16C-NS cracking issue
06-17-2019, 04:12 AM,
#1
16C-NS cracking issue
Dear Members.

I'v got experience for 16C-NS Ni Self-flux alloy few years.

Recently, I'v got coating and fusing roll.

There were occurred crack on surface and delaminated from substrate.

I never seen these before..

Our Coating and Fusing Process is as below.

1. Grit blasting substrate by #24 Al2O3 Grit media.

2. Preheat to over 50 Celsius. and spray 16C-NS powder using 6P-2 Gun.

3. Spray powder until to Dia. 304 mm at 80~90 Celsius.

4. The coated roll put in to vacuum furnace.

5. Fusing in the vacuum furnace.

6. Temperature up to fusing temperature slow and cooling in the furnace about 18 hours.


After these process, the cracks on all of roll surface and deraminated from substrates.

I try 4 times, all failed.

1st time according to as below,

2nd time preheat and spray powder a little(Dia 0.2~3 mm), heat again up to 250 Celsius, and spray up to Dia 304 mm

3rd time re heat up to 450 Celsius.

4th time heat up to 450 Celsius and keep temperature over 450 Celsius.


I'v got so much experience of Fusing(over 10 years, using vacuum furnace),

I don't know why this happen occurred.

Antone have this kind of experience or solutions?

Substrate materials's chemical compositions are as below.

C <0.4, Si <1.0, Mn<1.0, Cr 6.5- ~ 8.0, Mo 0.09 ~ 1.2, Fe Bal., Hardness Hs 65 +- 5

Material cod KCC7M


Thanks for your kindly help.

KyunTak.
Reply
06-17-2019, 06:04 PM,
#2
RE: 16C-NS cracking issue
In my experience self fluxing coating tends to crack and peel of a hard surface.
My guess it is because it is hard to achieve higher surface roughness while blasting on surfaces above ~55-60HRC. I was mostly using white alumina for the job. With different abrasives results may differ.
In this case i would heat the substrate (roller) to some 400-500C and then spray and fuse with flame torch immediately.
Reply
06-17-2019, 08:56 PM, (This post was last modified: 06-17-2019, 09:02 PM by Met.Eng..)
#3
RE: 16C-NS cracking issue
Can u send some photos?

Cracing problem may be due to the following reasons,

-poor blasting
Substrate materials is 65 HRc??? I thing its too hard to sandblastingSad

If no: I think chilled iron is the best surface preparation for spray and fuse process check the surface oxidation after preheating

-what is ur coating thickness ?

-I thing u may up to the preheating degree 90-120

-how long does it takes when u finish coating to furnace? What is the temperature before in the furnace

these are the possible problems that come to my mind. If you send some photos, I can analyze it better.




Reply
06-18-2019, 07:39 AM, (This post was last modified: 06-18-2019, 07:50 AM by kyuntak.)
#4
RE: 16C-NS cracking issue
(06-17-2019, 06:04 PM)sprayloud Wrote: In my experience self fluxing coating tends to crack and peel of a hard surface.
My guess it is because it is hard to achieve higher surface roughness while blasting on surfaces above ~55-60HRC. I was mostly using white alumina for the job. With different abrasives results may differ.
In this case i would heat the substrate (roller) to some 400-500C and then spray and fuse with flame torch immediately.

Thanks for your answer.

Hardness of substrate is HS(Shore Hardness) 65, It is about 48 ~ 49 HRC.

I think it is not so high.

We don't have enough facilities for flame fusing.

We have induction heater and vacuum furnace(vertical type).

Thanks again for your answer.
(06-17-2019, 08:56 PM)Met.Eng. Wrote: Can u send some photos?

Cracing problem may be due to the following reasons,

-poor blasting
Substrate materials is 65 HRc??? I thing its too hard to sandblastingSad

If no: I think chilled iron is the best surface preparation for spray and fuse process check the surface oxidation after preheating

-what is ur coating thickness ?

-I thing u may up to the preheating degree 90-120

-how long does it takes when u finish coating to furnace? What is the temperature before in the furnace

these are the possible problems that come to my mind. If you send some photos, I can analyze it better.

I attached photos of roll and surface after fill off coating as below link.

https://photos.app.goo.gl/FgdtAn5QnnNPuG4L8


Substrate hardness 65 HS(Shore Hardness) it about 48 ~ 49 HRC.

Coating thickness is about 3 mm.

After coating, The roll put into the vacuum furnace immediately.

Thanks for your kindly help and answer.

Reply
06-20-2019, 09:35 AM,
#5
RE: 16C-NS cracking issue
Hi KyunTak
Did you try with another productor of materials, there are some OEM that must do money, so the materials could have some little problems, like too fines, etc
Best regards
Luigi
Reply
06-20-2019, 09:39 PM, (This post was last modified: 06-20-2019, 09:53 PM by Met.Eng..)
#6
RE: 16C-NS cracking issue
Hi kyuntak,

When I check ur photos, I think u didnt fused coating. May be you can try increase the furnace temperature, I think ur job was exposed at high temperature but it didnt fuse. So ur coating expansion under high temp So when u down to the temp ur coating failed. When I checked it ur surface was too rough so it said us the coating didnt fuse.The surface must be smooth after fusing.

May be ur temp control was broken or something else.

And other thing is , 3 mm coating may be too much i dont know 16C ns max thickness limit but may be u cracked while coating, did u check the penetration test after coating finish??

Good luckSmile
Reply
06-21-2019, 01:19 AM, (This post was last modified: 06-21-2019, 01:25 AM by kyuntak.)
#7
RE: 16C-NS cracking issue
(06-20-2019, 09:35 AM)loriolo Wrote: Hi KyunTak
Did you try with another productor of materials, there are some OEM that must do money, so the materials could have some little problems, like too fines, etc

Dear loriolo.

This product is just one, it is for R&D item.

And the 16C-NS powder I have same lot, there was any problem to coating and fusing.

Thanks for your answer.
(06-20-2019, 09:39 PM)Met.Eng. Wrote: Hi kyuntak,

When I check ur photos, I think u didnt fused coating. May be you can try increase the furnace temperature, I think ur job was exposed at high temperature but it didnt fuse. So ur coating expansion under high temp So when u down to the temp ur coating failed. When I checked it ur surface was too rough so it said us the coating didnt fuse.The surface must be smooth after fusing.

May be ur temp control was broken or something else.

And other thing is , 3 mm coating may be too much i dont know 16C ns max thickness limit but may be u cracked while coating, did u check the penetration test after coating finish??

Good luckSmile

Dear Met.Eng.

Thanks for your advice.

But another product mot like this, used same furnace same Temp. there were any problems.

And, the temperature of furnace is little higher, the coating flow down.

According to your advice, i'll try to more higher temp. to fusing.


Thanks for your kindly advice.


Reply
06-26-2019, 03:18 AM,
#8
RE: 16C-NS cracking issue
(06-20-2019, 09:39 PM)Met.Eng. Wrote: Hi kyuntak,

When I check ur photos, I think u didnt fused coating. May be you can try increase the furnace temperature, I think ur job was exposed at high temperature but it didnt fuse. So ur coating expansion under high temp So when u down to the temp ur coating failed. When I checked it ur surface was too rough so it said us the coating didnt fuse.The surface must be smooth after fusing.

May be ur temp control was broken or something else.

And other thing is , 3 mm coating may be too much i dont know 16C ns max thickness limit but may be u cracked while coating, did u check the penetration test after coating finish??

Good luckSmile

Dear Met.Eng.

I tried one more according to Ur advice, but I'v got same results.

Another product which coated with 16 C-NS, it get into furnace with roll.

This product did not have any problem, fused perfectly.

I'v experience coating thickness more than 3 mm to another products ans substrates.

Thanks for your kindly help.
Reply
06-26-2019, 09:45 AM,
#9
RE: 16C-NS cracking issue
(06-26-2019, 03:18 AM)kyuntak Wrote:
(06-20-2019, 09:39 PM)Met.Eng. Wrote: Hi kyuntak,

When I check ur photos, I think u didnt fused coating. May be you can try increase the furnace temperature, I think ur job was exposed at high temperature but it didnt fuse. So ur coating expansion under high temp So when u down to the temp ur coating failed. When I checked it ur surface was too rough so it said us the coating didnt fuse.The surface must be smooth after fusing.

May be ur temp control was broken or something else.

And other thing is , 3 mm coating may be too much i dont know 16C ns max thickness limit but may be u cracked while coating, did u check the penetration test after coating finish??

Good luckSmile

Dear Met.Eng.

I tried one more according to Ur advice, but I'v got same results.

Another product which coated with 16 C-NS, it get into furnace with roll.

This product did not have any problem, fused perfectly.

I'v experience coating thickness more than 3 mm to another products ans substrates.

Thanks for your kindly help.

Whats the steel grade of the substrate material ?
And there were areas at the ends of the roll in your photo what looked machined ? What are those areas ? Whats their hardness ? Do you coat those areas as well ?
Reply
06-26-2019, 12:27 PM,
#10
RE: 16C-NS cracking issue
Hi kyuntak
So the fusing process is ok, if you had good result with the same lot of powder, the problem could be in other consumables that take place in the process, for example I had problem with O2/C2H2 6pII coting with an automatic system for plunger, every time that we changed acetylene tank, the fusing temperature changed, and one time there was problem with O2 with too much dirties, for this problem we changed to HP HVOF eGun with ethanol as combustible and we solved all troubles with variation of flame velocity, flame temperature variation, with O2/C2H2can happen this kind of problem, this if you are sure that the gun geometry is Ok, and that there is not changes at base metal, some martensitic steels has a low temperature eutectic point with volume increment, that could cause coating cracks
Best regards
Luigi
Reply
06-26-2019, 01:29 PM,
#11
RE: 16C-NS cracking issue
Hi Kyuntak

I think your problem is mainly down to substrate material. High hardenability alloy steel such as this one resist phase transformation from austenite on cooling, tending to finish transformation rapidly at a relatively low temperature causing a sudden material expansion just when your coating has lost ductility.

To fix the problem, chose a low hardenable steel substrate. If this is not an option then I would suggest a long isothermal rest on cooling, I guess somewhere between 550-700C held constant for a few hours to many hours to complete phase transformations, Cooling either side of this can be normal. If you can get a time-temperature-transformation (TTT) diagram for your specific material you can formulate the best hold temperature and time required (pearlite start (Ps) to transformation complete on Pf curve).

Good Luck Cheers
Reply




Possibly Related Threads…
Thread Author Replies Views Last Post
  Metco 204 cracking Christian_B 8 2,913 03-07-2017, 03:54 PM
Last Post: J!m
  HVOF 88 WC-12Co Cracking problem on wire drawing capstan Hector Monjardin 7 4,542 10-19-2016, 11:55 PM
Last Post: Hector Monjardin
  Wire drawing cracking problem Hector Monjardin 3 3,308 06-23-2016, 05:37 PM
Last Post: Hector Monjardin
  Cracking issue with NiCrSiB divanis 3 5,230 06-14-2011, 09:20 AM
Last Post: Frantisek
  PTA cracking problem Arturas 5 6,683 01-28-2010, 09:38 PM
Last Post: djewell
  Cracking of WC-Co-Cr coatings Graham Bulman 2 7,843 08-26-2006, 04:50 PM
Last Post: Vladimir



Users browsing this thread: 2 Guest(s)





Surface Engineering Forum Sponsor - Alphatek Hyperformance Coatings Ltd