Carbon Steel Turning Guide

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 making a certain part. If the properties of carbon steel can meet the requirements of a part, most users will choose carbon steel because it is less expensive than other steels.

The purpose of this paper is to help users who machine carbon steel parts to understand the composition of various carbon steel grades to improve the efficiency of turning operations; it also gives cutting speed parameters related to depth of cut, feed rate and tool material and hardness of carbon steel.

As early as 66 years ago, pioneers in the field of metal cutting, m. eugene merchant and Dr. Hans ernst have elaborated on chip formation, chip-to-tool friction, surface quality and metal removal efficiency. In his research, Dr. merchant used a variety of metal materials, including 1020 mild steel and 1112 easy-to-cut steel. Based on extensive testing, Dr. Merchant developed and continues to use a mathematical model of the metal cutting process that can be used to design chipbreakers for tools.

By setting the average machinability of aisi 1212 free-cutting carbon steel to 100%, it is possible to express the machinability class of ferrous and non-ferrous alloy materials in percent. The service life of various grades of indexable inserts can be determined by using aisi 1045 medium carbon steel as the standard workpiece material and conducting turning tests under specified cutting conditions.

Carbon steel is divided into six categories: low carbon steel, medium carbon steel, high carbon steel, re-vulcanization easy to cut steel, re-vulcanization and re-phosphorus easy to cut steel and non-vulcanization high manganese steel (manganese content of more than 1%).

Low carbon steel

Low carbon steel (aisi 1005 ~ 1026) carbon content of 0.06% ~ 0.28%, manganese content of 0.25% ~ 1%, phosphorus content of no more than 0.04%, sulfur content of no more than 0.05%. At present, there are 16 standard grades of low carbon steel.

When turning mild steel, if the tool breaker can not form a large enough shear angle so that the chip curl and get off the front surface of the insert, it will produce long chips and generate chip tumor on the surface of the indexable insert. Low-speed cutting is another cause of chip nodules. They act as tool extensions, which can change the size of the part and deteriorate the finish of the machined surface. 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, feed rate, tool material and hardness of the workpiece. Selecting the cutting speed is a challenging task. Generally, the depth of cut and feed rate parameters can be pre-selected more conservatively based on the machining accuracy requirements (roughing, semi-finishing or finishing)

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