本帖最后由 leomet 于 2011-5-1 07:15 编辑
H13, in annealed condition. Carbide particles tinted brown.There are more carbide particles on grain boundaries
than in the grains. This is NOT an ideal distribution of carbide particles, because
there will definitely be carbide films retained on grain boundaries after austenization,
and those retained carbide films (or blades) will serve as " crack initiation sites" and, more or less,
deteriorate service life of the tooling----depending on the continuity of the films.
本帖最后由 leomet 于 2010-8-29 10:59 编辑
H13, retained carbide particles on grain boundaries after Q/T from the previous post.
These grain boundary carbide particles are "toughness killer"-----as I always name them.
本帖最后由 leomet 于 2015-1-19 06:39 编辑
Good photos ! But very bad microstructure. Because most of the carbides
碳化物偏聚於晶界上. 淬後, 晶界仍會留下20~30%.
H13, same as #223, color etched,
Ferrite tinted in different degrees and colors. Carbide particles remain white.
哇，好多精彩片片，我在工作中也发现一些工件在渗碳层出现裂纹，而且是在倒角处，具体的金相图我还没有看到
材料40Cr， 调质处理，回火温度620度左右，硬度250-260HB，发现裂纹，基体应该是回火索氏体，但基体中有黑点不知是什么？
吴老师帮助，谢谢:)材料：40Cr
淬火：820℃
回火：620℃-630℃
热处理后硬度：HB250-260
本帖最后由 leomet 于 2010-8-3 08:14 编辑
回复 225# leomet
Observe directly on the surface that suffered
intergranular oxidation during carburization.
Sample was fine ground slightly, polished, etched and back polished slightly.
Care must be taken NOT to grind away this very thin oxygen-affected layer.
Very often, its thickness is less than 10 um.
leomet ：您好
感谢您的上传和说明，收益很大。
想请教一下：1.渗碳后表面微脱碳为什么易淬裂？2 渗碳后心部或者是次表层为何会出现拉应力，出现裂纹？
我是新手，请您指教。
谢谢！
本帖最后由 leomet 于 2010-8-11 07:22 编辑
回复 232# leomet
Printed Circuit Board. Copper foil+glass fiber+resin.
本帖最后由 leomet 于 2010-8-8 08:38 编辑
回复 234# leomet
Awater valve broke at an under-cooled area.
Under cooled grey iron melts always result in D-, or E-type graphite
which are very weak in tensile strength.
Vacuum pump rotor casting. QT 450. Found to have machining difficulty at corners of the rotor vanes.
White iron formed from under-cooled iron melt is the culprit for this machining difficulty.
本帖最后由 leomet 于 2010-8-29 11:06 编辑
回复 236# leomet
Specimens were cut from the "white" corners and annealed at 1020 C,
furnace cooled, and eutectic white iron are gone----- mostly, not all. Carbide turned into
graphite nodules. Note that the nodules line up and have the orientation of eutectic carbide plates.
回复 6# leomet
是不是疏松
2010-09-19 颱風天. 把我搏客這篇文章直接搬過來.
鋁合金腳踏車前叉（1984 Giant巨大送檢) A壓1182 kg才出現裂痕. 另一支B 壓540kg 就出現裂痕. 差異太大, 故委託檢查原因.
從金相看, A為Al基地+圓鈍形共晶矽顆粒, B則另外出現針狀物(Al-Fe-Si化合物). 尖銳角隅會使應力集中,是破裂起源點潛在位置(potential crack initiation sites) ,故B強度/韌性 遠不如A.經檢討, Fe來自鑄鐵坩鍋, 鋁水置鍋中隔夜, 少量的 Fe溶入鋁水中.
耐磨模具鋼(SKD 11, D2, 1.2379)內金相也類似此. 其碳化物顆粒微粒如較圓渾, 則韌性高.如果有尖銳角隅 則韌性低, 如果晶界出現細長型或針狀碳化物, 則韌性極度劣化.
本帖最后由 leomet 于 2010-10-11 09:45 编辑
2010-09-19 颱風天. 把我搏客這篇文章直接搬過來.
鋁合金腳踏車前叉（1984 Giant (巨大or 捷安特) 送檢) A 壓1182 kg才出現裂痕. 另一支B 壓540kg 就出現裂痕. 差異太大, 故委託檢查原因.
從金相看, A為Al基地+圓鈍形共晶矽顆粒, B則另外出現針狀物(Al-Fe-Si化合物). 尖銳角隅會使應力集中,是破裂起源點潛在位置(potential crack initiation sites) ,故B強度/韌性 遠不如A.經檢討, Fe來自鑄鐵坩鍋, 鋁水置鍋中隔夜, 少量的 Fe溶入鋁水中.
耐磨模具鋼(SKD 11, D2, 1.2379)內金相也類似此. 其碳化物顆粒微粒如較圓渾, 則韌性高.如果有尖銳角隅 則韌性低, 如果晶界出現細長型或針狀碳化物, 則韌性極度劣化. 此道理一成不變, 適用於任何合金與非合金系統.
本帖最后由 leomet 于 2011-2-7 07:07 编辑
A certain P/M tool steel tooling that failed prematurely. (only 100 hits)
This tool was made by aTaiwanese tool maker in China .
The end-user sent it to us to find what was wrong with it.
Too much R.A. in the matrix , I'd say.
本帖最后由 leomet 于 2010-10-16 13:03 编辑
回复 249# leomet
More SEM photos for you to keep---for good.
What will happen if too much R.A. is present in a tooling?
Well, I'd say it will swell.
Photo 14.jpg: specimen was tilted 30 deg against electron beams
to obtain a oblique lighting that makes the carbide particles
more 3-dimensional.
本帖最后由 leomet 于 2010-10-17 06:28 编辑
A low carbon steel casting (0.25~0.30%C, bucket tooth) that failed prematurely.
Photos show serious dendritic segregation in Q/T condition.
Bright areas in ~565 are dendrite arm boundaries
that are areas last to freeze. They are rich in :
1. carbon,2. alloying-3. impurity-elements
and 4. casting defects, like micro-shrinkage,
intergranular carbide, etc. Intergranular carbide particles are
present because homogenization annealing was not carried out
properly.
本帖最后由 leomet 于 2010-10-11 09:49 编辑
回复 252# leomet
More photos showing micro-shrinkage.
With so many defects inside,you really don't expect it to have a long service life. Do you?
本帖最后由 leomet 于 2010-11-1 15:46 编辑
A machine part always needs to have 2 kinds of precision. The first is dimensional precision, which is commonly known to the general public. The second is "metallurgical precision" which is less known to the general public. Metallurgical precision includes : grain size, microstructures that dictate hardness, toughness, wear resistance, etc. The latter is more important tohigh performance applications. That is why we metallurgists are needed in the metal industries.
Intergranular carbides in Hadfield manganese steel.
They are very detrimental to toughness/strength of any steels.
A solution heating + water quenching will get rid of these carbides
and restore toughness of the steel.