For the welding repair of important cast steel components, post weld heat treatment is generally required to eliminate thermal stress after the welding repair is completed. General defects can be locally heated to relieve stress using flame heating or electric heating strips as recommended in the table. When conducting local heat treatment, the range of heat treatment should be at least 1.5 times the width of the weld seam on both sides of the welding repair area, or at least 100mm on both sides of the welding repair area. Heat treatment should be covered with asbestos for cooling.
|Cast steel grade||Heat treatment status||General defects (℃)||Major defects (℃)|
|ZG230-450||Cast state||≥ 5||≥ 150|
|B-grade steel ZG310-570||Cast state||≥ 5||≥ 150|
|C-grade steel||Normalization||≥ 100||200 ～ 250|
E-grade steel ZG25MnCrNiMo
|Tempering treatment||≥ 180||200 ～ 250|
Unless otherwise specified in technical conditions, for major defects (with a depth exceeding 15mm or a minimum size greater than 20% of the wall thickness of the cast steel, or a groove area exceeding 10cm2), overall stress relief or re heat treatment should be carried out after repair welding.
The time required for post weld heat treatment of cast steel can be calculated by increasing the welding thickness by 15min for every 6mm. For welding repair thicknesses less than 6mm, the post weld heat treatment time should not be less than 15min.