DESC:FORM 2

THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003

COMPLETE SPECIFICATION

(See Section 10 and Rule 13)

Title of invention:
A SYSTEM AND METHOD FOR WELDING 18% Ni MARAGING STEEL TO LOW-CARBON CHROMIUM-MOLYBDENUM STEEL

Applicant:
BEML Limited
A company Incorporated in India under the Companies Act, 1956
Having Address As:
BEML Soudha, 23/1, 4th Main,
Sampangirama Nagar, Bengaluru - 560 027,
Karnataka, India

The following specification particularly describes the invention and the manner in which it is to be performed.

CROSS-REFERENCE TO RELATED APPLICATIONS AND PRIORITY
[001] The present invention claims priority from Indian patent application numbered IN 202241050157 filed on 02nd September, 2022.
FIELD OF THE INVENTION
[002] The present subject matter described herein generally relates to a system and method for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel, and more specifically for a system and method for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel using pulsated TIG welding.
BACKGROUND
[003] In many cases, combination of steels in structures is necessary for technical and economic reasons. Therefore, dissimilar joints are inevitable for connecting the components/systems made from different materials. Welding is a major route adopted for fabrication of such components. 18% Ni Maraging steels (MDN250) variety has very good fracture toughness coupled with high tensile strength. The steels achieve superior mechanical properties through a simple low temperature precipitation hardening heat treatment and they are easily weldable. Whereas low carbon chromium-molybdenum steels (AISI 4130) steel possesses moderate strength good machinability and weldability in hardened and tempered condition, makes it highly suitable for various critical Aerospace and Missile applications. Welding operation of these dissimilar material induce residual stresses, distortion and reduction of strength at Heat affected Zone (HAZ). The HAZ region is a weak link in the entire weldment. Due to internal residual stress between base material and HAZ leading to stress cracking after welding.
[004] The high strength low alloys (like low carbon chromium-molybdenum steels - AISI 4130 steel) are very sensitive to softening of the heat affected zone as compared to that of maraging steels. So the performance of weld joint majorly depends on mechanical and metallurgical properties of Heat Affected Zone region.
[005] Weld fabrication of dissimilar material, 18% Ni maraging steel to AISI4130 low carbon chromium-molybdenum steel with direct current TIG welding without proper heat dissipation during welding and post heating of weld and HAZ was leading to HAZ to base metal interface cracking and drastic reduction in mechanical properties thus resulting rejection and affecting the weld joint quality of end product.
[006] Hence to overcome the aforesaid drawbacks there is a requirement to control the extent of softening during dissimilar welding is highly essential.

OBJECTS OF THE INVENTION
[007] Main object of the present disclosure is to provide a system and method for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel to eliminate or reduce the residual stresses of welding joints.
[008] Another object of the present disclosure is to provide a system and method for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel to control the extent of softening.
[009] Yet another object of the present disclosure is to provide a system and method for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel to optimize the extent of Heat affected Zone.
[0010] Another object of the present disclosure is to provide a system and method for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel to remove heat during welding.
[0011] Yet another object of the present disclosure is to provide a system and method for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel to reduce extent of Heat affected Zone (HAZ) through pulsated current TIG welding.
[0012] Another object of the present disclosure is to provide a system and method for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel to eliminate Heat affected Zone for base metal interface cracking.
[0013] Yet another object of the present disclosure is to provide a system and method for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel to reduce the mechanical property deterioration.
[0014] Another object of the present disclosure is to provide a system and method for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel to produce better quality weld joint.
[0015] Yet another object of the present disclosure is to provide a system and method for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel to produce better performing structures or pressure vessels.
[0016] Another object of the present disclosure is to provide a system and method for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel to eliminate post weld effects on the fabricated hardware.
[0017] Yet another object of the present disclosure is to provide a system and method for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel to produce a defect free welding joint.
[0018] Another object of the present disclosure is to provide a system and method for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel which is cost effective and easy to implement.

SUMMARY
[0019] Before the present system is described, it is to be understood that this application is not limited to the particular machine, device or system, as there can be multiple possible embodiments that are not expressly illustrated in the present disclosures. It is also to be understood that the terminology used in the description is for the purpose of describing the particular versions or embodiments only, and is not intended to limit the scope of the present application. This summary is provided to introduce aspects related to a system and method for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel, and the aspects are further elaborated below in the detailed description. This summary is not intended to identify essential features of the proposed subject matter nor is it intended for use in determining or limiting the scope of the proposed subject matter.
[0020] The present subject matter discloses a system for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel comprising atleast one first work piece, atleast one second work piece, a heat transfer assembly, a work desk, a heater assembly. The first work piece and the second work piece are heat-treated at a predetermined condition. The heat transfer assembly is provided for transferring heat from the work pieces. The work desk is provided for mounting and aligning the first work piece and the second work piece. The heater assembly is adapted for the heat treatment of said welding joint.
[0021] Further, the present subject matter discloses a method for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel comprising the steps of i) atleast one first work piece and atleast one second work piece are mounted coaxially on a work desk. Step ii) a cooling assembly is mounted at a predefined position in proximity to the weld joint. Step iii) an insulating paste is applied at the joint of cooling assembly and the second work piece to act as a heat transfer means. Step iv) said work pieces are welded by pulsating TIG welding based on predetermined welding parameters. Step v) the insulating paste and the cooling assembly are removed post welding. Step vi) the welding joint and the heat affected zone (HAZ) region are heat treated comprising the steps of a) a shim type thermocouple along with a proportional integral derivative (PID) controller are mounted on the welded joint for sensing and controlling the temperature.b) a copper foil is wrapped to cover the welded joint along with the HAZ region and the shim type thermocouple. c) a heater assembly is mounted on at the center of the copper foil / welding joint covering the heat affected zone (HAZ) region on either side of the welding joint. d) the heater assembly is heated at a preset temperature with higher rate of heating and the heater assembly is maintained at said preset temperature for a predefined time period. e) the heater assembly is switched OFF. f) the heater assembly along with the copper foil, the shim type thermocouple and the PID controller are removed. g) the welded assembly (both the work pieces) are cooled at the ambient room temperature.

STATEMENT OF INVENTION
[0022] The present subject matter discloses a system for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel comprising atleast one first work piece, atleast one second work piece, a heat transfer assembly, a work desk, a heater assembly. The first work piece and the second work piece are heat-treated at a predetermined condition. The heat transfer assembly is provided for transferring heat from the work pieces. The work desk is provided for mounting and aligning the first work piece and the second work piece. The heater assembly is adapted for the heat treatment of said welding joint.
[0023] In an embodiment, the predetermined condition of heat-treatment of the first work piece is aging of 18% Ni maraging steel at the range of 485±5°C for 210 to 230 minutes.
[0024] In an embodiment, the predetermined condition of heat-treatment of the second work piece (104) is hardening at the range of 870±5°C for 30 to 35 minutes followed by oil quenching and tempering (QT) at the range of 595±5°C for 60 to 65 minutes followed by air cooling of low-carbon chromium-molybdenum steel.
[0025] In an embodiment, the 18% Ni maraging steel and low-carbon chromium-molybdenum steel are a MDN250 grade and an AISI 4130 grade respectively.
[0026] In an embodiment, the heat transfer assembly is provided with an insulating paste adapted as a heat transfer media and a cooling assembly for cooling alteast one of the work pieces.
[0027] In an embodiment, the cooling assembly is constituted with a copper square tube water jacket mounted on the second work piece.
[0028] In an embodiment, the heater assembly includes a mineral insulated band heater, a copper foil, a thermocouple and a proportional integral derivative (PID) controller.
[0029] In another embodiment, a method for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel comprising the steps of i) atleast one first work piece and atleast one second work piece are mounted coaxially on a work desk. Step ii) a cooling assembly is mounted at a predefined position in proximity to the weld joint. Step iii) an insulating paste is applied at the joint of cooling assembly and the second work piece to act as a heat transfer means. Step iv) said work pieces are welded by pulsating TIG welding based on predetermined welding parameters. Step v) the insulating paste and the cooling assembly are removed post welding. Step vi) the welding joint and the heat affected zone (HAZ) region are heat treated comprising the steps of a) a shim type thermocouple along with a proportional integral derivative (PID) controller are mounted on the welded joint for sensing and controlling the temperature.b) a copper foil is wrapped to cover the welded joint along with the HAZ region and the shim type thermocouple. c) a heater assembly is mounted on at the center of the copper foil / welding joint covering the heat affected zone (HAZ) region on either side of the welding joint. d) the heater assembly is heated at a preset temperature with higher rate of heating and the heater assembly is maintained at said preset temperature for a predefined time period. e) the heater assembly is switched OFF. f) the heater assembly along with the copper foil, the shim type thermocouple and the PID controller are removed. g) the welded assembly (both the work pieces) are cooled at the ambient room temperature.
[0030] In another embodiment, the predetermined welding parameters of the pulsating TIG welding are a voltage range of 7.5 to 9.0 v, a peak current range of 60 to 75 A, a duty cycle in the range of 45 to 55%, a background current range of 45 to 55%, a frequency range of 2 to 5 Hz, a filler material class MDN 250W2 with 1.2mm wire diameter, a wire feed range of 0.11 to 0.15 m/min, a weld travel speed of 65 to 80 m/min and with 1 weld pass.
[0031] In an embodiment, the preset temperature with higher rate of heating of the heater assembly is in the range of 485±5°C and the predefined time period for maintaing the temperature is 1 hour.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] The foregoing summary, as well as the following detailed description of embodiments, is better understood when read in conjunction with the appended drawings. For the purpose of illustrating the disclosure, there is shown in the present document example constructions of the disclosure, however, the disclosure is not limited to the specific methods and device disclosed in the document and the drawing. The detailed description is described with reference to the following accompanying figures.
[0033] Figure 1 illustrates a schematic diagram of welding setup of a system for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel, in accordance with an embodiment of the present subject matter.
[0034] Figure 2a illustrates a schematic for the welding setup of the system for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel, in accordance with an embodiment of the present subject matter.
[0035] Figure 2b illustrates the welded dissimilar metals setup of the system for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel, in accordance with an embodiment of the present subject matter.
[0036] Figure 3 illustrates a cooling assembly of the system for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel, in accordance with an embodiment of the present subject matter.
[0037] Figure 4a illustrates a schematics of the post welding stress relieving setup of the system for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel, in accordance with an embodiment of the present subject matter.
[0038] Figure 4b illustrates the post welding stress relieving setup for the dissimilar metal welded of the system for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel, in accordance with an embodiment of the present subject matter.
[0039] Figure 4c illustrates a heater assembly of the system for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel, in accordance with an embodiment of the present subject matter.
[0040] Figure 5 illustrates a flowchart of a method for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel, in accordance with an embodiment of the present subject matter.
[0041] The figures depict various embodiments of the present disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following discussion that alternative embodiments of the structures illustrated herein may be employed without departing from the principles of the disclosure described herein.
DETAILED DESCRIPTION OF INVENTION
[0042] Some embodiments of this disclosure, illustrating all its features, will now be discussed in detail. The words "comprising", “having”, and "including," and other forms thereof, are intended to be equivalent in meaning and be open ended in that an item or items following any one of these words is not meant to be an exhaustive listing of such item or items, or meant to be limited to only the listed item or items. It must also be noted that as used herein and in the appended claims, the singular forms "a," "an," and "the" include plural references unless the context clearly dictates otherwise. Although any devices and methods similar or equivalent to those described herein can be used in the practice or testing of embodiments of the present disclosure, the exemplary, devices and methods are now described. The disclosed embodiments are merely exemplary of the disclosure, which may be embodied in various forms.
[0043] Various modifications to the embodiment will be readily apparent to those skilled in the art and the generic principles herein may be applied to other embodiments. However, one of ordinary skill in the art will readily recognize that the present disclosure is not intended to be limited to the embodiments illustrated, but is to be accorded the widest scope consistent with the principles and features described herein.
[0044] The present subject matter discloses a system (100) for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel as shown in figure 1. The system (100) comprises atleast one first work piece (102), atleast one second work piece (104), a heat transfer assembly, a work desk, a heater assembly (404). The first work piece (102) is an 18% Ni maraging steel of MDN250 grade and the second work piece (104) is a low-carbon chromium-molybdenum steel of AISI4130 grade. Dissimilar welding of both the work pieces (102, 104) are performed and the welding joint is a butt joint. The butt joint is formed simply by placing two pieces (102, 104) of metal end-to-end and then welding along the joint. As in a butt joint, the surfaces of the work pieces (102, 104) are joined on the same plane and the weld metal remains within the planes of the surfaces. Thus, work pieces (102, 104) are nearly parallel and do not overlap. The first work piece (102) is welded to the second work piece (104) coaxially. The heat transfer assembly is provided for transferring heat from the work pieces (102, 104). The heat transfer assembly includes an insulating paste (106) adapted as a heat transfer media and a cooling assembly (108) for cooling alteast one of the work pieces (102, 104). The insulating paste (106) is a Magna 904 "Heat Ban" insulating paste (106). The cooling assembly (108) comprises of a copper square tube water jacket (108). The cooling assembly (108) is mounted on the second work piece (104) along with the insulating paste (106).
[0045] Now referring to figure 2a and figure 2b, figure 2a relates to a schematic (200a) for the welding setup of the system for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel and figure 2b relates to the welded dissimilar metals setup (200b) of the system for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel. The first work piece (102) and the second work piece (104) are mounted on a work desk and aligned before welding is performed. The Magna 904 "Heat Ban" insulating paste (106) is applied near a welding joint (110, 204) and the copper square tube water jacket (108) is mounted on the second work piece (104) in the proximity of the welding joint (110) as shown in figure 2a and figure 2b. The 18% Ni maraging steel (102) and the low carbon chromium-molybdenum steel (AISI 4130) (104) are welded using pulsating TIG welding. This results in better quality of the weld joint with less mechanical property deterioration due to minimum heat input as pulse current source for TIG welding is used and the heat insulation adjacent to the welding joint is improved with defect free joint.
[0046] Now referring to figure 3, relates to a cooling assembly (108) of the system for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel. The cooling assembly (108) comprises of atleast one inlet port (112) and atleast one outlet port (114). The coolant flows from the inlet port (112) to the outlet port (114) and absorbs the heat generated during welding and cools the work pieces (102, 104). The coolant is a liquid or a gaseous form as per the requirement.
[0047] The low-carbon chromium-molybdenum steel (AISI 4130) (104) used in this present invention is in quenched and tempered (QT) Condition. The low-carbon chromium-molybdenum steel is hardened at the range of 870±5°C for 30 to 35minutes followed by oil quenched and tempered (QT) at the range of 595±5°C for 60 to 65 minutes followed by air cooling. The 18% Ni maraging steel (102) is aged. The aging of 18% Ni maraging steel (102) is done at the temperature range of 485±5°C for 210 to -230 minutes. The welding of dissimilar material is performed in particular heat treated condition as mentioned in Table-1. The welding parameter used for the dissimilar welding of 18% Ni maraging steel to low-carbon chromium-molybdenum steel are as shown in Table-2 and Table-3.

Material Heat Treatment Condition Chemical Composition % by weight UTS
(Mpa) 0.2% PS (MPa) Elongation %
C Mn Si P S Cr Ni Mo Cu Co Ti Al
18% Ni Maraging steels (MDN250) Aged 0.03 Max 0.10 Max 0.10 Max 0.01
Max 0.01 Max 0.5
Max 17 to 19 4.6 to 5.2 - 7.0 to 8.5 0.3 to 0.5 0.05 to 0.15 1760 (Min) 1725 (Min) 2(Min)
Low- carbon chromium-molybdenum steel (AISI4130) Quench and Tempered 0.28 to 0.33 0.40 to 0.60 0.15 to 0.35 0.025 Max 0.025 Max 0.80 to 1.10 0.25 Max 0.15 to 0.25 0.35 Max - - - 1300 (Min) 980 (Min) 8 (Min)
Table-1

Weld Passes Type of Welding Technique Filler material Wire feed (m/min) Weld travel speed (m/min) Joint Type
Class Wire Dia. (mm)
01 Pass GTAW (TIG) MDN 250W2 1.2 0.11 to 0.15 65 to 80 Butt
Table-2

Voltage Peak Current (A) Duty Cycle (%) Back ground current (%) Frequency (Hz)
7.5 to 9.0 60 to 75 45 to 55 45 to 55 2 to 5
Table-3
[0048] After welding is performed using pulsated TIG welding as per the above mentioned conditions and parameters, the welding joint (204) appears as shown in figure 2a and figure 2b. Further, the Magna 904 "Heat Ban" insulating paste (106) and the copper square tube water jacket (108) are removed.
[0049] Now refering to figure 4a, figure 4b, figure 4c, figure 4a relates to a schematics of the post welding stress relieving setup (400a) of the system for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel, figure 4b relates to the post welding stress relieving setup (400b) for the dissimilar metal welded of the system for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel and figure 4c relates to the heater assembly (404). After the welding of dissimilar materials is performed, a stress-relieving treatment (400a, 400b) is carried out post welding locally at the welding joint and the HAZ region as shown in figure 4a, figure 4b. A heater assembly (404) is adapted for the heat treatment of said welding joint (110, 204). The heater assembly (404) comprises of an mineral insulated band heater, a copper foil, a thermocouple and a proportional integral derivative (PID) controller. The mineral insulated band heater is installed on the welding joint (204) such that the centre of the mineral insulated band heateris located at the centre of the welding joint (204). The mineral insulated band heater also covers the HAZ area on either side of the welding joint (204). The copper foil of thickness 0.4mm is wrapped around the welding joint (204) for conducting the heat of welding joint (204) and the heat effected zone (HAZ) region. The copper foil is placed between the mineral insulated band heater and the welding joint (204). The thermocouple (not shown in figure) is installed between the copper foil and the welding joint (204). The thermocouple used is a shim type thermocouple as the size of the shim type thermocouple is thin and can be easily installed. The PID controller (not shown in figure) is used with the shim type thermocouple for monitoring and controlling the temperature of the mineral insulated band heater. The mineral insulated band heater is heated to the set temperature of 485±5°C and the rate of heating is higher to reach the set temperature at a less duration of time. The mineral insulated band heater is maintained at the set temperature (refered as soaking) for 1 hour. After completion of soaking, the mineral insulated band heater is switched off and removed. Then the welded material is cooled due to the ambient air at room temperture for post weld stress relieving set up. The post welding quality and integrity of the dissimilar material welding joint meets the design and application requirements.
[0050] Now refering to figure 5, figure 5 relates to a method (500) for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel. The method (500) comprises step i) atleast one first work piece (102) and atleast one second work piece (104) are mounted coaxially on a work desk. Step ii) a cooling assembly (108) is mounted at a predefined position in proximity to the weld joint (110, 204). Step iii) an insulating paste (106) is applied at the joint of cooling assembly (108) and the second work piece (104) to act as a heat transfer means. Step iv) said work pieces (102, 104) are welded by pulsating TIG welding based on predetermined welding parameters. Step v) the insulating paste (106) and the cooling assembly (108) are removed post welding. Step vi) the welding joint (110, 204) and the heat affected zone (HAZ) region are heat treated (400) comprising step a) a shim type thermocouple along with a proportional integral derivative (PID) controller are mounted on the welded joint (110, 204) for sensing and controlling the temperature. Step b) a copper foil is wrapped to cover the welded joint (110, 204) along with the HAZ region and the shim type thermocouple. Step c) a heater assembly (404) is mounted on at the center of the copper foil / welding joint (110, 204) covering the heat affected zone (HAZ) region on either side of the welding joint (110, 204). Step d) the heater assembly (404) is heated at a preset temperature with higher rate of heating and the heater assembly (404) is maintained at said preset temperature for a predefined time period. Step e) the heater assembly (404) is switched OFF. Step f) the heater assembly (404) along with the copper foil, the shim type thermocouple and the PID controller are removed. Step g) the welded assembly (both the work pieces 102, 104) are cooled at the ambient room temperature.
[0051] Table 4 shows the mechanical property evaluation of the dissimilar material weld joint. The above test results shows that weld joint is free from defects, and due to optimization of HAZ and change in microstructure, test results are consistent and meets the target values repetatively.

Property Unit Target Value Results
01 02 03 04 05
Ultimate Tensile Strength N/mm2 994 min. 1245.2 1196.7 1206.2 1189.6 1156.6
0.2 % Proof Strength N/mm2 880 min 1232.1 1139.4 996.3 1160.2 1080.9
Elongation (25mm GL) % 1 min 2.16 1.93 2.41 2.29 2.05
Table-4
[0052] Exemplary embodiments discussed above may provide certain advantages. Though not required to practice aspects of the disclosure, these advantages may include the following.
[0053] Some embodiments of the subject matter enable to provide a system and method for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel to eliminate or reduce the residual stresses of welding joints.
[0054] Some embodiments of the subject matter enable to provide a system and method for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel to control the extent of softening.
[0055] Some embodiments of the subject matter enable to provide a system and method for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel to optimize the extent of Heat affected Zone.
[0056] Some embodiments of the subject matter enable to provide a system and method for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel to remove heat during welding.
[0057] Some embodiments of the subject matter enable to provide a system and method for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel to remove internal stresses after welding.
[0058] Some embodiments of the subject matter enable to provide a system and method for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel to eliminate Heat affected Zone to base metal interface cracking.
[0059] Some embodiments of the subject matter enable to provide a system and method for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel to reduce the mechanical property deterioration.
[0060] Some embodiments of the subject matter enable to provide a system and method for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel to produce better quality weld joint.
[0061] Some embodiments of the subject matter enable to provide a system and method for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel to produce better performing structures or pressure vessels.
[0062] Some embodiments of the subject matter enable to provide a system and method for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel to eliminate post weld effects on the fabricated hardware.
[0063] Some embodiments of the subject matter enable to provide a system and method for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel to produce a defect free welding joint.
[0064] Some embodiments of the subject matter enable to provide a system and method for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel which is compact, cost effective and easy to implement.
[0065] Following is a list of elements and reference numerals used to explain various embodiments of the present subject matter.
Reference Numeral Element Description
100 Welding Setup
102 18% Ni. Maraging Steel
104 Low-Carbon Chromium-Molybdenum (AISI4130) Steel
106 Insulating Paste
108 Cooling Assembly
110 Weld Joint Configuration
112 Inlet Port
114 Outlet Port
200 Pre-Welding Setup
204 Weld Joint
400a, 400b Post Welding Setup
404 Heater Assembly

Equivalents
[0066] With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity.
[0067] It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as "open" terms (e.g., the term "including" should be interpreted as "including but not limited to," the term "having" should be interpreted as "having at least," the term "includes" should be interpreted as "includes but is not limited to," etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases "at least one" and "one or more" to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles "a" or "an" limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases "one or more" or "at least one" and indefinite articles such as "a" or "an" (e.g., "a" and/or "an" should typically be interpreted to mean "at least one" or "one or more"); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of "two recitations," without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to "at least one of A, B, and C, etc." is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., "a system having at least one of A, B, and C" would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances, where a convention analogous to "at least one of A, B, or C, etc." is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., "a system having at least one of A, B, or C" would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase "A or B" will be understood to include the possibilities of "A" or "B" or "A and B."
[0068] Although implementations for a system and method for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel have been described in language specific to structural features and/or methods, it is to be understood that the appended claims are not necessarily limited to the specific features described. Rather, the specific features are disclosed as examples of implementation for the system and method for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel.
,CLAIMS:
1. A system (100) for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel comprising:
atleast one first work piece (102) configured to be heat-treated at a predetermined condition;
atleast one second work piece (104) configured to be heat-treated at a predetermined condition;
a heat transfer assembly configured for transferring heat from the work pieces (102, 104);
a work desk configured for mounting and aligning the first work piece (102) and the second work piece (104); and
a heater assembly (404) configured to be adapted for the heat treatment of said welding joint (110, 204).

2. The system (100) for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel as claimed in claim 1, wherein the predetermined condition of heat-treatment of the first work piece (102) is aging of 18% Ni maraging steel at the range of 485±5°C for 210 to 230 minutes.

3. The system (100) for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel as claimed in claim 1, wherein the predetermined condition of heat-treatment of the second work piece (104) is hardening at the range of 870±5°C for 30 to 35 minutes followed by oil quenching and tempering (QT) at the range of 595±5°C for 60 to 65 minutes followed by air cooling of low-carbon chromium-molybdenum steel.

4. The system (100) for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel as claimed in claim 1, wherein the 18% Ni maraging steel and low-carbon chromium-molybdenum steel are configured to be a MDN250 grade and an AISI 4130 grade respectively.
5. The system (100) for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel as claimed in claim 1, wherein the heat transfer assembly is configured with an insulating paste (106) adapted as a heat transfer media and a cooling assembly (108) for cooling alteast one of the work pieces (102, 104).

6. The system (100) for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel as claimed in claim 4, wherein the cooling assembly (108) is constituted with a copper square tube water jacket (108) mounted on the second work piece (104).

7. The system (100) for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel as claimed in claim 1, wherein the heater assembly (404) is configured with a mineral insulated band heater, a copper foil, a thermocouple and a proportional integral derivative (PID) controller.

8. A method (500) for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel comprising the steps of:
i) mounting, atleast one first work piece (102) and atleast one second work piece (104) coaxially on a work desk;
ii) mounting, a cooling assembly (108) at a predefined position in proximity to the weld joint (110, 204);
iii) applying, an insulating paste (106) at the joint of cooling assembly (108) and the second work piece (104) to act as a heat transfer means;
iv) welding, said work pieces (102, 104) by pulsating TIG welding based on predetermined welding parameters;
v) removing, the insulating paste (106) and the cooling assembly (108) post welding;
vi) heat treating (400) at the welding joint (110, 204) and the heat affected zone (HAZ) region comprising the steps of:
a) mounting, a shim type thermocouple along with a proportional integral derivative (PID) controller on the welded joint (110, 204) for sensing and controlling the temperature;
b) wrapping, a copper foil to cover the welded joint (110, 204) along with the HAZ region and the shim type thermocouple;
c) mounting, a heater assembly (404) on at the center of the copper foil / welding joint (110, 204) covering the heat affected zone (HAZ) region on either side of the welding joint (110, 204);
d) heating, the heater assembly (404) at a preset temperature with higher rate of heating and maintaining the heater assembly (404) at said preset temperature for a predefined time period;
e) switching OFF, the heater assembly (404);
f) removing, the heater assembly (404) along with the copper foil, the shim type thermocouple and the PID controller; and
g) cooling, the welded assembly (work pieces 102, 104) at the ambient room temperature.

9. The method (500) for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel as claimed in claim 7, wherein the predetermined welding parameters of the pulsating TIG welding are configured to be a voltage range of 7.5 to 9.0 v, a peak current range of 60 to 75 A, a duty cycle in the range of 45 to 55%, a background current range of 45 to 55%, a frequency range of 2 to 5 Hz, a filler material class MDN 250W2 with 1.2mm wire diameter, a wire feed range of 0.11 to 0.15 m/min, a weld travel speed of 65 to 80 m/min and with 1 weld pass.

10. The method (500) for welding 18% Ni maraging steel to low-carbon chromium-molybdenum steel as claimed in claim 7, wherein the preset temperature with higher rate of heating of the heater assembly (404) is configured to be in the range of 485±5°C and the predefined time period for maintaing the temperature is 1 hour.