February 16, 2024
So, what exactly do we mean when we say “use good material” for your gears? Once again, the answer is “it depends.” Even the “best” steel may be wrong for your application or the thermal processing may not be according to plan. Or that plan could be wrong. Before you can make any of those determinations, however, you need to learn enough about metallurgy to avoid being distracted by a sales pitch or a clever dodging of responsibility. Steel descriptions vary from country to country and every land has reasons to think its particular recipe is the best. There is a very popular reference book -probably online these days- called “The Key to Steel.” I won’t attempt to remember its German title, but it has the popular steel chemistries from every country with a steel mill. In today’s world of international sourcing you never know for sure where your next shipment is coming from. If you do nothing else as a design engineer, please require a certification of the chemistry on every lot of material you buy. Your supplier is undoubtedly very reputable but almost all metal dealers have to occasionally buy on the spot market. It is also not unheard of for the warehouse crew to pull bars off the wrong rack. Once you have the certification in your possession you can compare it to your specification. The chemistry, an accounting of the alloying elements added to it, are easily verified on a small sample by any competent metallurgical lab for a modest charge. If the lab report does not match the paperwork you have dodged a big bullet. Without the “right stuff” being mixed in you cannot get the final properties required. Most certifications will assert compliance with several third party reference standards. If your firm is ISO compliant you should have current copies of these standards on hand; you should have at least a minimum level of familiarity with their contents. The standards lay out the “ground rules” for the products covered. You would not want to participate in a sporting event without agreeing on the rules so why not put that same level of scrutiny on your raw materials? Knowing the many acronyms involved in your particular material will make you much more confident in discussing other metallurgical issues.