Alloys

Question 1

What is the effect of Mn and Si in steel?

Answer 1

These elements are always present in plain carbon steel

• Mn increases yield strength and has a limited effect on the resistance on the resistance to crack propagation
• Si increases both Youngs Modulus and the yield strength, but lowers the resistance to crack propagation.

Question 2

What is basic plain carbon steel?

Answer 2

A type of steel characterized by the carbon content and is typically between 0.2-0.9% for structural steels.

Question 3

which are the ditrimental elements always present in basic carbon steel?

Answer 3

S and P and both needs to be lower than 0.05 wt%

svavel och fosfor

Question 4

Whiche elements can form the different phases?

Answer 4

• Austenite-forming elements: C, Ni and Mn; these elements decrease A1
• Ferrite-forming elements: Cr, W, Mo, V, Al and Si; these elements increase A1
• Carbide forming elements: Cr (the weakest carbide former)

Question 5

What is the relative effect of the addition of an alloying element?

Answer 5

Expansion of the austenitic field:
* if γ-stabilizers content is high enough austenite is stable at Room Temperature (RT)
* If austenite is completely stable at RT, martensite transformation is not possible!

Contraction of the austenitic field:
* if α-stabilizers content is high enough the polymorphism of steel can be completely suppressed
* If ferrite is stable from RT up to solidus temperature the martensite transformation is not possible!

Question 6

What is the role of copper (Cu)?

Answer 6

• Above 0.30% can cause precipitation hardening, increases hardenability, and if present in appreciable amounts, it is detrimental to hot-working operations.
• Additionally, it adversely affects surface quality.
• However, it improves atmospheric corrosion resistance (when in excess of 0.20%) and enhances tensile properties in alloy and low-alloy steels.
• In austenitic stainless steels, a copper content above 1% provides improved resistance to H2SO4 and HCl and reduces susceptibility to stress corrosion.

Question 7

Explain the Schaeffler Diagram

Answer 7

Shows the effects of composition on the microstructure for stainless steels. The diagram is an important tool for predicting the constitution of autsnitic Cr-Ni steel welds with carbon content up to 0.12 %.

The values obtained will be transferred to this graph and the resulting phase can be determined,

The diagram shows the effects of the proportion of two elements on teh structure obtaines after rapid cooling from 1050 dC to room temperature

The diagram shows that chromium is a ferrite stabilizer and nickel is an austenite stabilizer and it also shows the limit of the austenitic, ferritic and martensitic phases in relation to the chromium and nickel equivalent.

Question 8

What doe sit mean with alloys can either be substitutional or interstitial?

Answer 8

Steels is an interstitial alloy sonce the carbon atoms are much smaller than the iron atoms.

Question 9

What is weathering steel and stainless steel?

Answer 9

• Weathering steel: structural steel with modified chemical composition. Small amount of copper, phosphorus, chromium limit the corrosion of the steel.
• Stainless steel: Is a combination of at least 13% Cr and also Ni, Mn and C.