shenfuhai 发表于 2012-1-21 19:23 static/image/common/back.gif
吴老师的每张图片都非常经典！第一次看到氮化层中的裂纹。又长见识了。
Mr. Shen:
It's also my first time seeing microcracks in a nitrided layer. So, it is my hope that you elite metallurgists can share my experience and broaden your horizon.
I'd say, without the help of SEM, there is really no way that you can see these microcracks.
To all readers of my posts:
My posts are only for systematically-trainedmetallurgists. If you are good, you can learn something from my posts---more or less. If you are not good enough, keep working on improving yourselves.
I used to teach college, so I am still in that state of mind.
偏析碳化物 = crack initiation sites
本帖最后由 leomet 于 2012-4-4 15:49 编辑Fatigue fracture of a connecting rod for a car engine.
Too much carbide flakes in the matrix of Tempered Martensite. In the area having
high density of carbide flakes, microcrack is more likely to initiate.
Read the photos from the bottom up.
Your questions will not be answered.
本帖最后由 leomet 于 2012-4-22 07:54 编辑fracture surface of another connecting rod, but of the same lot as above. leomet 发表于 2008-3-11 19:04 static/image/common/back.gif
8620 滲碳. 後天才有時間切片, 檢查其金相. 有失效分析的同行願先表達看法嗎?
3/13 : 試片沒做好, 表面失 ...
我最近就遇到这样的断口
相同材料8620
相同的断口
到目前也不知道是什么原因，请专家看看http://www.rclbbs.com/data/attachment/forum/201201/31/09372681jstsz3w1s8t2si.jpg
http://www.rclbbs.com/forum.php?mod=viewthread&tid=89475 我想知道前辈用的是什么牌子的显微镜啊和摄像头啊 ？太清晰了 真的很好
Grain boundary carbide---the toughness killer.
本帖最后由 leomet 于 2012-4-22 07:49 编辑Fracture Surface of an SNCM 439. Steel made by a Korea steel mill.
Photo 1130~1132 were taken from a severely rusted dark fracture surface, using
dark field illumination. Those that glitter are carbide flakes
because they do not rust and they reflect light well. Carbide flakes,
or carbide blades are crack initiation sites.
Any Q/T steel with GB carbide like this lurking in the matrix, cracking is always waiting to happen--for sure.
Advanced engineers should know this.
本帖最后由 leomet 于 2012-7-8 12:43 编辑SEM photos for this specimen, showing carbide "blade" (film) at larger magnification.
Carbide blades in the U.B. matrix is always the culprit forpremature failures.
They are stress raisers and therefore----crack initiation sites.Most of the times,
they are so minicule and can only be seen under SEM, but their adverse effect still exist.
Cast hammer made in China.
本帖最后由 leomet 于 2013-1-15 18:06 编辑不知何方天才(Mr. Smart),做這種鑄鋼的榔頭. 鑄鉄廠敲澆流道, 敲沒十下就斷了.
箭頭所指為縮鬆處.毛細管效應, 吸入油漆.
*: 後來看了金相,不是鑄鋼 是白鑄鐵.
leomet 发表于 2008-3-4 07:59 static/image/common/back.gif
加工後才发现小孔 ~ 1mm, 请高手参与讨论. 是蚀孔? 还是小气孔被挖开口?(opening up oftrapped gas holes ...
有没有做一下SEM的电子探针扫描. 如果有Cl离子等物质, 可能真是腐蚀.
有一张照片可以看到晶粒的特征, 但也可能是沿晶腐蚀.
所以这个还真不好判定 上面的图片为35simn正火、调质后的冲击断口。原始状态为铸态。请大家看看是什么断口。多谢！！！！1
Wrong initial microstructure
本帖最后由 leomet 于 2012-5-19 22:15 编辑Material: S45C; gear O.D.: 50mm.
Cracks are found a couple of days after this induction-hardened gear was accepted by QC.
Microstructure inspection of the gear was conducted to find the cause of the cracking.
Network of Ferrite is definitely improper initial microstructure for induction hardening.
You should know why if you are good in metallurgy.
Japanese brand, but made in China.
本帖最后由 leomet 于 2012-5-26 22:09 编辑非常不耐用的車刀把與它的鎖固螺絲 M5
本帖最后由 jackson 于 2012-5-28 10:50 编辑
leomet 发表于 2008-3-4 07:59 static/image/common/back.gif
加工後才发现小孔 ~ 1mm, 请高手参与讨论. 是蚀孔? 还是小气孔被挖开口?(opening up oftrapped gas holes ...
你好!
这个图应该是属于腐蚀缺陷引起的小孔.有晶界腐蚀的特征, 典型的泥状花样特征.
仅供参考! leomet 发表于 2008-7-3 19:08 static/image/common/back.gif
一短命另件之金相照片:
表面有脫碳 --> 硬度易誤判 -->韌性不足
高淬高回 -->1. 晶粒偏粗大. 2. 晶界易 ...
不知道吴老师, 对于这样的420J2材料, 金相标准有没有?
该零件失效的主要形式是什么? 脆断吗?
碳化物晶界的分布有标准吗?
请百忙之中抽出时间答复一下.
因为该种材料的热处理组织还是很不容易做好的. 我们经常也碰到类似的问题.
本帖最后由 jackson 于 2012-5-28 16:07 编辑
leomet 发表于 2008-8-25 12:33 static/image/common/back.gif
那是感應硬化區金相 HRC ~60. ASTM 8~9 晶粒號數
鍍前沒裂紋, 鍍后生裂紋, 當然是 殘留應力 + 氫原子兩者 ...
像45#20mm厚油淬是淬不透的.
但是吴老师, 你的作品有的看起来让人摸不着头脑,不知道你的取样位置.
像这个案例吧?淬硬的地方是在孔内壁吧?
为什么在开裂的裂缝里面也有镀层, 如果有的话, 是不是在镀前就已经开裂了.
淬硬的地方和调质的地方, 相隔那么近, 也不知道分别指向哪里, 没有具体位置啊.
补充一下, 我是一楼一楼地往下看, 看哪里就回帖回到哪里. 如果没有HRC等高工的询问, 谁看得懂你的内容呢!!
leomet 发表于 2008-11-16 13:26 static/image/common/back.gif
Crack initiated from one of the dendritic shrinkage pores shown.
鍛模束套, 2311那個未上線就裂了 ...
吴老师:
图22, 23和17怎么有这么大的差别, 但是其放大倍数一样啊?
请指导一下. :'( 本帖最后由 jackson 于 2012-5-28 17:09 编辑
leomet 发表于 2010-10-4 18:37 static/image/common/back.gif
A certain P/M tool steel tooling that failed prematurely. (only 100 hits)
This tool was made by a ...
吴老师,
你觉得我上图中的残奥有多少? 1000倍
请指导一下.
谢谢! 本帖最后由 leomet 于 2012-5-29 12:55 编辑
I share my photos only, and nothing more.That means---
NO INSTRUCTION WILL BE GIVEN TO ANYBODY.
Photo sharing only. No discussion here
本帖最后由 leomet 于 2012-12-16 23:25 编辑leomet 发表于 2012-5-29 12:54 static/image/common/back.gif
I quoted 6000 RMB for the failure analysis for 1 workpiece. But my customer submitted 4 pieces of failed parts,and asked me to analyze all 4 of them. In the end, they paid 24000 RMB happily because they got the root cause of the failure and knew how to avoid it from happening again. I am happy too, because I earned a big sum of "pocket money". This passage is meant to inspire young engineers to work hard. One of these days, you will be able to give consultant service to the metal industry.
I share my photos only---
NO INSTRUCTION WILL BE GIVEN TO ANYBODY here.
Multi-origin fatigue fracture surface.
Crack originated from broaching marks at a fillet.
cross section : 18 x 12