In the autumn of 1973, the Hunan Institute of Metallurgical Geology came to our institute with a request to smelt and process Ni76Mn24 alloy strips. The task was carried out by Cui Yongliu and me. We followed the general production process used for Ni-based alloys and produced two batches of strips for each other. Later, the 233 factory under the Second Machinery Department and the Guilin Institute of Metallurgical Geology also requested the smelting and processing of Ni76Mn24 alloy strips.
In December 1973, I was sent by the department head to investigate the development status of synthetic diamond catalyst alloys domestically. I visited major diamond research units and alloy manufacturers in Beijing and Shanghai, gaining a preliminary understanding of the industry’s overall situation.
In May 1974, the National Bureau of Three Departments held a seminar on the application of synthetic diamonds at the Hunan Tin Mine. During the meeting, the “Diamond 100†drilling rig, developed by the Hunan Metallurgical Geology Institute, was officially recognized. After the drill bit was made, the drilling performance using the “Diamond 100†rig was remarkably efficient—drilling 2 meters per hour in limestone, with a total footage of 11 meters. It ranked first nationally and was hailed as the "singles champion." As a result, the catalyst alloy from our institute became highly sought after, drawing attention from both superiors and the industry. Following the meeting, officials from the Ministry of Metallurgy, the Ministry of Machinery, and the State Geological Bureau visited our institute. The Director of the Department of Geology at the Ministry of Metallurgy urged the institute to strengthen research on catalyst alloys and allocated funds to improve our melting conditions.
In July 1974, Fang Jun and I traveled to Zhengzhou and Sanmao to discuss collaborative research on catalyst alloys. We proposed replacing the widely used NiMn binary alloys (such as Ni70Mn30, Ni76Mn20) and NiCrFe alloys with a NiMnCo ternary alloy, which was approved by Changsha. The institute would focus on developing catalytic alloys, while Sanmao would handle their application in diamond synthesis.
In August 1974, the First Machinery Department held a seminar on large particle synthetic diamonds in Shanghai, invited by our institute. At the meeting, we were designated to lead the development of synthetic diamond catalyst materials. I immediately reported this to higher authorities after the event.
In October 1974, we delivered the first batch of N70iM25nCo5 alloy strips to Sanmao. After one month, the three mills returned the results, confirming that the target indicators were met and the project was internally accepted by Sanmao.
At the beginning of 1975, the leadership decided to establish a catalyst alloy group, with Wang Guangzu appointed as the leader of the diamond and catalyst research project. As the team expanded, we developed additional catalysts, including the 2# catalyst (NiMnCoNbCu) and 3# catalyst (NiMnCu). These were later approved at the ministerial level in 1977 and 1986 and were widely promoted and applied across China.
The N70iM25nCo5 alloy (or 1# catalyst) became the main focus. Initially, there was debate over the composition ratio. Due to the high cost of nickel and cobalt, especially cobalt, which was imported and expensive, it was preferable to use less or avoid it altogether. We tested different cobalt contents—3%, 5%, 7%, 10%, and 15%—while adjusting the percentages of nickel and manganese. The resulting alloys were sent to Sanmao, the Guilin Institute of Metallurgical Geology, and the Hunan Institute of Metallurgical Geology. The test results showed that with less than 3% cobalt, the diamonds were lighter in color and weaker in strength. With more than 10% cobalt, there was no significant improvement in color or strength compared to the 5% cobalt alloy. After reaching a consensus on the composition, we focused on refining the alloying process and enhancing its properties, including improvements in smelting techniques and the addition of trace elements like carbon, boron, chromium, aluminum, cerium, and lanthanum. We also collected feedback from users nationwide to guide further improvements.
After ten years of research and development, the N70iM25nCo5 catalyst alloy became widely used in domestic diamond manufacturers and became the preferred choice for single-crystal diamond synthesis on six-sided top presses. In 1984, the Ministry of Metallurgy conducted a technical appraisal and rated it as "the first in China," noting its positive role in promoting the development of the diamond industry and its status as a standardized product.
Economically, the output of N70iM25nCo5 alloy in our hospital reached 13.5 tons in 1984 (with an output value of 1.475 million yuan), and by 1994, it had increased to 505 tons (output value of 88.678 million yuan). Over ten years, the output increased 37 times, and the output value grew 60 times.
During the ten years following the identification of the 1# catalyst, we remained attentive to industry trends. In 1986 and 1993, we introduced the 86-8# (containing Cr, Si) and CHS3 (containing Fe) catalyst alloys, which saw better promotion and application, and were also approved at the ministerial level. However, their impact was far less than that of the N70iM25nCo5 alloy.
I retired in December 1994, and since then, I have not been closely involved with developments beyond that point. (Author: CRIMM Liu Shuzhen)
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