Grinding marks with microcracks that led to a macrocrack across the diameter
on this anvil made of JIS SUJ 2 steel. 本帖最后由 leomet 于 2011-5-1 07:53 编辑
回复 295# leomet
Microstructures before and after grinding. Heat generated during
grinding re-Austenized the surface layer to a very high temp (>1200C) and
resultedin "giant prior Austenite grains---5~6 grains in photo 4.jpg,
and > 100 grains in "before". You can also see carbide particles in "before"
are gone and replaced with R.A. in photo 4.jpg. 本帖最后由 leomet 于 2011-4-11 06:48 编辑
This forging die was said to fracture at only a few hits.
A few means two or three in numbers. Very coarse Martensite + high % of
retained Austenite should be the reason for its short service life.
It was said to be Austenized at 1020C for 40 min, quenched, double tempered at 540 x 2 hr.
I took it with a grain of salt. 本帖最后由 leomet 于 2011-4-13 16:20 编辑
回复 298# leomet
熱履歷: 塩浴 1020 x 30, 540 回2 次;400回1次,
as I was told, but I doubt it.
DC 53 板手壓字模
本帖最后由 leomet 于 2011-4-22 20:27 编辑DC 53 板手壓字模
Grain boundary carbide, again, is the culprit.
原材料遺留下來的GBC.
Fractured surfaces
本帖最后由 leomet 于 2012-1-22 13:21 编辑Fractured surfaces of a hot forging tooling made of H13 and
gas nitrided. The tooling broke into 5 pieces only after a few hits.
Holes should be chamfered to avoid stress concentration. 本帖最后由 leomet 于 2011-6-4 23:04 编辑
回复 306# 雨落飞尘
會考慮破裂面光影問題, 吳老師已經可以算是這方面的攝影專家.
原材料晶界碳化物 殘留
本帖最后由 leomet 于 2011-6-4 23:18 编辑Grain boundary carbides before / after Q/T.
DF1: annealed condition, Dark field illumination.
The rest: Q / T condition, Dark (2~4 )and bright field (5) illumination.
Photo 4 & 5 are of the same field. 本帖最后由 leomet 于 2011-6-24 08:28 编辑
H13, Q/T.Surface 氧化/脫碳
Very light grinding on the surface. A 356 鑄鋁 Shrinkage pores.
破裂面 欣賞
本帖最后由 leomet 于 2011-7-4 19:45 编辑Failed housing_ Al alloy casting.
Fracture surface photos were
taken under tool maker's microscope.
破裂面 欣賞
本帖最后由 leomet 于 2011-7-4 19:43 编辑More photos from this failed housing.
Beautiful beach marks left on "corner A" of photo ~028 leomet 发表于 2011-7-4 19:35 static/image/common/back.gif
More photos from this failed housing.
Beautiful beach marks left on "corner A" of photo ~028
吴老师能解释一下图中均匀的弧形吗？谢谢！ ccfx99 发表于 2011-7-15 11:07 static/image/common/back.gif
吴老师能解释一下图中均匀的弧形吗？谢谢！
I think of them as "beach marks". leomet 发表于 2009-5-12 08:40 static/image/common/back.gif
1984年剛出校門沒幾年, 經驗不足.
不過, 園藝剪脫碳例, 就有一排Hv 顯示硬度變化.
當年也沒想到說二三十 ...
吴老师，不知道您的成功历程具体是怎么走过来的，作为一个只认识几个组织的后生，想跟您请教，您是怎样做到的呢？肯定不断的实践、不断的学习和自己的不断努力，可是我现在的状况是没有一个老师能带，不知道在没有一个老师带的情况下，有没有很好的自学方法呢？
谢谢 yanhaisheng007 发表于 2011-7-18 10:43 static/image/common/back.gif
吴老师，不知道您的成功历程具体是怎么走过来的，作为一个只认识几个组织的后生，想跟您请教，您是怎样做 ...
Work hard and work smart, and you will be as good as I am when you are as old as I am---60.
H13, ring forging. As-annealed, Macro-
本帖最后由 leomet 于 2011-10-13 19:02 编辑leomet 发表于 2011-10-6 19:43 static/image/common/back.gif
Fatigue Fracture of a crankshaft nose
Interdendritic carbide, AGAIN, is the root cause of a prema ...
H13, ring forging. As-annealed. H13, ring forging. Micro-
熱鍛模 破裂
本帖最后由 leomet 于 2012-4-22 08:08 编辑H13 nitrided tooling failed too early in its service life.
compound layer + sharp corner is a formular for a disaster like this.
Tooling broke into 6 pieces.
水準很低的模具---孔口不倒角.
氮化後以砂輪機將孔口倒大角, 磨去白層後, 要起裂就很難了.
If you do as I told you, tooling life will be greatly prolonged.
This will make everybody happy.
本帖最后由 leomet 于 2012-4-22 08:07 编辑
This is another tooling that broke into pieces.
Chamferring* before nitriding helps only a little because the tooling still cracked.
Grinding corners after nitridinghelps more in preventing cracking. *:Removing the brittle white compound layer at corners.
Networks of nitride and carbide are found on grainboundary, as
identified by the EDS results. Nitride and carbide are ceramic in nature.
They separate easily from matrix and result in microcracks.
Micrographes are taken from "diffusion layer".
Lots of microcracks are seen.This proves the fact that
nitriding increases wear resistance at the expense of toughness.