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Brazing-steelhow to do it right.SOLUTIONS with Effective, Practical Advice
Brazing-steel is generally easy to perform with the proper consumables and processes. One should have a good understanding of the basics, see Brazing. One should pay attention to the fine details of Brazing Joint Design and of proper gap clearance. Furthermore one should select a suitable heating method depending on the production quantities involved.
For an introduction to the different means and methods of heating for brazing, see our page on Brazing Heating. The mechanical properties (strength and hardness) of low carbon steel are not going to be affected by normal heating for Brazing-steel. Therefore the selection of heating processes and of suitable filler metals is quite open and should follow the easiest and most economic solution that meets requirements. This is likely to be manual Brazing-steel with an oxyacetylene torch, preferred for limited production of similar parts using a silver base filler metal. A Table of such filler metals can be found in our page on The only drawback can be the relatively high cost of silver base filler metal but that may be offset by the low cost of equipment.
For larger production series one may prefer less expensive consumables, like copper base filler metals. These materials melt at a higher brazing temperature and therefore are mostly used in furnace brazing under protective atmosphere. With proper flux provided in the joint, Brazing-steel can be done with mechanized torch setup or within induction coils, depending on requirements and availability of equipment. Pure copper and copper-zinc filler metals are used for Brazing-steel and other materials. A table listing copper base alloys can be found in a commercial publication.
Protective atmosphere for Brazing-steel in a furnace are based on combusted gas, hydrogen or dissociated ammonia. Copper-zinc alloys can be used for application not requiring corrosion resistance. Although these alloys can be used with manual flame Brazing-steel, their zinc containing fumes may be annoying. (See (3) in PWL#055). In certain manual application, trade name filler metal alloys called low fume may be preferred. Medium carbon and low alloy steels are responsive to heat treatment. Therefore the Brazing-steel cycle must consider the steel characteristics. If (copper base) filler brazing alloys are used whose solidus is above the temperature of steel heat treatment, then brazing will not be degraded by successive heat treatments like hardening and tempering. In some cases brazing can be combined with heat treating and parts can be quenched directly from brazing temperature and then tempered as needed. High carbon steels and high carbon tool steels may have hardening temperatures in the range from 760 to 820 °C (1400 to 1500 °F). With careful brazing filler metal selection it may be possible to combine heating for hardening with brazing and direct quench. Hardened tool steels high in chromium are tempered in the range 540 to 650 °C (1000 to 1200 °F) at which temperatures they can be brazed with suitable filler metals, combining tempering and brazing in the same operation. The Welding Handbook 9th edition Volume 2 gives at page 522 and Fig. 12.17 an example of Brazing-steel combined with carburizing on parts like low carbon gears. The operation is described as being performed in a continuous mesh belt hydrogen furnace. The brazing time cycle should be quite short. The second operation, carburizing, needs a carburizing atmosphere and quite long a time. The furnace is possibly the same, but the processes are sequential, not simultaneous. Filler metal paste and flux are preplaced in the joint. At the end of the carburizing cycle parts are directly quenched in oil and then cleaned and tempered as required. Due to the common characteristic of normal steels to rust immediately in air, cleaning should be particularly thorough, and brazing performed immediately afterwards. Galvanized sheet can be brazed but zinc risks to evaporate while heating, and therefore the galvanic protection may suffer, at least near the joint. If it is important not to compromise the zinc layer, one should consider substituting soldering for brazing so that the lower processing temperatures would not harm the zinc coating. Brazing-steel should not be difficult and could be a perfect joining solution for suitable applications. Nevertheless the details of the process should be examined with the available knowledge and previous experience in mind. Some testing will help identify problems and clarify costs before launching mass production. ANSI/AWS A5.8M/A5.8:2011
ANSI/AWS A2.4:2012
ANSI/AWS B2.2/B2.2M:2010
ANSI/AWS C3.2M/C3.2:2008 ANSI/AWS C3.3:2008
ANSI/AWS C3.4M/C3.4:2007
ANSI/AWS C3.5M/C3.5:2007 ANSI/AWS C3.8M/C3.8:2011
AWS BRH An Article on Filler Metal for brazing copper or steel to titanium was published (4) in Issue 133 of Practical Welding Letter for September 2014. An Article on New Silver-Free Brazing Filler Metals was published (4) in Issue 140 of Practical Welding Letter for April 2015. An Article on How to get dry Gas at the Brazing Furnace was published (3) in Issue 141 of Practical Welding Letter for May 2015. An Article on Furnace Brazing Carbon Steel was published(3) in Issue 147 of Practical Welding Letter for November 2015. An Article on Silver- Free Brazing Filler Metals Meet Strength Requirements was published (4) in Issue 148 of Practical Welding Letter for December 2015.
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