steels part two

Question 1

THREE MODES OF TOOL FAILURE

Answer 1

Fracture failure
Gradual wear
Temperature failure

Question 2

Taylor’s tool life equation

Answer 2

v Tn = C
v = cutting speed
n = cutting exponent
C = cutting constant

Question 3

CERMETS

Answer 3

Applications: high speed finishing and semi-finishing of steels, stainless steels, and
cast irons

Question 4

Sintered polycrystalline diamond (SPD)
What is structure

Question 5

cememted carbide

Answer 5

what is it used for
lathes,
milling

Question 6

manafacturing process of cemeted carbide

Answer 6

raw material
mixed
spray dryed
power mixutre
pressed into shape
sintered
grinding
coated at high temp

Question 7

properitites of cemented carbides

Answer 7

High compressive strength but low-to-moderate
tensile strength (brittle)
➢ High hardness (90 to 95 HRA) HRA: from Rockwell
hardness tester
➢ Good hot hardness
➢ Good wear resistance
➢ High thermal conductivity
➢ High elastic modulus - 600 x 103 MPa
➢ Toughness lower than HSS

Question 8

for steel cutting which type of cemented carbide is used

Answer 8

mixed carbides =yes
straight caribdes=no

Question 9

grain size vs properties

Answer 9

grain size increase= deformation resistance drops and toughness increases
same with cobalt percentage between 5 -12

Question 10

(CVD)- chemical vapor deposition

Answer 10

-chemical is fed into high temp chamber, which chemcal reaction takes place and then film of hardened particles are left on the surface of carbide.
make up 70% of all coated wc-co tools

Question 11

what do cobalt enriched grades have

Answer 11

high resistance to thermal deformation
significant increase in cutting edge strength

Question 12

advantages and disadvantages of CVD

Answer 12

suitable of high speed machincing
high wear resistance extends tool life
possible to apply mulit layer coating
disadvantages
substrate is limited to cemented carbides
cant be used for sharp egded tools
welding problems can occur during finsihing

Question 13

PHYSICAL VAPOR DISPOSITION (PVD)

Answer 13

done at low relaitvely low temps
conducted physically in form of either vacuum evaporation, sputtering or ion plating

Question 14

advantages and disadvantages of pvd

Answer 14

Advantages: Smooth, low-friction, fine-grained, and
crack-free coating even over sharp edges with
compressive residual stresses

➢ Lower cutting forces with sharp
edged tools
➢ Reduced tool-tip temperatures
➢ Finer workpiece finish
suitable for sharp edged
high fracture and thermal crack resistance
suitable for finishing
disadvantages-
coatings that are not conductive cant be used
low adhesion between substrate and coating

Question 15

Microalloyed steels

Answer 15

Basically low carbon (~ 0.05 – 0.10 wt% C) plain carbon steels with a very small
amount (< 1%) of strong carbide and nitride forming alloying additions, eg. Nb
(Niobium), Ti and V.

Question 16

improvements from mirco alloying

Answer 16

Refinement of the ferrite grain size, by formation of a fine sub grain structure.
2. Strain induced precipitation of carbides and nitrides.
(example of dispersion strengthening)

Question 17

procedure of treatment

Answer 17

before hot rolling, the ingots are soaked at higher than 1230 degrees which most of carbides and nitrides dissolve then austenitizing.

Question 18

cooling during rollig what does the carbides and nitrides do to grains

Answer 18

they pin the boundaries of the new formed austenite grains, which limited their size.

Question 19

dual phase steels

Answer 19

0.06 – 0.12wt% C; 0.4 – 2.5 wt% Mn

Question 20

what is intercritical annealing

Answer 20

at 720-780, the austenite-ferrite structure id quenched to formferrite and martensite.

Question 21

what aides martensite formation
dp contains

Answer 21

0.4% Mo
0.6 Cr
also use v,nb and Ti for carbide formation and grain size control

Question 22

duplex stainles steel

Answer 22

class of stainless steels that are intermediate between Ferritic
and Austenitic stainless steels.

Question 23

duplex structures contains

Answer 23

Duplex S.S. contains 18 – 30 % Cr to provide overall corrosion
resistance.
➢ 3 – 9 % Ni which improves the toughness and workability.
➢ Mo which again improves the corrosion properties, particularly
pitting corrosion.
➢ C contents are low (< 0.03wt%) to help reduce intergranular
corrosion (caused by Cr23C6 precipitation at grain boundaries).
* This also helps promote Cr2O3 formation
* Increases corrosion resistance
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