Preheat Wear Resistant Steel Before Welding
The deep freeze that covered most of the central and southern states recently, reminds us of the need to preheat wear plate before welding.
High quality, heat treated wear resistant steel contains several alloying elements, such as Nickel, Chromium, Molybdenum, Boron and several others.
The dark area to the left of the flame on the bucket side plate, is the moisture coming out of the steel. If preheat is not used, during welding any Hydrogen from the moisture goes to the bottom of the weld deposit. This will cause under bead cracking, and weld failure. Controlling moisture content in welding rods is where the term ‘Low-Hydrogen’ comes from.
It is also one of the last things you do before you start to weld.
Preheating involves heating the base metal surrounding the weld joint, to a specific temperature before starting to weld.
Preheating has many benefits, including reducing the risk of cracking. However over-heating wear plate often destroys the hardness of the steel.What Determines The Need To Preheat?
The need for preheat increases with the following factors:
1. The larger the mass being welded.
2. The lower the temperature of the steel.
3. The lower the ambient temperature.
4. The higher the Carbon content.
5. The greater the alloy content.
6. The greater the welding speed.
7. The more complicated the joint shape.
8. The smaller the weld rod/wire diameter.
When Should Preheat Be Used?
The following factors should be considered in determining whether or not to preheat: welding code requirements, steel thickness, base metal alloy chemistry, restraint, ambient temperature, filler metal hydrogen content or previous cracking problems.
With Alloyed Chemistry, The Demand For Preheat Increases With:
Hydrogen levels in the weld metal
Restrained joints
Section thickness
In production welding, codes generally specify minimum preheat temperature values. This may or may not be adequate to prohibit cracking in every application.
What Preheat Temperature Is Required?
See the Chart Below for direction.
Preheat is extremely important for High Strength, Low Alloy steels that have high hardenability.
Most wear resistant steels are Quenched and Tempered to achieve the desired hardness.
This is where JADCO QT-PLUS ® gets its name. Quality wear plates are included in the HSLA or high strength, low-alloy steel family.
It is essential minimum and maximum preheat temperatures be closely monitored when welding Quenched and Tempered steels.
IMPORTANT: Overheating Q&T steels will destroy the hardness of the wear resistant steel.
If the steel shows color, it is already overheated destroying your investment in longer life.
How is Preheat Applied?
The material thickness, size of the weldment and available heating equipment should be considered when choosing a method for applying preheat.
Large structural components may require multiple heating torches, electrical strip heaters, or induction or radiant heaters.
The preheat temperature must be tested a minimum of 3 inches away from the joint in all directions.
This means you don’t measure only in the weld joint location. To guarantee the material surrounding the joint is heated, check the heat the side opposite of the area to be welded. Then measure the surface temperature adjacent to the joint.
How Long Must You Maintain Preheat Temps?
Heating may be continued during the welding process, but frequently the heat generated from welding is enough to maintain the desired temperature.
Inexperienced welders tend to rush the preheat process. If the temperature is recommended to be 250° F, and you have the temperature at 150° F, you are NOT ready to weld.
The term ‘Interpass Temperature’, is defined as the base metal temperature between the first and last welding passes. Do not allow the interpass temperature to fall below the preheat temperature.
The temperature of the steel should be checked to verify that the minimum preheat temperature has been maintained for each pass.
NOTE: There are many inexpensive infrared temperature guns which will give you accurate readings.If you are using Tempil®crayons, NEVER APPLY THEM IN THE WELD JOINT TO TEST THE TEMPERATURE!
The recent cold temperatures throughout the USA are a challenge for heavy equipment welding repairs.
If you are planning to weld on wear plate in this weather, preheat is absolutely critical for a successful installation.
Allow JADCO to help you achieve the best wear plate performance for your equipment. We have the experience necessary in your industry to deliver improved wear results.
For the last 45 years JADCO has focused exclusively on delivering consistent, longer equipment life for our customers.
Allow us to help you today by emailing us at info@jadcomfg.com or calling (724) 452-5252.
We will schedule a meeting with one of our local wear plate specialists at a time that best fits your schedule.
Remember, the only thing you have to lose by not working with JADCO, are your profits.
When your flat back elbows give out, give JADCO a shout!
