Carbon steel is the “primary†material in the metal processing industry and is the most extensively processed steel grade to date. About 87% of steel produced in the United States is carbon steel.
The feasibility of using carbon steel depends on whether its mechanical properties (such as tensile strength, yield strength, fatigue strength, impact resistance, and required heat treatment) are suitable for the manufacture of a part. If the characteristics of carbon steel can meet the requirements of the parts, most users will choose carbon steel because it is cheaper than other steels.
This paper aims to help users of carbon steel parts to understand the composition of various carbon steel grades to improve the efficiency of turning; it also gives cutting speed parameters related to depth of cut and feed rate, and hardness of tool materials and carbon steel. .
As early as 66 years ago, Dr. M. Eugene Merchant and Dr. Hans Ernst, pioneers in the field of metal cutting, have described chip formation, chip-to-tool friction, surface quality, and metal removal efficiency. In the study, Dr. Merchant used a variety of metal materials, including 1020 mild steel and 1112 easy-cut steel. Based on a large number of experiments, Dr. Merchant established a mathematical model of the metal cutting process and continues to use it. This model can be used to design tool chip breakers.
By setting the average workability of AISI1212 free-cutting carbon steel to 100%, it is possible to express the grades of workability of iron and non-ferrous alloy materials. Using AISI1045 medium carbon steel as the standard workpiece material, the turning test can be performed under the specified cutting conditions to determine the service life of various grade indexable inserts.
Carbon steel is divided into six categories: low-carbon steel, medium-carbon steel, high-carbon steel, re-sulfidation easy-to-cut steel, re-sulfidation and re-recovery of phosphorus easily cut steel and high manganese steel without sulfur (containing more than 1% of manganese).
(1) Low carbon steel
Low-carbon steel (AISI1005 ~ 1026) has a carbon content of 0.06% to 0.28%, a manganese content of 0.25% to 1%, a phosphorus content of no more than 0.04%, and a sulfur content of no more than 0.05%. At present, there are 16 standard grades for low carbon steel.
When turning low-carbon steel, if the tool chip breaker does not form a sufficiently large shear angle to curl the chips away from the rake face of the insert, long chips will be generated and built-up edge will be generated on the surface of the indexable insert. Low-speed cutting is another cause of built-up edge. The built-up edge will play the role of tool extension, which will change the size of the part, and will deteriorate the surface finish. In this case, the cutting speed needs to be increased by 15% to 20% or more until the surface quality is improved.
The appropriate cutting speed depends on the depth of cut, the feed rate, the material of the tool and the hardness of the workpiece. Choosing cutting speed is a challenging task. In general, depth-of-cut and feedrate parameters can be conservatively pre-selected based on machining accuracy requirements (roughing, semi-finishing, or finishing). The cutting speeds used for machining low-carbon steels are slightly different and accordingly can be divided into two groups. Typical rough, semi-finish and finish cutting parameters of mild steel are shown in Table 1 and Table 2. (slightly)
The data in the table shows that the cutting speed decreases as the depth of cut and feedrate increase. If the depth of cut, one of the feed rates (or both) is different from the data in the table, the cutting speed needs to be adjusted so that the metal removal rate (mrr) calculated according to the cutting parameters in the table remains unchanged. The calculation example is as follows.
The metal removal rate for the first row of cutting parameters in Table 1 is:
Mrr=12′′×sfm×DOC×ipr=12×550×0.300×0.020=39.6 in.3/min
If the cutting depth is reduced to 0.200", the cutting rate must be equal to 825 sfm to keep the metal removal rate constant:
Sfm=mrr÷DOC÷ipr÷12=39.6÷0.200÷0.020÷12=825sfm
In this case, the cutting speed increases in the same proportion as the depth of cut decreases (0.300 ÷ 0.200 = 1.5, 550 × 1.5 = 825 sfm).
(2) Medium carbon steel
Medium carbon steel (AISI1029 ~ 1053) has a carbon content of 0.25% to 0.55%, a manganese content of 0.30% to 1.00%, a phosphorus content of no more than 0.04%, and a sulfur content of no more than 0.05%. Medium carbon steel has 16 standard grades. The cutting parameters are shown in Table 3. (slightly)
When carbon steel is turned, discontinuous chips are generated, and the surface quality to be machined is lower than that of low carbon steel, but the cutting force and tool wear will increase as the carbon content and hardness increase. Therefore, when the workpiece hardness increases, the cutting speed should be reduced.
(3) High-carbon steel
High carbon steel (AISI1055～1095) has a carbon content of 0.60% to 1.03%, a manganese content of 0.30% to 0.90%, a phosphorus content of no more than 0.04%, and a sulfur content of no more than 0.05%. There are 14 standard grades for high carbon steel, and the cutting parameters are shown in Table 4. (slightly)
When high-carbon steels are turned, due to the high carbon content, cutting forces and tool wear are greater than when turning medium-carbon steels. Therefore, lower cutting speeds should be used to reduce tool wear. Similar to machining low- and medium-carbon steels, the corresponding cutting speed should be used for workpieces with different hardness.
(4) easy to cut steel
Easy to cut steel is divided into re-vulcanization easy to cut steel (11XX series) and re-vulcanization, and then easy to cut back to the steel (12XX series).
Re-vulcanized easy-cut steel (AISI1108 to 1151) consists of 14 standard grades. Sulfur content of 0.33% improves the material's processability (AISI 1119 and AISI 1144). Most 11XX series grades increase the manganese content from 1.30% to 1.65% so that enough manganese and sulfur react to form MnS particles. As MnS particles form some micropores and microcracks in the process of chip formation, these microscopic defects diffuse into the cut-out layer of the workpiece, increasing the shear angle of the chips and accelerating the chip fracture process, so that good processing can be obtained. surface.
The re-vulcanized and rephosphorized easy-to-cut steel includes 4 lead-free standard grades (AISI 1211, 1212, 1213, and 1215) and 3 lead-containing standard grades (AISI12L13, 12L14, and 12L15) with a lead content of 0.15%-0.35%. The 12XX series of grades increased sulfur content (0.10% to 0.35%) and phosphorus content (0.04% to 0.12%). The effect of increasing sulphur content is similar to that of the AISI11XX brand.
After increasing the phosphorus content, phosphorus dissolved in iron promotes chip breaking, which helps to avoid the formation of long tendril-shaped chips and better surface finish.
In turning, the role of lead in the 12XX series of grades is similar to an internal lubricant, which reduces the friction between the tool and the workpiece and reduces heat generation. Lead-containing grades are mainly used for large-volume processing. The use of lead-containing grades can increase cutting speeds, obtain a good machining surface, and increase machining efficiency by more than 25%.
The re-vulcanized, re-phosphorized steel is widely used in the processing of threaded products. Due to economical reasons, the application of lead-free steel in high-speed machining of threads is limited, but its excellent machining characteristics can be fully reflected in the high-speed machining of threads.
Among all the easy-cut steels, the 12LXX grade is best suited for high-speed turning. The cutting parameters are shown in Table 5 (abbreviated). Discrete chips are generated when turning steel, so there is no chip control problem.
(5) High manganese steel
The manganese content of high-manganese steel is 0.75% to 1.65%, and the carbon content is 0.10% to 0.71%. The content of phosphorus and sulfur is the same as that of low, medium and high carbon steels. There are 12 standard grades. Most grades contain 0.0005% to 0.30% boron. The addition of boron increases the thickness of the hardened layer.
The 15XX series low carbon high manganese steel (AISI1513 ~ 1527) is mainly used for processing carburized parts whose surface hardenability is higher than that of ordinary carbon steel.
Medium-carbon high-manganese steel (containing 0.30% to 0.35% carbon) is generally used for bar processing parts. Whether heat treatment is required depends on the application and the required strength.
High-carbon high-manganese steel (AISI 1547 ~ 1566) has higher strength and wear resistance than ordinary carbon steel grades.
Boron-containing high-manganese steel (such as AISI15B48H) is generally used for shaft products. This kind of steel can replace alloy steels and high carbon steels that require heat treatment. The cutting parameters are shown in Table 6. (slightly)
Turning high manganese steel is similar to turning 10XX series medium carbon steel.
Tool Material Brand Description
The technical specifications for tool materials come from ANSI (American National Standards Institute) and ISO (International Organization for Standardization). ANSI uses an industry code that identifies uncoated hard alloy grades (C-1, C-2, etc.) and coated carbide grades (CC-5, CC-6, etc.). The digital part of the code gives only the basic characteristics of cemented carbide, such as toughness and hardness. C-1 to C-4 grades are pure tungsten carbide using a cobalt binder, but the cobalt content and tungsten carbide grain size are different.
CC-5 to CC-8 grades include composite tungsten carbide, tantalum carbide, titanium carbide, and niobium carbide using a cobalt binder. These grades have better resistance to crater wear than C-1 to C-4 and are therefore recommended for machining steel parts. From CC-5 to CC-8 grades, the hardness of the material increases in turn, while the toughness sequentially decreases.
The CC-6 grade is a universal hard alloy material with medium to high levels of impact resistance and moderate levels of wear resistance. It is recommended for roughing and semi-finishing. CC-7 grades have moderate levels of impact and abrasion resistance and are suitable for finishing. Carbides with larger brand numbers have better wear resistance and can use higher cutting speeds. The tougher carbide grades with smaller brand numbers are better and larger feed rates can be used.
The ISO standard code consists of letters and two digits. The letter C indicates coated cemented carbide and the following letter P indicates that the grade is suitable for processing carbon steel. CP-10 grades are suitable for high-speed cutting, small chip cross-section to medium; CP-20 is suitable for medium-speed cutting, medium chip cross-section; CP-30 is suitable for medium to low-speed cutting, and the chip cross section is medium to large. The larger the number, the greater the toughness of the cemented carbide and the lower the hardness. Carbide with a smaller number of grades has better wear resistance and can increase the cutting speed. The cemented carbide with a larger number of grades has good toughness and can increase the feed rate.
It should be noted that the carbide alloy grades specifically named by different manufacturers are not necessarily the same as the ANSI and ISO codes.
The cutting speed given in the previous table is only the initial recommended value, because with the adoption of new machine tools and coated carbide tools, the cutting speed can be increased by 15% to 30%, but this must take into account the power of the machine tool.
Coated carbide tools not only have a long service life, but also can perform high-speed cutting to improve machining efficiency. Cutting speed increased by 30%, processing costs can be reduced by 15%.
Among various coating materials, TiAlN coating using PVD process is the most commonly used and is generally used in dry high speed finishing and general processing. A three-layer coating (TiN in the outer layer, Al2O3 in the middle layer, and TiCN in the inner layer) using a CVD process is generally used for roughing and semifinishing.
Although turning of carbon steel is not complicated, part manufacturers need to understand the grades and material properties of carbon steel, and by selecting the tool, lathe (or turning center) and workpiece clamping device, the processing efficiency can be greatly improved.
The feasibility of using carbon steel depends on whether its mechanical properties (such as tensile strength, yield strength, fatigue strength, impact resistance, and required heat treatment) are suitable for the manufacture of a part. If the characteristics of carbon steel can meet the requirements of the parts, most users will choose carbon steel because it is cheaper than other steels.
This paper aims to help users of carbon steel parts to understand the composition of various carbon steel grades to improve the efficiency of turning; it also gives cutting speed parameters related to depth of cut and feed rate, and hardness of tool materials and carbon steel. .
As early as 66 years ago, Dr. M. Eugene Merchant and Dr. Hans Ernst, pioneers in the field of metal cutting, have described chip formation, chip-to-tool friction, surface quality, and metal removal efficiency. In the study, Dr. Merchant used a variety of metal materials, including 1020 mild steel and 1112 easy-cut steel. Based on a large number of experiments, Dr. Merchant established a mathematical model of the metal cutting process and continues to use it. This model can be used to design tool chip breakers.
By setting the average workability of AISI1212 free-cutting carbon steel to 100%, it is possible to express the grades of workability of iron and non-ferrous alloy materials. Using AISI1045 medium carbon steel as the standard workpiece material, the turning test can be performed under the specified cutting conditions to determine the service life of various grade indexable inserts.
Carbon steel is divided into six categories: low-carbon steel, medium-carbon steel, high-carbon steel, re-sulfidation easy-to-cut steel, re-sulfidation and re-recovery of phosphorus easily cut steel and high manganese steel without sulfur (containing more than 1% of manganese).
(1) Low carbon steel
Low-carbon steel (AISI1005 ~ 1026) has a carbon content of 0.06% to 0.28%, a manganese content of 0.25% to 1%, a phosphorus content of no more than 0.04%, and a sulfur content of no more than 0.05%. At present, there are 16 standard grades for low carbon steel.
When turning low-carbon steel, if the tool chip breaker does not form a sufficiently large shear angle to curl the chips away from the rake face of the insert, long chips will be generated and built-up edge will be generated on the surface of the indexable insert. Low-speed cutting is another cause of built-up edge. The built-up edge will play the role of tool extension, which will change the size of the part, and will deteriorate the surface finish. In this case, the cutting speed needs to be increased by 15% to 20% or more until the surface quality is improved.
The appropriate cutting speed depends on the depth of cut, the feed rate, the material of the tool and the hardness of the workpiece. Choosing cutting speed is a challenging task. In general, depth-of-cut and feedrate parameters can be conservatively pre-selected based on machining accuracy requirements (roughing, semi-finishing, or finishing). The cutting speeds used for machining low-carbon steels are slightly different and accordingly can be divided into two groups. Typical rough, semi-finish and finish cutting parameters of mild steel are shown in Table 1 and Table 2. (slightly)
The data in the table shows that the cutting speed decreases as the depth of cut and feedrate increase. If the depth of cut, one of the feed rates (or both) is different from the data in the table, the cutting speed needs to be adjusted so that the metal removal rate (mrr) calculated according to the cutting parameters in the table remains unchanged. The calculation example is as follows.
The metal removal rate for the first row of cutting parameters in Table 1 is:
Mrr=12′′×sfm×DOC×ipr=12×550×0.300×0.020=39.6 in.3/min
If the cutting depth is reduced to 0.200", the cutting rate must be equal to 825 sfm to keep the metal removal rate constant:
Sfm=mrr÷DOC÷ipr÷12=39.6÷0.200÷0.020÷12=825sfm
In this case, the cutting speed increases in the same proportion as the depth of cut decreases (0.300 ÷ 0.200 = 1.5, 550 × 1.5 = 825 sfm).
(2) Medium carbon steel
Medium carbon steel (AISI1029 ~ 1053) has a carbon content of 0.25% to 0.55%, a manganese content of 0.30% to 1.00%, a phosphorus content of no more than 0.04%, and a sulfur content of no more than 0.05%. Medium carbon steel has 16 standard grades. The cutting parameters are shown in Table 3. (slightly)
When carbon steel is turned, discontinuous chips are generated, and the surface quality to be machined is lower than that of low carbon steel, but the cutting force and tool wear will increase as the carbon content and hardness increase. Therefore, when the workpiece hardness increases, the cutting speed should be reduced.
(3) High-carbon steel
High carbon steel (AISI1055～1095) has a carbon content of 0.60% to 1.03%, a manganese content of 0.30% to 0.90%, a phosphorus content of no more than 0.04%, and a sulfur content of no more than 0.05%. There are 14 standard grades for high carbon steel, and the cutting parameters are shown in Table 4. (slightly)
When high-carbon steels are turned, due to the high carbon content, cutting forces and tool wear are greater than when turning medium-carbon steels. Therefore, lower cutting speeds should be used to reduce tool wear. Similar to machining low- and medium-carbon steels, the corresponding cutting speed should be used for workpieces with different hardness.
(4) easy to cut steel
Easy to cut steel is divided into re-vulcanization easy to cut steel (11XX series) and re-vulcanization, and then easy to cut back to the steel (12XX series).
Re-vulcanized easy-cut steel (AISI1108 to 1151) consists of 14 standard grades. Sulfur content of 0.33% improves the material's processability (AISI 1119 and AISI 1144). Most 11XX series grades increase the manganese content from 1.30% to 1.65% so that enough manganese and sulfur react to form MnS particles. As MnS particles form some micropores and microcracks in the process of chip formation, these microscopic defects diffuse into the cut-out layer of the workpiece, increasing the shear angle of the chips and accelerating the chip fracture process, so that good processing can be obtained. surface.
The re-vulcanized and rephosphorized easy-to-cut steel includes 4 lead-free standard grades (AISI 1211, 1212, 1213, and 1215) and 3 lead-containing standard grades (AISI12L13, 12L14, and 12L15) with a lead content of 0.15%-0.35%. The 12XX series of grades increased sulfur content (0.10% to 0.35%) and phosphorus content (0.04% to 0.12%). The effect of increasing sulphur content is similar to that of the AISI11XX brand.
After increasing the phosphorus content, phosphorus dissolved in iron promotes chip breaking, which helps to avoid the formation of long tendril-shaped chips and better surface finish.
In turning, the role of lead in the 12XX series of grades is similar to an internal lubricant, which reduces the friction between the tool and the workpiece and reduces heat generation. Lead-containing grades are mainly used for large-volume processing. The use of lead-containing grades can increase cutting speeds, obtain a good machining surface, and increase machining efficiency by more than 25%.
The re-vulcanized, re-phosphorized steel is widely used in the processing of threaded products. Due to economical reasons, the application of lead-free steel in high-speed machining of threads is limited, but its excellent machining characteristics can be fully reflected in the high-speed machining of threads.
Among all the easy-cut steels, the 12LXX grade is best suited for high-speed turning. The cutting parameters are shown in Table 5 (abbreviated). Discrete chips are generated when turning steel, so there is no chip control problem.
(5) High manganese steel
The manganese content of high-manganese steel is 0.75% to 1.65%, and the carbon content is 0.10% to 0.71%. The content of phosphorus and sulfur is the same as that of low, medium and high carbon steels. There are 12 standard grades. Most grades contain 0.0005% to 0.30% boron. The addition of boron increases the thickness of the hardened layer.
The 15XX series low carbon high manganese steel (AISI1513 ~ 1527) is mainly used for processing carburized parts whose surface hardenability is higher than that of ordinary carbon steel.
Medium-carbon high-manganese steel (containing 0.30% to 0.35% carbon) is generally used for bar processing parts. Whether heat treatment is required depends on the application and the required strength.
High-carbon high-manganese steel (AISI 1547 ~ 1566) has higher strength and wear resistance than ordinary carbon steel grades.
Boron-containing high-manganese steel (such as AISI15B48H) is generally used for shaft products. This kind of steel can replace alloy steels and high carbon steels that require heat treatment. The cutting parameters are shown in Table 6. (slightly)
Turning high manganese steel is similar to turning 10XX series medium carbon steel.
Tool Material Brand Description
The technical specifications for tool materials come from ANSI (American National Standards Institute) and ISO (International Organization for Standardization). ANSI uses an industry code that identifies uncoated hard alloy grades (C-1, C-2, etc.) and coated carbide grades (CC-5, CC-6, etc.). The digital part of the code gives only the basic characteristics of cemented carbide, such as toughness and hardness. C-1 to C-4 grades are pure tungsten carbide using a cobalt binder, but the cobalt content and tungsten carbide grain size are different.
CC-5 to CC-8 grades include composite tungsten carbide, tantalum carbide, titanium carbide, and niobium carbide using a cobalt binder. These grades have better resistance to crater wear than C-1 to C-4 and are therefore recommended for machining steel parts. From CC-5 to CC-8 grades, the hardness of the material increases in turn, while the toughness sequentially decreases.
The CC-6 grade is a universal hard alloy material with medium to high levels of impact resistance and moderate levels of wear resistance. It is recommended for roughing and semi-finishing. CC-7 grades have moderate levels of impact and abrasion resistance and are suitable for finishing. Carbides with larger brand numbers have better wear resistance and can use higher cutting speeds. The tougher carbide grades with smaller brand numbers are better and larger feed rates can be used.
The ISO standard code consists of letters and two digits. The letter C indicates coated cemented carbide and the following letter P indicates that the grade is suitable for processing carbon steel. CP-10 grades are suitable for high-speed cutting, small chip cross-section to medium; CP-20 is suitable for medium-speed cutting, medium chip cross-section; CP-30 is suitable for medium to low-speed cutting, and the chip cross section is medium to large. The larger the number, the greater the toughness of the cemented carbide and the lower the hardness. Carbide with a smaller number of grades has better wear resistance and can increase the cutting speed. The cemented carbide with a larger number of grades has good toughness and can increase the feed rate.
It should be noted that the carbide alloy grades specifically named by different manufacturers are not necessarily the same as the ANSI and ISO codes.
The cutting speed given in the previous table is only the initial recommended value, because with the adoption of new machine tools and coated carbide tools, the cutting speed can be increased by 15% to 30%, but this must take into account the power of the machine tool.
Coated carbide tools not only have a long service life, but also can perform high-speed cutting to improve machining efficiency. Cutting speed increased by 30%, processing costs can be reduced by 15%.
Among various coating materials, TiAlN coating using PVD process is the most commonly used and is generally used in dry high speed finishing and general processing. A three-layer coating (TiN in the outer layer, Al2O3 in the middle layer, and TiCN in the inner layer) using a CVD process is generally used for roughing and semifinishing.
Although turning of carbon steel is not complicated, part manufacturers need to understand the grades and material properties of carbon steel, and by selecting the tool, lathe (or turning center) and workpiece clamping device, the processing efficiency can be greatly improved.
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