WE CLAIM:
1. A method of interrupted quenching process in a single quenching
medium for producing higher strength steel product from a
carburised material, comprising the steps of:
a) immersing the carburised material into a quenching medium at a predefined temperature of first stage to cool the material rapidly until the material reaches below than martensite starting Ms temperature;
b) further cooling the said carburised material into the quenching medium by varying the temperature of the quenching medium to a predefined temperature of second stage to obtain the constant rate of slow cooling with a slow agitation rate below the martensite finish temperature; and
c) withdrawing the material from the quenching medium when the material has reached a temperature lower than martensite finish Mf temperature;
wherein the temperature of the quenching medium is varied and controlled by switching and/ or operating the variable agitation electric motor fans, variable power-controlled heaters and coolers.
2. The method as claimed in claim 1, wherein the carburised material
is quenched into the quenching medium having the predetermined
temperature of the first stage less than the predetermined

temperature of the second stage to obtain the higher strength steel product having hard case.
3. The method as claimed in claim 2, wherein the predetermined temperature of the first stage ranges from 80 to 140 degree Celsius.
4. The method as claimed in claim 1, wherein the carburised material is quenched into a quenching medium having the predetermined temperature of the first stage higher than the predetermined temperature of second stage to obtain the low distortion steel product.
5. The method as claimed in claim 4, wherein the predetermined temperature of the first stage ranges from 140 to 170 degree Celsius.
6. The method as claimed in claim 1, wherein the temperature of the
cooling medium is increased by operating the variable power
controlled heaters.
7. The method as claimed in claim one of the preceding claims 1-5,
wherein the temperature difference between the predetermined

temperatures of the first stage quenching medium and the second stage quenching medium is atleast 100 degree Celsius.
8. The method as claimed in claim 1, wherein the electric motor is operated between 800 to 2400 revolutions per minute for rapid cooling and the slow agitation rate is obtained by operating the electric motor fan between 200-800 revolutions per minutes.
9. The method as claimed in claim 1, wherein the viscosity of the cooling medium ranges between 70 to 150 centistokes.
10. .The method as claimed in claim 1, wherein the carburised product attains fifty percent of the martensite on the case of the said material to achieve the maximum compressive residual stress of the carburised material before reaching the martensite starting (Ms) temperature of the case of the carburised material and the hundred percent of martensite conversion is achieved by the carburised

material before reaching the martensite finish (Mf) temperature of the case of the material.