哈哈

JERRY18

The phenomenon of embrittlement in austenitic stainless steel welds exposed to high temperature is accelerated by the presence of delta ferrite.

To avoid solidification cracking in austenitic stainless steel welds (see What is hot cracking/solidification cracking?), the composition of the filler material must be optimised to ensure that there is some delta ferrite present in the weld metal (typically >3%).

, B- h, z! d! I$ K) p6 d  [) HHowever, delta ferrite transforms to intermetallic phases, notably sigma phase, faster than austenite either during high temperature service or during postweld heat treatment (PWHT). Sigma phase is an intermetallic with an approximate chemical formula FeCr and, as with most intermetallics, it is very brittle and hence has a deleterious effect upon mechanical properties. It has been shown that, for a variety of iron-chromium-nickel alloys, Charpy toughness drops off exponentially with increasing sigma phase content.[1] The more delta ferrite a nominally austenitic stainless steel has, the more susceptible it will be to sigma phase formation. To avoid significant embrittlement it is typically desirable to limit the delta ferrite content in the original microstructure to below 10%.

Weld metal containing delta ferrite will also be susceptible to '475°C embrittlement'. This phenomenon is observed when stainless steels are heated into the range 400 - 550°C (although the effect is most pronounced at 475°C) and a dramatic fall in toughness is observed after extended exposure. This is due to the formation of chromium-rich domains and precipitates within the iron-rich matrix by spinodal decomposition of ferrite at these temperatures. This effect becomes more pronounced as chromium content increases. However, 475°C embrittlement is not generally significant for materials with a ferrite number less than 14FN.

不紧张

哈哈  一篇关于 奥氏体 高温碎裂的 学术

JERRY18

不紧张 发表于 2015-5-15 21:48
哈哈  一篇关于 奥氏体 高温碎裂的 学术

有研究吗？it 专家

不紧张

JERRY18 发表于 2015-5-15 21:56
有研究吗？it 专家

! n% Z9 F" O3 ~# @2 W2 ]略知一二，不过我所了解的都是三十多年前的知识了，现代的新知识我还没有更新

jeffyu1988

是我理解有问题吗，一二两段互相矛盾

JERRY18

是矛盾。可以解决。热处理 。还要避免下面写的那个工作温度区间。

jeffyu1988

JERRY18 发表于 2015-5-16 08:59
是矛盾。可以解决。热处理 。还要避免下面写的那个工作温度区间。

/ x7 W4 k. V  z+ D你一点拨，我理解了，哈哈

卓越地毯清洗

太高深了。

mable

jeffyu1988

请教下，FN 是用那磁铁设备来测吗？还有别的方法吗？

JERRY18

jeffyu1988 发表于 2015-5-23 06:37
) c+ L1 r5 y2 {. W0 S1 y请教下，FN 是用那磁铁设备来测吗？还有别的方法吗？

谈不上请教。我也是在网上看到的。对，有磁铁依，还有x射线什么的