What Is Case Hardening?

The so-called surface hardening method refers to a process in which the surface layer of a part is hardened by a suitable method while the core of the part still has strong toughness.

Surface hardening

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So-called

Through this treatment, the wear resistance and fatigue resistance of the part can be improved, and since the core of the part still has good toughness and strength, it has a good resistance to impact loads.

Commonly used surface hardening treatment methods include carburizing, nitriding, hard anodizing, chrome plating, surface hardening, and metal infiltration.

Case hardening carburization

Carburizing of steel means that steel parts with low carbon content are heated or held in a carburizing medium to allow carbon atoms to penetrate the surface to obtain a certain surface carbon content. After quenching, the surface layer with high carbon content is very hard , And the low carbon content of the core hardness is still good toughness. The goal is to achieve high surface hardness, abrasion resistance, and high contact and bending fatigue strength. It is mainly used for parts that are subject to wear, alternating contact stress or bending stress and impact loads, such as shafts, gears, camshafts, etc. These parts require high hardness on the surface and sufficient strength and toughness at the core.

. Surface hardening . Nitriding

Nitriding refers to heating alloy steel (usually containing Al, Cr, Mo) in an anhydrous ammonia gas (NH3) stream at a temperature of about 500 ° C to 570 ° C for a long time, so that the surface of the steel forms a layer of high hardness and corrosion resistance. Nitrides (mainly Fe2N, Fe3N, Fe4N). Generally there are gas nitriding, liquid nitriding and glow ion nitriding.

Case hard hard anodizing

The anodic oxidation of aluminum uses aluminum or aluminum alloy as the anode, and a lead plate as the cathode to electrolyze in the electrolyte to form an oxide film layer on the surface. After anodizing, the surface of aluminum can form an oxide film with a thickness of several to several hundred microns. The surface of this oxide film is porous and honeycomb. Compared with the natural oxide film of aluminum alloy, its corrosion resistance, abrasion resistance and decoration are significantly improved. With different electrolytes and process conditions, anodized films with different properties can be obtained.

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Case-hardened chrome

The hardness of chromium can reach 800 ~ 10OOHV, making it the hardest metal. It has strong passivation properties, and is quickly passivated in the atmosphere. Therefore, the chromium layer is stable in the atmosphere and can maintain its gloss for a long time. It is in corrosive media such as alkali, nitric acid, sulfide, carbonate, and organic acid. Very stable, but soluble in hydrohalic acids such as hydrochloric acid and hot concentrated sulfuric acid.

. Case hardening

Surface quenching refers to a heat treatment process in which a workpiece surface is rapidly heated to a quenching temperature within a certain depth range and then rapidly cooled to achieve the purpose of quenching within a certain depth range. The purpose is to obtain a martensitic structure within a certain depth range on the surface of the workpiece, while the core still maintains the structure state before quenching (quenching or normalizing), so that the surface is hard and wear-resistant, and the core has sufficient plasticity And toughness. Mainly used for machine parts made of medium carbon quenched and tempered steel and ductile iron. ^[1]