A method for improving the properties of a welded structure and an improved welded structure

Abstract

Generally, the present invention relates to a method for improving the properties of a welded structure as well as the resulting improved welded structure. The weld joint is often the weakest part of welded structures. Especially, the coarse-grained area is usually the most critical zone in terms of the welded structure's properties, as its large grain size leads to a brittle microstructure. The present invention provides a method for improving the properties of a welded structure comprising at least steps of welding together a number of parts of the welded structure, and applying a heat treatment for the welded structure.

Description

[0001] A METHOD FOR IMPROVING THE PROPERTIES OF A WELDED STRUCTURE AND AN IMPROVED WELDED STRUCTURE

[0002] FIELD OF THE INVENTION

[0003] Generally, the present invention relates to a method for improving the properties of a welded structure as well as the resulting improved welded structure. Especially, the present invention relates to a method for increasing the strength of weld seams under various load conditions.

[0004] BACKGROUND

[0005] The weld joint is often the weakest part of welded structures. During the welding process, the peak temperature at the joint varies from the melting point of the steel to the working temperature within a narrow range. This results in different thermal effects across various parts of the weld joint, leading to zones with different microstructures. The properties of the joint and its zones are determined by the resulting microstructure.

[0006] Metallurgically, the welded joint is divided into zones: Weld metal, a fusion zone, a heat-affected zone (HAZ) and a coarse-grained area.

[0007] Weld metal consists of molten welding material mixed with the base metal. The degree of mixing depends on the welding process and parameters.

[0008] The fusion zone is located between the molten weld metal and the solid base metal, and it forms from the molten base metal.

[0009] The heat-affected zone (HAZ) includes the overheated coarse-grained area, the normalized fine-grained area, and the partially austenitized area.

[0010] The coarse-grained area is usually the most critical zone in terms of the welded structure's properties, as its large grain size leads to a brittle microstructure. In armored vehicles, the undercarriage is the most vulnerable part due to welded joints in the quenched steel components. This weakness is particularly problematic during mine encounters, where the weld seams may fail, putting occupants at higher risk.

[0011] Armored vehicles such as Armored Personnel Carriers (APCs), Infantry Fighting Vehicles (IFVs), Main Battle Tanks (MBTs), Reconnaissance Vehicles, Light Armored Vehicles (LAVs), Armored Cars, and Self-Propelled Guns (SPGs) serve various roles in military operations. Despite their strengths, the undercarriage weld joints remain a critical area for improvement to enhance overall performance and safety.

[0012] Therefore, improving the properties of welded structures, especially at the undercarriage, is essential to enhance the safety and effectiveness of armored vehicles.

[0013] SUMMARY OF THE INVENTION

[0014] The objective is to at least alleviate the problems described hereinabove not satisfactorily solved by the known arrangements, and to provide a feasible a method for improving the properties of a welded structure under various load conditions.

[0015] The aforesaid objective is achieved by the embodiments of a method according to the present invention, as claimed in claim 1.

[0016] Accordingly, in one aspect of the present invention a method for improving the properties of a welded structure comprises at least steps of: welding together a number of parts of the welded structure, and applying a heat treatment for the welded structure. In one embodiment, the heat treatment comprises at least soft annealing and quenching. Soft annealing involves heating the steel to a certain temperature and then cooling it slowly to soften the material, improve machinability, and relieve internal stresses.

[0017] Quenching involves heating the steel to a high temperature and then rapidly cooling it, usually in water or oil, to increase hardness and strength.

[0018] In one embodiment, the heat treatment is applied on the entire welded structure.

[0019] In another aspect of the present invention, a welded structure is provided as defined in independent claim 4.

[0020] In one embodiment, a welded structure, manufactured by the method in accordance with the present invention, comprises a number of parts, which the welded parts are heat treated as a whole.

[0021] In one embodiment, at least a part of the parts are made of hardened steel.

[0022] In one embodiment, at least a part of the parts are made of hot-rolled steel.

[0023] In further aspect, use of a welded structure is provided as defined in independent claim 7.

[0024] In one embodiment, the welded structure according to the present invention is used in an undercarriage of a vehicle.

[0025] In another embodiment, the welded structure according to the present invention the welded structure is used in an undercarriage of an armored vehicle.

[0026] The utility of the present invention follows from a plurality of factors depending on each particular embodiment. One advantage of the invention is that the method can modify the microstructures altered during welding to match the original microstructures, thus enabling the entire welded structure to match the properties of the base material. The method allows the zones with different properties formed during welding to be restored to match the original properties of the steel used or to make the entire manufactured structure meet the desired strength and hardness characteristics. Another advantage is that a welded structure made of hardened steel can be completely restored to its original hardness. Additionally, a welded steel structure can be made from hot-rolled steel and, after the welding process, be entirely quenched to achieve the desired hardness.

[0027] The heat treatment enhances the properties of the welded parts, particularly improving the strength of the weld joints. This improvement allows the welded structure to be used in various applications, including, but not limited to, the undercarriages of vehicles and especially armored vehicles. The improved welded structure can better withstand pressures from events such as mine explosions, thereby providing greater protection to the occupants inside the vehicle.

[0028] The expression “a number of’ refers herein to any positive integer starting from two (2), e.g. to two, three, or four.

[0029] Different embodiments of the present invention are disclosed in the dependent claims.

[0030] BRIEF DESCRIPTION OF THE RELATED DRAWINGS

[0031] Next the invention is described in more detail with reference to the appended drawings in which Fig. 1 is a flow diagram of an embodiment of a method in accordance with the present invention.

[0032] DETAILED DESCRIPTION OF THE EMBODIMENTS

[0033] Figure 1 is a flow diagram of an embodiment of a method in accordance with the present invention. At method start-up 102, preparatory actions may take place. In this case, a number of parts to be welded are cut and arranged so that those can be connected together. The skilled person will understand that the number of parts is not limited, but it depends on the desired welded structure to be formed. At 104, the number of parts of the welded structure are welded together to form a desired welded structure.

[0034] At 106, a heat treatment is applied on the formed welded structure. In an embodiment, the heat treatment comprises at least soft annealing and quenching.

[0035] Yet, in another embodiment, the heat treatment is applied on the entire welded structure.

[0036] Consequently, a skilled person may on the basis of this disclosure and general knowledge apply the provided teachings in order to implement the scope of the present invention as defined by the appended claims in each particular use case with necessary modifications, deletions, and additions.

Claims

CLAIMS1. A method for improving the properties of a welded structure, characterized in that the method comprises at least steps of:- welding together a number of parts of the welded structure, and- applying a heat treatment on the welded structure.

2. The method according to claim 1, wherein said heat treatment comprises at least soft annealing and quenching.

3. The method according to any preceding claim, wherein said heat treatment is applied on the entire welded structure.

4. A welded structure manufactured by the method of any one of claims 1 to 3, wherein said welded structure comprises a number of parts, which said welded parts are heat treated as a whole.

5. The welded structure according to claim 4, wherein at least a part of said parts are made of hardened steel.

6. The welded structure according to any preceding claim, wherein at least a part of said parts are made of hot-rolled steel.

7. Use of a welded structure according to any of claim 4-6 in an undercarriage of a vehicle.

8. Use of a welded structure according to claim 7, wherein said undercarriage is in an armored vehicle.

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