Steel Flashcards

1
Q

Strength and hardness of steel _____ with increase of CC, but ductility and toughness _____

A

increases; decrease

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2
Q

What happens if Mn is not added to steel?

A

S combines with Fe to form FeS at GB, which has low Tm. Steel containing FeS can’t be hot worked, as it will melt

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3
Q

What are the effects of adding Mn to steel?

A

> increases yield strength due to substitutional solid solution hardening
decreases diffusion coefficient of C
increases hardenability
decreases ductile to brittle transition temperature

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4
Q

What are the effects of adding Ca to steel?

A

> it forms calcium sulphide/silicate that remain equiaxed after hot rolling
the change from elongated to equiaxed grains improves ductility and toughness

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5
Q

What are some impurities in steel?

A

a. S must be <= 0.05wt%
b. P forms very brittle Fe3P on GB that affects ductility and toughness
c. Si leads to inclusions that adversely affect fracture-sensitive properties

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6
Q

Low carbon steels (CC<0.25wt%)

A

> 20-20-20 steel
low strength
high ductility, formability, weldability

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7
Q

Medium carbon steel 0.3-0.6wt% C

A

> higher strength than low carbon, but lower ductility and weldability
can be heat treated to increase strength and hardness
used for hammers, axles, shafts, etc.

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8
Q

High carbon steel 0.6-1wt% C

A

> high hardness, low ductility, toughness, and weldability

> used for springs, cables, cutlery, files, saw blades, etc.

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9
Q

Full annealing

A

hypo and eutectoid steels are are heated and furnace cooled slowly to get coarse pearlite

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10
Q

Isothermal annealing

A

> plain carbon and alloy steels to produce soft ferrite-pearlite microstructure
steel is austenized, held until transformation occurs, air cools and minimizes residual stresses

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11
Q

Patented heat treatment

A

> used for steel ropes and springs

> microstructure of fine pearlite with high hardness

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12
Q

Normalizing of steels

A

> steels heated and held to complete dissolution of C and cooled in air
normalizing refines grain structure and homogenizes

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13
Q

Quench hardening

A

> for max hardening, steel is quenched at rates faster than critical CR to ensure austentite –> martensite
martensite forms because kinetics are faster than pearilte, even though it is metastable
martensite may transform into ferrite and carbide

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14
Q

Hardenability:

A

ability of steel to form martensite on quenching from

austenitic state

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15
Q

Depth “d” to which at least 50% martensite is present is a measure of:

A

the depth up to which the steel has hardened

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16
Q

Depth of hardening:

A

the depth up to which the microstructure contains at least 50% martensite

17
Q

Effects on depth

A

> thickness of the component ^ d v
rate of quenching v d v
austenite grain size v d v
component size ^ d v

18
Q

Depth of hardening is ____ for AISI 1045 steel specimens thicker than about 3”

A

zero

19
Q

Critical diameter

A

the largest (thickest) bar that has 50% martensite at its center

20
Q

All the bars of diameter larger than dc have ___ ___ 50% martensite at the center, and all therefore, not
effectively hardened throughout.

A

less than

21
Q

The critical diameter dc is ________ of specimen

diameter (thickness).

A

independent

22
Q

A component of thickness ____ dC can be

effectively hardened

A

less than or equal to

23
Q

Critical diameter depends on

A

> rate of cooling v dc v

> grain size v dc v

24
Q

Ideal critical diameter

A

the diameter of the thickest
cylindrical bar whose quenched microstructure contains 50%
martensite at the center, when the rate of cooling at the
component surface is infinite

25
Q

Ideal critical diameter is a measure of

A

the intrinsic hardenability of steel

(material property), a quantative measure of it that doesn’t depend on dimensions of sample or cooling rate

26
Q

Ideal critical diameter depends on

A

> coarse austenite grains = easier to form martensite and increases Di
Di increases with increasing CC

27
Q

Hardenability depends on

A

> coarse austenite grains = increase in hardenability (not recommended as toughness and strength decrease)
increase in CC increases hardenability
cobalt decreases hardenability
Mn, Cr, Mo, and V substantially increase hardenability of steel