It is understood that most of the key parts of hydraulic turbine use stainless steel castings, such as ZG06Cr13Ni4Mo, zg06cr16ni5mo and so on. This kind of material casting performance is poor, poor liquidity, large volume and linear shrinkage, thermal stress, easy to crack.


Stainless steel casting crack is not only unsightly, more important is to affect its function. Once the casting cracks, need rework processing, if the problem is serious, it may be discarded, resulting in significant economic losses. Therefore, reduce the production of stainless steel casting crack is an important content of the work in the process of casting. Lead stainless steel castings crack is one of main factors of casting structure and casting process. 


The following measures are usually adopted in production to prevent cracks in stainless steel castings:


1.casting structure

Casting to take full account of the casting structure, shape, scale, thickness and transition factors such as casting liquid and solid shrinkage, proper selection of parameters, to prevent shrinkage and other casting defects. The design of gating system of castings to be reasonable, if a cold iron process measures, at site to be reasonable, to ensure the compactness of the casting structure, but also to avoid the stress concentration situation.

2.smelt

In the process of smelting, the harmful elements such as P and S can be reduced as much as possible, and the content of gases and inclusions such as N, h, O and so on can be reduced. The low phosphorus steel master alloy can be used to achieve good results.

3.preserve heat

By appropriately prolonging the holding time of casting in sand mold,the main control is out of the box temperature below 70 degrees centigrade, to ensure that the casting in the sand mold fully liquid and solid contraction, to avoid external stress concentration caused by the situation.

4.shakeout

In the process of casting sand cleaning, it is forbidden to water the sand mould and casting when the box is hit. It is strictly prohibited to use sand box and other powerful external impact way to avoid sand and to avoid internal force and casting stress interaction to produce cracks.

5.armspruecut

According to the conditions of selecting the appropriate casting hot cutting riser technology, ensure that not less than 300 degrees. The initial temperature of hot cutting operation, cutting gun and blowing pipe cutting by vibration. The important cutting time after covered with asbestos processing across the mouth or into the furnace heat. For the crown and axial flow blades of a class of complex structure the process to take special measures, the casting, using two hot cutting.

6. preheat

The defect treatment of stainless steel castings, to adhere to the principle of preheating. In order to blow, welding processing, workpiece must be preheated to 108 degrees to the top of the operation. If it is found that the crack defect, should be carried out to stress annealing, and then processed. 

7.increase anneal

An increase in the final stress relief annealing process on major stainless steel castings, strictly control the holding time and temperature. The purpose is to reduce the stress concentration generated in the production process, more thoroughly eliminate casting stress, prevent cracks.

Fengli precision casting factory as a professional casting enterprises, to undertake the processing and casting stainless steel parts. Welcome to visit our factory, we will wholeheartedly for your service! 


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Measures to prevent cracks in stainless steel castings

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