Stainless steel castings, with the material such as ZG06Cr16Ni5Mo, ZG06Cr13Ni4Mo, etc, which are used in the key parts of the hydraulic turbine. The casting properties,fluidity of this material casting is poor,while the body shrinkage and the line shrinkage is large,also the thermal stress is large, which cause that it is easy to crack. Once the casting were cracked, it will not only to spend much tim to repair,the worse which can brought the casting be wasted,The main factor which cause the cracks are casting structure and casting process, the following measures are normal which can prevent the cracks in the production:

1, casting structure
The engineers should consider enough for the casting structure,casting shape,large or small, wall thickness, transition and other factors which affect the liquid and solid shrinkage of the casting when the design the process, select the appropriate process parameters to prevent shrinkage porosity, etc.. Casting's riser system design should be reasonable, if use the cold iron process,the riser should be placed reasonable,which not only can ensure the compactness of the casting internal organization, but also try to avoid stress concentration.

2, smelting
It need to try best to reduce the content of harmful elements such as P.S, etc.in smelting,reduce the content of N,H,O etc. It will have a good result by using the intermediate alloy of low phosphorus steel.

3, heat preservation
Prolonging the warm-keeping time in the sand apprapriatly,Control the temperature below 70 DEG C to open the box.in order to make sure the casting were finished the liquid and solid contraction in sand mold,and this can avoid to happen stress concentration from external factors.

4, falling sand
In the cleaning process of shakeout, it is strictly prohibited to watering the sand mold and casting, is is strictly prohibited to hit the box, such as a strong force of the impact to shakeout,in order to avoid the crack which was caused from casting internal force and external force due to the interaction.

5, cutting the riser
According to the casting conditions,selecting the appropriate hot cutting riser technology, ensure that the temperature not less than 300 degrees when cutting the riser, using cutting gun and oxygen lance by vibration cutting. For important parts,use asbestos cover the cutting mouth timely or do the heat treatment in furnace. For the upper crown and axial flow type structure parts, Considering to hot cutting riser technology twice.

6, preheating
When rework the defects of stainless steel casting, it need to adhere the principle of preheating. In the sequence, blowing process, workpiece must be preheated to 108 DEG C then operation. If find a large crack defect, it should remove the stress by annealing firstly, and then operate.

7, increasing annealing
increasing one process of annealing for large and important casting in order to remove the stress.control the holding time and temperature strictly. The aim is to reduce the new stress concentration in the production process, and eliminate the internal stress radically and prevent the cracks.