On-line Solution Heat Treatment Process for Austenitic Stainless Steel Plates

Abstract

An on-line solution heat treatment process for austenitic stainless steel plates is disclosed, which comprises continuous casting billet heating, high pressure water dephosphorization, rough rolling, finish rolling, softening process, ultra fast cooling, straightening, cutting to length, shot peening, pickling. The process of the present invention makes full use of the residual rolling temperature, without the need of reheating steel plates from the room temperature to the solid solution temperature. Compared with the conventional steel plate rolling process, the process needs to perform the softening process on the steel plates after rolling to ensure that the deformed austenite is fully softened before cooling. After the softening process, ultra fast cooling is performed to cool the steel plates from above 800° C. to below 430° C. so as to prevent intergranular chromium depletion caused by a large amount of precipitation of high chromium carbides from affecting the stain resistance of stainless steel.

1 . An on-line solution heat treatment process for austenitic stainless steel plates, comprising the following steps:
 step 1, heating stainless steel continuous casting billets to 1200-1250° C. in a heating furnace, and preserving heat for 2-3 h to fully dissolve alloying elements and carbides;   step 2, heating and preserving heat for the austenitized continuous casting billets, performing high pressure water dephosphorization after tapping to remove the surface iron scale, and then using a rolling mill to conduct multi-pass rolling to reach the target thickness required for a finished product;   step 3, fully softening the steel plates which are work-hardened after rolling deformation; when heating and heat preservation conditions are available, heating the rolled steel plates to the solid solution temperature and preserving heat for 10-100 s;   and when heating and heat preservation conditions are not available, selecting thin-gauge continuous casting billets with the thickness of ≤220 mm as raw materials in step 1, reducing rolling passes, ensuring that the finishing rolling temperature is above 1050° C., and swinging steel for 10-200 s after rolling;   step 4, putting the stainless steel plates softened in step 3 in a cooling zone for ultra fast cooling to make the stainless steel plates quickly pass the temperature range of high chromium carbide precipitation;   step 5, putting the cooled steel plates with shape defect of strips such as warpage in a straightener for straightening;   step 6, cutting the cooled and straightened steel plates to length according to the finished size requirements, and then transporting to a cooling bed for cooling;   step 7, putting the steel plates cooled to the room temperature in a shot blasting machine for shot blasting, and then putting in a pickling tank for pickling to remove the surface iron scale and impurities.   
     
     
         2 . The on-line solution heat treatment process for austenitic stainless steel according to  claim 1 , wherein in step 3, when heating and heat preservation conditions are available, heating and heat preservation equipment is arranged between a finishing mill and a cooling zone or beside a steel rolling bay, and the heating and heat preservation method is one of induction heating, direct-fire heating or roller hearth type heating furnace. 
     
     
         3 . The on-line solution heat treatment process for austenitic stainless steel according to  claim 1 , wherein in step 3, when heating and heat preservation conditions are not available, steel is swung on the front mill table of the cooling zone after rolling; and to shorten the steel swinging time required for softening after rolling and improving the production efficiency, the deformation in the rough rolling process in step 2 accounts for more than 80% of the total deformation, and the deformation in the finish rolling process does not exceed 20% of the total deformation to reduce work hardening in the rolling process. 
     
     
         4 . The on-line solution heat treatment process for austenitic stainless steel according to  claim 1 , wherein in step 3, when heating and heat preservation conditions are not available, a heat preservation hood is arranged in the steel swinging zone to reduce temperature drop in the steel swinging process. 
     
     
         5 . The on-line solution heat treatment process for austenitic stainless steel according to  claim 1 , wherein in step 4, for ultra fast cooling, the starting cooling temperature is not lower than 800° C., and the finishing cooling temperature is not higher than 430° C. 
     
     
         6 . The on-line solution heat treatment process for austenitic stainless steel according to  claim 1 , wherein in step 4, the method for ultra fast cooling is high-pressure jet water cooling; and plates are cooled by passing the ultra fast cooling zone at one time or by swinging in the ultra fast cooling zone.