Part 2 of 3
MAKING RAILS
a. if you start with cold rolled or cold drawn material remember that the manufacturing process for that product generally contributes to a noticeable amount of “retained stress”. That stress will tend to be released by temperature, and/or, vibration; meaning, while you are making the rail, or when the rail is in service.
b. if you start with a hot rolled bar, you must allow more stock removal, not only for potential decarb on the surface, but also distortion in shape (out-of-square, etc.). The mill allowance for out of square with hot rolled bars is significantly more than it is for cold drawn material. Often, a final grind is needed after processing.
So, there will be limits of what you can do to that piece of steel. Many variables will have to be taken into consideration. When we say, “Our steels machine better, weld better, or wear longer”, you must understand that is within a certain context. The statements we make are relative to other high strength steels used for maintenance applications (apples to apples). We are not saying they machine better than free-machining steel, or mild steel, or copper, or plastic.
A round bar that has been supplied as hardened from the mill, may not want to be straightened to a very tight T.I.R. To achieve a specific T.I.R. the straightener will have to overcome many factors. Consideration will have to be given to size vs length, the bar’s propensity to retain stress, etc. The operator will have to know something about the specific material’s “memory” properties and be familiar with all the potential conditions that might prohibit the required end result.
Conditions that might prohibit achieving that, are present in different forms for all fabrication jobs. They may relate to; number of pieces, grade, hardness, length, configuration, tolerance, surface finish, service temperature, etc. In addition, there are a limited number of companies offering value added services who are comfortable dealing with maintenance steels.
Metals fabrication shops only work with “serious” experienced companies, or the people they trust at those companies. They can easily lose faith in a job if you don’t have all the information needed. They can back away from a job if you keep feeding them additional or changing information every couple of days. Maintenance jobs cannot afford delays.
Metals fabrication is serious business. It is not a training ground for eager novices. Some words of wisdom you might want to tattoo somewhere on your person are: “Fabrication may be late, wrong, and dangerous.”, “Wear Plate is big and ugly!” and,” If you can’t stand the heat, stay out of that kitchen.”
Rule #1
Steels for maintenance and tooling need to be hard and tough. They need to resist abrasive wear, or gouging, or bending, or fatigue failure, or all of those issues.
Rule #2
Once you have made the base metal hard and tough, you have made a material that does not want to be messed with.
Let’s review
Making finished hardened and machined custom wear rail is not for the faint of heart. Anyone who has done so knows there is truth in that statement. If you are familiar with Murphy’s Law, when rail is being discussed, think of it as “Murphy’s Rail”.
-Howard Thomas, June 21st 2022
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
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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
