The main method of Ultrasonic detecting technique assesses defect qualitative

The main method of Ultrasonic detecting technique assesses defect qualitative。

Currently ,the most widely used is A scanning displayed type ultrasonic pulse reflecting type detector。 Being long term ultrasonic detection ,many ultrasonic detecting staffs have adequately understanding on material、products、and manufacturing technology，and by amount of anatomical analysis verify ,accumulate abundant experience,during detection,it can cross A scanning displayed type ultrasonic pulse reflecting type flaw detector，according to shape of flaw echo on the oscilloscope screen,such as video display or radio frequency,echo forefront steep degree and echo decrease degree,wave peak shape,echo width and the change condition of flaw echo when move probe,and also according to times of observing bottom wave,bottom wave loss condition,then according to the flaw in the position of being detected workpiece ,Distribution condition,flaw size,extension status,combined to concrete products ,material features、and manufacturing technology to get comprehensive judge,assessing the kinds and properties of flaws,sometimes can change launch ultrasonic pulse frequency to change  diameter to observe change features of flaw echo ,so as to identify it is metallurgy flaw in material or organization reflection。

In this aspect ,we have already much experience and information report,such as judge white spot、slag inclusion、 reminded shrinkage hole 、 coarse grain 、central loose 、square shape segregation of forging piece ，and air hole、slag inclusion 、 lack of penetration 、lack of fusion、crack of weld。

Here must to point ,this judge method to a great extent depend on experience 、technique level、understanding on specific products、material and manufacturing technology of ultrasonic detecting staffs,its limitation is very big,hard to popularize to be a commonly used assessing method。In addition ,as A scanning displayed flaw echo and flaw information is extremely limited,mainly display amplitude strength 、position、and echo shape、but flaw can’t display ultrasonic response to  Position、frequency spectrum and other important information，but latter two has closed relationship with flaw properties and kinds,this is also the problem that current wide ultrasonic detecting staffs are devoting to research 。

 As follows is partly normal flaw echo properties。

(1) the coarse grain and loose in steel forging piece --widely appear as noise wave、plexiform wave or bottom altitude loss gaining、bottom wave reflecting times decreased。

(2)  central crack in bar --when along with circular surface to do 360° radial direction longitudinal wave scanning,due to radiant directionality of crack ,its reflectivity amplitude has change of high and low,and has different extent movement，do axial scanning,reflected wave amplitude and position change change a little and display certain extended length。

(3)  crack in forging piece --due to inclusion of crack type flaw has air hole, has big difference with basis material acoustic impedance,ultrasonic reflectivity is high,flaw has certain extended length,echo forefront is steep,wave peak is sharp，echo back porch slope is big,when probe crosses crack and move along with extended direction ,wave inception is quick,disappearance is quick too.

(4)the white spot in steel forging piece--wave peak is sharp and clear,normal is multiple head type,reflect intensively,fast speed of wave inception ,echo forefront steep, echo back porch slope is big,echo position changes so quickly when move probe,one falls another rises, be in a condition that centre of steel bar is in range of 1/2 radius,or the 1/4 -3/4 middle position of biggest section of steel forging thickness,have a feature of piling up。When the quality of white spot is more、area is big or over disperseIt also leads to bottom wave altitude decrease apparently and even disappeared。

(5)nonmetal slag inclusion in forging --most of them are reflecting signal ,wave inception is slow,echo forefront is not steep,wave peak is more obtuse，echo back porch slope is not too big and echo width is bigger。

(6)high density slag inclusion in titanium alloy forging-- most of them are single reflecting signal,echo of the width is not too big,but bigger than crack，echo forefront is steep, back porch slope is bigger,when change detecting frequency and beam diameter ,its reflection change is not big 

(7) casting or air hole in weld -- wave inception is fast with low amplitude,have spot scope flaw feature。

(8) lack of weld in welding joint--most are incomplete root penetration,or middle lack of weld,normally extended condition is straight,echo regulation is single,strong reflection, can be discovered by both side of welding joint。

(9) casting or slag inclusion in welding joint -reflecting wave is disordered,irregular position,mobile probe with change of echo,but waveform change is relevant slow,reflectivity is low,wave inception speed is slow and back porch  slope is not too big,echo width is big。

(10)Normally under possible condition,for moving forward s single step to make sure flaw properties,it should also adopts other nondestructive detecting methods,such as X ray photograph,magnetic powder and penetration test to assist judge。