Cold Drawn – a Process Not a Material 

Cold Roll or Cold Drawn bar is often requested from a supplier as if the term indicated a grade of steel. Those terms refer to production methods not chemistry or grade. I point this out not to be stuffy, but to try to eliminate potential safety problems in the field.

Cold Roll, Cold Drawn, or Cold Finished bars may be made from 1018, 1020, 1045, 8620, 4140, etc. While most often they would be annealed (soft), there is the chance a cold drawn bar could be supplied in a hardened condition. The real problem is somewhat related to geography. In certain parts of the country, Cold Roll (Cole-roll), is most often produced as 1018 or 1020. Elsewhere, in other mills, the preponderance of production might lean toward 1045. The 1045 grade is hardenable; 1018 and 1020 are not. Expecting a material to be ductile in all circumstances could lead to significant problems should that steel turn out to be brittle.

Cold Drawn or Hot Rolled – When?
Cold Drawn steel materials may be used for various types of rails in heavy industrial applications. Hot Rolled Hardened wear bars may also be used for types of rails. If smooth and accurate travel along a rail is a concern, or if a finished cam/wheel is riding on it, you will probably want Cold Drawn, Cold Rolled, or Cold Finished (all the same) bars. If the application is “Big & Ugly”, let’s say a large heavy tank car is rolling over the rails and the rails eventually fail due to gouging, deforming, weight and wear, think Hot Rolled and Hardened. (Q&T).

Basically, a flat bar (cold drawn or hot rolled) is referred to as a rail when it has undergone some machining, and/or, hardening, or is used in an application where something is conveyed along it, or guided by it. A roller cam or trolley may ride along any surface of the flat bar, whether the bar is lying down flat, or is positioned up on end. Product may simply be slid along one surface of a flat, with no cam to assist movement. In the case of sliding, you will want to review “galling”.

If the application is “Big and Ugly”, such as moving bins of molten metal in a steel mill, the rail may be just hardened hot rolled bar stock. Pay close attention to the “out-of-square” allowable tolerance on hot rolled hardened mill bars. It is much more open than the tolerance of cold drawn bar.

WEAR BARS OR HOT ROLLED FLATS AS RAIL
Where the configuration is not sensitive to smooth uninterrupted movement (such as is required in an automation facility), hot rolled hardened bars may be used. These could be sizes like 3/8” x 2 ½”, or 5” x 8” depending on the weight of what is travelling the rail.

Generally, these types of rails will be welded or bolted to a substrate. Even Big and Ugly rails may require precise hole locations on the bars for alignment to pre-drilled holes in the substrate. When this is a requirement it is important to measure the holes centered on the length of the rail. So, you would not measure from the outside length dimension of the flat bar. You would find the center of the bar length and index the holes from that point radiating out in both directions. Otherwise, if the length was a bit oversize or undersize, the holes would not line up. The same goes for the width of the flat bar.

Our next post will focus on fabricating finished “Rails”; specifically impediments to fabrication and subsequent service-life. The third, and final post on CD bars will be an introduction to the trade-name rails produced and marketed by Associated Steel.

-Howard Thomas, May 9th, 2022

ASSOCIATED STEEL PRODUCTS: KROMITE® #3 (Hot Roll) & MIRRALOY® (TG&P)
The following tips assume you have an existing piece of shafting in 4140 or 4150 alloy steel, that is presently at a through hardness of approx. 30RC. And, that you require an increased hardness of approximately high 40’s to low 50’s RC.

PREFERRED METHOD: Long cycle anneal
Anneal at 1525F, one hour per inch of greatest cross section.
Cool in a furnace to 800F, at a rate of about 20F per/hour.
Re-heat to 1525F, one hour per inch of greatest cross section.
NOTE: In the event you have to move the material a significant distance between the heat temp and the oil quench, take precautions not to let the temperature drop below 1525F between the heat and quench. Cool in oil until smoking but no flame, approximately 250F to 300F.

NOTE: Alternate is a “sub-critical anneal”. Heat the bar to 1350F – 1400F, hold for one hour per inch of greatest cross section, atmosphere cool (in a protected atmosphere) to 350F. If the carbon is closer to .50, temper at approx. 700F to 800F for three hours per inch of greatest cross section (even for small diameters) should yield about 50 to 54RC. If carbon is closer to .40, lower the temp to approximately 400F to 600F.

NOTE: These are intended to be, and should be taken to be, suggestions for consideration, not instructions. This is not exact. If the material is too hard, repeat the cycle and try a higher tempering temperature. Repeated thermal cycling is not detrimental to the material, provided excessive temperatures are not encountered. If you do have to try several times, you may develop significant surface de-carb (powdery surface coat), which you will have to remove if you are not getting the results expected. CAUTION: Do not overlook removing all decarb in the area you will be checking hardness, no matter if using Rockwell “RC” or Brinell (bhn) equipment. Just grinding to “bright metal” does not mean you have removed all decarb. If your tests indicate you are only getting 18RC or lower, you are probably still into decarb. Even in an annealed condition those alloys would likely register a higher hardness than that.

Simply reaching for a higher hardness is not always the answer. If you try to go too high, brittleness may become a factor. In shaft applications where 28 to 32RC are deemed to be insufficient, you may want to try 32RC to 38Rc. Years ago, I was advised by an old friend; “With 4140 and 4150, “funny things begin to occur when you exceed 40RC (they tend to spit carbides). Don’t ask me what that means. I just got a strong negative visual and have been happy to follow that little gem for many years. (Real hard things can shatter like glass).

The above “tips” are just that; TIPS, as in “Hey, my brother in law’s uncle’s wife tried this once.” Plus, they are reduced to the simplest form. These basically relate to shaft stock and do not take into account a host of variables that may affect your safety and results. Part configuration, cross sectional differences, experience, etc. In all instances it is our recommendation that you utilize experienced thermal treatment personnel familiar with thermal conditioning alloys, who make use of all appropriate safety gear.

-Howard Thomas, April 8th, 2022

4140 and 4150 – KROMITE #3 AND MIRRALOY – modified grades of high strength alloy.

Last month, we talked about the word “modification” appearing on a Mill Test Report (MTR). This month I have been asked to clarify just how modifications have been incorporated into two key shaft materials provided by Associated Steel. Those items are Kromite #3 and Mirraloy. Both of those products incorporate changes (metallurgical and non-metallurgical), that address requirements of Heavy Industrial Maintenance.

Many times, in fact in most cases, modifications incorporated into the production of a grade of steel fall within the parameters of an established grade. They are usually adjustments to processing requirements and are specific to a particular customer. Modifications will appear on the MTRS. Some will change the allowable range of a chemical element but still carry the original numeric grade identifier, such as in the case of “H” Band Steel. H-Band steels have altered chemical ranges of certain elements to assist in thermal treatment. The change may allow slightly higher Carbon and Chromium content. The grade, however, remains basically the same. It retains the base metal grade numeric designation, plus a suffix addition. In this case “H”.

There are times when the modifications, intentional or not, may change the grade, i.e., prohibit the intended grade from being certified without an exception noted. Even a very small change in the content of an element may be sufficient to change the grade.

Many years ago, a manufacturer required a slight increase in resistance to service temperature for a part made of 4150. Over time, fatigue from repetitive motion, in elevated temperature, contributed to failure. One of the effects of vanadium is that it increases temperature resistance. The addition of approximately .15 vanadium content, to the 4150 chemistry resolved the customer’s problem and introduced a new grade of steel, 6150. In applications involving stainless steel, lowering the carbon content to .030, in type 304 stainless, created 304L, a modified grade. An “H” suffix in grades of stainless steel indicates elevated carbon content; again, a modification to the base grade.

The point is modifications are neither good nor bad. You just need to know how they will affect your application. The alloy steel grades Kromite #3 and Mirraloy, supplied by Associated Steel, are chemically modified to improve cleanliness of the melt. They incorporate bracket restrictions, (high-side for beneficial elements, low-side for detrimental or tramp elements). Improved cleanliness results in improved “toughness”, the key property that resists fatigue failure in shaft applications.

Associated Steel has been in continuous service to heavy industrial maintenance customers for nearly a century. Their products have been field proven in critical service.
The round bar shafts Kromite #3 and Mirraloy are both the same chemistry and follow the same thermal processing and grain refinement. Mirraloy is the precision finished product produced from Hot rolled Kromite #3.

-Howard Thomas, March 7th, 2022

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Howard Thomas

Howard Thomas

Experience

Sr. Acct. Mgr. (US Southwest) / Metallurgical Consultant
Associated Steel Corporation
Jan 2017 – Present

Past Vice President / General Manager
Associated Steel Corporation
Apr 1998 – Jan 2017

Past Vice President / General Manager
Baldwin International
Apr 1974 – Mar 1997

Education

Cleveland State University
Kent State University
University of Denver

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