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MMET207 ex 2
Review for exam II for Dr. Price's ENTC 207 course
Terms in this set (84)
Cold Work Prefixes
W (water hardening), O (oil quenching), A (air hardening), D (high C, high Cr)
Shock Resisting Prefix
Hot Work Prefixes
H10-H19 (chromium types)
H20-H39 (tungsten types)
H40-H59 (molybdenum types)
High Speed Prefixes
Mold Steels Prefix
Special Purpose Steels Prefix
Safety in hardening
Risk of damage form the hardening (quench cracks)
Depth of hardening
hardenability, through hardeing
(high alloy steels have better depth of hardening)
Size change in hardening
very important for design net part size change after hardening and tempering
Resistance to decarburization
scale, oxidation of surface during heat treatment
Resistance to heat softening
if enough heat is generated during operations that could cause tempering, softening of tool steel
difficulty to quantify, dependent upon specific application or wear criteria
the ability of a material to absorb energy and plastically deform without fracturing, all tool steels have little or no toughness, some are just worse than others
thermally induced dislocation and defect movement to remove internal strains, done to give it more dimensional stability
Reasons for Stress Relieving
-Weldments that require machining of weld deposits
-Machining of cold-finished shapes
-Casting that require significant machining
-Parts with extremely close dimensional tolerances
-Long slender parts machined from heavier shape
-an hr/inch thickness with an air cool
High-Strength, Low Alloy Steel
Steels with alloy additions that strengthen w/o need for customer heat treatment. Grade numbers indicate minimun yield strength in ksi.
Ultra-High Strength Steel
steel with yield strengths greater than 175 ksi
Mill-heated Treated Steel
-Composition can be like HSLA
-Supplied in heat treated condition
-High tensile and yield and also high hardness
-Many proprietary steels here
steel with designated additions of other elements
heating a steel hot enough to transform room temperature structures in steel to austenite
the sum of the alloy additions that promote hardening similar to carbon
an alloy of iron and carbon with carbon below 2%
hardening just the surface of the steel
steel rolled at room temperature
the elemental makeup of a material (usually expressed as weight percent)
the attributes (strength, hardness) of the substrate of a case hardened steel
a metal with a second phase in a host phase
the ease and chances of success (no failures) in bending, and drawing, etc.
metals containing additives to facilitate chip formation and improve tool ife
the mean diameter of crystallites in a metal as viewed in cross section
the process of taking microhardness readings in small increments inward from a case-hardened surface
mill shapes produced by elevated temperature (red) processes
steel alloy additions that strengthen without the need for customer heat treatment
a steel hardenability test in which the end of a heated bar is water quenched
Mill-heated Treated steel
steel that is already hardened when purchased from the manufacturer
SAE designation number
the four-digit numbering system for steels, originated by AISI and DSAE in the US
Ultra-High strength steel
steel with the yield strengths greater than 250,000 psi
steel with copper additions to promote the formation of a tenacious oxide when exposed outdoors
the ease with which a material can be successfully welded
Ex. 4140, 4340
-Toughness approximately same as low C steel
-YS 4-5x that of low C steel
-Better hardenability that low C steels
-Have relatively low C contents with alloy additions (most) Ex: 4617, 8615
-1020 can be used on thin/small sections ( < 1" )
-Have guaranteed hardening characteristics
-Uses H in number as suffiz to identify (4140H)
-Has highest alloy levels in range
-Boron relatively inexpensive way to greatly increase hardenability of low C steels
-B in center of number (50B44)
-Boron added to high C steels decrease hardenability
-Boron in difficult to control (levels) so it is not used more
Dual Phase Steels
have martensite or bainite "islands" in ferrite matrix achieved through special alloy content and heat treatment
Heating a steel to its austenitizing temperature ant then cooling it at a slow rate to prevent the formation of a hardened structure.
-Soak time: 1 hr/ 1 in thinckness
-cooling rate:100F/ hr (some steels require a rate as low as 30 F/ hr)
improves toughness of quench-hardened steels. When desired tempering temp is reached it is soaked for additional 2 hours then air cooled. Used to decrease the brittleness in a quenched metal
-below the Ac3
-Soak time varies on how much ductility and impact you want to gain
-Hardening should be followed if you want to form martensite
Is usually a subcritical heat treatment. Used to agglomerate iron carbide in the structure of carbon steels. increases machinability and soak times are usually very long
-48 - 96 hrs
-Ferrite grains and spheroidized cementite
-Quenching a hardenable steel from the austenizing temp to slightly above temo where martensite starts to form (Ms temp) and below temp where annealing type structure would result (AC3).
-held at temp until transformation is complete, them quenched or air cooled
-done in steps
-for thin pieces
-put in bath of molten salt then dumped in water
-Bainite is produce
AKA marquenching (similar to austempering except part is quenched from the austenitizing temp to a temp few degrees above the martensite start temp.
-held until temp is uniform in the piece then oil or air quenched to room temp
-Same as austempering but martensite is produced
Heating to the austenitizing temp and quenched to form hard martensite
-Surface hardening method using a combustible gas flame as the source of heat for austenitizing.
-Usually used on low-alloy or plain carbon steels with low hardenability, quenching after heating to the transformation temperature is usually done by water quench.
-same as flame hardening except for the source of heat input
-electric current flow induced into the work piece to produce a heating action
-Interstitial diffusion: atoms going into space between host atoms
-substitutional diffusion: Solutes find their way to vacancies
-Series of heat treatment processes that involve diffusion of alloying elements into a metal substrate that normally has only a low concentration of that element.
-Purpose is to provide a hard surface on normally unhardenable steels
-deterioration of a material or its properties because of reaction with its environment
used to describe materials that will corrode with nature more
describe a materials that won't corrode with nature as much as one that's more active than it
-Deterioration of a material or its properties because of a reaction of a material or its properties bc of reaction with its environment
-simplest for of corrosion
-uniform attack of all surfaces exposed to corrodent
-elecrochemical or natural
-ordinary atmospheric rusting
*can be prevented by removing the electrolyte or by using a material that is unaffected by the corrodent
local corrosion, surface cavities, usefulness of a part can be lost completely by removal of a relatively small area, caused by chemical nature of environments (Ex. brackish water, salt water, chloride bleaches), stainless steels are prone to pitting, occurs more in stagnant solutions that in moving solutions
-Corrosion is between metal to metal surfaces or between metal to non-metal surfaces.
-one side of the crevice must be exposed to the corrodent and the corrodent must be in the crevice
-commonly occurs in poorly gasketed pipe flanges and under bolt heads and attachments immersed in liquids
-destructive bc damage is so localized
-stainless steels & aluminum are highly susceptible
-2 different metals with diff energies, (anodic or cathodic)
-occurs with 2 opposite metals of metals in an opposite solution
Stress Corrosion Cracking
-cracking of metal under static stress
-material deterioration due to cracking
-stainless steels are prone to cracking at elevated temps
-happens only when surfaces are under tensile stresses
-alloy segregation at grain boundaries, atomic disarray
-occurs in grain boundaries in metals
-caused by alloy segregation at grain boundaries
-Sensitization of stainless steels, caused by welding
-leaves metal weak and spongy
-one constituent of metal alloy is preferentially removed from the alloy, leaving altered residual microstructure, dezincification, and dealloying is usually weak and spongy
Corrosion occurs because...
metals are not i natural state until they return to the Ore from which they were found
Magnesium and Magnesium alloys ( most active, Anodic) & Platinum (most Passive, least active, cathodic)
Anode, least noble
Cathode, most noble
ion with positive charge
ion with negative charge
solutions containing dissolved ions.
May be described as concentrated if it has high concentration of ions, or dilute if it has low concentrations. Strong if high proportion of solute dissociates to form free ions.
How does paint protect against corrosion?
Prevents oxygen from touching the metal, acts like a coat
What environments affect corrosion?
pH, Temperature, velocity, concentration, inhibitors, cleaning, aeration, gases, acids, bases, salts, & solvents
operating conditions affect corrosion: Temperature
increase rate of reaction
operating conditions affect corrosion: Velocity
veolocity of a corrodent over a metal surface affects corrosion rate
operating conditions affect corrosion: Impurities
Abrasive impurities, (increase corrosion). Chemical impurities (organic solvent pitting corrosion)
operating conditions affect corrosion: Aeration
none, increased, or decreased corrosion; introducing oxygen into a reaction
What microstructure is produced by hardening 4340 steel?
austenite and cementite
That phases are present after 52100 steel has been raised above the Ac3, soaked for the appropriate time, then oil quenched?
A welded steel structure is raised to 1100F and held for 1 hour per inch of thickness What probably is being done to it?
What is thd result of heating a 1020 steel 50F above the Ac3, soaking for the appropriate time, then furnace cooling?
When should Martempering be used?
AKA marquenching. is similar to austempering, expect the part is quenched from the austenizing temp to a temp a few degrees above the martensite start temp, held there till it is uniform in the piece. (process is used to minimize quench distortion)
Interstitial carbon weakens an iron crystal lattice.
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