All right, well let me first start by explaining a few things about steel in general, including Ordnance grades of steel. Hardness does not necessarily equate to brittleness, that is a function of heat treating and alloy. Even softer steels can crack and be brittle, it's a matter of how the internal stresses are relieved, or not, by annealing and hardening processes, as well as upon carbon on other constituent elements found in the steel.
Also should mention, I'm comparing apples to apples, so only the CroMo Colt is being compared to the CroMo Norinco here. The stainless guns have their own quirks (like spalling problems, corrosion resistance benefits, etc.)
In layman's terms, the more important characteristics to crafting firearms is the toughness of the steel and modulous of elasticity of the steel. You want steel that is ductile enough to flex at the microscopic level and return to its original shape but hard enough to have good wear resistance and, in higher end guns, be able to take and keep the desired finish without dinging up too easily.
Now if we want to talk about relative hardness of steels, Norincos are made from a different steel formulation than Colts are. Comparing Rockwell hardnesses really won't tell you much, but as a general observation, on average the Norincos are at least 30% harder on the surface than most other 1911's, including the Colt. This does not mean they are more brittle - it means that the alloy used to Make the Norincos (5100 tool steel*) results in a much harder surface when heat treated than does the Colt alloy (4140 Ordnance grade tool steel*).
*Although the exact alloy formulations are "industrial secrets", destructive testing done in the USA by the DCM (circa 1997) determined that Colt uses 4140 and the Chinese formulation used in 1911's and M14S receivers is an exact match to AISI 5100 series steel.
Perhaps this is the time to mention something else about Colts. Colt does not use the same alloy today it used in WW2 and earlier. In WW1, the guns were not even given what we think of today as "heat treating". Those older guns were only spot-treated at high stress areas and today have a rather high incidence of slide cracking using full factory loads due to a number of factors, including metal fatigue, crack propagation, creep, etc. coupled with the fact that vast portions of the slide and frame have no treatment at all. That being said, the steel is very ductile and in the event of failure, it should just bend and crack - not fracture like a grenade. A good thing, but at the same time - these babies should be collected and admired more than turned into a range marathon pistol!
I could get further into heat treating, including annealing, case hardening, gas carburizing, cyanide dips, etc. and the resulting pearlitic and/or martensitic grain structures, but frankly, unless you work in a foundry or have a mechanical engineering degree and understanding of materials science, it would be way too far over everyone's head so I'll try to keep this explanation understandable for the average fellow
Now for a short note on Chinese steel "quality". The Chinese are as advanced as we are in Steel production. Is Chicom steel of poorer quality on average on a gross domestic production basis? Yes, absolutely. This is because the majority of China's manufacturing is devoted to the Wal-Marts of the world at a very low price point, so cheaper steels are generally produced and used for those products. The steel used in their weapons, however, is every bit as up to snuff as North American steel is.
So now we get into the 5100 alloy Norinco 1911 in particular. 5100 is an EXCELLENT receiver material. It hardens very well on the surface but maintains an adequately ductile core. This gives great wear resistance and great resistance to plastic deformation (deformation that causes the parts to permanently deform or warp). The one achilles heel to 5100 series alloys is that they are notoriously hard to machine. Norinco, I suspect, machines their parts with carbide cutters prior to heat treating. On a finished gun the only way you're going to cut it with HSS mill bits is if you spot-anneal the steel with a torch first. Most smiths have to buy carbide mill bits to work the steel, and even then there's a very high tool wear rate. This is probably why so few smiths will do Novak cuts to a Norinco slide - they probably only have HSS tooling!
5100 alloy is, most probably, the alloy most manufacturers WOULD chose to build receivers if tool bits were cheap and labor costs were low. It really does have better end-product properties than 4140 steel does, and it's also easier to smelt at the steel mill and forges beautifully. Virtually all Cro-Mo guns made in the west that aren't cast, however, are made of 4140 or other 4100 series alloys. 4140 is an entirely adequate steel for use in guns, it also wears tools at a much slower rate and can still be machined easily after hardening. The Chinese are fortunate in that they make many of the tool steel bits on the market (cheap supply) and lobor costs are very low. This makes 5100 steel actually cheaper for them to use b/c of the lower costs associated with making the steel stock.
All this to say, you can complain about the design, fit, finish, and economics of a Norinco 1911. But frankly, trashing the steel is a bigotted and unfounded arguement based on ignorance and reliance on the Go-USA writings of most internet experts. (
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). This looks good enough to be sticky'd just for the raw data even if it's inconclusive.
