1. Jennifer H.–Water Bottles
Materials Moments:
Jennifer H.–Water Bottles
Background image:

2. The “Ferrari” of Steel Microstructures:
Martensite

3. More on Case Hardening Carburizing: Case can be much deeper
Somewhat lower hardness
Used on lower-alloy steels (less expensive)
Continuous processing (less expensive)
Nitriding
Thinner, harder case
Used on Higher-alloy steels (pricier)
Longer run timesoften more costly
Run at lower temperaturesless part distortion
Can have white, hard, brittle surface prone to cracking
Batch processing (pricier)
Carbonitriding: increases case hardenability to obtain martensitic structure
The graph illustrates that some Nitrided steels have a higher surface hardness than Carburized steels but a lower overall total case-depth. The higher hardness comes from combining Nitrogen and alloying elements in the steel and usually for straight Nitriding you would use what is termed as an alloyed steel. For Carburized steels you would normally use a lower alloy steel (unless Vacuum or Low Pressure carburizing). 
For basic components that require some improvement in material properties, generally the lower cost treatments are to harden and temper (through harden) or carburize to shallow depths. However,  engineered components require more sophisticated processing that may result in additional costs but as previously explained this is more than offset by the increase in the material properties that result from the treatment. - See more at:
 Typically the higher the alloy content of the steel, the higher the cost of the base material. The Nitriding process CAN be a more costly process to run based on batch processing and long cycle times. However, other benefits of the Nitrided process such as lower temperature giving less distortion, additional strength properties from an alloyed steel, higher hardness (can lead to higher wear resistance) and other material properties can help to offset these costs.
See more at:
Carbonitriding can be applied to low cost, low alloy steels. The com- bination of adding nitrogen as well as carbon to the case increases the case hardenability sufficiently to result in a martensitic case that would not be possible with pure carburizing.
All three processes rely on the transformation of austenite into martensite on quenching. The increase in carbon content at the surface must be high enough to give a martensitic layer with sufficient hardness, typically 700HV, to provide a wear-resistant surface. The required carbon content at the surface after diffusion is usually 0.8 to 1.0%C. These processes can be carried out on a wide range of plain carbon steels, alloy steels and cast irons where the bulk carbon content is a maximum of 0.4% and usually less than 0.25%. Incorrect heat treatment can lead to oxidation or de-carburisation. Although a relatively slow process, carburising can be used as a continuous process and is suitable for high volume, surface hardening.
Carbonitriding is undertaken on a similar range of steels although the bulk carbon content can be as high as 0.4 to 0.5%. The process is particularly suited for hardening the surface of components that need a through-hardened core, such as gears and shafts. Carbonitriding is a modification of gas carburisation where ammonia is added to the methane or propane and is the source of nitrogen.
Which heat treatment method is better for precision gears?
Both carburizing and nitriding are acceptable heat treating methods for precision gearing. Through engineering, development and testing, Onvio has determined that carburized gears offer critical advantages for precision gearboxes.
HARDNESS DEPTH & CORE STRENGTH
Carburized gears feature a significantly deeper hardened layer whose hardness gradually decreases to the core hardness. This structure provides superior surface contact fatigue properties and ductility/impact resistance and strength of the core. In addition sufficient case depth obtained in the carburizing process is required as a needle roller bearing surface in the planet gears.
Nitrided gears can have a “white layer” on the surface which is very hard and brittle. If is not removed it can be prone to flaking and cracking leading to heavy surface fracture and gear failure. The hardened case depth is significantly thinner than in similar carburized gears and transitions to the core hardness immediately behind the case.
SURFACE HARDNESS
While both technologies offer very good surface hardness, Onvio believes that the depth penetration of carburizing provides our customers with superior performance and reliability for their demanding applications.
SURFACE HARDENING – INDUCTION PROCESS
It is frequently desirable to harden only the surface of steels by simply changing their microstructure without altering the chemical composition of the surface layers.  If steel contains sufficient carbon to respond to hardening, it is possible to harden the surface layers only by very rapid heating for a short period of time, thus conditioning the surface for hardening by quenching.
Hardenability—ability of steel to form martensite when quenched.

4. Case hardening Techniques compared

5. Elastic Deformation: Stress vs. Strain
t02_05_pg119
Elastic Deformation:
Stress vs. Strain
t02_05_pg119.jpg

6. Linear Elastic Behavior: Hooke’s Law
Stress is linearly proportional to strain
Stiffness – E – resistance to elastic deformation

7. Elasticity in Metals– Stiffness

9. Brittle Failure: Tensile test of Nodular Graphite Cast Iron
fig_06_11

10. YouTube
REAL Golf Ball hitting steel in slow motion by the USGA - YouTube 10

11. Comparison of E values

12. Types of Deformation
Elastic
Plastic
t02_05_pg119
t02_05_pg119.jpg

13. Plastic Deformation: Permanent

14. Plastic (adj.) 1630s, "capable of shaping or molding"
from L. plasticus, from Gk. plastikos "able to be molded, pertaining to molding,"

15. Plastic (adj.)
Main modern meaning, "synthetic product made from oil derivatives," first recorded 1909, coined by Leo Baekeland (see bakelite).
Counterculture slang: adjective meaning "false, superficial" (1963).

16. Plastic Deformation by Design

17. Plastically-formed paperclip can behave elastically
under normal use

18. Plasticity by design
Radial profile segments

19. Formed by plastic deformation; Behaves elastically
Binder Clip

20. Plastic deformation of Metals–Spring shape
Elastic deformation: Shock absorbers
Springs absorb shock transmitted from road to vehicle.

21. Plastic deformation of Metals
Galvanized steel
Chain link fence

22. Plastic deformation of Metals
Pipe bending

23. Plastic deformation of Metals
Sterling Silver chain

24. Plastic deformation of Ceramics Usually only at high temperature
Glassware fabricated plastically

25. Plastic deformation of Ceramics Usually only under high temperature
Ornate glassware fabricated plastically

26. Plastic deformation of Plastics Usually only under high temperature
Legos are thermoplastics
Plastic deformation of Ceramics Usually only under high temperature

27. Plastic deformation of Plastics
Thermoplastic
Motorcycle
helmet

28. Plastic Deformation by Accident

29. Mechanical Property: Plasticity—permanent deformation
Paper clip
under abuse

30. Plasticity by accident
Street lamp damaged during storm
(Bridgeport, CN)

31. Plasticity by Accident: Plastic Spoon

32. Plastic Deformation Plastic deformation – Permanent
Yielding – onset of plastic deformation
Yield strength – Stress at yield
(specified amount of strain).

33. t02_05_pg119
Stress-strain curve
t02_05_pg119.jpg 33

34. Strength Strength–stress at which “something” happens Yield strength
Tensile strength
Fracture strength

35. Yield Strengths for Metal Alloys
Table 6.2

36. t02_05_pg119
Tensile Test
t02_05_pg119.jpg 36

37. Tensile Test t02_05_pg119 AlMgSi alloy ductile fracture
t02_05_pg119.jpg
AlMgSi alloy ductile fracture 37

38. fig_06_11
Engineering Stress-strain curve for typical metals
fig_06_11

39. True Stress

40. YouTube: Aluminum Tensile Test.
Stress-strain curve shown

41. How does Ductility relate to Plastic Deformation?
Question of the Day:
How does Ductility relate to Plastic Deformation?

42. Ductility % plastic strain at fracture
(after subtracting off elastic recovery)

43. Toughness
A material’s ability to absorb energy and plastically deform before fracture
(also, A material’s resistance to fracture when a crack is present)
“The effect of aging on crack-growth resistance and toughening mechanisms in human dentin”
Dentin—The main, calcareous part of a tooth, beneath the enamel and surrounding the pulp chamber and root canals.
The effect of aging on crack-growth resistance and toughening mechanisms in human dentin

44. Hardness Resistance to scratching, denting

45. Brittle Deformation

46. Brittle Deformation
New Steel
Pressure Vessel
Failed during
Hydraulic Test
Improper heat
Treatment after
Welding (PWHT)
Need to consider the PWHT—post weld heat treatment—of welded steel fabrications. Need to temper the weld?
Brittle—Little or no plastic deformation before failure

47. Brittle Materials Very little plastic deformation before failure
Fracture strains <5%

48. Brittle Deformation
Cast Aluminum
Motorcycle Engine Cover

49. Brittle Metals
Cast Iron
Cast Aluminum
Very Hard (Ultra High-C) Steel

50. Brittle Materials mild steel: 0.16–0.29 wt% C Cast Iron: 3.0-4.5 wt% C
(ductile)
(brittle)
mild steel: 0.16–0.29 wt% C
Cast Iron: wt% C

51. fig_06_11 Brittle Failure: Tensile test of Nodular Graphite Cast Iron
Cast iron tends to be brittle, except for malleable cast irons. With its relatively low melting point, good fluidity, castability, excellent machinability, resistance to deformation and wear resistance, cast irons have become an engineering material with a wide range of applications and are used in pipes, machines and automotive industry parts, such as cylinder heads (declining usage), cylinder blocks and gearbox cases (declining usage). It is resistant to destruction and weakening by oxidation (rust). Nodular graphite reduces stress concentrations because of its spherical shape.

53. Deformation on the atomic scale
Elastic
Plastic
Brittle

55. Mechanical Property terms
Elastic - Elasticity
Plastic - Plasticity
Stiff - Stiffness
Ductile - Ductility
Strong - Strength
Brittle - Brittleness
Tough - Toughness
Hard - Hardness