Question

1- What is the purpose of alloying a metal?

2- What amounts of carbon are contained in low, medium, and high carbon steel?

3- Describe what “PH” and “17-7” means in PH17-7.

4- What are the three stages that a metal undergoes during annealing? Describe them.

5- What is a metallic phase change?

Answer 1

#1

purpose of allowing is to get all the desirable properties of different mentals in single metal.

example stainless steel:chromium provides crossion resistance with the property of formation of chromium oxide layer,nickel provides ductility and toughness

#2

low carbon steel :less than 0.25 percent by weight

medium carbon steel: between 025 to 060 percent by weight

high carbon steel: between .6 to 1.4 percent by weight

#3 PH 17-7 stainles steel grade 631

PH: Precipipitaton hardening ( by any chemical)

17 -7;17percent chromium,7 percent nickel

#4

3 stages are

RECOVERY:In this phase internal strees is reduces up to some extend due to reduction in dislocation of material recovery of properties like conductivity(electrical and thermal) take pace

RECRYSTALIZATION:New stress free grains are formed,it depends on time and temperature,more the cold working recieved previously my metal lesser will be the recrystalization temperature,ductility increase at the expense of strength and hardness

GRAIN GROWTH:size of grain increase but number of grain per volume decrease which result in lower grain boundary area and hence lower eergy state is achieved

metalic phase change:it is solid solid phase change,by changing temperature or pressure or both the crystal structure can be transformed which result in formation of new properties

example of pure iron

at 912 degree centegrate