as a rule, the following problems: If the welded joints are made with austenitic welding-material, the welded construction may not be heat-treated; however, if the welded joints'are made with material of the same type, this can only be effected by the use of special patented measures.

During the Second World War surface-hardened sheets were used, for example on the "Tiger tank", which had strengths of about 1,800 N/mm2'on the hardened side, while they were softer on the rear side and could be welded with ferritic electrodes. This arrangement was chosen because austenitic electrodes were practically unavailable for the manufacture of armoured hulls. With these surface-hardened armour steel sheets only a very thin hard layer of a martensitic type was present on the one side, while on the other side there was a thick pearlitic ferritic zone which could be welded only with great difficulty and after preheating with standard ferritic electrodes.

This arrangement had, in the-first place, the disadvantage that the hardened layer was very thin and did not permit a uniform thickness at all points of an armour-plating.

Furthermore, the softer zone had to consist ofa low-alloy high-strength steel so that its suitability for welding was, in actual fact, only small.

Cracks arising in the hard, very brittle, thin layer could be propagated into the softer region.

Finally, the surface hardening necessary to create the hardened thin layer was a very expensive process which could not be achieved without distorting the construction. Consequently, this process was not developed further, since it no longer meets the presentday requirements in the manufacture of armouring.

A process for the manufacture of an armouring is known from German OLS 2,142,360, in which process two steel sheets are connected to one another by plating and are subsequently heat-treated. For this purpose, the known process starts from a first steel sheet which consists of 0.3 to 1% C, 0.5 to 1% Si, 0.1 to 1% Mn, 3 to 10% Cr, 0.5 to 3% Mo, 0.2 to 1% V and the remainder Fe, the second steel sheet consisting of 0.1 to 0.3% C, 0.1 to 1% Si, 0.1 to 2% Mn, 2 to 10% Ni, 0.2 to 2% Cr, 0.2 to 2% Mo, traces of V and the remainder Fe.The two steel sheets are heated after plating to a temperature between 900 and 10500C, quenched or cooled in air and subjected to a tempering treatment at a temperature between 200 and.6500C, The ranges which are specified for the individual constituents in German OLS 2,14 1 360 are so wide that practicable solutions cannot be achieved therewith.

According to the present invention we provide a process for the manufacture of an armoured wall consisting of multi-layer steel with least one hard outer layer and with at least one softer inner layer, wherein:a) the chemical composition of the hard outer layer and the chemical composition of the softer inner layer and the heat treatment thereof are coordinated with one another so that sufficient hardness is achieved in the hard outer layer to provide ballistic protection and ductility and suitability for welding with ferritic electrodes are achieved in the softer inner layer; b) the armoured wall consisting of multi-layer steel is heated to about 870 to 940 C; c) the temperature reached according to b) is maintained for about one minute for each millimetre of total thickness of the armoured wall, but at least for 20 minutes; d) the armoured wall heated according to b) and c) is quenched to room temperature; e) whereupon the armoured wall quenched according to d) is tempered at less than 2000C, the tempering temperature reached being maintained for at least 2 minutes for each millimetre of total thickness of the armoured wall, but for at least 20 minutes; f) whereupon the armoured wall treated according to e) is cooled to room temperature in still air; g) and in that the softer ductile inner layer of the multi-layer steel has the following composition: C less than 0.15%, Si 0.15 to 0.35%, Mn 0.85 to 1.60%, P and S less than 0.020%, Ni 0.50 to 0.80%, and Al 0.020 to 0.040% (all percentages being percentages by weight), the remainder being Fe.

We have shown that in an armoured wall made by the process according to the invention and consisting, for example, of two-layer steel, optimal ballistic protection properties can be achieved in the outer and inner layers of such a two-layer steel. By such "optimal properties" is meant that the outer layer of multi-layer steel facing the bombardment has very great hardness, while the inner softer layer has very great ductility. This can be achieved only by the application of heat treatment according to the invention in conjunction with the material compositions, proposed according to the invention, of the inner and outer layers of the multi-layer steel.

As regards the steel composition, it is important that a steel with as low a carbon content as possible is used in the softer layer. However, a high energy absorption capacity is to be achieved only if a certain strength is also present in addition to the ductility.

Whereas such a steel in the normalised state has a yield point of 350 N/mm2, a strength of 490 to 610 N/mm2 and an elongation at break (Lo = 5 do) of 22%, this steel has, after the treatment according to the invention, a Brinell hardness of, for example, 265 HB. This corresponds to a strength of -900 N/mm2 which makes a good contribution to safety against bombardment. At the same time, bombardment tests have demonstrated that the material has a high deformation capacity. Thus, for example, with an armoured wall consisting of twolayer steel, less material is thrown off from the inner layer due to the shell than with standard armour steel.

The danger of injury is consequently substantially reduced.

Since in the process according to the invention the tempering temperature is very low at, for example, about 180 C, during welding of the softer layers the common tempering temperature may not be exceeded in the harder layers of the multi-layer steel. This is achieved by using thin electrodes which are welded in several beads or passes, if an intermediate cooling is effected, for example, between the individual passes. Secret tests have shown that in this way it has been possible in all cases safely to avoid heating hard outer layers to above 100 C. Nevertheless, the outer layer facing the bombardment can be made extremely hard, that is with high hardness.

During the secret tests comparative twisting tests were also conducted, namely on a steel bar with a hardness of 670 HB. It was shown that this steel broke even after an angle of twist of less than 90 .

On the contrary, it was possible to twist a bar of a two-layer steel prepared according to the invention with the same measured length through about 10000 without its breaking. The ductile softer layer of the two-layer steel obviously exerts on the high-hardness layer a very favourable effect with regard to deformability and the energy absorption capacity of a multi-layer steel according to the invention is increased extraordinarily to an unforeseeable extent.

The advantages of the process according to the invention can be summarised as follows: 1. An armoured wall of multi-layer steel, especially of two-layer steel, can be manufactured, with which S.m.K.

bombardment safety can be achieved under otherwise identical conditions with an about 50% smaller wall thickness (pointed shell with core, calibre 7.62 mm x 51 mm).

2. When an armoured wall manufactured by the process according to the invention is bombarded, a large dissipation of energy occurs, among other things, due to a strong bulging of the ductile (relatively softer) inner layer of the armoured wall.

3. If an armoured wall according to the invention is bombarded, a kind of deep-drawing effect takes place on the relatively softer inner layer of the multi-layer steel, which leads to a larger energy absorption of this ductile inner layer which has, however, also relatively high strength.

The high-hardness outer layer behaves within certain limits like an elastic body. After the breaking strength has been exceeded, energy (destructive energy) is dissipated to a considerable extent by the particles of the high-hardness outer layer, the ductile inner layer supporting the particles of the hard outer layer so that with increasing deformation, the pressure per unit of area is correspondingly reduced and bulging of the ductile inner layer takes place.

4. The advantages of the strong deformability of multi-layer steel made by the process according to the invention and constructed, for example, as two-layer steel, is not only of great importance for ballistic protection, but ensure, in principle, that this two-layer steel is suitable for body production, but with less production difficulties than those which can arise in the processing of conventional armour steel.

5. Armour steels used today can be employed only up to a certain hardness in armour building. This hardness limit is not only the limit of weldability, but also the limit of operability in the operating state. Neither limit arises with a multi-layer steel, for example twolayer steel, which has been manufactured by a process according to the invention. An armoured wall manufactured by the process according to the invention can be welded ferritically via the relatively ductile layer.

6. If reduction of the wall thickness in comparison with conventional armour steel is rejected, correspondingly higher bombardment safety can be achieved due to the use of multi-layer steel according to the invention.

7. Due to the good deformability of armour walls manufactured by the process according to the invention, body parts for motor vehicles to receive ballistic protection can be connected to one another more easily.

Mass-produced civil motor vehicles can thereby be converted economically by welding into them armour walls which have been manufactured by the process according to the invention.

8. No special armour steel electrodes are necessary for any welded joints. Austenitic electrodes are about ten times as expensive as the fer-ritic electrodes which can be used according to the invention.

9. No advanced welding experience is needed to weld armoured walls according to the invention.

10. Armoured walls according to the invention can be mitred with one another and connected to one another at the more ductile inner layers by the above-mentioned ferritic welding seams. It is thereby possible to provide ballistic protection due to the high-hardness outer layers in the immediate proximity of the mitre joint, so that such mitre connections need not be protected ballistically by special covers.

According to a further feature of the invention we provide a method of forming armour plating whereby several armoured walls according to the invention are connected to one another by welding seams between the more ductile inner layers, preferably using several overlapping welding-beads.

To generate high hardness in the hard outer layer of heat-treated steel, only hardening at a very low tempering temperature is considered. The chemical composition of the softer inner layer is therefore of substantial importance. Unalloyed steels with carbon contents of about 0.2%, as are conventionally used as structural steels suitable for welding, become relatively brittle due to the above-mentioned heat treatment.

Unalloyed steels with a very low carbon content below 0.15% would acquire good ductility and also suitability for welding due to the above-mentioned heat treatment, but they would not permit any substantial increase in hardness and, due to their low strength, would make almost no contribution to the energy absorption capacity of the composite material. Due to the use a armoured walls of a multi-layer steel, especially twolayer steel, made by the process according to the invention, such armoured walls can be connected to one another easily, without any fear that the steel, which after the heat treatment according to the invention at an extremely low tempering temperature, has very good ductility and good suitability for welding but on the other hand a strength of about 1000 N/mm2, will lose these favourable strength properties again.If the above procedure using multiple welding beads is adopted, local heat peaks can be avoided.

In one advantageous embodiment, the ballistic protection reaches to the immediate proximity of the point of the mitre joint of armoured walls connected to one another.

The invention is illustrated with reference to exemplary embodiments shown partly schematically in the accompanying drawings wherein: Figure 1 shows the application of multi-layer steel sheets made according to the invention to the armouring of a limousine; Figure 2 shows examples of application for the manufacture of individual body parts for a saloon car; Figure 3 shows a cross section along the line III-III of Figure 2.

Figure 4 shows on a larger scale the corner connection illustrated in Figure 3 with beads; Figure 5 shows such a corner connection as a welded joint; Figure 6 shows the corner connection according to Figure 4 or 5 after bombardment at the point of the welding seam; Figure 7 shows an armoured wall of two-layer steel after a shell hit; Figure 8 shows an armoured wall of two-layer steel after a double hit; Figure 9 shows a further armoured wall of two-layer steel after a shell hit with strong eruptions towards the outside; Figure 10 shows a conventional high-hardness armoured wall after a penetrating shot, the large fragmentation effect occurring due to eruptions towards the inside; Figure 11 shows an armoured wall consisting of twolayer steel after a penetrating shot;; Figure 12 shows a further armoured wall of two-layer steel after a shell penetration with no or only small fragmentation effect towards the inside, in contrast to Figure 10; Figure 13 shows a diagram in which the upper curve represents conventional armour steel and the lower curve multi-layer steel according to-the invention (the sheet thickness from which bombardment safety is achieved is shown in relation to the shell impact angle); Figures 14 to 23 show in a series of drawings on the basis of time-lapse photographs bombardment of an armoured wall of two-layer steel according to the invention deliberately not made bombardment-proof.

Figure 1 is intended to illustrate how standard limousines can be made bombardment-proof by the application, for example by welding-in, of armoured walls consisting of multi-layer steel, especially two-layer steel to the body-shell 2 of the limousine. The outlines of these armoured walls are represented by broken lines in Figure 1.

Since multi-layer steel sheets made according to the invention can be kept relatively thin and consequently correspondingly light, they can be fitted to conventional limousines, so that, for example, such limousines can also be made S.m. K. -bombardment-proof in the abovementioned way.

Figure 2 is intended to illustrate merely that all the parts of the body of a vehicle can be produced from multilayer steel made according to the invention, since this steel can be handled relatively simply. Of the details illustrated in Figure 2 only the roof sheet 3 and the side sheets 4 and 5 have been designated especially, while Figures 3 to 6 illustrate regions of the roof plate 3 and of the one side plate, here 4, which are connected by welding seams. The individual parts can, of course, be shaped otherwise, if required, than illustrated in Figures 2 to 6. A vehicle produced according to Figure 2 can be used, for example, as an armoured patrol vehicle, as a roving police car or for frontier protection.

Moreover, in the embodiments according to Figures 1 to 6 the armoured walls are made of two-layer steel.

The high-hardness outer layer facing the bombardment X is designated by the reference numeral 6, while the inner ductile and softer layer is denoted by the reference numeral 7. The outer layer 6 is so hard that optimal hardness is achieved (this having otherwise to be abandoned due to the above-described welding difficulties) while the inner layer 7 has a large energy absorption capacity.

Two adjacent sheets are connected to one another by ferritic welding seams (Figure 4) and it is illustrated exaggeratedly in Figure 4 that several welding beads 8, 9 and 10 have been applied with a relatively thin electrode, although said beads have not been represented separately in Figures 5 and 6 for the sake of simplification of the drawing. In this way, during welding, only relatively small heat is applied and the high-hardness outer layer 6 is prevented from being heated too strongly and the temperature values mentioned in the introduction are not exceeded.

If the welded corner joint according to Figure 5 is bombarded in the direction X, the high-hardness outer layer 6 is partly destroyed, as is shown in Figure 6, but eruptions of the outer layer (i.e. fingers or projections of metal remaining after the impact) are driven into the relatively soft and ductile material of the inner layer 7 and are arrested thereby, while the inner layer 7 is deformed inwardly, namely together with the equally relatively soft welding material, without penetration occurring. Accordingly, when multi-layer steel sheets made according to the invention are used, welded joints no longer need to be specially covered on the exterior, for example, by armour steel strips.

In Figure 7 an armoured wall of two-layer steel has been bombarded in the direction X. The deviation from the original plane 11 is designated by D. It is also clearly recognisable from Figure 7 that the highhardness outer layer 6 is fragmented and partly "destroyed", while the inner layer 7 merely bulges out, but no penetration occurs.

Figure 8 shows an especially unfavourable situation, namely so-called double hits in the direction X. Again, the outer layer is fragmented and the deviation from the original plane 11 is likewise designated by D and is relatively large. Despite the comprehensive destruction of the high-hardness outer layer 6, the fragments and the shell cannot penetrate the inner layer 7. On the contrary, the inner layer 7 only bulges inwardly at the shell impact points at 12 and 13 Figure 9 shows the bombardment with S.m.K ammunition of the two-layer steel already illustrated in Figure 7.

Eruptions of the high-hardness outer layer 6 have been designated by A, while. all the other designations correspond to those already used in Figures 7 and 8.

In this case, also, a penetration does not occur, but merely, at 14, an inwardly directed bulging. Strong eruptions are visible on the outside. Figure 9 also reveals that dissipation of the surface pressure is achieved due to the destruction of the high-hardness outer layer.

In comparison therewith, Figure 10 illustrates the bombardment in the direction X of a sheet consisting only of conventional high-hardness armour steel. C represents the point of exit and the strong inwardly directed fragmentation effect. Despite the relatively large wall thickness the shell has penetrated this highhardness armour steel wall 6. Accordingly, Figure 11 illustrates again an armour steel wall made of two-layer steel according to the invention, this wall having deliberately not been made bombardment-proof, to explain the conditions which obtain during penetration and after penetration respectively. In this case, strong eruptions A occur on the high-hardness outer layer 6, while the inner layer 7 has been deformed far inwardly in relation to the original plane 11.At the point where the shell has penetrated the inner layer 7 at C, the material has been deformed inwardly in a neck-shaped manner. In so doing, there occurs a kind of deep-drawing operation associated with a corresponding reduction of the wall thickness of the relatively ductile inner layer 7.

Despite the cracks in the region of the penetration C, fragments of parts of material of the inner layer 7 are not thrown off.

Figure 12 illustrates the bombardment of a further two-layer steel sheet which has likewise deliberately not been made bombardment-proof. In this case, bombardment was effected merely with a different calibre. Figures 7 to 12 and 14 to 23 were prepared on the basis of actual bombardment results, so that they partly overlap, but are intended to demonstrate how a multi-layer steel sheet according to the invention behaves.

In Figures 14 to 23 the conditions resulting from bombardment in the direction X with S.m.K. ammunition on an armour steel wall deliberately not made bombardmentproof are illustrated in a plurality of metallurgical drawings on the basis of time-lapse photographs. Figure 23 reveals extraordinarily large deep-drawing capacity of the inner layer 7 in comparison with Figure 14. If an attempt is made to restore to the original plane the deep-drawn parts of the inner layer 7 which run inwards in the manner of the neck of å bottle, it must be recognised that these parts can be brought into an overlapping position, which means that the wall thickness in the region of the penetration has been considerably reduced and the material has been deformed extraordinarily far in the direction X.With this movement is supports the fragments of the high-hardness outer layer 6 and holds these together, so that they largely fly outwards and cannot come inwards. Due to the. relatively large path which the layers of a multi-layer steel according to the invention cover during the bombardment or upon a penetration, an extraordinarily larger amount of energy of the respective shell is captured and dissipated.

Figure 13 shows with the curve E the S.m.K. safety of a high-hardness conventional armour steel sheet in standardised representation. The sheet thicknesses at which bombardment safety is achieved are represented on the ordinate, while the associated angles of impact of a shell have been plotted on the abscissa.

Curve F illustrates the S.m.K. bombardment safety of a two-layer steel according to the invention. As is clearly recognisable, bombardment safety is. already achieved over a substantial range of the angles of impact with an about 50% smaller thickness, which signifies a corresponding saving of weight and also costs.

The features described in the description and in the patent claims and illustrated in the drawing can be material to the realisation of the invention either individually or in any combinations.

The bulging and deep-drawing capacity of the relatively softer ductile inner layer which result during bombardment of a multi-layer steel according to the invention are also suitable for obstructing the spike of a hollow-charge shell at certain angles of impact.

Furthermore, several or a plurality of armoured walls according to the invention can be arranged behind one another, also with spacing. Finally, it is not absolutely necessary for armoured walls according to the invention to be welded. It is also possible to glue such armoured walls to one another with a suitable. adhesive, for example based on "Baypren".

In conclusion, armour plates according to the invention can also be used with especial advantage for the adaptation of objects to be armoured, especially armoured vehicles or armoured combat tanks.

Claims (11)

CLAIMS:

1. Process for the manufacture of an armoured wall consisting of multi-layer steel with at least one hard outer layer and with at least one softer inner layer, wherein:a) the chemical composition of the hard outer layer and the chemical composition of the softer inner layer and the heat treatment thereof are coordinated with one another so that sufficient hardness is achieved in the hard outer layer to provide ballistic protection and ductility and suitability for welding with ferritic electrodes are achieved in the softer inner layer; b) the armoured wall consisting of multi-layer steel is heated to about 870 to 940 C; c) the temperature reached according to b) is maintained for about one minute for each millimetre of total thickness of the armoured wall, but at least for 20 minutes; d) the armoured wall heated according to b) and c) is quenched to room temperature; e) whereupon the armoured wall quenched according to d) is tempered at less than 2000C the tempering temperature reached being maintained for at least

2 minutes for each millimetre of total thickness of the armoured wall, but for at least 20 minutes; f) whereupon the armoured wall treated according to e) is cooled to room temperature in still air; g) and in that the softer ductile inner layer of the multi-layer steel has the following composition: C less than 0.15%, Si 0.15 to 0.35%, Mn 0.85 to 1.60%, P and S less than 0.020%, Ni 0.50 to 0.80%, and Al 0.020 to 0.040% (all percentages being percentages by weight), the remainder being Fe; 2.A process as claimed in claim 1 in which the highhardness outer layer has the following composition: C 0.35 to 0.7%, Si 0.10 to 0.70%, Mn 0.50 to 1.00%, P and S each less than 0.02%, Cr 1.3 to 2.6%, Ni 0.20 to 3.60%, Mo 0.40 to 0.70%, V 0.04 to 0.30%, (all percentages being percentages by weight).

3. A process as claimed in claim 1 or claim 2 in which the high hardness outer layer has the following composition: C 0.5%, Si 0.25%, Mn 0.75, P and S each less than 0.02%, Cr 1.45%, Ni 0.35%, Mo 0.50%, and V 0.20%.

4. A process as claimed in claim 3 in which the inner softer layer has the following composition: C less than 0.12%, Si 0.25%, Mn 1.20%, P and S each less than 0.020%, Ni 0.65% and Al 0.020 to 0.40%.

5. A process as claimed in any of the preceding claims in which stages (b) and (c) are effected at 91OOC.

6. A process as claimed in any of the preceding claims in which processes (c) and (e) are effected in a continuous-heating furnace.

7. A process as claimed in any of the preceding claims in which stage (d) is effected by quenching in oil.

8. A process as claimed in any of the preceding claims in which tempering in stage (e) is effected at 1800 C.

9. A process as claimed in any of the preceding claims in which the multi-layer steel is a two layer steel.

10. A process as claimed in claim 1 substantially as herein described.

11. Armoured walls when made by the process as claimed in claim 1.

11. Armoured walls when made by the process as claimed in claim 1.

12. A method of manufacturing armour plating wherein one or more armoured walls as claimed in claim 11 are connected together by welding seams at the inner softer layers thereof.

13. A method as claimed in claim 12 in which the welding is carried out using several welding beads.

14. Armour plating when made by the method as claimed in claim 12 or claim 13n 15. Armour plating as claimed in claim 14 in which two or more armoured walls as claimed in claim 11 are mitred together by welding seams provided on the softer ductile layer, in such a way that the armour protection reaches through the high-hardness outer layer to the common mitre joint.

Amendments to the claims have been filed as follows 1. Process for the manufacture of an armoured wall consisting of multi-layer steel with at least one hard

outer layer and with at least one softer/inner layer,

a) the chemical composition of the hard outer layer and the chemical composition of the softer inner layer and the heat treatment thereof ar coordinated with one another so that sufficient hardness is is achieved in the hard outer layer two provide ballistic protection and ductility and suitability fo welding with ferritic electrodes are achieved in the softer inner layer;

the armoured wall consisting of multi-layer steel is heated to

870 to 940 C;

the temperature reached according to

is maintained for about one minute for each millimetre of total thickness of the armoured wallq but at least for 20 minutes::

the armoured wall heated according to

and

is quenched to room temperature;

whereupon the armoured wall quenched according to

is tempered at less than 200 C the tempering temperature reached being maintained for at least 2 minutes for each millimetre of total thickness of the armoured wall, but for at least 20 minutes;

whereupon the armoured wall treated according to

is cooled to room temperature in still air;

and in that the softer ductile inner layer of the multi-layer steel has the following composition:: C less than 0.15%, Si 0.15 to 0.35%, Mn 0.85 to 1.60%,

P and Sess than 0.020%, Ni 0.50 to 0.80%, and Al 0.020 to 0.040% (all percentages being percentages by weight), the remainder being Fe; 2. A process as claimed in claim 1 in which the highhardness outer layer has the following composition: C 0.35 to 0.7%, Si 0.10 to 0.70%, Mn 0.50 to 1.00%, P and S each less than 0.02%, Cr 1.3 to 2.6%, Ni 0.20 to 3.60%, Mo 0.40 to 0.70%, V 0.04 to 0.30%, (all percentages being percentages by weight).

3. A process as claimed in claim 1 or claim 2 in which the high hardness outer layer has the following composition: C 0.5%, Si 0.25%, Mn 0.75, P and. S each less than 0.02%, Cr 1.45%, Ni 0.35%, Mo 0.50%, and V 0.20%.

4. A process as claimed in claim 3 in which the inner softer layer has the following composition: C less than 0.12%, Si 0.25%, Mn 1.20%, P and S each less than 0.020%, Ni 0.65% and Al 0.020 to 0px0%.

5. A process as claimed in any of the preceding claims in which stages (b) and (c) are effected at 91OOC.

6. A process as claimed in any of the preceding claims in which processes (c) and (e) are effected in a continuous-heating furnace.

7. A process as claimed in any of the preceding claims in which stage (d) is effected by quenching in oil.

8. A process as claimed in any of the preceding claims in which tempering in stage (e) is effected at 1800C.

9. A process as claimed in any of the preceding claims in which the multi-layer steel is a two layer steel.

10. A process as claimed in claim 1 substantially as herein described.