A brief history of Boron in steels and its recent influence on weldments BRIEF HISTORY OF BORON IN STEELS AND INFLUENCE ON WELDMENTS Using a steel with the addition of the alloying agent boron (B) is known to provide some benefits, including its ability to improve steel hardenability. However, it can also affect mechanical properties of various chemical compositions, along with cooling rates. Also, steels containing boron should only be used with hardenability in mind, as the lowered alloy content can be harmful to some applications.. New Zealand Technical Specification Recently the use of boron in common grades of structural steel has been discovered. The latest version of AS/NZS 1554.1,5 & 7 (2014) introduces a total boron content limit of 0.0008%wt, in addition to parent materials which comply with steel standards; however, this restriction has since been overruled. Instead, the Technical Specification – SA TS 103: 2016 requires the same boron limitation, however, does not specify it as a New Zealand Technical Specification. Boron – The effect on steel and weld joint The addition of boron and carbon in steel can enhance steel strength 1, however, a more complicated behaviour can result from commercial steels due to the possibility of titanium 2 and nitrogen being present. The cooling rate is also a significant factor as it can change the steel hardness 1. When welding, this can occur when the parent metal undertakes a thermal circle in a very short period. Within a welded joint, there are three areas to consider, the integrity of the parent metal, the heat affected zone (HAZ), and the weld metal. 18 June 2017 The key focus of boron content is the effect of the weld quality has on the HAZ, due to the possible fast cooling rate which can result in high hardness, leading to hydrogen assisted cold cracking (HACC). To overcome this the pre-heating temperature should be improved, or alternatively, a weldment test can be performed 3. Why boron exists in steel and welding consumable? Commercially, using a steel with the addition of boron can improve hardenability to achieve a desired mechanical and heat treating properties, like other common elements such as carbon, magnesium, nickel, chromium and molybdenum, etc. Such addition of micro-alloy in recent decades produces a steel category known as high strength low-alloy (HSLA), which is developed to provide specific desirable combinations of strength, toughness, formability, weldability and atmospheric corrosion resistance instead of meeting certain chemical composition 4. Boron has also been used in welding consumables, known as micro alloyed filler metals. The addition of boron in such filler metals is to achieve a desired strength and impact value. Research shows that including boron content above 0.001%wt 5, and the combined effect of boron and titanium 2 can improve impact properties under certain thermal conditions. The current American Welding Society (AWS) A5.20 (2010) 6 and A5.29 (R2015) 7 does not require a boron content limit from deposited metal chemistry composition, however the equivalent AS/ NZS ISO 18276 (2006) 8 requires all intentionally added micro alloys must be included on a conformance certificate. References: 1. T.G.Digges, CR. Irish & N. L. Carwile, Effect of Boron on the Hardenability of High-Purity Alloys and Commercial Steels, 1948 2. D.W.OH, D.L. Olson & R.H. Frost, The influence of Boron and Titanium on Low-Carbon Steel Weld Metal, 1990 3. M. Karpenko, S. Hicks, A. Fussell & P. Wilcox, Welding to AS/NZS 1554.1 of Boron Containing Steel, 2017 4. ASM International, Alloying: Understanding the Basics (#06117G), 2001 5. J.H. Deyletian & R. W. Heine, Effect of Boron Content on Carbon steel Welds, 1975 6. AWS A5.20: Specification for Carbon Steel Electrodes for Flux Cored Arc Welding, 2015 7. AWS A5.29: Specification for Low-Alloy Steel Electrodes for Flux Cored Arc Welding, 2009 8. AS/NZS ISO 18276, Welding consumables – Tubular cored electrodes for gas shielded and non-gas shielded metal arc welding of high-strength steels – Classification, 2006 By Fuhai Liu, Weldwell Using a steel with the addition of the alloying agent Boron (B) is known to provide some benefits, including its ability to improve steel hardenability. However, it can also affect mechanical properties of various chemical compositions, along with cooling rates. Also, steels containing Boron should only be used with hardenability in mind, as the lowered alloy content can be harmful to some applications. New Zealand Technical Specification Recently the use of B in common grades of structural steel has been discovered. The latest version of AS/NZS 1554.1,5 & 7 (2014) introduces a total B content limit of 0.0008%wt, in addition to parent materials which comply with steel standards; however, this restriction has since been overruled. Instead, the Technical Specification – SA TS 103: 2016 requires the same B limitation, however, does not specify it as a New Zealand Technical Specification. Boron – The effect on steel and weld joint The addition of B and Carbon in steel can enhance steel strength 1, however, a more complicated behaviour can result from commercial steels due to the possibility of Titanium 2 and Nitrogen being present. The cooling rate is also a significant factor as it can change the steel hardness 1. When welding, this can occur when the parent metal undertakes a thermal circle in a very short period. Within a welded joint, there are three areas to consider, the integrity of the parent metal, the Heat Affected Zone (HAZ), and the weld metal. The key focus of B content is the effect of the weld quality has on the HAZ, due to the possible fast cooling rate which can result in high hardness, leading to Hydrogen Assisted Cold Cracking (HACC). To overcome this the pre-heating temperature should be improved, or alternatively, a weldment test can be performed 3. Why Boron exists in Steel and welding consumable? Commercially, using a steel with the addition of Boron can improve hardenability to achieve a desired mechanical and heat treating properties, like other common elements such as Carbon, Magnesium, Nickle, Chromium and Molybdenum, etc. Such addition of micro-alloy in recent decades produces a steel category known as High Strength Low-Alloy (HSLA), which is developed to provide specific desirable combinations of strength, toughness, formability, weldability and atmospheric corrosion resistance instead of meeting certain chemical composition 4. Boron has also been used in welding consumables, known as micro alloyed filler metals. The addition of B in such filler metals is to achieve a desired strength and impact value. Research shows that including B content above 0.001%wt 5, and the combined effect of B and Ti 2 can improve impact properties under certain thermal conditions. The current American Welding Society (AWS) A5.20 (2010) 6 and A5.29 (R2015) 7 does not require a B content limit from deposited metal chemistry composition, however the equivalent AS/NZS ISO 18276 (2006) 8 requires all intentionally added micro alloys must be included on a conformance certificate. Author: Fuhai Liu, Weldwell Best products. Best service. Easysteel offers the highest quality steel and welding products available. Backed by the best service, we’re your one stop shop. Check out our new welding website: fswelding.co.nz References 1. T.G.Digges, CR. Irish & N. L. Carwile, Effect of Boron on the Hardenability of High-Purity Alloys and Commercial Steels, 1948 2. D.W.OH, D.L. Olson & R.H. Frost, The influence of Boron and Titanium on Low-Carbon Steel Weld Metal, 1990 3. M. Karpenko, S. Hicks, A. Fussell & P. Wilcox, Welding to AS/ NZS 1554.1 of Boron Containing Steel, 2017 4. ASM International, Alloying: Understanding the Basics (#06117G), 2001 5. J.H. Deyletian & R. W. Heine, Effect of Boron Content on Carbon steel Welds, 1975 6. AWS A5.20: Specification for Carbon Steel Electrodes for Flux Cored Arc Welding, 2015 7. AWS A5.29: Specification for Low-Alloy Steel Electrodes for Flux Cored Arc Welding, 2009 8. AS/NZS ISO 18276, Welding consumables – Tubular cored electrodes for gas shielded and non-gas shielded metal arc welding of high-strength steels – Classification, 2006 WELDING FEATURE
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