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JP-7857408-B2 - Calcium-containing graphite steel with excellent cutting performance and method for manufacturing the same

JP7857408B2JP 7857408 B2JP7857408 B2JP 7857408B2JP-7857408-B2

Inventors

  • チェ， サンウ
  • イム， ナムソク

Assignees

  • ポスコ カンパニー リミテッド

Dates

Publication Date
20260512
Application Date
20221213
Priority Date
20211214

Claims (7)

  1. In mass percent, it contains carbon (C): 0.60–0.90%, silicon (Si): 2.0–2.5%, manganese (Mn): 0.7–1.3%, sulfur (S): 0.2–0.5%, aluminum (Al): 0.01–0.05%, titanium (Ti): 0.005–0.020%, nitrogen (N): 0.003–0.015%, calcium (Ca): 0.0001–0.050%, with the remainder being iron (Fe) and unavoidable impurities. A calcium-containing graphite steel with excellent cutting performance, characterized by a fine structure in which graphite particles are distributed within a ferrite matrix, a graphitization rate of 95% or more , and a total content of MnS inclusions and pearlite of 5% by mass or less .
  2. The aforementioned graphite steel is characterized by having a graphitization rate of 99% or more, and is a calcium-containing graphite steel with excellent cutting performance as described in claim 1.
  3. The calcium-containing graphite steel with excellent cutting performance according to claim 1, characterized in that the aforementioned unavoidable impurities include phosphorus (P) .
  4. A method for producing calcium-containing graphite steel with excellent cutting performance, A step in manufacturing a billet containing, by mass %, carbon (C): 0.60-0.90%, silicon (Si): 2.0-2.5%, manganese (Mn): 0.7-1.3%, sulfur (S): 0.2-0.5%, aluminum (Al): 0.01-0.05%, titanium (Ti): 0.005-0.020%, nitrogen (N): 0.003-0.015%, calcium (Ca): 0.0001-0.05%, with the remainder being iron (Fe) and unavoidable impurities. The steps include: hot rolling the billet to produce a wire rod, and graphitizing the produced wire rod; The method for producing calcium-containing graphite steel with excellent cutting performance is characterized in that the graphite steel has a fine structure in which graphite particles are distributed in a ferrite matrix, has a graphitization rate of 95% or more, and contains a total of 5% by mass or less of MnS inclusions and pearlite .
  5. The method for producing calcium-containing graphite steel with excellent cutting performance, as described in claim 4, is characterized in that the hot rolling step is performed in a temperature range of 900 to 1150°C.
  6. The method for producing calcium-containing graphite steel with excellent cutting performance, as described in claim 4, is characterized in that the graphitization heat treatment step is performed at a temperature range of 700 to 800°C for 5 hours or more.
  7. The method for producing calcium-containing graphite steel with excellent cutting performance, as described in claim 6, characterized in that the graphitization heat treatment is performed for 5 to 20 hours.

Description

This invention relates to graphite steel with excellent cutting performance and a method for producing the same. More specifically, it relates to calcium-containing graphite steel with excellent cutting performance and a method for producing the same, which can promote graphitization by forming Ca-Al oxides that act as nuclei for graphitization by containing calcium (Ca), and can improve machinability by generating Ca-based sulfides. Generally, for machine parts and other materials requiring high machinability, free-cutting steel with added machinability-enhancing elements such as Pb and Bi is used. To improve the machinability of steel, low-melting-point machinability-enhancing elements such as Pb and Bi are added to the steel to utilize the liquid metal bromide phenomenon, or large amounts of MnS are formed within the steel. Such free-cutting steel exhibits excellent machinability during machining, including surface roughness, chip resolving properties, and tool life. However, in the case of commonly known Pb-added free-cutting steel with excellent machinability, harmful substances such as toxic fumes are emitted during cutting operations, making it extremely harmful to human health and highly disadvantageous for steel recycling. Therefore, the addition of S, Bi, Te, Sn, etc., has been proposed as an alternative, but this has been known to be problematic due to the high likelihood of crack formation during steel manufacturing, making production extremely difficult, and the tendency to cause cracks during hot rolling. To solve the aforementioned problems, graphite steel was developed. Graphite steel is a type of steel containing fine graphite particles within a ferrite matrix or a ferrite and pearlite matrix. These fine graphite particles act as crack sources during cutting, functioning as chip breakers, resulting in excellent machinability. However, despite these advantages of graphite steel, it has not yet been commercialized. This is because, when carbon is added to steel, graphite, although a stable phase, precipitates as cementite, a metastable phase. Therefore, it is difficult to precipitate graphite without a separate, long-term heat treatment. This long-term heat treatment process leads to decarburization, negatively impacting the performance of the final product. Furthermore, even if graphite particles are precipitated through graphitization heat treatment, if they are unevenly distributed in an irregular shape, the uneven distribution of physical properties during cutting results in very poor chip processing and surface roughness, shortening tool life and making it difficult to obtain the advantages of graphite steel. Therefore, there is a need to provide a manufacturing method for graphite free-cutting steel that utilizes graphite particles while also leveraging MnS inclusions to achieve superior cutting performance. Korean Published Patent No. 10-2015-0057400 The graphite steel of the present invention contains, by mass %, carbon (C): 0.60-0.90%, silicon (Si): 2.0-2.5%, manganese (Mn): 0.7-1.3%, sulfur (S): 0.2-0.5%, aluminum (Al): 0.01-0.05%, titanium (Ti): 0.005-0.02%, nitrogen (N): 0.003-0.0150%, calcium (Ca): 0.0001-0.050%, with the remainder being iron (Fe) and unavoidable impurities. It has a fine structure in which graphite particles are distributed in a ferrite matrix, with a graphitization rate of 95% or more, and contains MnS inclusions and pearlite totaling 5% by mass or less. The following describes preferred embodiments of the present invention. However, embodiments of the present invention can be modified into a variety of other forms, and the technical concept of the present invention is not limited to the embodiments described below. Furthermore, embodiments of the present invention are provided to more fully explain the present invention to a person with average skill in the art. The terminology used in this application is for illustrative purposes only. For example, a singular expression includes plural expressions unless it is explicitly required to be singular in the context. Unless otherwise specified below, units are in mass percent. Furthermore, when a part is described as "containing" a certain component, this does not exclude other components, unless otherwise stated. On the other hand, unless otherwise defined, all terms used herein should be considered to have the same meaning as that generally understood by a person of ordinary skill in the art to which this invention pertains. Therefore, unless explicitly defined herein, no particular term should be interpreted in an overly idealistic or formal sense. For example, in this specification, singular expressions include plural expressions unless the context clearly indicates otherwise. Furthermore, the terms "approximately," "substantially," etc., as used herein, are used in the sense of or close to the numerical tolerances of manufacture and materials inherent to the meaning referred to, and are used to prevent unscrupu