Study on Surface Flame Hardening of High-Strength Ductile Cast Irons
Date Issued
2014
Date
2014
Author(s)
Lee, June-Wei
Abstract
In this study, flame (surface) hardening was performed on the high-strength grade ductile cast irons to achieve the required surface hardness for wear resistance purpose. Firstly, a single flame – single pass was conducted to establish the optimal operation conditions, including the flame travel speed and the gap between the flame nozzle and the surface of the workpiece, to achieve a full surface hardening effect. The experimental results indicate that a flame travel speed of 70mm/min, and a gap of 20mm between the flame nozzle and the surface of the workpiece were determined to be the optimal operation conditions that can produce a transverse hardened width of around 8-9mm with an average surface hardness of some 57 HRC. Secondary, tests with single flame – multiple pass were performed to examine once again the hardened width and also the possible softening effect due to tempering caused by the thermal energy from the subsequent neighboring flame pass. It was found that the already hardened regions were softened by the subsequent neighboring flame pass. As a result, the surface hardness was reduced to around 45HRC from a fully hardened value of some 55~60HRC. In addition, the softened region can extend up to around 10.45-10.55 mm both sides from the edge of the hardened region. It is quite obvious that using single flame – multiple pass is not practically feasible if the minimal surface hardness of 50HRC is going to be obtained. Alternately, surface hardening using multiple flame – single pass was proposed and test runs were conducted. The results show that full hardening was achieved across the hardened region with the hardened width (single flame) and depth being 8~9mm and 2.0~2.2mm, respectively.
Subjects
高強度球墨鑄鐵
火焰表面硬化
淬火
回火
Type
thesis
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