basic meturrlegy and welding

8/10/2019 Basic Meturrlegy and Welding

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Basic Metallurgy and Steel Classification

Understanding the effect that welding has on steel is a critical part of any

fabrication procedure. It is important that Elevator Constructors familiarize

themselves with the some of the properties of metal and its reaction to the

welding process.

Properties of Metals

Mechanical Properties-Mechanical properties refer to the reaction that metals

have when they are under loads. These include properties such as brittleness,

ductility elasticity!, yield load!, and tensile pulling! strength.

Chemical Properties-Chemical properties are those associated with o"idation,

corrosion, and reduction. #eduction is the affect of atmospheric contamination

within the weld area. $ll metals o"idize. Corrosion is the wasting away of o"idized

metal.

Physical Properties- %hysical properties involve the alteration of a metals

internal structure by heat. Melting point, thermal conductivity, and grain structure

are e"amples a materials physical property.

If you loo& at a piece of steel through a microscope you can see that it is

composed of tiny grains. These grains are arranged in patterns that will be

changed by the welding process. The 'uality of a weld during fabrication and

during its service life is directly related to maintaining correct welding operations.

The transformation temperature of steel is ()))*. This is referred to as the

critical temperature,when steel begins to change from a solid to a molten state.

+elding temperatures ta&e place at -)-*. o it is easy to see that elevator

components such as brac&ets and stands can be distorted or defected bye"cessive heat.

The ability of a metal to absorb heat is called its Coefficient of Thermal

Conductivity. Using too much heat, the wrong polarity, or even e"cessive voltage

can cause the grain structure of the metal to become martensitic brittle! during


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cooling. Mild steel is the most common type of steel used in construction

materials. Mild steel, called $TM $)/, is ductile while still maintaining strong

mechanical properties. 0owever, it is easily altered by improper welding. Cold

welds caused by long arcing, laying down to many beads, and slag inclusions are

ordinary defects in welding mild steel.

Common Weld Defects Resulting in Weld Failure

Porosity- %inholes that occur when gasses are trapped within the weld.

%orosity is caused by oily, painted, or dirty metal. E"cessive current and high

travel speed will not allow the base metal to properly solidify.

Root Cracks-Crac&ing in the root of the weld. Caused by incorrect welding rod

and rapid shrin&ing. $ more ductile elastic! rod such as 12(3 should be used if

root crac&ing happens.

Inclusions-4oreign body such as slag trapped within the weld. Caused by

improper rod manipulation.

Caron Steel Classifications

!o" Caron-Commonly referred to as mild steel or $TM $)/. Carbon range of

.2- to .)2 percent. 0ighly ductile and is easily machined and welded.

Medium Caron-Carbon content of .)2 to .5- percent. Must be welded with

special rods such as E6((2(3. 0eat treatable.

#igh Caron-7ot usually welded. Carbon amounts of .5- to (.1 percent. 0igh

carbon steels are often heat treated and used in the manufacturing of hoist

ropes, springs, and tooling.

#ot Rolled Steel-$TM $)/. 8enerally formed into I6beams, channel, plate,

and angle iron.

Cold Rolled Steel-%recise control of dimensions, surface finish, and shape.

Cold rolled steels are identifiable by their sharp corners and are coated with mill

oil by the manufacturer.

Stainless Steels-Iron6carbon alloy with (2.-9 chromium content. The )22

series is used e"tensively in the elevator industry. $pplications include Car


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:perating %anels and e"terior surfaces that re'uire corrosion resistance. Can be

welded with T.I.8 process or with E6)23 welding rod.

basic meturrlegy and welding

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