1.0122 (S235JRG2C): Technical Specifications and the Role of Black Oxide Surface Treatment in CNC Machining

In the competitive world of industrial manufacturing and structural engineering, selecting the right material is a balance of performance, cost-effectiveness, and aesthetic appeal. Among the specialized steel grades recognized by the European EN 10025-2 standard, 1.0122—often referred to as S235JRG2C—holds a unique position. At Tuofa CNC Machining China, we recognize that while structural integrity is paramount, the final finish often dictates the success of a component in its end-use environment. This article provides an in-depth analysis of the 1.0122 steel grade, its machining characteristics, and the technical advantages of applying a black oxide surface treatment to this specific carbon steel.

The designation 1.0122 (S235JRG2C) conveys specific metallurgical properties that are vital for engineers to understand. The prefix "S" identifies it as a structural steel, while "235" indicates its minimum yield strength of 235 MPa for standard thicknesses. The "JR" suffix confirms its impact toughness, tested at 27 Joules at room temperature. The "G2" denotes a fully killed steel, meaning it has been deoxidized during production to ensure a uniform grain structure. Most importantly, the "C" at the end signifies that this material is specifically intended for cold drawing or cold forming. This cold-finished nature gives 1.0122 a smoother surface finish and tighter dimensional tolerances compared to its hot-rolled counterparts, making it an excellent candidate for precision CNC machining.

Chemically, 1.0122 is a low-carbon steel, typically containing carbon levels below 0.17%, with manganese acting as the primary alloying element to improve strength and hardness. This low carbon content is the secret to its exceptional weldability. Whether using MIG, TIG, or spot welding, 1.0122 can be joined without the risk of hardening in the heat-affected zone or the formation of brittle cracks. For custom fabrication projects at Tuofa, this material is frequently chosen for complex assemblies that require high-precision milled components to be integrated into larger welded structures.

In the machine shop, 1.0122 is prized for its consistent machinability. Because it is a cold-finished (C) grade, the material lacks the abrasive mill scale found on hot-rolled steel, which preserves tool life and allows for higher spindle speeds. It responds well to turning, milling, and drilling, producing reliable results with a high-quality surface finish. However, because it is a relatively soft structural steel, it can be prone to "tearing" if the cutting tools are not sharp or if the feed rates are not optimized. Our experts at Tuofa CNC Machining use specific geometries and coatings on our carbide tools to ensure that 1.0122 parts meet the rigorous surface roughness requirements demanded by modern engineering.

Despite its mechanical versatility, 1.0122, like most carbon steels, is vulnerable to atmospheric corrosion. If left untreated, the surface will quickly develop iron oxide (red rust), which can compromise both the appearance and the functional tolerances of the part. While plating or painting are common solutions, many precision applications—particularly in the tool-making, automotive, and firearm industries—require a finish that does not alter the part's dimensions. This is where black oxide (also known as "blackening" or "bluing") becomes the ideal surface treatment for 1.0122.

Black oxide is a conversion coating, meaning it does not sit on top of the metal like paint or electroplating. Instead, it is the result of a chemical reaction between the iron on the surface of the 1.0122 steel and the oxidizing salts in the blackening solution. The process typically involves cleaning the part, rinsing it, and then immersing it in a bath of sodium hydroxide, nitrates, and nitrites heated to approximately 140 to 145 degrees Celsius. This creates a magnetite layer (Fe3O4) on the surface of the steel. Because this is a conversion process rather than an additive one, the dimensional change is virtually zero—usually less than 0.1 to 0.2 microns. This makes it perfect for high-precision components where tight tolerances must be maintained after the finishing process.

The primary benefit of blackening 1.0122 is the reduction of light reflection. For optical equipment, machine tool components, and specialized hand tools, a matte black finish is essential to prevent glare and eye strain for the operator. Furthermore, black oxide significantly improves the "lubricity" of the steel surface. The porous nature of the magnetite layer allows it to hold onto supplemental oils or waxes much more effectively than raw steel. This "oil-retaining" property provides a dual benefit: it creates a secondary barrier against moisture (improving corrosion resistance) and reduces friction in moving parts, such as gears or sliding rails made from 1.0122.

At Tuofa CNC Machining, we often recommend black oxide for 1.0122 components used in indoor environments where moderate corrosion resistance is needed. It provides a professional, sleek aesthetic that masks the "raw" look of industrial steel. It is also an environmentally and economically friendly choice compared to chrome plating or advanced PVD coatings. While it does not offer the heavy-duty salt-spray resistance of stainless steel or electroless nickel, when maintained with a light film of oil, a blackened 1.0122 part can last for decades in a typical factory or workshop setting.

The applications for 1.0122 with a black oxide finish are diverse. In the automotive sector, it is used for fasteners, brackets, and internal engine components that require a balance of strength and wear resistance. In the machine tool industry, it is the standard finish for collets, tool holders, and guide pins. Even in the consumer goods sector, 1.0122 is used for high-end furniture frames and architectural hardware where the industrial, "blackened steel" look is a key design element.

When ordering 1.0122 (S235JRG2C) parts from a supplier like Tuofa CNC Machining China, it is important to communicate the specific end-use requirements. Our team ensures that the cold-drawn material is sourced from reputable mills to guarantee that the "C" grade specifications are met. During the machining phase, we maintain strict control over surface finishes to ensure that the black oxide bath reacts uniformly across the entire part. A poorly machined surface with varying degrees of roughness can result in a "splotchy" or uneven black finish; therefore, our precision milling and turning processes are optimized specifically for the subsequent chemical treatment.

In conclusion, 1.0122 (S235JRG2C) represents the workhorse of European structural steels, offering a unique combination of strength, weldability, and superior cold-finished precision. When enhanced with a black oxide surface treatment, this material transcends its humble origins as a structural alloy. It becomes a sophisticated choice for precision components that demand dimensional stability, reduced glare, and improved wear resistance. By understanding the synergy between the metallurgical properties of 1.0122 and the chemical advantages of blackening, engineers can design parts that are not only functional and durable but also cost-effective and visually striking.

At Tuofa CNC Machining, we are dedicated to helping our global clients navigate these material choices. Whether you are developing a new prototype or scaling up production for industrial machinery, our expertise in 1.0122 machining and black oxide finishing ensures that your components perform exactly as intended. We invite you to explore the possibilities of this robust material for your next precision project.