Tips for Welding Austenitic Stainless Steel

Tips for Stainless Steel

June 2022 - Welding Alloys Manufacturers In India

Tips for Welding Austenitic Stainless Steel

Stainless steel is the type of high alloy steel with at least 11.5% Chromium. Iron content exceeds that of any other element. Carbon is generally less than 1.5%.

Properties of Stainless Steel:

    • Mechanical Properties: Compared to other materials, stainless steel has strong mechanical properties at ambient temperatures, In particular, it combines ductility, elasticity, and hardness, In addition, it offers good mechanical behavior at both low and high temperatures. So widely used in all Industries.
    • Oxidation Resistance: Stainless steel has the best resistance of all metallic materials when used in structural applications, having a critical temperature above 800°C. Grades of Stainless steel can be used for Sub-zero temperatures.
    • Corrosion Resistance: With a minimum chromium content of 10.5%, stainless steel is continuously protected by a passive chromium oxide layer, This special feature gives stainless steel its resistance to corrosion.
    • Versatility: Stainless steel has a wide variety of finishes, from matte to bright, including brushed and engraved. It is widely used by architects for building envelopes, interior design, and street furniture.
    • Easy Maintenance: Stainless steel objects are easy to clean, and common cleaning agents.
    • Environment friendly: Stainless steel is the “green material” and is infinitely recyclable. It is environmentally neutral and inert when in contact with elements like water, and it does not release compounds that could change their composition.

Types of Stainless Steel Used in Industry:

  • Austenitic  Non-Magnetic & work Hardening 
  • Ferritic Soft & Magnetic 
  • Martensitic  Magnetic & Hard
  • Duplex Magnetic & Wok Hardening 
  • Precipitation Hardening

Problems in Welding Austenitic SS:

  • Carbide Precipitation or IGC 
  • Heat of Welding 
  • Porosity
  • Contamination

Carbide Precipitation or Inter Granular Corrosion:

The major problem encountered in welding austenitic stainless steel is intergranular corrosion or carbide precipitation.

  • When welding Austenitic SS  between 420 to 880 deg. C base metal temperature also known as “Sensitisation Temperature”  a large volume of Cr is picked  in the grain Boundaries of the HAZ area
  • This forms Chromium Carbide which precipitates and forms at grain boundaries –the area adjacent to the HAZ area
  • So on working condition or in service, the HAZ area starts corroding at a faster rate as this area cannot form Cr2O3 due to Cr depletion 
  • This phenomenon is called Inter Granular Corrosion or Carbide Precipitation

Remedies:

  • Controlling the carbon content (0.03% or below)
  • Addition of Carbide stabilizers like Ti, Nb.
  • Heat Treatment (Solution annealing).
  • Controlled welding below 450 Degrees 

The heat of welding:

  • Cracking from the HAZ area
  • Loss of Corrosion Resistance 
  • Warping or Distortion of Material 
  • Loss of Mechanical Properties 

Porosity :

  • This is caused by Dirt, Grease & marking material 
  • Poor Quality of Flux coating 

Contamination:

  • Contaminants in SS like Sulphur, Carbon, Iron, Copper & lead is the root Couse of failure of welded joints and also poor corrosion resistance 

 Remedies: Do’s for Welding Austenitic Stainless Steel: 

  • Rigid Fixturing with more tack welds
  • Sequence welding to control heat 
  • Baking of electrode 200 deg –one hour before welding.
  • Proper Cleaning of weld area before starting the job 
  • Use short arc & low heat Input Welding Electrodes 
  • Use Correct or optimum diameter electrode during welding 
  • Clean slag after every pass / between passes.

Hence with these simple strategies, we can weld all applications of austenitic stainless steel.

We at Ador Fontech have designed & developed this exclusive range of LH- Low heat Input Welding Electrodes, TIG & MIG wires for welding of all types of stainless including austenitic stainless steels.

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Tips to Weld Cast Iron

 Cast iron can be described as a wide variety of iron-based materials containing Carbon of 1.7%-4.5%

types of weldable cast ironIt also contains Silicon- 0.5%-3%, Manganese-0.2%-1.3%, Phosphorous-0.8% max & Sulphur -0.2%max. The major distinguishing feature between steels is carbon content, it has maximum influence on the property of CI. A low percentage promotes the formation of hard white cast iron & higher percentage promotes the formation of grey cast iron.

Properties of Cast Iron:

  • Hardness: Cast iron is hard and it can be hardened by heating and sudden cooling. This makes it quite durable.
  • Melting Point: Cast iron has a lower melting point (1200 deg. C) as compared to the melting point of mild steel which lies in the range of 1300 deg. C and 1400 deg. C.
  • Castability: Cast iron is easier to cast when it comes to casting shapes out of the material. Due to the extra carbon & silicon present in cast iron, its molten form is more fluid and this makes it easier to cast the material into complex shapes.
  • Machinability: Cast iron is almost elastic up to ultimate tensile strength and produces discontinuous chips which break away from the sample easily. This helps to improve the cutting ability. Due to this, cast iron is the preferred material when it comes to high machinability and strength.
  • Highly porous hence it can be used in machine bases etc. as it provides good self-lubrication properties as oil & grease remain in the porous mass of cast iron.
  • It’s Porous and sponge-like structure means it can be used in machine bases as it has good damping properties 

Types of Cast Iron Used in Industry:

  • Grey Cast Iron
  • White Cast Iron
  • Chilled Cast Iron
  • Nodular Cast Iron
  • Malleable Cast Iron
  • Alloyed Cast Iron

Depending on carbon content and the procedure it is manufactured and these are common grades used in industry.

Problems in Welding Cast Iron:

  • CI is Brittle, so it tends to crack easily 
  • Porous & Contaminated so cleaning is very tough 
  • Too much Carbon tends to crack during welding 
  • Lesser Heat Conductivity, so heat dissipation is fast 
  • Carbon Pick up in the weld metal will be there leading to cracks in the HAZ.

Techniques to Weld Cast Iron.

Considering the above problems in cast iron, there are two methods or techniques to weld cast iron.

  • Hot Technique
  • Cold Technique

Hot Technique:

  1. Preheat the cast iron component to 350 deg. C – 400 deg. C
  2. Do the welding at the same temperature, ensure the temperature is maintained above 350 deg. C during the entire process of welding
  1. Slow cool the welded component by gradually cooling the component, if the job was done with heating cold reduce 50 deg. C per hour for per inch thickness of the job, If done in a furnace switch off & allow it to cool.

Cold Technique

Limit heat input in the cast iron welding  job by adopting the following methods :

  • Low current: Use low heat input welding electrodes & use lower diameter and lower amperages.
  • Stringer bead: Strictly no weaving during welding use only stringer beads
  • Short arc: Use arc length less than the diameter of electrode, preferable touch & weld type LH products 
  • Short bead length: Weld not more than 25 -30mm bead length only, always weld with a job on hand heat 
  • Peening: Hot peening with the ball-peen hammer is recommended for removing any residual stress in welding.

For welding of all weld-able grade cast iron, Nickel-based electrodes either pure nickel or Ferro-nickel type electrodes are used depending on the application requirements.

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We at Ador Fontech have designed & developed this exclusive Range of LH Low heat Input Welding Electrodes for welding cast iron using both welding techniques required for cast iron welding  

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Steel : Types of Steel and its Weldability

One of our most important manufactured products used in all industries has many applications & uses. Steel can be molded, pressed, machined, welded & woven to suit different purposes.

Steel making:  It’s a three-step process.

Types Ador

  1. Iron Making: Iron ore, coke & a flux (limestone) are combined in a blast furnace to produce molten iron containing about 4% carbon.
  2. Steel Making: Excess carbon is removed in a basic oxygen steel making vessel and the required alloy is added. The molten steel is then cast into billets, blooms, or slabs.
  3. Shaping: Steel is rolled to various sizes and shapes in a rolling mill.

Steels are basically a wide range of iron-based alloys with carbon up to 1 .7 %.

  • In plain carbon steels other elements are silicon (up to 0.6%), manganese(up to 1.65%), sulphur (up to 0.35%) & phosphorous (up to 0.13%).

      1. Elements in Steel: 

  • Carbon 
    • Up to 1.7 %
    • Promotes formation of carbides (cementite, pearlite & martensite)
  • Manganese
    • Deoxidizes the metal and facilitates hot working
    • Neutralizes sulfur by forming manganese sulfide which increases strength
    • Provides work-hardening property
  • Silicon
    • Deoxidizes steel
    • Increases resistance to scaling
  • Phosphorous
    • An impurity
    • Decreases ductility and toughness
  • Sulfur
    • An impurity
    • Decreases strength and impact resistance
    • Improves machinability

     2. Types of Steel :

  • Low Carbon Steels
    • Carbon up to 0.3 %
    • Good ductility & weldability
    • Comparatively low strength & not easily heat treatabletypes of steel

Welding: Have very good weldability.

No special precautions required

  • Medium Carbon steels
    • Carbon 0.3 to 0.6 %
    • Better strength & hardness than low carbon steel

Welding: Slight preheat around 200-250 deg. C and slow cooling.

 Use a low hydrogen type electrode

  • High Carbon Steels
    • Carbon : 0.6 % to 1.71 %
    • Easily heat treatable to high hardness

Welding: Poor weldability.

                                      Tendency to crack

                                       High preheat around 300 deg. C and very slow cooling

                                       Maintain high interpass temperature-300 deg. C

                       Post weld heat treatment and stresses relieving desirable

  • Alloy Steels

Contain alloying elements other than silicon, manganese, sulfur & phosphorous

  • High Alloy Steels

Alloying elements more than 10 % ( Ni, Mn, Cr)

Welding: High carbon equivalent hence form martensite.

                 Preheat around 300 deg. C and maintain interpass

                 Cool slowly

  • Low Alloy Steels

Alloying elements less than 10 %

           Welding:  Preheat requirements minimum.

                 

Types of High Alloy Steels :

  • Austenitic Manganese steels: 

More than 10 % manganese & high carbon

    • Known as Hadfield Steels
    • Work harden in service

Welding: Forms hard Carbides at temperatures above 175 deg. C.

                 No, preheat and fast cooling

  • Stainless Steels :
    • Chromium minimum 11.5 %
    • Excellent corrosion resistance
    • The addition of nickel gives good toughness & strength at sub-zero and elevated temperatures

Welding: Loose corrosion resistance on exposure over 500 deg. C

                                      No, preheat and fast cooling

                                      Low current & stringer beads

  • Tool Steels:
    • Used as Cutting Tools, Shear Blades, Dies, etc. 
    • Contain high carbon
    • Have a high amount of tungsten, molybdenum, chromium, cobalt, etc., and withstand temperatures up to 550 deg.

Welding: Difficult to weld.

                  High preheat around 350 deg. C & cool slowly

Hence, we at Ador Fontech have designed & developed this exclusive range of LH low heat input welding electrodes, TIG rods & MIG wires to weld all types of steel used in industry, resolving all problems as the unique solution provider for maintenance & repair welding.

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A Complete Guide to Welding

Welding Metals – An Introduction

To join ferrous with non-ferrous metals, various methods can be adopted.

  • Mechanical methods: Fasteners, rivets, etc.
  • Adhesive bonding method: Brazing and Soldering (a.k.a. welding)
  • Base metal does not fuse: Molten filler gets drawn into close-fit joints through capillary action (surface tension forces).
  • Brazing filler melts at >450⁰C, soldering at <450⁰C

Welding is the most commonly used process of all.

Welding – A Definition 

Welding can be described as a process of joining two or more pieces /edges of metal by producing a localized union through heat (fusion) with or without pressure to create a homogenous joint.

Types of Welding by Metal:

Autogenous: In this process, similar materials are joined without filler wire or electrode
Heterogeneous: Process of joining dissimilar materials, using a filler wire or welding electrode

Types of Welding by Method:

1. Fusion Welding (Electrical Energy):

  • Manual Metal Arc welding / Flux Cored Arc welding / Shielded Metal Arc Welding
  • TIG –Tungsten Inert Gas welding
  • Metal Inert Gas welding or Metal Active Gas welding
  • SAW – Submerged Arc Welding

2. Solid-State and other Non-electric Fusion Welding: Examples of non-fusion, non-electric process welding are:-

  • Thermit welding
  • Ultrasonic welding
  • Diffusion welding
  • Deformation welding.

Welding Processes

  • Fusion welding: Welding in the liquid state with no pressure, Union is by molten metal bridging
  • Solid State welding: Carried out below the melting point of the metal without filler additions, Pressure is often used,
    Union is often by plastic flow.

Solid State welding:

DEFORMATION WELDING: Two Surfaces in contact are brought into very close contact by applying high pressure, which deforms them. E.g., – Forge welding, Roll welding, Extrusion welding. (Not at very high temperatures)

 

deformation welding

DIFFUSION WELDING: Joining takes place by atomic diffusion of 2 surfaces in contact. Surfaces are usually heated to high temperatures (below the melting point) & pressure may be employed. E.g., Brazing, Braze welding & Soldering. Soldering is an oxy-fuel process of joining metals. The process temperature does not exceed 450⁰. Brazing is also an Oxy-Fuel joining process. The process temperature is between 450⁰ Degrees – 750⁰ degrees. Braze welding is similar to Brazing; the process temperature is above 750⁰ Degrees but below the melting point of the base metal.

Non-Fusion Process: Thermit welding is the most common process used in joining of railway tracks. In this process iron powders and Al binders are kept in Vat or a conical container above the joining rails. When they are fired due to chemical reaction and exothermic reaction, the iron powder melts and forms a joint between rails.

non fusion process

Introduction to Arc Welding: Basic welding processes used in Industry are

  • MMAW – Manual Metal Arc Welding or Shielded Metal Arc welding
  • GMAW – Gas Metal Arc Welding/ Flux Cored Arc Welding (MIG, MAG)
  • GTAW – Gas Tungsten Arc Welding (TIG)
  • SAW – Submerged Arc Welding

MMAW or SMAW- Shielded Metal Arc process: In the Shielded Metal Arc process or Manual metal Arc welding process the arc is established between Parent Metal and a flux coated welding electrode using electrical energy to melt and deposit weld metal. This is the most commonly used process in the world.

Basic Requirements for the SMAW process:

Heat source: Welding Equipment Current Range 30-400 A –depending on size of the electrode in general, even though there are welding machines used up to 600 Amps AC or DC welding machines can be used in SMAW Operation.

Welding Consumable: Flux coated welding electrode (1.6- 8 mm diameter)
A trained welder is required to operate the process, So SMAW or MMAW is the most commonly used process in the world.

SMAW Process advantages:

  • This is the simplest of all welding process.
  • Equipment Portable
  • Economical Cost of Equipment
  • Variety of application & wide availability of electrodes
  • Range of metals & their alloys can be welded
  • Welding in all Positions
  • Welding in Indoor & Outdoors
  • Extended welding cable to long distances in comparison to another process

Limitations of SMAW process:

  • Low productivity as in a 10-minute cycle welding happens only for 6 minutes
  • Process also involves a frequent changes of welding electrode
  • Moisture from flux coatings can create weld-related problems
  • Safety problems like arc strike, Stray current & electric shock risks
  • Absolutely Manual process – hence called Manual metal arc welding

GMAW & FCAW processes: 

  • A continuous solid wire, small diameter

                               GMAW uses solid wire, no flux

                               FCAW use flux-filled wire

  • Wire feed through the gun to the arc by wire feeder.
  • Weld pool may be protected from oxidation by shielding gas.
  • High productivity 3 kg/h or more
  • Direct current (DCEP mostly).

Process Requirement:

  • Welding power source
  • Wire feeder mechanism- In-built/separate
  • Gun with gas supply & trigger switch
    1. Manual/semi-automatic guns
    2. Automatic torches available
    3. Can be fitted to automation etc.

Advantages in GMAW:

  • Faster as compared to TIG & SMAW.
  • Can produce joints with deep penetration.
  • Thick & thin, jobs can be welded effectively.
  • Can be used for fabrication and maintenance repair job.
  • Can be mechanized easily
  • Reduced distortion.

Limitation in GMAW: 

More Complex due to

  • Electrode stick-out
  • Torch angle
  • Welding parameters
  • Type and size of electrode
  • Welding torch manipulation
  • Not suitable for outdoor welding applications

GTAW or TIG welding: GTAW or Tungsten Inert gas welding uses a consumable Tungsten electrode as the heat source.
This consists of the below.
Heat source – welding power source to create an arc between a tungsten tip and the parent metal
30-400A, AC or DC welding machine and 0-20V
Inert gas shielding is used in the process.
Consumable: filler rod can be used between 1 to 4mm diameter
Process Features:

  • Excellent control
    1. Stable arc at low power (80A at 11V)
    2. Independently added filler
    3. Ideal for intricate welds eg root runs in the pipe or thin sheet
    4. Low productivity 0.5kg/h manual
  • High quality
    1. Clean process, no slag
    2. Low oxygen and nitrogen weld metal
    3. Defect-free, excellent profile even for single-sided welds

Advantages in GTAW/TIG Process:

  • No slag inclusion
  • Clear visibility of arc and job
  • All position weldability
  • Suitable for high quality welding of thin material
  • Root run of thick materials
  • Ideal for Aluminum, Stainless steel & Titanium

Limitations in GTAW:

  • Slow as compared to SMAW/MIG/MAG & SAW welding
  • Possibility of tungsten inclusion in the weld deposit which is hard & brittle
  • Not suitable for outdoor welding

Submerged Arc welding process (SAW Process): In the Saw Process, as the name signifies, welding happens submerged beneath the flux. SAW process also employs welding consumables usually a wire & arc is established between the welding wire and base metal and welding happens underneath the metal powder of flux, shielding the arc from the atmosphere and its gases.

saw process

Heat source: Arc between a wire and base metal
Current Range: 200 Amps -1200 Amps
DC operation
Power Consumption

  • 35-56 KVA
  • Power source
  • Welding head and control box
  • Welding head travel
  • Flux recovery system (optional)
  • Positioners and Fixtures

Hence the basic difference between the two processes is that in the SMAW process, the flux-coated electrode provides the shielding from the atmosphere & in SAW process an external flux is delivered at the arcing area to act as a shield, so welding happens underneath the powder flux fed by a delivery system.

SMAW Process – Advantages:

  • Simplest of all Arc welding process
  • Equipment is portable
  • Economical cost of equipment
  • Variety of application & wide availability of electrodes
  • Range of metals & their alloys can be welded
  • Welding in all Positions
  • Welding in Indoor & Outdoors
  • Extended welding cable to long distances when compared to other processes

SAW Process advantages:

  • High productivity up to 2 to 10 kg per hour
  • Speed almost up to 2m/ min
  • Can be easily automated for even higher productivity

Limitations of the SAW process:

  • Bulky, expensive, and heavy equipment
  • Flat and horizontal positions only
  • Thicker sections (6mm and above)
  • Mostly ferrous materials (also Ni alloys)

Conclusion: A wide variety of processes are available for joining or hard surfacing ferrous and non-ferrous materials. Each of these processes provides different mechanical properties and works in specific conditions, with a welding power source. There are several factors to consider in welding rod selection:

  • Base metal properties
  • Tensile strength required
  • Welding current
  • Base metal thickness, shape and joint fit-up
  • Welding position
  • Specification and service conditions
  • No. of similar jobs – Scope for automation
  • Environmental job conditions

These methods are all commonly used by Industry. Before we select any particular method for welding, we need to analyze each of the factors listed above.

ADFL serves the industry with the manufacture and supply of all types of consumables for MMAW, MIG /Mag, TIG, SAW & non-fusion processes like soldering, brazing, and braze welding. This is why Ador Fontech’s name is synonymous with total solutions for any maintenance & repair problem, ensuring the Life Enhancement of Industrial components, to the complete satisfaction of customers.

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