Why Heat Treat?

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What is heat treating?

Heat treating is a process used to change the crystalline structure of steel to improve its strength, toughness, and hardness.   By using a controlled process, heat treating can double the tensile strength of alloy steel while still maintaining its toughness and ductility.

Why is it important to heat treat?

Increasing the tensile strength of the material improves the material’s resistance to fatigue and improves its durability in highly stressed applications.   However, increasing tensile strength must be done in a manner that also maintains the ductility of the material or it will be brittle.   The process used at Hellwig is a multi-step process that provides a tough, durable product that will last a lifetime.   Hellwig sway bars are used in many demanding military and off road applications because of their toughness and durability.  In these applications a non-heat treated sway bar will fail in a matter of weeks and sometimes days.   Hellwig sway bars will last for many years in the harshest of environments including vehicles used by the US Border Patrol on desert patrol.   Hellwig sway bars are installed by the  US Border Patrol before the vehicle goes into service because the addition of a Hellwig sway bar prevents downtime of the vehicle.   For this reason, Hellwig insists on manufacturing heat treated sway bars for heavy duty applications.

One thing to keep in mind is that not all aftermarket sway bars are heat treated.  They may be made from alloy steel, but unless it has been heat treated,  the alloy steel is not being processed to its full potential.   Hellwig uses 4140 chrome moly steel in its heat treated sway bars.  We receive it as hot rolled material from the steel mill.  In this state, it has a minimum tensile strength of 95,000 psi.     After heat treating at Hellwig,  the tensile strength of the material  is raised to an average tensile strength of 180,000 psi.  Our ISO 9000 certified quality system employs statistical process control and computer control in our heat treatment  process to provide consistent parts that can be counted on when the going gets tough.

How does Hellwig Heat Treat their Sway bars?

The following photos show the steps that are used at Hellwig to make heat treated sway bars.

Coining

The ends of the sway bars are coined, a forming process that maintains the integrity of the sway bar.   The ends of a Hellwig heat treated sway bar are never welded as the heat affected zone of the weld will compromise the material.
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2. Forming

The sway bars are heated to 1600 deg F and formed on tooling to the desired shape.

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3. Quenching

After the bar is formed to shape,  the bar is moved to the quench tank while it is red hot.   Quenching the sway bar in specially formulated quench oil improves the crystalline structure of the steel, increasing its tensile strength.  During this process, the sway bar is rapidly cooled from  1600 deg F to approximately 150 deg F in a matter of seconds.
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4. Tempering

Once the sway bars have been quenched,  they are moved to the tempering furnace where they are heated to 1000 deg F.  This process improves the toughness and ductility of the sway bars while maintaining a high tensile strength.  After tempering,  the sway bars are checked for correct dimensions and then powdercoated.   Once tempered, the sway bars meet the standards necessary to be put into service.

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Posted on Tuesday, April 16th, 2013 in Tech Advice.
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