Cr-Mo vs Cr-V Impact Sockets.

tl;dr (too long, didn’t read)

Thorium Tools - 32mm Deep Socket Wrench - Laser etched

Cr-Mo is a heat-hardened steel alloy, with the inclusion of molybdenum that gives the alloy a property of toughness and flexibility. Cr-Mo will absorb percussive impact better than Cr-V without being brittle. Over time Cr-Mo sockets may stretch and lose their shape, but they are less likely to shatter and cause injury.

Cr-V is a also a heat-hardened steel alloy that doesn’t have the same properties of flexibility and toughness under impact load. This means that Cr-V sockets under impact can be brittle, and prone to shattering, endangering the user.

MD-1032-MO
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  1. Introduction
  2. CR-V – Chrome Vanadium
    1. What are Chrome Vanadium sockets made of?
    2. What are the properties of Cr-V used in sockets?
    3. What Cr-V steel good for? 
  3. Cr-Mo – Chrome Molybdenum – aka: Chrome-Moly, aka: chromoly
    1. What are chrome-moly impact sockets made of?
    2. What are the properties of Cr-Mo used for impact sockets? 
    3. Why are impact sockets made of Cr-Mo?
  4. How can I tell them apart?
  5. Conclusion

Introduction

If you’re just getting started filling up your tool chest or you’re in the market for a new set of impact sockets, you might be wondering about the differences in Cr-Mo vs Cr-V impact sockets.  In particular, what type of steel impact sockets are made of, and why there is an important difference. 

32 mm deep impact socket - Stamped Sizing

Impact sockets available today are made of two types of steel. Chrome Molybdenum, and Chrome Vanadium. Both of these are steel alloys which are approximately 96 to 98% Iron (Fe). In addition to Iron, the differences in these alloy lay in the small remainder of elements that compose them, which change the mechanical properties that they exhibit. These small remainder elements are known as alloyants, and imbue different characteristics to the steel alloy.

Let’s scratch the surface of the differences between Chrome Molybdenum (Cr-Mo) and Chrome Vanadium (Cr-V) sockets. 

Cr-V – Chrome Vanadium

What are chrome vanadium sockets made of?

As indicated above, the largest component of chrome vanadium steel is Iron (Fe). The smaller component elements are Chromium (Cr) 0.8% to 1.1%, Manganese (Mn) 0.7% to 0.9%, Carbon (C) 0.48% to 0.53%, Silicon (Si) 0.15% to 0.35%, Vanadium (V) 0.15% to 0.30%, Sulfur (S) 0% to 0.040%, and Phosphorus (P) 0% to 0.035%. 

Alloy Composition – % weight    (Based on AISI Standard – Cr-V 6150) 

Cr-V steel chemical composition

       * Some / most Cr-V sockets will be made of an alloy other than Cr-V 6150, but the proportions of alloy elements will only vary slightly

What are the properties of Cr-V used in sockets?

Some of the “alloying” elements listed above that form the remainder of the steel join with carbon to form carbides during the steel smelting process.

In the case of Vanadium, it creates a stable carbide within the steel that drastically increases the steel’s strength while retaining ductility through the promotion of a fine grain structure within the steel. Through further forging and annealing the steal is then hardened to a particular hardness for use in hand tools and sockets. This hardness and strength in the steel alloy allows the sockets made from it to be thinner than Cr-Mo sockets without deforming or breaking easily under normal load.

One of the side effects of Chrome Vanadium alloy’s hardness is that it also is brittle, and when it reaches its breaking point, it can let go all at once and shatter into many sharp pieces. The ability to absorb energy without deforming is a quality known as “toughness,” and as an alloy, Cr-V isn’t very tough.

This is not a desirable property for use as a tool under high impact loads and  great force. 

What is Cr-V steel good for?

Chrome vanadium is not without its uses. One of the first large-scale uses of Cr-V steel was by none-other than Henry Ford in his Model T. The alloy is relatively light weight with a higher tensile strength than regular steel, which made it perfect for use at the time in automobile production.

Cr-V steel is still widely used as tool steel, and in hand tools like screw drivers and chisels to name only a couple of uses. It is just not the safest choice when it comes to usage in impact sockets. The potential risk of the tool shattering with little or no advanced notice while under high load and rotational velocity places the mechanic, you, at risk of greater injury than using a Cr-Mo socket.

Read on to see why Cr-Mo has other properties that make it better suited to usage with impact wrenches. 

Cr-Mo – Chrome Molybdenum – aka: Chrome-Moly, aka: chromoly

What are chrome-moly impact sockets made of?

As with chrome vanadium steel, the largest component of chrome-moly steel is Iron (Fe). The smaller component elements are Chromium (Cr) 0.8% to 1.1%, Manganese (Mn) 0.75% to 1.0% , Carbon (C) 0.38% to 0.43%, Silicon (Si) 0.15% to 0.35%, Molybdenum (Mo) 0.15% to 0.25%, Sulfur (S) 0% to 0.040%, and Phosphorus (P) 0% to 0.035%.

Alloy Composition – % weight    (Based on AISI Standard – Cr-Mo 4140)

Cr-Mo steel chemical composition

What are the properties of Cr-Mo used for impact sockets?

In the case of Molybdenum, it joins to form a carbide that is stable and inhibits grain growth and contributes to a quality of increased toughness (“…the ability of a material to absorb energy and plastically deform without fracturing”), as well as a reduction of brittleness, and an increased flexible quality known as ductility (a measure of a material’s ability to undergo significant plastic deformation before rupture).

Toughness, brittleness and ductility, are really three words describing a similar property. That property is essentially, take a beating without losing shape or shattering

Why are impact sockets made of Cr-Mo?

In short….  Safety. Safety for the user while a rotating tool, under large amounts of force and rhythmic, percussive stress is operating close to soft flesh. When it comes to risk mitigation, chrome-moly sockets are really tough to beat when it comes to reducing the chance of a socket shattering under load and causing personal injury. If or when a Cr-Mo impact socket starts to crack and show signs of fatigue, the user should have enough advanced notice to stop using the socket and be protected from personal injury. Particularly if the user is in the habit of inspecting their tools before and after each use to look for signs of wear, stress, and material fatigue. 

How can I tell them apart?

For seasoned mechanics who have been around tools their whole lives, determining Cr-Mo vs Cr-V impact sockets will be fairly easy. For someone new to the tool world, here is how you can tell them apart and keep yourself safe as a result. 

Historically, most Cr-V sockets were finished with a shiny nickel / chrome finish. These days though, it is getting to be a little more difficult to simply say that all Cr-V sockets are shiny and chrome colored. Cr-V sockets are now available on the market with a black oxide or phosphate finish. The process of phosphating steel is done on Cr-Mo and now Cr-V steel sockets. Phosphated steel is protected from corrosion, and will take on further corrosion resistance when oiled. This was historically the purpose of applying the chrome finish to a Cr-V socket. It was a hard finish that would protect the underlying steel from corrosion.

In order to identify Cr-V sockets, the chrome finish is still a dead give-away. Do not use chrome finished sockets with an impact wrench. Other black CR-V sockets can also be identified by the stamped Cr-V included on each socket. 

Finally, another good indicator of Cr-Mo vs Cr-V impact sockets will be price. Vanadium sockets are quite a bit cheaper than chromoly socket sets of the same number and size of sockets (they will typically be available for about half the price). If you are in the market to buy a set of impact sockets and it seems like you have found a great deal!…. Look a little closer. They may be a Cr-V socket with a black phosphate / black oxide finish. 

Conclusion – Cr-Mo vs Cr-V Impact Sockets. Which is the safer choice?

The type of alloy that your sockets are made of only tells part of the story. Each alloy can achieve different properties based on how it was hardened, and to what value it was hardened. There are certainly many mechanics out there that have been using Cr-V sockets as impact sockets without injury for a long time. For my personal piece of mind though, I am sticking to Cr-Mo sockets for use with an impact wrench. If I can avoid the risk of a socket shattering under load and rotating around to cut me…. I will. 

In the end…. Arm yourself with information so that you can make an informed decision about the right set of sockets for you. After that, find a company that you trust, buy their sockets (we hope that you’ll decide to buy ours!), and get out there and do your best work!