Technical

Hard Facing by Thermal Spray & Fuse Process

Wear-resistant coatings that enhance component durability, performance, and service life.

  • Hard facing can be done on metals like : CF8M, CF8, CF3. CF3M, CA15, etc. Except CA15 Type Metal, all other metals can be cooled in atmospheric condition. For CA15 material, uniform cooling is necessary. Hence, it has to be cooled in lime or in oven. This procedure is required for every type of powder deposited.
  • The metal powder coating deposition is from minimum 0.2mm to 10mm maximum considering the wall thickness of the job. A 0.2-mm coating is possible in case of maintenance job. Hardness will not be as per the requirement.
  • The metal powder coating deposition is minimum of 1.7 to 2.0 mm in the radial direction for Casing / Impeller Wear Rings, Shaft Sleeves, Drums, Liners. As we are doing the process manually; the surface after coating is uneven for finish machining. After finish machining we can get coating thickness of 0.8 to 1.0mm including 0.3 mm grinding allowance in the radial direction.
  • Procedure of coating on ID and OD is similar but for ID coating, before should be minimum 50 mm and the job length should be maximum 100 mm or 2 * ID).
  • The spray guns, which are used for the process, are L&T make Eutalloy Torch and MEC make Superjet 100 Torch. Flame has to be set as per the requirement of the coating. Pressure and other parameters vary for different types of coating.
MAKEGRADEHARDNESS
Hoganas 1040
1060		 37 to 40 HRc
58 to 62 HRc
OMG Corp. 72W40
75W62
402P
602P		 37 to 40 HRc
60 to 63 HRc
35 to 40 HRc
60 to 65 HRc

1.Destructive Testing

(A) Rockwell “C” Hardness Test for Sample Piece

A sample piece is prepared with the given base metal and specified metal powder. This piece is then machined and checked for the required surface hardness using the Rockwell “C” Hardness Tester. When the specified hardness is reached, the metal powder is then cleared for the hard facing of the jobs to be supplied to the customer.
Note : Required hardness is not possible with 0.5 mm or less coating thickness. The following table describes the hardness achievable for a given coating thickness of 0.5 mm.

POWDERCOATING THICKNESSROCKWELL – C
10400.5 mm35 max.
10600.5 mm50 to 55
72 W 400.5 mm35 max.
75 W 620.5 mm50 to 55
402P0.5 mm33 max.
602P0.5 mm50 to 55

(A) Deposit Chemical Analysis

The sample piece prepared is drilled and the deposit chemical analysis is done.

(C) Micro-etching Test

The base metal is sectioned transversely to the direction of the hard-faced overlay. The microetching test is then performed on the sectioned faces. Then the sectioned faces are visually examined with X5 magnification for cracks in the base metal and or i the heat-affected zone, lack of fusion or other linear defects, which may result in weakness or brittleness. If none of the above defected is visible then the job is cleared for further process.

2. Non-destructive Testing:

Dye Penetration Test (D.P.T.) is performed on each finished job to ensure that there is no crack or blowholes present on the hard-faced surface.
Acceptance Criteria : Zero Porosity, Blowholes and Cracks.

Hard facing procedure specification

PROCESS:DETAILS
Process:Spray & Fuse Method.
Base Metal: ASTM A 240 Gr. 316/316L/304/304L
ASTM A 743 Gr. CF8/CF8M/CF3/CF3M.
Hard Facing Powders: Grade 1040 & 1060 of Hoganas.
Grade 102P & 602P of OMG America.
AWS Classification of Powder: AWS A5.13 R Ni Cr-A & AWS A5.13 R Ni Cr-C.
Base Metal Thickness:Min. 6mm.
Coating Thickness:Min. 1mm. Max. 2mm.

Hard Facing by Welding Overlay

Stellite (Cobalt Base Alloy) Coating with TIG Welding

Inspection and Testing

Destructive Testing
(A) Rockwell “C” Hardness Test for Sample Piece

A sample piece is prepared with the given base metal and specified Bare Rod. This piece is then machined and checked for the required surface hardness using the Rockwell “C” Hardness Tester. When the specified hardness is reached, the Bar Rod is then cleared for the hard facing of the jobs to be supplied to the customer.

Note : Required hardness is not possible with 2.0 mm or less coating thickness.
(B) Deposit Chemical Analysis
The sample piece prepared is drilled and the deposit chemical analysis is done.
(C) Micro-etching Test

The base metal is sectioned transversely to the direction of the Stellited overlay. The micro-etching test is then performed on the sectioned faces. Then the sectioned faces are visually examined with X5 magnification for cracks in the base metal or in the heat-affected zone, lack of fusion or other linear defects, which may result in weakness or brittleness. If none of the above defected is visible, the job is cleared for further process.

Note: Destructive-testing procedure is the same for each type of Bare Rods. The following table shows the hardness achievable for a coating thickness of 3.00 mm.
BARE RODSCOATING THICKNESSROCKWELL – C
Stellite 63.00 mm39 – 42
Stellite 63.00 mm45 – 50
Stellite 63.00 mm50 – 55
And other respective grades of Cobalt Alloy.

Inspection and Testing

Dye Penetration Test (D.P.T) is performed on each finished job to ensure that there is no crack or blowholes present on the hard-faced surfaces.
Acceptance Criteria : Zero porosity, blowholes and cracks.

PARAMETERSPECIFICATION
Preheat Temp.200° Celsius Min.
Interpass Temp.300° Celsius Max.
Shielding GasArgon
Mixtures (Gas)99.5%
Flow5 lit/min
CurrentD.C.
PolarityPositive +
Amperage70 to 100 A
Bare Rod Size3.16