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School me on heat treating 4130 tube. In the Ultra4 race in TN I bent some steering. I’m running stock class and cramped for space, so I really need to use 1.5” x .25” wall. I’m thinking about moving to 4130 and having it heat treated. I just want to make sure I’m telling my local heat treater the right thing. Do I want annealed, normalized, or ??? What’s going to be the strongest or have the best memory to go back to its original shape?


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Let your heat treater school you. But basically you want it hard enough to resist bending but not so hard it cracks. CoMo has the best strength characteristics by weight. And it yields (bends permanently ) before or if ever, it cracks or breaks. You should not think about CroMo as bending and returning to straight like 7075 Aluminum....but it does resist bending the harder it is. And at that point it yields permanently and resists cracking the best.. It is not a "spring steel."

Annealing is softening so you can machine or bend it (back) easier. Normalizing is returning the whole piece that you may have work hardened by welding or bending to a "normal" condition where it is more ductile to be Bent instead of cracking from the bending-work or heat treater hardening.

So what you are looking for is a hardness number for your link (like 52 Rc - "52 on the Rockwell C scale") And there are many ways to get to it. Straight heat and cooling (usually fast) or over heating and "drawing back" to the hardness you want. All this gets the molecules to do different things. Your heat treater should know. Because he should intuitively question what qualities an engineer is looking for before actually going ahead with the work.... Unless he trusts them of course with a complete heat/cooling schedule.

Welding and quick chilling will harden the Cromo next to the weld . They call this the heat affected zone. (HAZ) In the "old" days it was common to use a gas torch on the welds to normalize the tube in a race car cage to resist cracking in the HAZ. The cracking from hardness or too much heat from welding and annealing the HAZ. Many cages were gas welded so they didn't have to do that extra process..Usually with DOM tube. TIG welding offers a cleaner weld and CroMo blends have changed some so the post normalizing is not as necessary.

Cliff Notes ONLY!!!!! Not Gospel for sure. Don't be afraid to ask... But a start on the understanding.
 

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Let your heat treater school you. But basically you want it hard enough to resist bending but not so hard it cracks. CoMo has the best strength characteristics by weight. And it yields (bends permanently ) before or if ever, it cracks or breaks. You should not think about CroMo as bending and returning to straight like 7075 Aluminum....but it does resist bending the harder it is. And at that point it yields permanently and resists cracking the best.. It is not a "spring steel."

Annealing is softening so you can machine or bend it (back) easier. Normalizing is returning the whole piece that you may have work hardened by welding or bending to a "normal" condition where it is more ductile to be Bent instead of cracking from the bending-work or heat treater hardening.

So what you are looking for is a hardness number for your link (like 52 Rc - "52 on the Rockwell C scale") And there are many ways to get to it. Straight heat and cooling (usually fast) or over heating and "drawing back" to the hardness you want. All this gets the molecules to do different things. Your heat treater should know. Because he should intuitively question what qualities an engineer is looking for before actually going ahead with the work.... Unless he trusts them of course with a complete heat/cooling schedule.

Welding and quick chilling will harden the Cromo next to the weld . They call this the heat affected zone. (HAZ) In the "old" days it was common to use a gas torch on the welds to normalize the tube in a race car cage to resist cracking in the HAZ. The cracking from hardness or too much heat from welding and annealing the HAZ. Many cages were gas welded so they didn't have to do that extra process..Usually with DOM tube. TIG welding offers a cleaner weld and CroMo blends have changed some so the post normalizing is not as necessary.

Cliff Notes ONLY!!!!! Not Gospel for sure. Don't be afraid to ask... But a start on the understanding.
Thanks for the info.


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Let your heat treater school you. But basically you want it hard enough to resist bending but not so hard it cracks. CoMo has the best strength characteristics by weight. And it yields (bends permanently ) before or if ever, it cracks or breaks. You should not think about CroMo as bending and returning to straight like 7075 Aluminum....but it does resist bending the harder it is. And at that point it yields permanently and resists cracking the best.. It is not a "spring steel."

Annealing is softening so you can machine or bend it (back) easier. Normalizing is returning the whole piece that you may have work hardened by welding or bending to a "normal" condition where it is more ductile to be Bent instead of cracking from the bending-work or heat treater hardening.

So what you are looking for is a hardness number for your link (like 52 Rc - "52 on the Rockwell C scale") And there are many ways to get to it. Straight heat and cooling (usually fast) or over heating and "drawing back" to the hardness you want. All this gets the molecules to do different things. Your heat treater should know. Because he should intuitively question what qualities an engineer is looking for before actually going ahead with the work.... Unless he trusts them of course with a complete heat/cooling schedule.

Welding and quick chilling will harden the Cromo next to the weld . They call this the heat affected zone. (HAZ) In the "old" days it was common to use a gas torch on the welds to normalize the tube in a race car cage to resist cracking in the HAZ. The cracking from hardness or too much heat from welding and annealing the HAZ. Many cages were gas welded so they didn't have to do that extra process..Usually with DOM tube. TIG welding offers a cleaner weld and CroMo blends have changed some so the post normalizing is not as necessary.

Cliff Notes ONLY!!!!! Not Gospel for sure. Don't be afraid to ask... But a start on the understanding.
There's so many details wrong with this post I don't know where to begin. 🤦‍♂️
 

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In general heat treating it will give you a stronger part which will "spring back" more than an annealed part (not heat treated, aka lower hardness).
It all depends what kind of stress the part is under. If you're getting to a point where your existing tube is bending permanently then you know you're stressing it over its yield point. This can be addressed by heat treating the steel to achieve a higher tensile strength, but as you heat treat it to a higher strength (and hardness typically) you will lose that ductility. This is OK as long as you don't exceed the yield strength of the now higher strength part, but if you do it may not bend and stay in one piece, but instead break and come apart which would be very bad for a steering part.

4130 is a little low on carbon to be heat treated by quench and temper, but talk to your local heat treating vendor. Tell them you're looking to increase the yield & ultimate strength of the tube and they'll tell you if they can help you. You won't be able to achieve the 52 HRC hardness that the person above suggested without some kind of case hardening like carburizing or carbonitriding which involves diffusing increased carbon into the surface of the steel so it can be hardened to a higher level; carbon content is the largest factor in determining how hard steel can be heat treated. Case hardening isn't going to increase the overall strength of your tubing enough to matter anyway; those processes are typically used to increase the wear life of parts (think gears).

If you're bending your existing parts I'd encourage you to try increasing the size (o.d.) or thickness of the part first. If you can't do that you may want to consider moving to a higher carbon content tube that can be quench and tempered to achieve a higher strength, but this will lead to other issues. 4140 pre-hardened bar stock is always a good option; it's pre-hardened so it's fairly strong (about 120ksi) but it can still be machined.
 

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Discussion Starter #7
In general heat treating it will give you a stronger part which will "spring back" more than an annealed part (not heat treated, aka lower hardness).
It all depends what kind of stress the part is under. If you're getting to a point where your existing tube is bending permanently then you know you're stressing it over its yield point. This can be addressed by heat treating the steel to achieve a higher tensile strength, but as you heat treat it to a higher strength (and hardness typically) you will lose that ductility. This is OK as long as you don't exceed the yield strength of the now higher strength part, but if you do it may not bend and stay in one piece, but instead break and come apart which would be very bad for a steering part.

4130 is a little low on carbon to be heat treated by quench and temper, but talk to your local heat treating vendor. Tell them you're looking to increase the yield & ultimate strength of the tube and they'll tell you if they can help you. You won't be able to achieve the 52 HRC hardness that the person above suggested without some kind of case hardening like carburizing or carbonitriding which involves diffusing increased carbon into the surface of the steel so it can be hardened to a higher level; carbon content is the largest factor in determining how hard steel can be heat treated. Case hardening isn't going to increase the overall strength of your tubing enough to matter anyway; those processes are typically used to increase the wear life of parts (think gears).

If you're bending your existing parts I'd encourage you to try increasing the size (o.d.) or thickness of the part first. If you can't do that you may want to consider moving to a higher carbon content tube that can be quench and tempered to achieve a higher strength, but this will lead to other issues. 4140 pre-hardened bar stock is always a good option; it's pre-hardened so it's fairly strong (about 120ksi) but it can still be machined.
Thank you!


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...4130 is a little low on carbon to be heat treated by quench and temper, but talk to your local heat treating vendor. Tell them you're looking to increase the yield & ultimate strength of the tube and they'll tell you if they can help you. You won't be able to achieve the 52 HRC hardness that the person above suggested without some kind of case hardening like carburizing or carbonitriding which involves diffusing increased carbon into the surface of the steel so it can be hardened to a higher level; carbon content is the largest factor in determining how hard steel can be heat treated. Case hardening isn't going to increase the overall strength of your tubing enough to matter anyway; those processes are typically used to increase the wear life of parts (think gears).
I dont think ISDTBower was suggesting 52 HRC for the part, but just using a random number to give an example.
 
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