失效及缺陷组织照片

leomet

Grinding marks with microcracks that led to a macrocrack across the diameter
on this anvil made of JIS SUJ 2 steel.

leomet

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
resulted  in "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.

leomet

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.

leomet

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.

leomet

DC 53 板手壓字模
Grain boundary carbide, again, is the culprit.
原材料遺留下來的GBC.

leomet

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.

leomet

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.

leomet

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.

leomet

H13, Q/T.  Surface 氧化/脫碳

Very light grinding on the surface.

leomet

A 356 鑄鋁   Shrinkage pores.

leomet

Failed housing_ Al alloy casting.
Fracture surface photos were
taken under tool maker's microscope.

leomet

More photos from this failed housing.
Beautiful beach marks left on "corner A" of photo ~028

ccfx99

leomet 发表于 2011-7-4 19:35

                               
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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！

leomet

ccfx99 发表于 2011-7-15 11:07

                               
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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".

yanhaisheng007

leomet 发表于 2009-5-12 08:40

                               
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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

leomet

yanhaisheng007 发表于 2011-7-18 10:43

                               
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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.

leomet

leomet 发表于 2011-10-6 19:43

                               
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Fatigue Fracture of a crankshaft nose

Interdendritic carbide, AGAIN, is the root cause of a prema ...

H13, ring forging. As-annealed.

leomet

H13, ring forging. Micro-

leomet

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.

leomet

This is another tooling that broke into pieces.
Chamferring* before nitriding helps only a little because the tooling still cracked.
Grinding corners after nitriding  helps 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.