DESC:FIELD OF THE INVENTION

The present invention relates to post-weld thermal treatments and methods. More particularly, this invention is directed to method for elimination of delayed cracking during welding bigger size weldment having physically separated weld joints.

BACKGROUND

Delayed cracking is also called as hydrogen induced cracking or cold cracking. Delayed cracks are formed in the heat affected zone (HAZ) of the weld joint between high strength metal forging to plate material, after the weldment cools down to room temperature. An example of the high strength metal forging is EN24 (EQUIVALENT OF SAE4340). Example of the plate material is IS2062-E410C.

Generally, during welding of the high strength metal forging to plate material, post weld heat treatment / stress relieving operation is adopted immediately upon completion of welding in addition to preheating, maintaining interpass temperature, and post heating operations. There exist procedures for smaller size weldment with high strength forging to plates without delayed cracking. Preheating is carried out to 250°C before welding, inter pass temperature is maintained during welding and post-heat is carried out after welding and the weldment is immediately loaded into the stress relieving furnace (for stress relief operation) before it cools to 250°C. This is done to facilitate easy evolution of hydrogen from the weld metal and to prevent the start of Martensite formation in the weld & HAZ.

However, in case of bigger size weldment, for e.g., forging material EN24 having outer diameter as 2076millimetres (mm) and height as 381mm, stress relieving cannot be done immediately upon completion of welding. For bigger size weldment having physically separated weld joints,(more than one), it is difficult to maintain the post heat temperature (250°C) of all the weld joints on both sides simultaneously, which is a main requirement before stress relieving operation.
In this case, two peripheral weld joints are present in two opposite sides. After completion of first weld joint with post heating, the structure will be turned for carrying out welding in the second side. By this time, the temperature of the first weld joint will drop down below 250°C. So the first weld joint will be susceptible to delayed cracking. Also, it is highly expensive to carryout stress-relieving immediately after completion of weld joint in one side only.Hence, in this case, stress relieving cannot be done immediately upon completion of welding of weld joint in one side only.

Therefore, there is a requirement of a solution that overcomes the above mentioned issues.

SUMMARY OF THE INVENTION:
This summary is provided to introduce a selection of concepts in a simplified format that are further described in the detailed description of the invention. This summary is not intended to identify key or essential inventive concepts of the claimed subject matter, nor is it intended for determining the scope of the claimed subject matter.
The present subject matter illustrates a method for preventing delayed cracks in a weldment having a plurality of weld-joints. The method comprises
a) preheating, at a first temperature in a furnace, a first portion comprising a first proposed weld-joint between a metal forging and a plate-material;
b) welding the metal forging to the plate material at said first portion;
c) post-heating said first portion comprising the first weld joint at a second temperature by a heating element
d) soaking the post-heated first portion in the furnace at a third temperature higher than the second temperature for a pre-determined duration;
e) cooling the first-portion within the furnance to cool; and
f) subjecting the steps a) to c) to a second portion comprising a second proposed weld joint, followed by loading the component in furnace maintained at second temperature and carryout thermal stress relieving with stress relieving cycle starting from second temperature ) to obtain a weldment of the metal forging and the plate comprising the plurality of weld joints.
To further clarify advantages and features of the present invention, a more particular description of the invention will be rendered by reference to specific embodiments thereof, which is illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. The invention will be described and explained with additional specificity and detail with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

FIGURE 1 illustrates method for elimination of delayed cracking during welding bigger size weldment having physically separated weld joints, in accordance with an embodiment of the present invention.

FIGUREs 2A, 2B, 2C, and 2D illustrates an example manifestation of welding bigger size weldmentEN24 forging with IS2062-E410C Plate material in accordance with the embodiment of the present invention.

DETAILED DESCRIPTION

It will be understood by those skilled in the art that the foregoing general description and the following detailed description are explanatory of the invention and are not intended to be restrictive thereof.

Reference throughout this specification to “an aspect”, “another aspect” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrase “in an embodiment”, “in another embodiment” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

The terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process or method that comprises a list of steps does not include only those steps but may include other steps not expressly listed or inherent to such process or method. Similarly, one or more devices or sub-systems or elements or structures or components proceeded by "comprises... a" does not, without more constraints, preclude the existence of other devices or other sub-systems or other elements or other structures or other components or additional devices or additional sub-systems or additional elements or additional structures or additional components.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skilled in the art to which this invention belongs. The system, methods, and examples provided herein are illustrative only and not intended to be limiting.

The present invention provides method for elimination of delayed cracking during welding bigger size weldment having physically separated weld joints. In an implementation, bigger size weldment is high strength metal forging to plate material. An example of the bigger size weldment is welding of EN24 forging with IS2062-E410C Plate material.

As described earlier, in case of bigger size weldment, for e.g., forging material EN24 having outer diameter as 2076 millimetres (mm) and height as 381mm, stress relieving cannot be done immediately upon completion of welding, on one side only. As such, in the present invention, the entire weldment is considered as two sides. (Say Side A and Side B)

FIGURE 1 illustrates method 100 preventing delayed cracks in a weldment having a plurality of weld-joints. More specifically, the method relates to elimination of delayed cracking during welding bigger size weldment having physically separated weld joints, in accordance with an embodiment of the present invention.

Referring to FIGURE 1, the steps102 to 110 of the method100 are adopted separately for side A and side B welding of high strength metal forging to the plate material.

At step 102, the method 100 includes preheating, at a first temperature in a furnace, a first portion comprising a first proposed weld-joint between a metal forging and a plate-material. In an implementation, the method includes preheating side A of the weld joint of high strength forging to plate material at 250°C in furnace.

At step 104, the method 100 includes welding the metal forging-plate to the plate material at said first portion. Specifically, the method comprises conducting full welding of the preheated side A with the plate material using Gas metal arc welding (GMAW) process. In an implementation, the GMAW process uses ER70S-6 (1.2mm) electrode.
At step 106, the method comprises post-heating said first portion comprising the first weld joint at a second temperature by a heating element. Specifically, the method 100 includes post-heating the welded side A at 250°C by heating torch.

At step 108, the method comprises soaking the post-heated first portion in the furnace at a third temperature higher than the second temperature for a pre-determined duration. Specifically, the method 100 includes loading the post-heated side A in furnace at 250°C and soaking the post-heated side A in the furnace at 400°C for 1 hour.

At step 110, the method comprises cooling the first-portion within the furnace. Further, method100 includes switching off the furnace and allowing the prepared side A to cool inside the furnace.

At step 112, the method comprises subjecting the steps 102 to 106, to a second portion comprising a second proposed weld joint, followed by loading the component in furnace maintained at second temperature and carryout thermal stress relieving with stress relieving cycle starting from second temperature. to obtain a weldment of the metal forging and the plate comprising the plurality of weld joints. Specifially, the method 100 includes repeating the above steps 102 to 106 followed by loading the component in furnace maintained at second temperature and carryout thermal stress relieving with stress relieving cycle starting from second temperature for side B.

At step 112, the stress relieving techniques corresponds to only Thermal Stress Relief.

FIGUREs 2A, 2B, 2C, and 2D illustrates an example manifestation 200 of welding bigger size weldmentEN24 (EQUIVALENT of SAE4340) forging with IS2062-E410C Plate material in accordance with the embodiment of the present invention.

FIGURE 2A illustrates a perspective view of Side A 202 of EN24 forging before the welding. The Side A 202 of EN24 forging is then welded with IS2062-E410C Plate material 204 in accordance with the method 100 (steps 102 to 110).

FIGURE 2B illustrates a perspective view of welding of Side B 206 of EN24 in accordance with the method 100 (step 112).

FIGURE 2C illustrates a perspective view of final product 208 that is obtained using the above method 100, i.e., after welding, shot blasting and primer.

FIGURE 2D illustrates a perspective view of product 210 that is obtained after gear cutting operation on the final product 208.

Table 1 below illustrates the experimental data obtained using convention method and the above method 100.

Table 1:
Side A Side B Result
Pre-
heating
In furnace Full welding Post heating by heating torch Heating from 250 to 400°c and soaking for 1 hour in furnace for desirable phase change Pre-
heating
In furnace Full welding Post heating by heating torch Heating from 250 to 400°c and soaking for 1 hour in furnace for desirable phase change Regular stress relieving in furnace
Trial 1 v v v v v Cracks formed
Trial 2 v v v v v v v Cracks formed
Trial 3 v v v v v v v v No cracks formed

As can be gathered above, the welding of forging (EN 24) with plate material (IS2062), of bigger size using conventional methods result in formation of cracks, as represented by Trial 1 and Trial 2. However, welding of forging (EN 24) with plate material (IS2062), of bigger size using the method 100 avoids formation of cracks, as represented by Trial 3.

Advantages of the present invention include the following:
• Elimination of the formation of delayed cracks in bigger size weldment having physically separated weld joints;
By adopting the above procedure, at any point of time, martensite (susceptible microstructure for cracks) formation is never allowed. In the present case, austenite is converted to bainite, without giving any chance for martensite formation.
• Avoidance of welding rework.
• Enables to fabricate the weldment “right at first time” itself; and
• Enables use of the matching strength filler material.
Plate material is IS 2062 and its tensile strength is 410MPa.Forging material is EN24 and its tensile strength is 745MPa. Filler material matching with lower strength base material is ER70S-6 (480MPa) and the same is used for joining EN24to IS 2062.
The drawings and the forgoing description give examples of embodiments. Those skilled in the art will appreciate that one or more of the described elements may well be combined into a single functional element. Alternatively, certain elements may be split into multiple functional elements. Elements from one embodiment may be added to another embodiment. For example, orders of processes described herein may be changed and are not limited to the manner described herein.
Moreover, the actions of any flow diagram need not be implemented in the order shown; nor do all of the acts necessarily need to be performed. Also, those acts that are not dependent on other acts may be performed in parallel with the other acts. The scope of embodiments is by no means limited by these specific examples. Numerous variations, whether explicitly given in the specification or not, such as differences in structure, dimension, and use of material, are possible. The scope of embodiments is at least as broad as given by the following claims.
Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any component(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature or component of any or all the claims.
While specific language has been used to describe the present subject matter, any limitations arising on account thereto, are not intended. As would be apparent to a person in the art, various working modifications may be made to the method in order to implement the inventive concept as taught herein. The drawings and the foregoing description give examples of embodiments. Those skilled in the art will appreciate that one or more of the described elements may well be combined into a single functional element. Alternatively, certain elements may be split into multiple functional elements. Elements from one embodiment may be added to another embodiment.
,CLAIMS:1.A method for preventing delayed cracks in a weldment having a plurality of weld-joints, said method comprising:
a) preheating, at a first temperature in a furnace, a first portion comprising a first proposed weld-joint between a metal forging and a plate-material;

b) welding the metal forging to the plate material at said first portion;

c) post-heating said first portion comprising the first proposed weld joint at a second temperature by a heating element;

d) soaking the post-heated first portion inthe furnace at a third temperature higher than the second temperature for a pre-determined duration;

e) cooling the first-portion within the furnance; and

f) subjecting a second portion comprising a second proposed weld joint to steps a) to c), followed by:
loading the component at furnace kept at 250 °C, and
application of thermal stress relieving technique with stress relieving cycle starting from second temperature
to obtain a weldment of the metal forging and the plate comprising the plurality of weld joints.

2. The method as claimed in claim 1, further comprising:
applying only thermal stress relieving technique for preventing delayed–cracks within the weldment,
wherein the first side and second side are opposite sides (side A, side B) comprising the first and second weld joint as the physically separated peripheral weld joints.

3. The method as claimed in claim 1, wherein the preheating in step a) comprises preheating a first side of the weldment with weld joint of a high strength metal forging to plate material at 250°c in the furnace

4.The method as claimed in claim 1, wherein the welding in step b) comprises:
welding the metal forging defined by EN24 (Equivalent of SAE 4340) to the plate material IS 2062 at said first portion using a GMAW process with 100% CO2 shielding gas, filler material : ER 70S6.

5. The method as claimed in claim 1, wherein the post-heating in step c) comprises post heating the first portion comprising the welded side at 250°C by a heating torch

6. The method as claimed in claim 1, wherein the soaking in step d) comprises loading the post-heated first portion in the furnace at about 250°C.

7. The method as claimed in claim 6, wherein the soaking in step d) comprises soaking the post-heated first portion in the furnace at 400°C for about 1 hour.

8. The method as claimed in claim 1, wherein the step e) comprises switching off the furnace and allowing the first portion comprising the first weld joint to cool inside the furnance.

9. The method as claimed in claim 1, repeating the steps a) to c), followed by:
loading the component at furnace kept at 250°C,
applying thermal stress relieving technique with stress relieving cycle starting from second temperature for the second side of weldment.
10. The method as claimed in claim 2, wherein the regular stress relieving techniques corresponds to Thermal Stress Relief.