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Machining Properties of Steel

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Machining Properties of Steel

Issue Time:2019-10-30
The concept of machinability of metal materials
The machinability of a metal material generally refers to a property or quality of a metal material that can be clearly defined and measured as a measure of how easy it is to be machined. In general, good machinability should be: good tool durability or high cutting speed under certain durability, low cutting force, low cutting temperature, easy to obtain good workpiece surface quality and chip shape Control or easy chip breaking.

The concept of machinability of materials is relative. The so-called material cutting process is good or bad relative to another material. When discussing the machinability of steel materials, it is customary to use carbon structural steel 45 as a reference. For example, high-strength steel is more difficult to process, compared to 45 steel.

The cutting performance of the tool is most closely related to the machinability. The cutting performance of the material to be processed cannot be discussed in isolation from the cutting performance of the tool. Instead, the two should be combined. After understanding the machinability of the workpiece material and taking effective measures, it is possible to improve the processing efficiency, ensure the processing quality, and reduce the processing cost.
Main indicators for evaluating the machinability of workpiece materials
The machinability of materials is the degree of difficulty in guiding the machinability of a material. The degree of ease is generally related to the chemical composition of the material, the heat treatment state, the metallographic structure, the physical and mechanical properties, and the cutting conditions. The machinability of the workpiece material is usually measured by one or several of the following indicators:

1, measured by tool life

The cutting speed allowed for cutting a workpiece material while maintaining the same tool durability;

2, measured by processing quality such as surface finish

3. Measured in unit cutting force

4. Measured by the limit metal removal rate

5, measured by chip breaking performance, including chip shape
Ways to improve the machinability of materials
1. Improve the chemical composition of the material
Taking common metals as an example, 1% to 3% of lead is added to the brass, and 0.1% to 0.25% of lead is added to the steel. Lead can be present in the metallurgical structure of the material by spherical particles. It can lubricate well during cutting, reduce friction and improve tool durability and surface quality. Adding MnS to carbon steel, which is distributed in the pearlite, acts as a lubricant to improve the durability of the tool and the surface quality after cutting, increase the brittleness, and the chips are easily broken.

2. Proper heat treatment before material processing
After normalizing the low carbon steel, the grain is refined, the hardness is improved, and the plasticity is reduced, which is beneficial to reduce the bond wear of the tool, reduce the accumulated chips, and improve the surface roughness of the workpiece. After the spheroidizing annealing of the high carbon steel, the hardness Decrease to reduce tool wear; stainless steel is suitable for quenching and tempering to HRC28, hardness is too low, plasticity is large, surface roughness of the workpiece is poor, and the hardness is high, the tool is easy to wear; White cast iron can be annealed in a range of 950 to 1000 ° C for a long time, making it easier to cut.

3. Select a good material state 
After low-carbon steel is cold drawn, the plasticity is reduced and the processability is good;The forged blank has an uneven amount of allowance, and has a hard skin, and has poor workability, and the workability after hot rolling is improved.

4. Other:
Using appropriate tool materials, selecting reasonable tool geometry parameters, and rationally determining the amount of cutting and the choice of cutting fluid can also affect the cutting performance of the material.
Florence Tang
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