Dilution, Free Machining & Tungsten

Weld Dilution

mixing of filler material and base material in the weld pool and fusion zone

Dilution

listed as a percentage and refers to the percentage of the weld pool that comes from the base material (metal)

What are the factors affecting dilution?

joint design

Fillet Welds Joint Design and Dilution

have lower dilution than groove welds

Square grooves Joint design and Dilution

generally have greater dilution than “v” or “u” or “j” groove welds

Thinner base material generally result in…

higher dilutions than thicker base metals and root pas will typically have dilution

Each pass in a large multipass fillet or groove weld will have…

a different dilution

Explain how the dilution of the weld pass will look like.

Weld pass 1 will have the greatest dilution, followed by pass 2,3,4& 6. Pass 5 will have almost no dilution.

In single pass groove welds the joint design will result in:

50% to 80% dilution

What will result in high dilution?

small groove angles, small root openings, and large root faces

Just like fillet welds the root pass…

mulitpass groove welds will have the highest dilution

Fill passes will typically have what?

less dilution

When welding metals such as cast iron, aluminum, dissimilar alloy, low alloy steel, free machining alloys, etc. you should pay particular attention to:

the root pass

What is the one of the goal of dilution when welding?

to minimize dilution

Do each welding process inherently produce a different dilution?

True

What is the percentage of dilution in electron beam, laser and orbital welding (performed autogenously)?

100%

Welding processes like submerged arc, flux core, shielded metal arc, and plasma arc where penetration is high, dilutions are high

True

Welding parametes have….

a large effect on dilution rate

For each welding process there is a range of dilutions depending on welding parameters

True

In welding parameter, generally higher amperages results in..

higher dilution rates

Generally higher preheat temp. results in …

higher dilutions

Parameters can be varied so that weld passes that are adjacent to base metal can be low heat input and low dilution

True

Can subsequent passes have a higher heat inpit and dilution in welding parameters?

True

What are the side weld beads called?

Butter passes

How are butter and fill passes made?

can be made using different filler metals or even different welding processes as well as different weld parameters

Why is dilution important?

can determine whether a weld is sucessful or not

What are some areas of welding where dilution is critical?

surfacing, heat treatable aluminum alloys, cast iron, dissimilar metal welding, free machining alloys, tool steels

What is surfacing welds?

a heat-, wear-, and corrosion-resistant metal coating is deposited on a workpiece's surface or edge. can be hard facing alloy for wear or a stainless alloy for corrosion resistance

In surfacing welding, how much dilution do you want?

as little dilution as possible

The greater the dilution of the base material into the weld,,,,

the softer the hard facing will be

How much dilution do you want for corrosion resistant surfacing alloys?

the more dilution the less corrosion resistant they are

Many heat treatable luminum alloys are:

not weldable autogenously (no filler metal)

How do you weld without cracking in aluminum alloys?

minimum base metal dilution is required with specific filler metals

In aluminum alloys, base metals with alloy elements in certain ranges are very crack sensitive.

True

In aluminum alloys, what is the goal of dilution?

Get enough dilution so the weld chemistry is out of these ranges

What metal has high carbon?

cast iron

In cast iron, if too much base metal is diluted into the weld pool the carbon content gets too high and causes cracking during cooling.

True

How do you prevent cracking in welding cast iron?

Dilution must be kept very low

Which filler metal can be used when welding cast iron?

nickel filler metal

What are free machining alloys?

metal alloys specially formulated to be easily cut, drilled, or turned during machining operations. They consume less power, produce a better surface finish, generate small broken chips (rather than long stringers), and extend cutting tool life

Free machining materials are free machining due to evenly dispersed, soft inclusions which allows….

chips to be removed with little force and low heat build up

In free machining, alloy elements typically form inclusions of…

the cutting tool from within the material

In free machining alloys…

heating and water of the tool is reduced

What is the result of free machining alloys?

a metal that can be machined very efficiently with excellent surface finish

What microstructure of free machining alloy is this?

manganese sulfide inclusion

What microstructure of free machining alloys is this?

manganese sulfide inclusion

What are common free machining alloys?

lead, bismuth, sulfur, phosphorus

Welding free machining alloys inclusions have….

low melting and vaporization temperatures

During welding, welding free machining alloys inclusions…and what does it cause during welding?

stays vapors and liquid to very low temperatures; cause cracking and porosity in the welds

What is considered unweldable?

all commonly used free machining alloys

In welding free machining alloys, if welding is unavoidable…

dilution must be high, heat input must be low, and there is no restraint

Chronic exposure to fumes from welding free machining alloys can be a health hazard.

true

Brazing and soldering of some free machining alloys are possible however, the particular braze alloy and base metal combinations must be evaulated.

True

Is aluminum 2011 brazable?

False - not brazable with any braze alloy

Is stainless 303 brazeable?

True- brazable using a variety of alloys

Vacuum furnace brazing should mot be performed since the low vaporization temperature is worsened by the vacuum and the furnace can become contaiminated.

True

What is the density of tungsten?

18.8g

What is the density of iron?

7.8g

The element symbol “w” comes from the word “Wolfram” which tungsten is called in Germany

True

What is the melting temperature of Pure tungsten?

6192F

Tungsten has the lowest thermal expansion of any metal.

True

The properties of tungsten make it an excellent chooice for applictions requiring extremely high temperature.

True

Tungsten is produced as powder and is usually sintered to form usable shapes such as welding electrodes

True

What is a common application for tungsten?

welding electrodes

Tungsten welding electrodes involve alot of metallurgy`

True

Typically only tungsten diameter, tip preparation, and oxide type (AWS classification) are thought of during welding.

True

What are critical factors of tungsten welding electrodes?

oxide type (AWS classification), grain size, oxide size, oxide dispersion, tungsten size, preparation

Tungsten welding electrodes are either pure or alloyed with an oxide

True

What is the code AWS A5.12?

Standardized electrodes for welding

What is the purpose of an oxide?

reduce the “work function” of the electrode

What is work function?

is the amount of energy required to remove one electron from the surface of the electrode

The oxide alloy determines the operating characteristics of the electrode

True

The unit for work function is electron volt or “eV”

True

The lower the energy required to strike and maintain an arc for a given amerage…

the lower the eV

the lower the energy required to remove electrons from the surface the cooler the electrode will run for a….

given amperage and the more stable the arc will be

In oxide evaporation and migration…

oxides from a thin layer on the surface of the elctrode which lowers the work function

Oxides slowly evaporate off the…

surface of the electrode with use

As oxide are depleted from the surface,….

they are replaced by fresh oxides migrating from the inside of the tungsten