For 1 inch (i.e. 25.4 mm) thickness it takes 1hour to fully austenitize the sample. As far as other transformations are considered, for patenting (isothermal pearlite transformation) holding time can be decided by trial and error otherwise you have to go through rigorous phase transformation calculations. Moreover time it takes for austenite to get fully converted in to pearlite also depends on its grain size. Bainitic tranformation is very fast in low alloyed steels but in heavily alloyed steel it depends on the chemical composition. 

You can try 10 minutes + 1 minute per each 1 milimeter of sample thickness. In your case, it is about 42 minutes.

Good luck

For 1 inch (i.e. 25.4 mm) thickness it takes 1hour to fully austenitize the sample. As far as other transformations are considered, for patenting (isothermal pearlite transformation) holding time can be decided by trial and error otherwise you have to go through rigorous phase transformation calculations. Moreover time it takes for austenite to get fully converted in to pearlite also depends on its grain size. Bainitic tranformation is very fast in low alloyed steels but in heavily alloyed steel it depends on the chemical composition. 

there is some rule of thumb as suggested by Piotr and Abhinav, although I'd like to see more to believe this. We have a similar problem and although not a complete solution I will run a DEFORM simulation on this in June, and can let you know the results.

It depends on the thickness of the materials. generally, we used to consider one hour for a single inch (optimized by trial and error). But, it can be varied as because the treatment is totally operated by manual. So, better set your holding time +/- 10 minute extra. For your sample, It will be around - > 1 hours. One thing you have to be careful, while you will open the furnace door at a said temperature temperature will fall down. So calculate the holding time after the temperature will reach the same, or one thing you can do, set the temperature above your required one (say 20 deg C). By this temperature drop will be in your limited required values. I have done austenizing on three austenitic structural materials followed by the same rules. Microstructural characterizations are uploaded in my profile.

Thank you Piotr, abhinav , Thomas and soumya for suggestions..

WELCOME

ASM handbook volume 4 gives holding time for different heat treatment and different materials. Usual thumb rule is 1hr/inch of radius for cylindrical bars and for big blocks it is 1h/inch of thickness. Bohler handbook also give you the details about soaking. Again one needs to pay attention on how the sample loading is done before determining the soaking time.  

Very late and not exactly what you wanted but thought this DEFORM simulation at 540C was interesting at least. 

To explain the 1st stage assumes the furnace is at 540C and the sample is initially at 20C and the second stage the environment is at 20C and the sample is allowed to cool. The material is a steel alloy

But soaking time is depended on salt bath furnace or box furnace.The block is packed or not

excuse me, what is your material?

high carbon steel

The first thing to calculate (roughly considering radiation heating only if holding in a preheated Muffle furnace) is how long it would take for the entire thickness of the sample (24 mm in this case) to reach the Austenitization temperature if you are placing the sample at RT. As the main aim of holding is to covert into austenite phase which is again a diffusion transformation process alloying will play a major factor.

One thumb rule predominantly used for low to medium C steel is

(minimum thickness in mm )*(1 min) +15 mins

However you can add extra time ( say a minute for each 0.1 wt % Mn) if you have heavy alloying.

first , she must tell which grade is his steel. Then we can suggest the holding time.

Dear sir,holding time is calculated according to the section or cross sectional area of the specimen,generally 1 inch/1 hour.

Dear Kritika,

Plain carbon and low-alloy steel with easily dissolved carbides only require a few minutes holding time after reaching the austenitizing temperature, and a holding time of 5 to 15 minutes is usually sufficient. For medium-alloy structural steels a holding time of 15 to 20 minutes is suggested.

The AMS2750E is a standard for the heat treatment. The “AMS” (Aerospace Materials Specifications), standard is published by SAE Aerospace, part of SAE International Group. ASM International and specific data can be gathered from steel data sheet. There is a general rule of thumb for time at temperature. It must be stated that the time is taken when the part is at temperature, not when the furnace is at temperature.

Soaking is actually holding time of particular thing at constant temperature so that there is uniform distribution of heat throughout the material. A uniform temperature distribution is obtained by soaking a particular thing for a definitely time interval. Thermal stress developed in cooling/ annealing/ normalizing is negligible if proper soaking time is given to a material for definite interval of time.

There is couple of relationship can be derived such as temperature vs. distance, sample temperature vs. sample length, sample temperature vs. processing time and sample size vs. furnace capability. In diameter, the holding time per inch of section thickness should be no more than 5 minutes for low-carbon and medium carbon steels, or more than 6 minutes for low-alloy steels. For stock 3 to 9 in. in diameter, the heating time should be no more than 15 minutes/inch of thickness."

Diameter or thickness inches can give you the time requirement (not a rule but a straight specification) for plain carbon steels. The period of soaking depends upon the size of the section and the nature of the steels. This is just for a guide.

Diameter is 1 inch- 45 minutes- soaking time 30 minute

Diameter 1-2 inch- 75 minutes- soaking time 30 minute

Diameter 2-3 inch- 105 minute-soaking times 45 minute

Diameter 3-4 inch- 135 minute- soaking time- 1 hour

Diameter 4-5 inch- 165 minute- soaking time- 1 hour

Diameter 5-8 inch- 210 minute-soaking time- 90 minute

As you can see above, heating time is different for medium carbon, low carbon and plain carbon steels. So it depends, just for example, soaking time for 2 inch low alloy steel is 12 minutes, for plain carbon steel this is 30 minutes, for medium carbon steel is 10 minutes. But it is predicted according to diameter or thickness.

Calculation: for heat on object

1. Q= mc△T, m= mass, s-specific heat, △T- differences in temperature

Then time taken(heat time) t= Q/P= Heat Q required/Power supplied

2. Calculation for soaking time- inch/hour

For strength forward quick calculation please look at this site for soaking calculation.

https://www.dillinger.de/d/en/e-service/tools/hollomon/index.shtml

Hope it help you out.

Ashish