9SMnPb28 (1.0718) belongs to the German standard free cutting steel, the implementation of the standard: EN 10087-1999
9SMnPb28 is a kind of free cutting structural steel . Free cutting structural steel referred to as easy to cut steel, is containing a small amount of easy to cut elements, with good machinability of the steel. Free cutting structural steel is the use of certain elements in the role of steel to improve the cutting performance of steel, in order to be suitable for high-speed cutting in automatic machine tools on the steel. Commonly used to improve the machinability of elements such as S, Pb, Ca, etc., of which S is most commonly used, S in the formation of steel MnS inclusions, MnS is very brittle, and a certain lubrication and thus chips are easy to break, high surface finish of the workpiece, reduce tool wear, improve cutting speed.
9SMnPb28 (1.0718) chemical composition is as follows:
With the modernization of industry to automation, high-speed and precision machining direction, the requirements of steel with good cutting process performance, improve productivity to adapt to mass production. Therefore, the need to use more to improve and improve the cutting performance of steel, easy to automatic cutting machine tool processing. This kind of steel is mainly used for large and unimportant parts. For example, in the automatic machine tool often processed parts, such as screws, nuts and other standard parts. Free cutting steel also belongs to the special steel.
Free-cutting steel is mainly used for the production of less force and the size and roughness of the strict requirements of the instrumentation, watch parts, automobiles, machine tools and various other machines; strict requirements on the dimensional accuracy and roughness, and the mechanical properties of the relatively low requirements of the standard parts, such as gears, shafts, bolts, valves, bushings, pins, pipe fittings, springs, and machine tools and seat cushions, machine tools, screws, molds, plastic molding and surgical and dental surgical appliances. dental surgical appliances, etc.
Free cutting steel is good or bad on behalf of the material is cut and processed easily, due to the complexity of the material cutting process, easy to cut with a single parameter is difficult to express. Usually, the steel cutting processability, is to tool life, the size of the cutting force, the roughness of the machined surface, cutting heat, and chip exclusion easy to measure the synthesis.
The use of the need to pay attention to: free cutting steel can be final heat treatment, but generally do not carry out pre-heat treatment, so as not to damage its cutting and machinability. Free cutting steel metallurgical process requirements than ordinary steel strict, high cost, so only for mass production of parts, in the must improve the cutting and machining of steel, using it to obtain good economic benefits.
The elements added to the free-cutting steel are S, Pb, Ca and P and so on. Their main role is as follows:
1, the role of sulfur
Sulfur in steel and Mn to form MnS inclusions, can interrupt the continuity of the matrix, so that the chip is easy to brittle, reducing the contact area of the chip and tool. Sulfur can also play the role of friction reduction, so that the chip does not adhere to the cutting edge. But the presence of sulfur will make the steel produce thermal brittleness, so the content of sulfur should generally be limited to w (s) = 0.10% ~ 0.30% range, and to appropriately increase the content of Mn with it.
2, the role of lead
Pb can improve the cutting performance of steel, due to the Pb in steel does not dissolve into the ferrite, nor the formation of compounds, it is in a free state and the formation of fine particles (2 ~ 3μm) uniformly distributed in the matrix organization, when the heat generated during the cutting process to reach the melting point of the Pb particles, that is, the state of melting, to become a cutting tool and the chip, as well as Tool and workpiece machined surface between the "lubricant", so that the friction factor decreases, the tool temperature decreases, the wear is reduced. the amount of Pb added in the w (Pb) = 0.1% ~ 0.35% range.
3, the role of calcium
Ca in steel can form Ca, Al silicate inclusions, attached to the tool to form a thin film, has a friction reduction effect, to prevent tool wear. the amount of Ca added is generally w (Ca) = 0.001% to 0.005%.
(4) the role of phosphorus
In the sulfur-containing easy-to-cut steel to add P, so that it is solidly dissolved in ferrite, causing strengthening and embrittlement, in order to improve its cutting performance. To prevent "cold embrittlement", w(P) ≤ 0.15%.
The addition of these elements can also improve the surface quality of the workpiece and extend the life of the tool.