Rust

[Kingsman]

That technique of "thermite welding" is used throughout the UK by Railtrack for joining rail lengths for renewal and repair.  Although I believe their incendiary mix also includes powdered metal because they leave a gap between the pieces - and they ignite it.  I had no idea it was ever used - or even practical to use - in AFV construction.  That being said, Bovington has Automotive Test Rig 2 for the Challenger 2 programme where the hull is steel up to the engine firewall while the rear hull is aluminium.  You can't weld those together remotely conventionally and they are said to have been "explosively welded" together.  I can't see explosives being used in a manufacture setting and it is hard to control that accurately so I wonder if that really means thermite welding, which looks quite spectacular.

[StuartH]

Also interesting:

 

'(a) Homogeneous Armor. The metal edges of holes or cracks made by an anti-tank projectile in homogeneous armor plate are ragged and bent, with the metal drifted in the direction of penetration. Cracks in homogeneous armor are usually caused by stresses in the metal. These cracks are present at severe bulges or bends in the damaged armor plate.

 

(b) Face Hardened Armor. The metal edges of holes and cracks in face hardened armor are relatively clean cut and sharp. The plates do not bulge to any great extent before cracking. By examining the edges of freshly broken face hardened armor, it can be noted that the metal at the face side is brighter and of a finer structure than the metal at the soft side. The brighter metal extends to a depth of approximately 1/5 to 1/4 inch in thickness from the outside surface.'

[stevehnz]

I welded enough to know how little of the subject I knew while at the same time understanding there was stuff to know. A thread like this I find utterly fascinating. Thanks to all contributing. Sorry @Kipsley for your thread being derailed but it is very much to a worthy cause to my mind & for modelling, such knowledge is gold imho.

Steve 

[Pig of the Week]

Having done some stints on the railway I've seen some thermite welding done, though my own welding work was concerned with engineering wagons and track laying equipment etc rather than the track itself. 

The thermite mix is essentially aluminium plus iron Oxide, (effectively aluminium powder and rust !) 

This when ignited burns fiercely enough to melt the steel, which is then ground to profile as described in an earlier post. 

 

[Kingsman]

To have a proper understanding of the original subject, rust, it is necessary to explore some of the chemistry and metallurgy involved. So many people seem to believe that anything metal rusts to orangey shades in no time at all.  And in the context of AFVs it is important to understand what does  and doesn't corrode and oxidise and how that progresses over time. I've even seem rusted models of aluminium vehicles like M113s. And then there are the many models of vehicles  only in service for a short time looking like 20 year range wrecks.  Unfortunately I have to lay a lot of the blame for that on The Spanish School of artistry in modelling. Artistry over realism.

[StuartH]

Interesting how in spite of Armour plate alloys having anti-corrosion elements the destroyed AFVs in Russia/Ukraine have rusted very quickly. I guess fire causes rapid oxidation?

 

 

 

 

[Kingsman]

Yes, fire will cause oxidation.  Burned-out AFVs will be rusty as the photos show.  So will Salt water immersion: vehicles salvaged from the sea bed.  Buried vehicles recovered in Eastern Europe often show little or no corrosion as the peaty soils are essentially anaerobic.  IIRC near-freezing water also slows corrosion.

[Tigerausfb]

I was reading the latest posts in this thread while playing with a hardened steel machinists 1-2-3 block. I dropped it and it fell on my toe, which hasn't been face hardened.

[Circloy]

Such a fast moving, twisting, thread its been hard to keep up & add to the discussion.

 

I was quality contoller at a Tool & Special Steel manufacturer in Sheffield which included in its product range armour plate & I believe we were the last to melt armour in the UK, production of armour at the British Steel corporation ceasing 2 years previously. Any armour production in the UK is done using foreign sourced plate.

 

I'd been compiling a point by point answer on some of the items raised when @Kingsman posted on the information he'd located which looks to have covered most of what had been questioned before. Now we appear to have moved even further on and raised more queries.

 

Whilst I'm not a trained metallurgist, actually more a nuclear chemist (untested) hopefully I picked up enough in nearly 4 years in the metals industry to get by.

 

Let me start by attacking the old enemy rust (Iron Oxides)

 

It is an undisputable fact that chemically Iron & Oxygen are attracted to each other, otherwise we'd find metallic iron ores, the result of this is that all iron based alloys rust. I've seen 18/8 Stainless steel (think cutlery) as rusty as those two tanks, I've also seen mild steels that have stood many years in the open with, what appears to be, a rust free surface.

 

Numerous factors come into play to determine the rate of rust formation these include (but are not limited to):

 

Alloy composition - It's a well known fact that adding elements such as Chromium & Nickel to steel reduce the rate that iron oxides form (stains less)

Temperature - as with most chemical reactions iron oxide formation will be faster at higher temperatures.

Surface condition - iron oxides will start to form at surface defects and spread from the formation points, highly polished surface has less defects from which rust can start.

Surface coatings - paint, oil, grease etc provide a barrier to prevent oxygen getting to the iron.

Environmental conditions - presence, or absence, of other elements , electricity will accelerate or decelerate the formation of rust.

Processing - complex but the whole operational sequence (forging, rolling, cross rolling, cold rolling, heating, cooling, heat treatment cycles, furnace conditions etc., etc.) all contribute, mainly via the surface condition, to controlling the rate of rust protction.

 

I'll come back later and fill in what I can regarding armour plate specifically, It's been a long day.

 

 

 

[Kingsman]

@Circloy thank you for the intervention. Much appreciated. Most of what I've said on tnis subject has been observational from 30-odd years in Defence, 8 years as an army reservist and now 7 years working with preserved vehicles.  I'm no engineer, chemist or metallurgist. I did work on armoured and protected vehicle projects.  Finding cogent understandable explanations is not always easy. Or we'd all be doing it!

[Circloy]

Thanks @Kingsman hopefully  can meet those expectations.

 

Armour.

 

The specification for armour up to around 2000 when we ceased production was mainly MVEE 816, developed by the Military Vehicle Engineering Establishment @ Chobham and issued around 1970. It had been developed from the alloys used in WW2 & was more to incorporate the benefits of newer production methods. Towrds the end of our production newer specifications were being developed again benefiting from other new technologcal developments and catering for higher hardness plate.

 

The alloy itself is not too exotic (.3C, .6Mn, 1.5Cr, .7Ni, .3Mo) The Cr & Ni will impart mild resistance to rust.

 

Electric arc melted from scrap and alloying additions, cast into ingots, of around 2 to 3 tonne (from memory),  forged or pressed into slab form and rolled into billets suitable for plate rolling, cutting to squares, heat treating. Plate was then either laser or plasma cut to the profile required vehicle manufacturer before being despatched.

 

From my metallugical understanding

 

The structure of an ingot is not dissimilar to that of an ice lolly which when snapped across the diameter shows fingers of ice, jut as the juice forms these fingers the metal as it solidifies forms long thin crystals of steel, growing from the outside of the ingot towards its centre. As metal shrinks when it cools voids can form down the cetntre of the ingot known a 'pipe'. Controlling the cooling and making provision for a 'head' of molten metal will minimise it. An ingot will have little intrinsic strength which can be improved by controlled cooling on initial pouring or re-heating the ingots and furnace cooling will allow these crystals to restructure themselves and alter the properties favourably. Controlling cooling rates on large sand casting can be difficult and is most likely the reason fo the poor balistic performance of cast bodies when compared to constructed bodies.

 

Following casting the first process will usually be hammer forging or press forging this occurs at high temperature and not only changes the cross section of the material will, at the right temperatures, close up and 'weld' any internal voids. An additional benefit is that the crystals structure is further distorted & re-arranged.

 

Subsequent thermomechanical processing adds to the this distortion and re-orientation of the crystal structure.

 

The final plate rolling operation involves rolling in one direction, spinning the plate by 90 degrees and re-rolling and repeating until the plate reaches the final thickness.

 

This ensures both the structure and properties of the steel are uniform.

 

Once at final thickness plates would be smithed, or thicker sections pressed, flat. The surface cleaned by shot blasting prior to heat treatment.

 

First plates would be hardened (800/850 C)in a gas fired furnace, little to no excess oxygen to prevent oxide formation, and quenched in oil. Plates would then be at maximum hardness with a dark smooth surface.

 

Tempering (approx 500C) would follow to achive the required/maximum hardness, impact and other mechanical properties. This was done in a rolling bed furnace open to air so surface oxidation would occur, this would be thin and tightly bound to the surface, little more than discolouration of the surface.

 

If the batch of plates was intended for use in vehicles destined for the UK armed forces a test coupon would be supplied to the test range @ Eskmeals for balistic testing.

 

At 17 mm thick the resulting plate is capable of withstanding direct 90° impact from a high speed 20 mm shell without penetration or spalling from the rear of the plate.

 

Our approved production range 3 - 17mm was at the thinner end of the specification limited mainly due to the need to manhandle material in our plate mill.

 

 

An insight into armour production but from a modellers perspective what does it mean.

 

Surface - Rolled homgeneous armour plate does not have a heavily textured surface as portrayed on some of the more modern kits, neither is it bright as grinding of armour is not permitted. for me I prefer Tamiya's typical kit surface.

 

Rust - Armour plate is moderately resistant to rust, we held stock outside for years unprotected with only a light rusting that was nowhere near some of the effort seen.  Protected by paint on an acive in-srvice vehicle I'd seriously doubt any rust being present. I'd bow to your experience in this matter @Kingsman. We were not involved with tracks so I can't comment on those but when i hear manganese steel i think of railway crosssings & frogs. In place for years, unprotected & not heavily rusted on non wearing surfaces.

 

Welding - very limited experience so little to add. Rods of the same or similar alloys are suitable for using, there is a datasheet for suitable welding rods on the web - these have a 20% Cr content which would explain the bright weld many years on. pre-heating would potentially destroy the temper & properties of any heated area if the temperature exceeded the temperature stated above. Electrically formed welds would have a limited heat affected zone.

 

I don't think that when explosive welding is referred to above that they are referring to Thermite welding. My thinking, and I could be very wrong, is that shaped charges are being used to blast a jet of molten metal along the joint of two disimilar metals to fuse both together much in the way a shaped charge directed at armour plate will burn a hole through to a tanks interior.

 

Hope this has been useful and helps understanding at a material level.

 

 

 

 

[StuartH]

Many thanks @Circloy. Very informative.

 

What determines the shade/colour of rust? i.e. from a yellowy/light orange to a deep red/dark brown.

 

Is it the metal itself and any element additions/contaminants or more due to the atmospheric conditions and speed of rust?

 

 

[Bozothenutter]

On 2/9/2024 at 12:05 AM, Circloy said:

Thanks @Kingsman hopefully  can meet those expectations.

 

Armour.

 

The specification for armour up to around 2000 when we ceased production was mainly MVEE 816, developed by the Military Vehicle Engineering Establishment @ Chobham and issued around 1970. It had been developed from the alloys used in WW2 & was more to incorporate the benefits of newer production methods. Towrds the end of our production newer specifications were being developed again benefiting from other new technologcal developments and catering for higher hardness plate.

 

The alloy itself is not too exotic (.3C, .6Mn, 1.5Cr, .7Ni, .3Mo) The Cr & Ni will impart mild resistance to rust.

 

Electric arc melted from scrap and alloying additions, cast into ingots, of around 2 to 3 tonne (from memory),  forged or pressed into slab form and rolled into billets suitable for plate rolling, cutting to squares, heat treating. Plate was then either laser or plasma cut to the profile required vehicle manufacturer before being despatched.

 

From my metallugical understanding

 

The structure of an ingot is not dissimilar to that of an ice lolly which when snapped across the diameter shows fingers of ice, jut as the juice forms these fingers the metal as it solidifies forms long thin crystals of steel, growing from the outside of the ingot towards its centre. As metal shrinks when it cools voids can form down the cetntre of the ingot known a 'pipe'. Controlling the cooling and making provision for a 'head' of molten metal will minimise it. An ingot will have little intrinsic strength which can be improved by controlled cooling on initial pouring or re-heating the ingots and furnace cooling will allow these crystals to restructure themselves and alter the properties favourably. Controlling cooling rates on large sand casting can be difficult and is most likely the reason fo the poor balistic performance of cast bodies when compared to constructed bodies.

 

Following casting the first process will usually be hammer forging or press forging this occurs at high temperature and not only changes the cross section of the material will, at the right temperatures, close up and 'weld' any internal voids. An additional benefit is that the crystals structure is further distorted & re-arranged.

 

Subsequent thermomechanical processing adds to the this distortion and re-orientation of the crystal structure.

 

The final plate rolling operation involves rolling in one direction, spinning the plate by 90 degrees and re-rolling and repeating until the plate reaches the final thickness.

 

This ensures both the structure and properties of the steel are uniform.

 

Once at final thickness plates would be smithed, or thicker sections pressed, flat. The surface cleaned by shot blasting prior to heat treatment.

 

First plates would be hardened (800/850 C)in a gas fired furnace, little to no excess oxygen to prevent oxide formation, and quenched in oil. Plates would then be at maximum hardness with a dark smooth surface.

 

Tempering (approx 500C) would follow to achive the required/maximum hardness, impact and other mechanical properties. This was done in a rolling bed furnace open to air so surface oxidation would occur, this would be thin and tightly bound to the surface, little more than discolouration of the surface.

 

If the batch of plates was intended for use in vehicles destined for the UK armed forces a test coupon would be supplied to the test range @ Eskmeals for balistic testing.

 

At 17 mm thick the resulting plate is capable of withstanding direct 90° impact from a high speed 20 mm shell without penetration or spalling from the rear of the plate.

 

Our approved production range 3 - 17mm was at the thinner end of the specification limited mainly due to the need to manhandle material in our plate mill.

 

 

An insight into armour production but from a modellers perspective what does it mean.

 

Surface - Rolled homgeneous armour plate does not have a heavily textured surface as portrayed on some of the more modern kits, neither is it bright as grinding of armour is not permitted. for me I prefer Tamiya's typical kit surface.

 

Rust - Armour plate is moderately resistant to rust, we held stock outside for years unprotected with only a light rusting that was nowhere near some of the effort seen.  Protected by paint on an acive in-srvice vehicle I'd seriously doubt any rust being present. I'd bow to your experience in this matter @Kingsman. We were not involved with tracks so I can't comment on those but when i hear manganese steel i think of railway crosssings & frogs. In place for years, unprotected & not heavily rusted on non wearing surfaces.

 

Welding - very limited experience so little to add. Rods of the same or similar alloys are suitable for using, there is a datasheet for suitable welding rods on the web - these have a 20% Cr content which would explain the bright weld many years on. pre-heating would potentially destroy the temper & properties of any heated area if the temperature exceeded the temperature stated above. Electrically formed welds would have a limited heat affected zone.

 

I don't think that when explosive welding is referred to above that they are referring to Thermite welding. My thinking, and I could be very wrong, is that shaped charges are being used to blast a jet of molten metal along the joint of two disimilar metals to fuse both together much in the way a shaped charge directed at armour plate will burn a hole through to a tanks interior.

 

Hope this has been useful and helps understanding at a material level.

 

 

 

 

Oh god, you made me dig out my metallurgy book!

Austenitic, martensite, brinell....🤯

Going to lie down now.....

[Tigerausfb]

Very interesting @Circloy. Thanks for taking the time. I think armour modelling, as I mentioned above, evolved around the late 80s and sort of peaked to what we know now in the mid -2000s. Broadly in-line with the expansion of the internet, many modellers, such as myself, from across the world came together with like-minded individuals around that time and started sharing techniques. I'm sure there were parallels in the aircraft modelling world too.  Tony Greenland, who was a little older than most of us and I consider the godfather of armour modelling, used to use a rotary tool and burr to lightly bounce around 'plate' to give a more textured effect on his models and artists pastels for shading and streaking, Later some modellers started adding black-brown scratches and scrapes simulating vehicles that had had a mortar round or two dropped near them, battle scars if you like, thus removing paint and going down to metal. This on top of slightly varying the main colour by drybrushing.

 

So a real quest for realism based on photographic research rather than just get a just get a Airfix Afrika Korp Panther, painted it desert yellow, bit of a wash and dry brush in white and into the display cabinet. Maybe in some cases that realism has gone past real. in to art.

 

 

[Circloy]

9 hours ago, StuartH said:

Many thanks @Circloy. Very informative.

 

What determines the shade/colour of rust? i.e. from a yellowy/light orange to a deep red/dark brown.

 

Is it the metal itself and any element additions/contaminants or more due to the atmospheric conditions and speed of rust?

 

 

The colour of rust - good title for a film and I can vouch that there are more than 50 shades.

 

The formation of rust is complex, Iron will not rust in either pure water or dry air (even pure dry oxygen) it requires the presence of both even then the reaction is slow. However the world is not perfect and our atmosphere is not just made up of oxygen and nitrogen and water is never found pure in nature.

 

Air contains not just nitrogen and oxygen but also small amounts of other gases including carbon dioxide, carbon monoxide, nitrogen oxide nitrous oxide, sulphur dioxide in various concentrations, these gases, including oxygen, disolve in water (during rainfall) to form very mild acids. Additionally as water wends its way back to the seas and oceans it will come into contact with minerals and salts disolving some along the way.

 

This has now set up the conditions required. Iron, oxygen and acidic/salty water all in direct contact allows for electrochemical reactions to take place forming rust.

 

Iron oxdes & hydrated iron oxides exist in two forms Iron(II) & Iron(III). Initial formaton of rust exist in the Iron(II) form which is much the colour of the two burnt out tanks pictured above. This form is relatively unstable and continued contact will result in the reactions continuing though various intermediary form concluding with Iron(III) oxides & hydrated oxides.

 

The Iron(II) form of rust is the orangy form Iron(III) is the dark, at times almost black, form.

 

Other than delayng the rate of rust formation the alloying elements appear to have little influence on the colour of rust.

[Circloy]

5 hours ago, Bozothenutter said:

Austenitic, martensite, brinell....🤯

Didn't want to get to that level.

 

I'm less special steels thee days & more super alloys.

[Longbow]

Rust is a funny old thing. 
Heres a Stug III, still in its original Tropen paint, lost in a lake in Russia sometime between December 1942 and February 1943. 
 

Pulled out of the lake not too long ago. 
Note how only the mild steel parts have really rusted. 
 

[Longbow]

On 2/7/2024 at 7:10 AM, StuartH said:

Interesting how in spite of Armour plate alloys having anti-corrosion elements the destroyed AFVs in Russia/Ukraine have rusted very quickly. I guess fire causes rapid oxidation?

 

 

 

 

Ever seen a Kia, after an engine fire ?

Looks just like those Russian vehicles. 
 

Makes you think… just sayin’… 🤔

 

 

[stevehnz]

11 hours ago, Longbow said:

Ever seen a Kia, after an engine fire ?

Looks just like those Russian vehicles. 
 

Makes you think… just sayin’… 🤔

 

 

Ever see an Alpha Sud more than a few years old, looks  looked, ( they've all dissolved now), a lot like those Russian tanks, maybe a property of Russian steel?

Steve.

[Circloy]

13 hours ago, Longbow said:

Rust is a funny old thing. 
Heres a Stug III, still in its original Tropen paint, lost in a lake in Russia sometime between December 1942 and February 1943. 
 

Pulled out of the lake not too long ago. 
Note how only the mild steel parts have really rusted. 
 

lack of heavy rust is probably due to  lack of disolved oxygen in the lake

[Bullbasket]

IMHO, we appear to be in danger of over thinking this subject. Various shades of rust? It'll get to the point where someone calls out another modeller over the colouring of the rust that he's applied to his (or her) pride and joy. We've had years of "Oh that's the wrong shade of green for SCC15". We're in danger of now hearing "Oh the rust coming from that bracket should be more red" or some such. In competitions, I doubt whether there will be any one judge who could honestly state that the shade of rust was wrong. When all is said and done, if it looks right...................

 

John.

[Black Knight]

Just put rust/corrosion of the appropriate type where it is appropriate

I once saw at SMW, Telford a nicely done scene of an abandoned Chevrolet Corvette with rusty wheel arches, bonnet and sills

[Kingsman]

Vehicles recovered from lakes and especially bogs in Eastern Europe are often in comparatively good condition compared to those of similar vintage above ground on ranges because of reduced oxygen content.  Peaty bogs can be almost completely anaerobic.

[StuartH]

Pulled from a peaty bog after 62 years. 2 previous owners very good condition.

 

 

 

 

 

[Circloy]

Quick wash, service, new battery & fresh fuel and its odds on it'll start first  time