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Answer:
the carburizing time necessary to achieve a carbon concentration is 31.657 hours
Explanation:
Given the data in the question;
To determine the carburizing time necessary to achieve the given carbon concentration, we will be using the following equation:
(Cs - Cx) / (Cs - C0) = ERF( x / 2√Dt)
where Cs is Concentration of carbon at surface = 0.90
Cx is Concentration of carbon at distance x = 0.30 ; x in this case is 4 mm = ( 0.004 m )
C0 is Initial concentration of carbon = 0.10
ERF() = Error function at the given value
D = Diffusion of Carbon into steel
t = Time necessary to achieve given carbon concentration ,
so
(Cs - Cx) / (Cs - C0) = (0.9 - 0.3) / (0.9 - 0.1)
= 0.6 / 0.8
= 0.75
now, ERF(z) = 0.75; using ERF table, we can say;
Z ~ 0.81; which means ( x / 2√Dt) = 0.81
Now, Using the table of diffusion data
D = 5.35 × 10⁻¹¹ m²/sec at (1100°C) or 1373 K
now we calculate the carbonizing time by using the following equation;
z = (x/2√Dt)
t is carbonizing time
so we we substitute in our values
0.81 = ( 0.004 / 2 × √5.35 × 10⁻¹¹ × √t)
0.81 = 0.004 / 1.4628 × 10⁻⁵ × √t
0.81 × 1.4628 × 10⁻⁵ × √t = 0.004
1.184868 × 10⁻⁵ × √t = 0.004
√t = 0.004 / 1.184868 × 10⁻⁵
√t = 337.5903
t = ( 337.5903)²
t = 113967.21 seconds
we convert to hours
t = 113967.21 / 3600
t = 31.657 hours
Therefore, the carburizing time necessary to achieve a carbon concentration is 31.657 hours