Effect of Heat Treatment on Chemical Plating of Ni-Cr-P on 65Mn Alloy Steel

Effect Of Heat Treatment On Chemical Plating Of Ni-Cr-P On 65Mn Alloy Steel

Knitting needles (hereafter referred to as “needles”) are essential components of modern knitting machines. The raw materials needed for the manufacture of needles often include carbon tool steels, such as 70 steel, T9A, and T10A, and alloy steels, such as 65Mn (Bing & Mapibo, 2022). Indeed, 65Mn alloy steel, with its advantages of a high degree of hardness, good elasticity, and easy processability, is a promising advanced raw material for the manufacture of high-quality needles. In recent years, with the emergence of various high-speed, high-end knitting machines and the widespread application of diverse high-performance yarns, more exacting requirements have been proposed for the performance, especially the surface performance, of needles (Fenglin, 2019). There is therefore an urgent need for in-depth studies of the surface enhancement of needles.

Feng and Shigen (2018) achieved a hard chrome plating layer with a microhardness of approximately 700HV_0.1 using electroplating technology on the surface of SWP-B, a frequently utilized material for yarn guide needles. They examined the impact of various plating temperatures and time gradients on the characteristics of the chrome layer, including its appearance, bonding, hardness, microstructure, and other features. Meanwhile, the study examined the impact of chrome plating on the alignment of the outer arcs of the pinholes and tongues of the essential components of yarn guide needles. The proposal suggests that the concentricity should not exceed 12μm, which means it should stay within the designated size tolerance range of the yarn guide needle.

Xing and Shigen (2020), Zikang et al., (2021), and Cong and Shigen (2022) conducted chromium plating on the hook section of warp knitting slot needles, as seen in Figure 1; they examined the effects of heat treatment temperature and plating jig on the morphology, hardness, abrasion resistance, and appearance of the plated layer. The study revealed that the environmentally friendly chromium plated layer had a hardness of approximately 520 HV_0.1. The microhardness of the chromium plated layer remained relatively stable when the heat treatment temperature was below 200°C. However, the microhardness of the plated layer significantly increased when the heat treatment temperature exceeded 200°C, reaching a maximum of 781 HV0.1 at 400°C.

Figure 1.

Topography of the groove needle hook before and after environmental chrome plating

During the electroplating process, challenges such as difficulty in controlling coating uniformity, complexity in treating intricate shapes, poor environmental performance, and high energy consumption present themselves. In contrast, chemical plating technology enables the deposition of Ni-P coatings, multi-element alloy coatings, and nano-composite coatings on parts with complex shapes and with high precision. Moreover, this is a more environmentally friendly process and holds greater developmental potential compared to electroplating. Since the late 1990s, researchers have explored Ni-P-based multi-element alloy chemical plating.

Maozhong et al. (1994) utilized chromic anhydride (CrO₃) as the chromium salt, proposed the use of high concentrations of chloric acid to convert Cr⁶⁺ to Cr³⁺, and, after sufficient complexation of Cr³⁺ with citric acid, prepared a Ni-Cr-P plating solution. They deposited a Ni-Cr-P coating on cold-rolled low-carbon steel sheets, with the coating containing approximately 1% Cr. Xinyi (1997) employed an alkaline chemical plating solution with chromic chloride (CrCl₃·6H₂O) as the chromium salt and obtained a Ni-Cr-P coating on low-carbon steel surfaces with a Cr content of 2.85 wt% and a deposition rate in the range of 5–15 μm/h.