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  • 1.  Hardenability of H steels, Boron treated steels, for Caterpillar Tractor and John Deere.

    Posted 01-24-2021 07:44
    David and Paul,
    While at U.S. Steel(now Mittal), and Quanex MacSteel(now Gerdau), from 1980 to 1989, I reviewed 10,000 to 20,000 heat numbers, for production of
    Boron treated, Silicon-Aluminum killed steels.  This was done to promote consistency  within Caterpillar Tractor and John Deere heat treating lines for their equipment and parts production lines.  In these studies, I took the best 10 production heats, and compared them to the absolute 10 worst  heats ( hardenability wise, heat treating wise, and scrap rate wise ), to come up with best practice on generic grades, H grades, Boron grades, especially for the T-1 steels, and military grades.  As you can imagine, it was highly confidential, copyright protected, and very eye-opening for efficiency and scrap rates.

    I too, feel the need before I retire, to formalize the body of knowledge, set forth before us, by some of the greats like George VanderVoort (Micro-structures) and Deming(statistics).  Multilevel regression analyses were part of the studies, but the bottom line was consistency, and doing it right the first time, to reduce re-heat treatments/repours, which were never as good as the initial heat treatments,  and wasted so much manpower/resources, in so many ways. 

    Respectfully,

    Kyle Gibson 
    Argen Labs 
    TBRC Chair


  • 2.  RE: Hardenability of H steels, Boron treated steels, for Caterpillar Tractor and John Deere.

    Posted 01-25-2021 05:58
    Kyle, I worked at Caterpillar from 1978 to 1982. One of my duties included the creation of the dividing factors for boron grade steels for their 1E38 specification.  Got into a rather heated discussion with my boss about regression analyses.  I believe Caterpillar finally codified 1E38 (now in 1E24) into the ASTM A255 standard long after I left Cat.  During the late 70's there were two conference proceedings on hardenability and boron.  One of the European contributions bounded the B, Al and free nitrogen to a range. I have always called it the Ugine-Aciers test. See S.K. Banerji and J.E. Morral, Boron in Steel, TMS-AIME Conference Proc. Sept. 18, 1979 p.11.  My workbook attempts to incorporate that test and includes the alloy factors used by Caterpillar (1E38/ASTM A255) to reduce the boron effectiveness.  There is also some interesting synergy between AlN and BN.  For example, if first solution treated at 1250°C, B, N, and Al can be in solution. Upon cooling BN forms preferentially, but is eventual displaced to form AlN. See S.K. Banerji and J.E. Morral, Boron in Steel, TMS-AIME Conference Proc. Sept. 18, 1979 p.46. Now you have a kinetics mess dealing with B effectiveness. One of the pitfalls of ASTM A255 is the loss of the grain size effect on hardenability.  I was able to work that back into the calculation while maintaining the Caterpillar modified carbon factors.

    All that said, I'm amazed that any continuously cast B steel has a boron effectiveness.

    ------------------------------
    David Van Aken
    Missouri University of Science
    Rolla MO
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  • 3.  RE: Hardenability of H steels, Boron treated steels, for Caterpillar Tractor and John Deere.

    Posted 01-25-2021 09:40

    A couple of comments on boron hardenability and A255.

    I have had some experience with boron going back to research at the Climax Molybdenum Labooratories in about 1967 to 1970 where we showed that a stoichiometric addition of Ti can tie up all of the nitrogen leaving the boron to segregate to austenite grain boundaries where it is fully effective for hardenability. Excess boron will form borocarbides. I have since set up practices for producing large quantities of boron treated steels – first for seamless tubes at CF&I Steel in about 1985 and then in bar steels at North Star Steel in about 1997 for automotive and heavy equipment (CAT, John Deere, etc). The amount of titanium needed for electric furnace steels is higher than that for BOF steels due to the higher normal nitrogen levels of 70 – 100 ppm versus 30 – 60 ppm, respectively.

     

    A255, based on the CAT database is very useful for many purposes – particularly for melt control where DI is used along with restricted carbon ranges to achieve consistent heat treat response. However, the absolute prediction of the Jominy curves depends on the base composition (steel grade). For example, grades like 20MnCr5 where there is no boron, but high  (over 1.1%) levels of Mn and Cr have higher actual DI levels than would be predicted by A255.

     

    The development of element ranges for steel grades was based on the available technology for chemical analysis and steelmaking. For example, in my experience at J&L steel in mid to late 70's steel was melted in a BOF and all alloy additions were made in the ladle during tapping. There was no ladle stirring and final chemical analysis was performed on spoon samples obtained during teeming into ingots. It was not uncommon to have large deviations in chemical composition on the last few ingots of a heat due to incomplete mixing of the alloys that floated on top of the steel in the ladle. About 15 – 20 % of the heats had at least one element out of the standard range. Today, it is common practice to add the initial bulk addition during tap, stir and arc heat in the ladle, and then add trim additions to meet the more exacting requirements for composition. Control of carbon to +/- 0.01 and DI to a 0.30 range is possible. This has been made possible by the improvement in sampling methods and rapid, accurate chemical analysis using OES. In changing suppliers, it should be recognized that different melt shops may have different aim values for a given grade. For example, some melt shops will aim for the lowest nickel content and use control by Mn or Cr contents to minimize alloy costs while others may take a different approach.

     

    Bob Cryderman

    Research Associate Professor

    Colorado School of Mines.

     

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