Grain growth in low carbon steel after heating to 930¦
Grain growth in low carbon steel after heating to 930¦
(OP)
Hello everybody,
I´ve been experincing a problema with a low carbon Steel. Two materials with similar chemical composition and subjected to the same process show very different behaviour.
Chemical composition: Material 1: C=0.018; Mn=0.17 residual:content low. Al-killed=0.040
Material 2: C=0.020; Mn=0.18 residual:content low. Al-killed=0.040
Both materials have been hot rolled, subjected to a 700ºC annealing, stamped and heated to 930º.
The first one presents very coarse grain size after heating to 930ºC, and the second one doesn´t.
If chemical composition is very similar and the process they have been subjected to is identical,which factors could be influencing this grain growth? Is more difficult this grain growth to happen if carbon content is higher?
Thank you very much,
I´ve been experincing a problema with a low carbon Steel. Two materials with similar chemical composition and subjected to the same process show very different behaviour.
Chemical composition: Material 1: C=0.018; Mn=0.17 residual:content low. Al-killed=0.040
Material 2: C=0.020; Mn=0.18 residual:content low. Al-killed=0.040
Both materials have been hot rolled, subjected to a 700ºC annealing, stamped and heated to 930º.
The first one presents very coarse grain size after heating to 930ºC, and the second one doesn´t.
If chemical composition is very similar and the process they have been subjected to is identical,which factors could be influencing this grain growth? Is more difficult this grain growth to happen if carbon content is higher?
Thank you very much,





RE: Grain growth in low carbon steel after heating to 930¦
RE: Grain growth in low carbon steel after heating to 930¦
RE: Grain growth in low carbon steel after heating to 930¦
Yes, we checked grain size after 700ºC heat treatment and in both cases grain size was 7-8. The hot rolling supplier and final thickness were the same in both cases, so I suppose the reductions and finishing and coiling temperatures were similar in both cases.
Could be that 930ºC heating temperature is too high, or maybe is in the limit to start grain growth and this is why sometimes grain growth happens and other times do not? I have read the normalizing temperature must be Ac3+30ºC for hypoeutectoid steels, so 930ºC should`t be too high.
And, do you think that a higher carbon content could help avoiding it????
Apologies for my english.
RE: Grain growth in low carbon steel after heating to 930¦
It takes very little cold work to trigger grain growth.
I would also look at residual chemistry, some very minor elements can help inhibit growth.
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RE: Grain growth in low carbon steel after heating to 930¦
RE: Grain growth in low carbon steel after heating to 930¦
Identical grain szie after 700C anneal has somewhat indicated the hot rolling process is identical for material 1 and 2. By the way, what is your purpose to anneal at 700C before stamping? For stamping, people normally prefer harder material. Was that for uniformity?
RE: Grain growth in low carbon steel after heating to 930¦
For one of my alloy, I have diffent heat treatment systems according to carbon ranges: .005-.006, .007-.010, .011-.016, the higher the range, the higher the annelaing temperature.
RE: Grain growth in low carbon steel after heating to 930¦
RE: Grain growth in low carbon steel after heating to 930¦
Where they rolled and welded ?? the same way?
The same direction w/r grain and width?
Both "thick plates" or very thin sheetmetal-type rolls of material?
Same mill and heat/pour?
RE: Grain growth in low carbon steel after heating to 930¦
The residual content is the one below, it is higher in the case of material 1, so the pinning effect should be higher, isn´t it?
Material 1: Ni=0.018 Cr=0.018 Mo=0.002 Cu=0.010
Material 2: Ni=0.016 Cr=0.013 Mo=0.001 Cu=0.018
On the other hand, analizing carbón content, it´s true it should be considered as a pure iron (<0.02%C) more than a hypoeutectod Steel. Is it a pure iron more prone to grain growth than a hypoeutectoid Steel? In order to avoid this to hapen again, do you think that raising carbon content to values higher than 0.03 could help?
RE: Grain growth in low carbon steel after heating to 930¦
my suggestions are 1. decrease normalizing temperature to 910-920C, 2. control your cooling rate. the cooling rate maybe key, during cooling, there will be new nucleation and growth of α-phase from ϒ-phase. Both the original grain size of ϒ and cooling can affect final α grain size.
RE: Grain growth in low carbon steel after heating to 930¦
Mb, Al, Ti, and Si are key to pinning.
Yes, irons are much more sensitive to grain growth than steels, there are fewer things in them to inhibit it.
With material this clean you should be able to lower the temp.
I would do some lab work and find out where the lower limit really is.
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