Hot/Warm forming of steel

[Hotmetalman]

I have developed a product that requires warm forming to produce. How would I go about selecting the best steel chemistry for hot or warm forming (800 to 1400 deg f). This material would be used in high volume and reasonable cost. ie. not exotic. Any and all comments welcome.

 

[metengr]

Hotmetalman;
Ease of fabrication is only one consideration in selecting material for use in a specific application. What is the end use of this component? Your final selection of material (steel) depends on strength requirements for service, static or dynamic load conditions in service, environmental conditions, cost and availability and .....

 

[dbooker630]

Hotmetalman,

In my experience that entire range is warm forming, but I digress...anyway, you may need to consider control of certain elements as they can adversely affect the forming operation. Depending on the severity of the forming steps, you may need to limit sulfur or silicon to avoid splitting. You may also require turned and polished stock as well. Of course the more you tighten the range from general mill tolerances the higher the steel price.

Let us know if there is any machining involved or final property requirements. That will influence your forming temperature range.

 

[CoryPad]

Formability is best when all alloying elements have low concentration, including carbon.

Strength is best when alloying elements are in higher concentration.

Microalloy elements like V, and Nb help avoid excessive grain growth during hot forming.

Most of the common alloys would be suitable for the actual process, so your material selection should be based on the final properties required of the part.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[stanweld]

Are you warm forming steel materials to make a part or are you asking about a steel part used to warm form another part? Do you wish to know the alloy to use to make the warm formed part or the material used to warm form the part. It is noted that 1400 F may be above the lower critical temperature of a number of carbon and low alloy steels.

 

[Pressed]

Traditionally the product requires a certain metal and that determines the heat of processing, or lack of heat. There are some cases where a part can be made with different processes obtaining similar characteristics.

===================================
Forging

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Ddraig Breuddwydia....

http://www.tailofthedragon.com

 

[Hotmetalman]

Thank you all for your responses,
We are trying to stretch a 2.5”long x 0.25”wide x .018”thk by 15%. Due to the direction of the forces, we are heating the center 2” of the 2.5” leg. The heat is only to reduce the yield strength in the area intended to stretch. If no heat is applied, the material tears at the web (I have pictures to send but this web site seems to be malfunctioning. Help?).
We have tried both HSLA 950 and 1010. The HSLA fractured with minimal elongation around the point of the fracture. The 1010 fractured with significantly more uniform elongation around the fracture.
The strength of the end part is significantly determined by the shape of the part. This being said, the higher the end strength of the material, the less material needed and the lower the cost to manufacture.
Questions:
1) Do you think the difference between the 950 and 1010 was more the result of yield and tensile, chemistry or other?
2) Do you have suggestions in regard to steel chemistry / grades etc.?
3) Can you explain what is meant by “1400 may be above the lower critical temperature”?
4) How can I get the photo’s on line?

 

[Hotmetalman]

Try these photo's

 

[CoryPad]

What is the initial condition of the 1010 before piercing and expansion? I am surprised you can't do this work at room temperature.

The difference between HSLA and 1010 is due to differences in strain hardening, uniform elongation, and total elongation.

Metallurgically speaking, the lower critical temperature refers to steel's phase change from BCC (ferrite) to FCC (austenite) crystal structures.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Hotmetalman]

The 1010 is galvanized and in coil form. no special handling or working of the material.

The reason that we can't do it at room temperature is the tearing action at the end of the strip that occurs. The force to tear is significantly lower than the yield strength of the steel strip in the area we want to stretch. To lower the force we heat it.

Are you saying that 1010 or other plain carbon steels would be more likely to succeed?

Is there a concern with going above the critical temperature for what we are doing? Is heat treating the concern?

Best Regards,
Jeff

 

[CoryPad]

Tearing on the end that you grip for expansion (perpendicular to the expansion direction)? Or an end that is being expanded and is parallel to expansion?

There is no question that low carbon steel like 1010 will be more formable than anything else.

The critical temp consideration was a metallurgical one for us "experts" to help understand the distinction between warm and hot. I don't think you need to reach hot working temperatures.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Hotmetalman]

Attached are 2 pictures showing the tearing with and without heat.

Does the addition of heat make the HSLA elongation look more like that of 1010? In other words, I would think that heating the material will enhance the elongation of both materials?

Regards

Jeff

 

[CoryPad]

Thanks for the pictures, they are very helpful.

Have you done a basic calculation of stress and strain on the legs? Get some data for your incoming material at various temperatures and compare what you have with what you need.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Pressed]

Just from a quick look, can you try heating a larger area and is it possible to create larger radii, maybe pre-drill?

===================================
Forging

http://mech.e.tripod.com

-------------------------------------------------
Ddraig Breuddwydia....

http://www.tailofthedragon.com

 

[Hotmetalman]

We have as close to uniform heat across the entire length of the leg as possible. Per video tape, there is no visible difference in color (ie heat) across the 2" heated area leg.

It wants to fracture at we assume is the hottest spot. More noticeable on the 950 than the 1010.

By "pre-drill", do you mean to create a hole at the ends of the legs?

Regards

 

[Hotmetalman]

CoryPad,
We have done heated pull tests and are showing 25 to 30% elongation at approx 1100 deg f. The part requires 15%.



regards

 

[CoryPad]

15 % elongation is not that much for either 1010 or HSLA steels, even at room temperature. I guess the piercing operation creates cracks that cause fracture. When you use elevated temperature forming, the stresses go down considerably, so fracture is avoided. You are putting a lot of cost into the product by using elevated temperature forming. If you have to use it, you should see if you can get HSLA to work, then you can reduce the thickness (lower cost) or have higher strength (premium product at premium price).

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Hotmetalman]

Thanks for the advice. This process saves about 40% on material over existing product, I'm hoping that will offset the cost of the final product.

Do you think higher carbon such as 1014 1016 would allow me to keep the formability advantage (and cost?) over 950 and give me added strength on the final product?

Regards

 

[Pressed]

Drill holes where the split occurs before slitting (pierce) and expanding. So when expanding, the force is acting on a nice radius area, instead of a concentrated point. That should be easy enough to test.

Or if larger radii is obtainable on the tooling, same place; where the split is occurring.

Otherwise, it seems a wider leg or beam (whatever you call the broke piece) should be tried.



===================================
Forging

http://mech.e.tripod.com

-------------------------------------------------
Ddraig Breuddwydia....

http://www.tailofthedragon.com

 

[Hotmetalman]

Update:
I have successfully formed 1010 material as shown in the above pictures.
If I wanted to increase the strength of the material and maintain the uniform elongation under elevated temperatures, am I better to to go with a higher carbon steel (1012,1014, etc.) or an HSLA (035,050, etc)?

Thanks

Jeff