The relationship between tempering process and mechanical properties of JIS SCM435 bolt

• Main Authors: Jian-De Cheng, 成建德
• Other Authors: Dong-Yih Lin
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/00214071413240653002

碩士 === 國立高雄大學 === 化學工程及材料工程學系碩士班 === 101 === The purpose to process heat treatment in the manufacturing process of the fastener is to achieve the expected mechanical strength and quality by transferring the microstructure inside or on the surface of the material. In this study, the Cr-Mo high-strength steel bolt (JIS SCM435), bolt size: M14(mm), thread pitch: 2.0(mm) used in a series of heat treatment was to find the relation of the mechanical properties in the different tempering conditions. The first direction of this study reviewed the original derivation of the Hollomon-Jaffe tempering parameter concept from literatures, and then employed the Hollomon-Jaffe tempering parameter by using my experimental data to identify the sticking point. This study employed the hardness values of spheroidizing annealing, quenching and tempering in the heat treatment process of the fastener as the basic parameters, and tried to combine Arrhenius equation and Johnson-Mehl-Avramie equation to describe the variation of various parameters of tempering process. For the experimental results showed that Hollomon and Jaffe tempering parametric equation could not describe the tempering process of SCM435 steel bolt properly, and also SCM435 steel at the temperature（460 to 560 ℃） did not produce secondary hardening phenomenon. Hardness test results were shown that the average hardness value was 52.5HRC at the austenitizing temperature 890℃ (oil quenching) under the hardness value（95HRB）of spheroidizing annealing state ,and after the process of tempering temperature (460 to 560℃)、time(30 to 120 min) the average hardness values were between 30 and 41HRC .In addition , the tensile test results were shown that tensile strength values were 1331.43 to 1254.03 MPa under the tempering temperature(460℃ ), time( 30 to 120 min) and the tensile strength values were 1037.49 to 969.13 MPa under the tempering temperature(560℃ ), time( 30 to 120 min) . It means as the tempering temperature increase, the tensile strength will decrease. Fastener heat treatment process parameter (Hp) could explicitly describe the degree of hardening at tempering state between quenching and spheroidizing annealing state. The value (Hp) will be essential to research tempering relations. Finally, Hp combined with the diffusion and kinetic relations of tempering process from literature and then derived tempering relation equation. If this relation equation is correct, then any hardness values of tempering states will be calculated.