Hardfacing Process for Cobalt Base Bare Rods

(1) OXY – ACETYLENE PROCESS

(2) GAS TUNGETEN ARC (GTA) PROCESS  

 

(1) OXY – ACETYLENE PROCESS

 This is the best process to control dilution of the hardfacing alloy by the base metal because the OXY-ACETYLENE flame temperature is much lower than that of an arc, so melting of the rod and preheating of the base metal are easily controlled. A general oxy-acetylene hardfacing guide is:

 

(i)                  The surface of the part to be hardfaced must be free from rust, scale, grease, dirt and other foreign material.

(ii)                Preheat and postheat the work (if necessary) according to Table 1 to minimize the possibility of cracks developing in the deposit or base metal.

(iii)               Produce “sweating surface” (i.e. just melting the surface) by excess acetylene feather before starting hardfacing.

(iv)               Use excess acetylene feather as shown in figure 1 for depositing rod.

       Flame Adjustment

Hardfacing Alloy No	Recommended Flame
No.1, 6, 12	3X

 

 Table 1. Guide for Pre-heating and post-heating

BASE METAL	PRE-HEATING	POST-HEATING
Low Carbon Steels (C:0.4% Max) (Small items)	Unnecessary	Air-Cool
Low Carbon Steels (C: 0.4% Max) (Large Items) High Carbon Steels Low Alloy Steels (Small Items)	350 ~ 450o C 660 ~ 840o F	Slow – Cool in Diatomaceous Earth
High Carbon Steels Low Alloy Steels (large items)	500 ~ 600o C 930 ~ 1100o F	Slow – Cool in Diatomaceous Earth
Air-Quench Type Steels	600 ~ 650o C 1100 ~ 1200o F	Hold for 30 minutes in 650o C (1200o F) furnace and slow cool
Austenitic Stainless Steels (Small items)	Unnecessary	Air – Cool
Austenitic Stainless Steels (Small items)	500 ~ 600o C 930 ~ 1100o F	Slow-Cool in Diatomaceous Earth
13 Cr-Type Stainless Steels	600 ~ 650o C 1100 ~ 1200o F	Heat uniformly in 800 ~ 850o C (1480 ~ 1570o F) furnace and keep 650 ~ 700o C (1200 ~ 1300o F) for 4hrs per 1 in. (25mm) thickness and cool 50o C90o F) per hour.

 (2) GAS TUNGETEN ARC (GTA) PROCESS

 When the oxy-acetylene process is not suitable for the base material or when carburization by oxyacetylene deteriorates corrosion resistance of the base material, GTA is recommended. The general guide for this process is:

 (1)  The surface of the part to be hardfaced must be free from rust, scale, grease, dirt and other foreign material.

(2)  Preheat and or postheat the work according to table 1 if it is necessary to minimize the possibility of cracks developing in the deposit or  base metal.

(3)  Use direct straight polarity. Recommended nominal current settings are shown in Table 2.

(4)  Horizontal position is preferable.

Table 2. Guide for GTA Welding Current

Rod Dia Base Metal	1/8” (3.2mm)	5/32” (4.0mm)	3/16” (4.8mm)	1/4" (6.4mm)
Mild Steel / Low Alloy Steel	70 ~ 110A	90 ~ 130A	130 ~ 170A	170 ~ 220A
Austenitic Stainless Steel	80 ~ 120A	100 ~ 140A	140 ~ 180A	180 ~ 230A

 NOTE:   Use direct current straight polarity

            Electrode: Thorium – Tungsten 3.2 to 5.0 mm dia

            Ar flow rate : 10 to 15 liters per minute

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