Common main flaw in Ultrasonic flaw detection crack analyze casting

1、air hole

They are small empty hole generated that in process of metal solidification some gas hadn’t escaped from internal metal,its inside wall is smooth , containing air,has high reflectivity on ultrasonic ,but due to they are basically present ball shape or axiolitic ,namely dots shape flaw,affect its reflecting amplitude。Air hole in Steel ingot being forged or rolling then pressed into area type defect and good to be discovered by ultrasonic inspection。

2.  Shrinkage hole and Loose hole

Casting piece or steel ingot cooling solidification,the volume will shrink,at the last part of solidification due to can not get added liquid metal and form hollow shape flaw  。Big and concentrated hollow hole is called shrinkage cavity,thin small distributed  interspace is called loose ,they normally located in the central last solidification of steel ingot or casting piece ,its inside wall is roughness,around almost has impurities and air hole,due to the rule of heat makes somethings expand and cold makes somethings contract，shrinkage hole is necessary exist，just along with different processing technology has different form dimension and position，when it extends to casting piece or steel ingot itself then becomes flaw。Steel ingot will be remanent shrinkage hole if its shrinkage holes are not  eliminated thoroughly and bring into forging piece when forging ,if casting piece modes haven’t designed properly and casting technique is nor proper,this will also generate loose at the part of casting and molded form ,the black part in cross section photo is loose part,it presents black due to the workpiece has been annealing treatment,make loose part being oxidized and permeate engine oil。

3.  Slag inclusion 

During the process of smelting, slag and fireproofing on the melting furnace desquamate into liquid metal,get involved in casting piece or inside steel ingot when teeming,  then form slag flaw。Slag usually is not exist alone,always present  intensive state or distributed at different depth，it is similar to volume type flaw and however with certain line。

4.Inclusion

Reaction products in Smelting process -nonmetal inclusion,or additive of ingredient in metal ingredient is not completely melted and remained to form metal inclusion， Such as high density 、high melting point ingredient、 tungsten 、molybdenum，

Pour titanium segregation in Titanium alloy rods 。

5. Segregation 

Segregation in Casting piece or steel ingot mainly is in process of smelting or metal fusion ,due to ingredient is not even distributed and formed segregation,the area with segregation,its mechanical property is different from whole metal body,the difference exceeds allowed range will be flaw。

6.  Forging crack

The crack in casting is generated by mainly due to the shrinkage stress of metal cooling solidification exceeds ultimate strength of material ,it is related to casting shape and casting technology,it is also related to some high content of impurities and generate crack sensitivity in metal material 。In steel ingot ,it also generates cracks in crystal boundary,in the later process of billet forging ,if can not forge,it will leave in the forging piece and be internal defect。