4130 post heat treating welding

[atomicjoe23]

"Best" depends on what the specific application is. . .and it's not the same for everything. . .some parts on your truck may be best treated one way, while other parts are best treated another way.

As far as a roll cage and/or tube frame I would weld it and then at most stress relieve it. . .for most (most not all) heat treating an entire frame and/or roll cage would not be worth the effort/cost.

When it comes to smaller components like the uprights, spindles, etc. then I would weld them and heat treat them. . .stress relieving them prior to heat treating isn't going to mean much because heat treating them is just going to re-introduce stress. If you stress relieve them after heat treat you could potentially screw up the heat treat of the part (depending on the alloy and HT condition the parts are put in. . .I don't have a HT book with me here at the airport so I'm speaking in general terms here). . .

. . .when stress relieving would be a good idea would be post welding and pre-machining. . .the welding will induce stresses iin the part and when you start machining on the part the internal stresses will be released and the part will warp like crazy!!! By stress relieving the part prior to machining you minimize the warpage that will occur during post-weld machining. . .

. . .it's all dependent upon the specific application and there is no one "best" answer.

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[9er3ranger]

can some one explain in plain english what I think (and could be wrong) is weld it run a torch oover it then what beat on it with a hammer or somthing??

talking about 2" 120 wall cromo

There is a lot of naive statements in this thread. Atomic Joe is about the only one that made sense. A lot of people are throwing Heat treatment statements out that are out of place in a way. By the way beating on it with a hammer is called peening and its not usually recommended (not allowed in a lot of code work welding). basically when people are saying "have them annealed" etc. you must understand there are several different methods of heat treatment that all result in a different result depending what you are trying to get. To properly understand heat treatment first we have to look at what is happening at the molecular level. atoms in the material you are working on maintain a certain spacing related to the temperature that they are at. as heat (energy) is applied the atoms begin to vibrate causing them to move apart which can be seen as the metal expanding under temperature. As heat (energy) is reduced the atoms spacing shrinks (Contracting) the distance between the atoms moving them closer together back to their orignal spacing at room temperature. after a certain amount of heat is reached the atoms are vibrating and expanding so much that they are no longer attracted enough to maintain a specific structure and this is what has happened when you reach the liquid stage. Atoms in the steel cannot "move" unless energy (Heat) is present therefore if an isolated area in the steel is heated and the metal around it is not heated uniformly then you have an isolated area expanding with the surrouniding molocules maintaining their original spacing. this creates stress in the material due to the non heated metal resisting the heated metal. there is a specific number associated with each metal alloy that describes how much a metal will expand for its given temperature increase(known as coefficient of thermal expansion). iron molecules align themselves in lines and rows at room temperature known as body centered cubic structure and with heat they can assume what is called face centered cubic structure. It is important to understand the relationship between Iron (The main ingredient of steel) and the amount of carbon content in the steel. The amount of carbon determines what happens in the microstructure as heat is applied therefore typically higher carbon steels require heat treatment where as mild steel doesnt. as mentioned above in body centered and face centered, steels undergo changes in their crystallographic arrangement as a result of temperature changes. there are different stages based on the temperature that go from pearlite/cementite stage, ferrite and cementite, austenite and ferrite, austenite, then liquid. basically the amount of carbon determines at what tempurature the steel will reach these stages, however most steel is the same up to about 1300°F known as the lower transformation temperature. since we sort of know what is happening at the molecular level now, to put it into laymans terms, iron molecules in the steel wont move unless you apply energy (Heat) there fore if you heat the steel it changes its structure (Body centered, face centered) and if you throw a bucket of water on the hot metal while its in face centered structure then it cannot move back to its body centered arangement which causes the structure to be arranged in a jagged (martensitic) hard brittle structure seseptible to cracking. If it was allowed to slow cool all these things would happen in reverse leaving a Pearlite structure which is softer more ductile structure. So, back to the heat treatment process names being used incorrectly, Basically you have Annealing, Normalizing, Qunching, Teempering, Preheating, Post heating, And Stress relieving. Annealing increases ductility at the expense of its strength. it is done by raising the steel slightly into the austenitic range, held for 1 hour per inch of thickness or one hour minimum, then cooled very slowly in an oven. Normalizing also increases ductility (Softness) for strength but is not quite as severe as anealing. this is done by raising the steel to the austenitic range and holding for a short time it is allowed to cool in still air. since this is slightly faster cooling rate than in an oven, the result will be a slightly harder steel and therefore slightly less ductile. Quenching is different in which you raise the steel to the austenite range and rapidly cool it to room temperature with either water or oil. the result is a very hard metal with a martensitic (Brittile) grain structure. This is great for things like drill bit but if you try to bend a drill bit it will snap in two because it is hard and brittle with low ductility. now tempering goes along with quenching hence the term quenched and tempered. tempering is done after the piece has been quenched it is re heated to just below the lower transformation temperature, held for a short time to allow the martensitic structure to relax then slowly cooled. the result is a hardened steel with some ductile properties. pre heat basically applies heat to the steel before welding because it slows down the cooling rate allowing the microstructure to return to its happy place. Post heat is used after welding to reduce residual stresses but if you havent really put a bunch of heat into the surrounding metal then the weld and heat affect zone are resisting against the parent metal so this helps them relieve residual stress between the two. stress relief is similar to post heat just at different tempuratures typically below the lower transformation stage. basically speaking 4130 has a high carbon content therefore the need for heat treatment is much higher than mild steel. it would be best to pre heat the material to prevent as much shrinkage and warpage as possible during the cooling process, then post weld heat treat the whole part. once you go welding on it again after heat treat you have completely voided the postweld heat treat process because you have altered the grain structure and it must be done all over again.

[Scott_F]

Paragraphs are free.

[atomicjoe23]

Despite his lack of paragraphs 9er3ranger was very accurate in describing what is going on. . .most mild steels (as we think of mild steel anyway. . 1018, 1020 etc.) don't have enough carbon content to heat treat (i.e. harden with a heat and quench cycle) anyway which is why it isn't done (the exception being case hardening). . .

. . .in the limited time I have been heat treating parts I have discovered that it is equal parts art and science. Science tells you what should be happening and what should be done, but practice and experience turn it into an art where actually get out what you intend to. . .easier said than done at times.

[9er3ranger]

Paragraphs are free.

Sorry scott ima noob

[CRAIG_HALL]

Once you have the heat treat figured out. You get to play with keeping pivot aligned, center to center correct, uniball bores needing to be cut to size. Many times the heat treater is used to straightening parts after a cycle

[A Vance]

I ran a heat treat shop for years and worked mostly with Motorsport guys. A good heat treater would pre heat/ stress relieve a welded part prior to the heat treat process. They should fixture the part to keep part from moving or distorting.

[9er3ranger]

Once you have the heat treat figured out. You get to play with keeping pivot aligned, center to center correct, uniball bores needing to be cut to size. Many times the heat treater is used to straightening parts after a cycle

thats an excellent point craig, I should have mentioned that. heat treat can definitely make your final dimensions off so you have to be careful and take preventative measures.