Welding ASTM A514 or A514M-05 steel?
Before you do, take a close look at filler metals, heat input
As manufacturers strive for lower costs and greater efficiencies, they tend to substitute high-strength materials for standard materials. One such high-strength material is ASTM A514/514M-05. Although it is not difficult to weld, joining it successfully requires paying close attention to the preheat temperature, interpass temperature, and filler metal.
Cost and efficiency dictate manufacturing and fabricating trends in most industries. In addition to implementing lean work flow practices—better, faster transportation and processing and minimal inventory—many companies turn to the use of higher-strength, lighter-weight materials to reduce costs and improve welding productivity.
ASTM A514 and A514M-05 high-strength, low-alloy, quenched-and-tempered steels are among these materials. Although they have been available for many years, they continue to pose some distinct challenges for welders. Welding these materials successfully is a matter of understanding some key factors, including filler metal choices and preheating and interpass heat requirements.
What It Is, Why It Is
ASTM A514 is a specification for 100 kilopounds-per-square-inch-yield, low-alloy, quenched-and-tempered steel intended for structural applications and is typically known in the industry as USS (United States Steel) nomenclature T1®, regardless of the manufacturer.
A514 grades are A, B, E, F, H, P, Q, and S. Each grade has a unique chemistry and may differ in the maximum thickness to which it is rolled, from 1-1⁄4 in. to 6 in. The material thickness affects the mechanical properties. For instance, A514 rolled to 21⁄2 in. or less must have 110-KSI to 130-KSI tensile strength, 100-KSI minimum yield strength, and 18 percent elongation. For materials 21⁄2 to 6 in. thick, the mechanical properties are 100-KSI to 130-KSI tensile strength, 90-KSI minimum yield strength, and 16 percent elongation.
The hardness for material thickness up to and including 3⁄4 in. is 235 to 293 HBW (Brinell). Note that the specification does not list hardness requirements for materials thicker than 3⁄4 in.
One of the reasons for the difference in properties among these thicknesses is the quenching. The thicker the material, the slower the quench rate, which results in lower minimum yield and tensile strengths.
Typically, this material is used for structural applications. In many cases, the term structural refers to buildings, but the material also is used in heavy equipment structures to reduce weight and improve payload capacity, such as in railcars and their components, large mining truck frames, semitrailer frames, and crane boom sections.
Because the typical hardness of the materials is 22 to 27 Rockwell C, it is also used for wear strips, cutting edges, and side cutters. Typical applications are backhoe buckets and other wear components in earthmoving equipment.
Making the Choice: Filler Metals
Welding A514 is not complicated when some precautions, especially with filler metal choices, are used.
A primary concern is filler metal hydrogen content. You should not use filler metals that deposit weld metal with diffusible hydrogen content greater than 8 ml per 100 grams of deposited weld metal. A514 is sensitive to diffusible hydrogen, which may result in hydrogen cracking.
The filler metal strength depends on the application of the A514. Figure 1 shows filler metals you can use to match the strength of base materials up to 21⁄2 in. thick where the same mechanical properties as the base material are required. On base material thicknesses greater than 21⁄2 in., you can use the same filler metals, but their strength exceeds that of the base metal, a condition called overmatching strength (see Figure 2).
When joining A514 to other low-alloy steels or carbon steels of lower strength, use a filler metal with strength that meets the lower-strength base material's properties. For example, when welding ASTM A36 to A514, use a 70-KSI-tensile-strength electrode to match the lower-strength material. Don't focus solely on strength; keep the hydrogen cracking risk in mind.
Heat Input Control
Even though A514 is readily weldable, excessive preheat and interpass temperatures and welding heat input can affect the alloy's chemical properties. Figure 3 lists typical preheat and interpass temperatures for A514. These temperatures apply whether you are welding A514 to itself or to other, lower-strength materials.
It should be noted that preheat and interpass temperatures higher than those shown in Figure 3 may alter the mechanical properties of the material. Tempil® Sticks, contact pyrometers, infrared thermometers, or other heat-measuring devices should be used to control preheat and interpass temperatures.
In addition to the preheat and interpass temperature controls, heat input, which is a function of amperage, voltage, and travel speed, must be restricted. Heat input is expressed in joules per inch. The formula is:
Heat Input (joules/in.) = (Amperage ¥ Voltage ¥ 60) ÷ Travel Speed (IPM)
Typical heat input is about 55,000 joules per in. (±20 percent). For other heat inputs, it is advisable to contact the steel manufacturer for recommendations.
As a final precaution, A514 is not intended to be used in the postweld heat-treated (PWHT) condition, as it will alter the mechanical properties for which the material was intended.
Other sources of information for welding A514/A514M-05 steel are the steel manufacturers' fabrication guides and:
· AWS D1.1, Structural Code—Steel
· D14.3, Specification for Welding
· Earthmoving, Construction, and
· Agricultural Equipment
· D15.1, Railroad Welding Specification— Cars and Locomotives.
Want more information?
Visit www.thefabricator.com; enter the article number (digits only) in the home page search box:
· "Cracking the case" 1397
· "MIG—welding tips and resources" 1083
· "Preventing welding-related fires" 952
Wednesday, December 10, 2008
Welding ASTM A514 or A514M-05 steel?-Before you do, take a close look at filler metals, heat input
Posted by BR at 10:19 AM
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