Machining of High Strength Steel
High strength steel refers to the steel with a yield strength of more than 115 N/mm2. Its machinability and cutting properties are significantly influenced by the composition and structure of the steel. The structure of high strength steel is mainly martensite and/or bainite, and there is more carbide in it and impurities such as sulfur and phosphorus. The carbide end is sharper, the structure is relatively dense and the toughness is poor. These factors have an adverse effect on the machinability and cutting properties of high strength steel and should be considered when selecting cutting tools and process parameters.
Milling is one of the most important machining processes for high strength steel. The cutting force is large, the wear of the tool is fast, the cutting temperature is higher, and the cutting speed is generally low. Therefore, attention should be paid to the selection of tool materials and cutting parameters when milling high strength steel parts. Generally, coated tungsten steel or cemented carbide inserts are used for milling high strength steel. When milling high strength steel parts, pay attention to the following points:
1、Use a large cutting edge angle as far as possible and select a tool with a large size and better rigidity;
2、Adjust the cutting speed according to the specific cutting situation, reduce the cutting speed appropriately, and keep the cutting layer amount and allowance of the parts at a lower level;
3、Frequently replace the cutter;
4、Pay attention to cooling, the recommended chipbreaker should be used for machining high strength steel, and pay attention to the cooling of the cutting point;
5、Use a process that takes into account the economy and effectiveness of the parts such as ramping, and try to use as few tools as possible.
The selection of cutting tools is also very important for the cutting of high strength steel parts. Low-alloy high-strength steel (yield strength more than 800MPa) is difficult to machine. In order to ensure the normal machining of such parts, high-strength cutting tools with high wear resistance and heat resistance should be selected.
When turning high strength steel parts, carbide tools are generally used. If the cutting force is large and the cutting temperature is high, PVD or CVD coating tools can be used to improve the tool life. Compared with general alloy steel parts, the cutting depth of high strength steel parts is generally shallow, and the cutting edge should be arranged as far as possible to reduce the cutting force and cutting temperature, which can effectively improve the tool life and reduce the cutting deformation of the parts.
Drilling of high strength steel parts requires high cutting performance tools. Generally, cobalt high speed steel drills or high-temperature alloy drills with good heat resistance, wear resistance, and galling resistance should be selected. Pay attention to reduce cutting speed and select large helix angle and small cutting edge angle. It is better to finish surface drilling in multiple steps. The small drill bit should be used first, and the larger drill bit should be successively drilled.
As for reaming of high strength steel parts, since the hardness of high strength steel is generally higher than that of alloy steel, a reamer made of high speed steel or industry grade tungsten steel should be selected, and the heat resistance should be considered when selecting the coating type.
High strength steel components are usually difficult to cut and have high requirements for cutting tool materials, cutting operations and cutting parameters. Therefore, the selection and control of cutting tools and cutting parameters should be carried out according to the actual situation, and the machinability and cutting properties of high strength steel should also be taken into account. Machining of high strength steel requires the use of specialized cutting tools, sufficiently considered cutting parameters and properly designed machining process to ensure the accuracy and quality of parts manufacturing.
