Mild steel is one of manufacturing's most common raw materials with the advantageous properties of easy machinability, good ductility and low cost. It forms the backbone for constructing everything from automotive parts and buildings to industrial equipment and tools.
However, in certain high-friction, wearing or load-bearing applications, additional surface hardening is required to withstand intensity of use over time. Traditional hardening techniques like quenching or case hardening can be complex and costly. This is why manufacturers seek simpler methods of fortifying mild steel parts after initial shaping.
In this post we’ll analyze an intriguing possibility – can computer guided laser cutting beams, already proven for precision slicing through steel, replace whole workflows for hardening low carbon steels? Let’s delve into the viability of laser cutting for steel hardening.
Before assessing laser hardening efficacy, we must first define what mild steel is and why it needs additional hardening for robust manufacturing uses.
Mild steel refers to a range of low carbon steel alloys comprising iron with up to 0.25% carbon content by weight along with 1.65% manganese and small amounts of silicon, copper and phosphorus. This holds an advantage over higher carbon steels for ease of machining, bending and welding with reduced brittleness.
However, mild steel lacks hardness, measuring less than 27 HRC (Rockwell Scale C) in its annealed state. For applications involving wear, friction and dynamic loads over time, surfaces require hardening to beyond 50 HRC through processes altering its microscopic grain structure without compromising bulk strength and shock resistance.
Common workshop techniques for adding surface hardness to mild steel include:
Quenching in oils/brine after heating above upper transformation temperature
Case hardening via packed carbide diffusion at high temps
Nitriding through ammonia gas treatment in specialized chambers
Induction hardening using electromagnetic coil shot penetration
While effective, these methods require significant energy, workspace and logistical overheads that hamper productivity via extended workflow complexity to harden batch components.
This is what makes laser cutting an intriguing possibility for simplifying hardening operations. But can concentrated photon energy match the hardness imparting effects of traditional techniques listed above? Let's analyze the laser hardening mechanism.
In fact multiple interdependent effects unique to laser cutting can produce a hardened skin depth up to 1mm deep on mild steels. This makes laser suitable for high wear applications like forming dies and blanking punches without entirely compromising ductility.
Let’s examine the tandem laser hardening effects:
Laser cutting heats a microscopic width of steel intensely to melt point before traversing onwards
This almost instantly self quenches steel behind narrow cut line, transforming structures
The rapid temperature shifts induces formation of harder martensitic compounds
The localized input intensity alters grain morphologies like ferrite and pearlite
Finer grains sizes related to hardening according to the Hall-Petch relationship
The melted steel strand instantly fuses during the beam’s pass
This chaotic rapid solidification fixes harder crystalline structures
Impurities like sulfides melt and disperse into new formation
Newly formed oxides and carbides act as hardness imparting particulates
The chaotic transitions between heating and cooling phases surrounding the laser path creates locked in stresses
These tensile stresses make dislocation motion difficult, increasing hardness
Through this combination of rapid self quenching, grain refinement, inclusion alterations and thermal tensile stresses, laser cutting can boost surface hardness into the 50+ HRC range comparable to conventional steel hardening.
However hardness depth remains shallow at under 1mm penetration. And effects depend greatly on laser settings and base material composition. But for specified applications not requiring bulk hardening uniformly across sections, laser cutting presents notable workflow simplifying benefits.
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In conclusion, against popular perception of being just an extremely precise slicing method, the thermal chaos and intensity of laser cutting provides a set of hardness imparting effects on mild steels.
While shallow and dependent on optimizing input settings, the ability to locally enhance surface hardness to upwards of 50 HRC during regular fabrication cutting operations is highly promising. It points towards streamlining hardening requirements without running lengthy conventional heat treatment or case hardening routines on finalized components.
With further research into expanding hardening depth and application scope, laser cutting could emerge as the standard not only for precisely shaping, but also simultaneously enhancing robustness of mild steel elements for production efficiency.
For additional visuals of laser hardening effects see this video:
