Crystalline Materials:
A crystalline material is one in which the atoms are situated in a repeating (or) periodic array over large atomic distances.
Non Crystalline Materials:
Materials that do not crystallize are called non-crystalline (or) Amorphous materials
What is sintering in powder metallurgy process?
The operation of heating the green compact at high temperature in a controlled atmosphere (Reducing atmosphere which protects oxidation of metal powders). The Sintering increases the bond between the particles and therefore strengthens a powder metal compact. Sintering temperature and time of sintering depends on the type of powders and the strength required in a final product. The Sintering temperatures usually 0.6 to 0.8 times the melting point of powders.
The Process of producing components from metallic powder parts made by powder metallurgy may contain non-metallic constituents to improve the bonding qualities and properties.
Bureau of Indian Standard shortly BIS uses the following designation. Symbolic Letters and Numbers to designate the steel grade (e.g. Mechanical, Physical, and Chemical). The standard IS No. is 7598:1990.
For the purpose of the designation, steels are classified into two types. They are:
Group 1 – According to their application and Mechanical or Physical properties
Group 2 – According to their Chemical composition
G – Steel casting
P – Steel for pressure purposes
D – Flat products for cold forming
R – Rails
nnn – specified minimum yield strength for the smallest thickness range
Cnn – Cold rolled
Dnn – Hot rolled for direct cold forming
Xnn – Product where rolled conditions are not specified
B – Gas bottles
M – Thermo-mechanically rolled
N – Normalized rolled
Q – Quenched / Tempered
S – Simple pressure vessels
T – Tubes
G – Other
H – High Temperature
L – Low Temperature
R – Room Temperature
X – High and Low temperature
These are denoted as x, C, y
Where,
x – Number 100 times the average percent of carbon
y – Number 100 times the average percent of Manganese
Example:
30C8
Where,
30 = 100 times the average % of Manganese
8 = 100 times average % of Carbon
Average % of Carbon = 30/100 = 0.3%
Average % of Manganese = 8/100 = 0.08%
Actual means, the actual carbon % is not 0.3, but varies between 0.2 – 0.4%, so that the average becomes (0.2 + 0.4)/2 = 0.3%, and
Manganese from say 0.07 – 0.09%, so that the average (0.07+0.09)/2 = 0.08%
Alloy steels are denoted by arranging the alloying elements in the descending order of their proportion, and the average % of each element is shown with its chemical symbol before that number. The letter C is omitted here, and just the number is written to denote carbon percentage. When an alloying element is less than 1% that element is denoted by an underline after writing up to two decimal places.
Example:
Alloy steel of the following composition is to be designated
Carbon = 0.13 to 0.17%; Silicon = 0.1 to 0.4%; Chromium = 0.5 – 0.8%; Manganese = 0.4 – 0.5%
Here,
Carbon varies from 0.13 to 0.17
Therefore average % of C = (0.13 + 0.17)/ 2 = 0.15
Among the other alloying elements, Chromium is the largest in composition with the average % being 0.5 to 0.8%
Therefore average % of Cr = (0.5 + 0.8) / 2 = 0.65
Therefore the above example’s designation will be 15 Cr 65
Note: since it is less than 1% it is shown by an underline
Selection of Materials based on mechanical properties for a design has a very important component in Machine design. When put into service, different machine elements face different working conditions, which hey have to survive. This, in turn depends on the material by which they are made. Hence we say that a correct choice of material determines the working of any machine component.
Steel with Alloying elements such as
Often, a material cannot possess all the required qualities. Some materials are added together in certain proportions to achieve the collective goodness of them. The resulting composition is called as Alloys.
Some important alloys and their typical uses are given below:
