Webley Senior piston repair?

[ggggr]

Ok--you lot know what you are talking about with this-----but a couple of questions now
(1) Is low carbon steel the same as mild steel?

(2) do you think the pistons are then hardened after machining (and if so , how?) or are they not hardened at all?

(3) are the later pistons (Hurricane /Tempest) different from the earlier ones (Mk1, Senior, Premier) in how or what they are made from and / or hardened?

[edbear2]

Ok--you lot know what you are talking about with this-----but a couple of questions now
(1) Is low carbon steel the same as mild steel?

(2) do you think the pistons are then hardened after machining (and if so , how?) or are they not hardened at all?

(3) are the later pistons (Hurricane /Tempest) different from the earlier ones (Mk1, Senior, Premier) in how or what they are made from and / or hardened?

1.........Mild steel is a type of low carbon steel. Carbon steels are metals that contain a small percentage of carbon (max 2.1%) which enhances the properties of pure iron. The carbon content varies depending on the requirements for the steel.
Low carbon steels contain carbon in the range of 0.05 to 0.25 percent.

2........No idea

3........no idea

ATB, Ed

[rancidtom]

Ok--you lot know what you are talking about with this-----but a couple of questions now
(1) Is low carbon steel the same as mild steel?

(2) do you think the pistons are then hardened after machining (and if so , how?) or are they not hardened at all?

(3) are the later pistons (Hurricane /Tempest) different from the earlier ones (Mk1, Senior, Premier) in how or what they are made from and / or hardened?

1 "Mild steel" is a general term for low carbon steels. These steels show very little hardening if any under heat treatment and are very easy to machine, hence the term "mild". It encompasses steels with other minor alloying elements that are usually to help with toughness (not hardness) and ductility as well as "free machining ability". No matter how you heat treat, hammer, bend, drill, punch or whatever this group of steels don't harden or become brittle within the bounds of what is considered normal machining, bending, forming processes used in pruduction. They do not require annealing (softening) after most operations and will only harden if the carbon content is raised for example in the case hardening process where carbon is dissolved into the surface crystal structure of the steel raising the carbon content in the "skin" of the steel (only a few thousandths of an inch depth is necessary). This process allows the surface of the steel to become hard with a soft core that means the steel becomes wear resistant yet will still not be brittle unlike a through hardened high carbon steel that has been heat treated.
High carbon steels once hardened can be nearly as hard as glass but they become brittle in this process (heating to the required temp, generally red hot, holding at this temperature for a certain amount of time depending how thick the steel is to allow the temperature to become even through to the core and then quenching). The quenching process can vary in the way it is done, generally the faster the cooling the harder the steel becomes, brine (salt water) gives one of the fastest quenches, followed by water, then oil. We also have "air quenching" steels. Different alloying metals in the steel will dictate what process will give the hardness required.
After quenching most steels are too brittle for the purpose they're needed for so they have a further heat treatment where they are heated to a certain temp and quenched again. We often use the oxidation colour of the steel to show the temp it is at before quenching, a knife blade that requires to be hard and retain a good edge may be quenched at "straw" while a spring will require a blue surface colour (higher temp) to be quenched at. Knives are brittle, springs are not, the higher the tempering temperature the more springy (less brittle) the steel will be yet it loses some hardness in the trade off.
The above heating and cooling processes occur when welding steels, some are going to brittle if the wrong rate of cooling is used but mild steel as it doesn't harden is pretty much immune to the rate of cooling after welding and shouldn't harden in the heat affected zone (HAZ) either side of the weld.
Signs of a steel that has been heat treated after a machining operation are blueing or the tempering colour evident on the surface of any part which has not been ground or polished after heat treatment. Once heat treated (to harden rather than to anneal) a steel is generally too hard to drill or turn in a lathe, very hard to file if not almost impossible. The same applies to case hardened steel, the surface is too hard for drilling/turning with most lathe tools and drills (diamond being an exception, but not usually used!) Once a steel has been hardened and tempered if it is required to have a bearing surface (say for instance a camshaft or crankshaft) that surface is locally ground to size and the finish will be chosen (grit size) to produce the best oil retention and wear resistance for that part.

2 Webley pistons don't appear to have been hardened because the surface finish of the non-load bearing areas isn't blued or oxididsed from a subsequent tempering operation. The bearing areas would have been ground to remove the oxidation from hardening tempering and provide the correct size and finish for wear.

3 The later pistons look to be turned and no subsequent heat treatment so to my mind they will be a mild type steel as per the early ones, it should be perfectly OK to build up with a weld using a "mild steel" type filler wire or rod using any process MIG/MAG, TIG, MMA (manual metal arc or "stick" welding) or oxy acetylene process. Oxy propane is not suitable as it will cause a problem with hydrogen pollution in the weld leading to cracking of even the mildest steel.

I've tried to keep it pretty basic as I know you don't need a qualification in metalurgy!
If you can file it easily it's mild steel or non-heat treated medium carbon steel. After a bit of experience you can tell whether you have a medium/high carbon steel or a mild steel after one or two strokes with a file. Files are generally the hardest we can get with a steel but as everyone knows they are brittle, not springy! Tempering a file could make it springy if you wanted to but it wouldn't be as hard.
Spring steels often have other alloying elements as well as carbon, such as nickel, chrome, molybdenum etc. These may add corrosion resistance, spring or other properties to the steel depending on the quantities used and the heat treatment given after shaping the metal.