Analysis and Application of Welding Technology for 4130 (30CrMo) + 16Mn
Abstract: The author analyzes and introduces the welding technology of 4130 (30CrMo) + 16Mn for reference. Keywords: Welding technology; Experiment; Application
Introduction
From June 12 to August 15, 2010, Xinjiang Tuha Oilfield Construction Co., Ltd. undertook the Yudong Gas Injection Improvement Project for Lukqin Oil Production Plant. The project was 6.7 km long, using material 16Mn. During construction, the valves supplied by the owner came with welding flanges made of 4130 (30CrMo), which follows API (American Petroleum Institute) standards. This was the first use of this material in Tuha Oilfield. Through experimentation, we established a qualified welding process, providing technical support for the smooth progress of the project.
Analysis of Welding Technology Performance for 4130 (30CrMo) + 16Mn
2.1 16Mn has been widely used and does not require further analysis here.
2.2 Analysis of Weldability of 4130 The determination of weldability for any metal material involves assessing its ability to be welded, a necessary process.
2.2.1 Simple Analysis of Weldability Based on Chemical Composition of 4130 According to the quality certificate provided by the supplier, 4130 material is equivalent to the domestic grade 30CrMo, with the following alloy composition:
Based on the above table, it contains 0.3% carbon, indicating average weldability (less than 0.25% carbon is good for welding; 0.25-0.4% carbon is average; 0.4-0.6% carbon is poor).
2.2.2 Analysis of Characteristics of 4130 (30CrMo) Material Material Delivery Condition: This material is delivered in a quenched and tempered state, which is a medium-carbon quenched and tempered steel.
Features of Medium-Carbon Quenched and Tempered Steels: 2.2.2.1 Hot Cracking: The material has a high content of alloy elements, a large liquid-solid phase interval, and severe segregation, making it prone to hot cracking. 2.2.2.2 Cold Cracking: It has a significant tendency to harden, increasing the likelihood of cold cracking. 2.2.2.3 Heat-Affected Zone (HAZ): To reduce brittleness in the over-heated zone, reducing the hardening tendency is crucial. While higher welding line energy might be beneficial, this steel’s high hardening tendency means that simply increasing the line energy often cannot prevent the formation of martensite and coarse grains, leading to severe brittleness. Therefore, small welding line energy combined with preheating, post-weld heat treatment, and controlled cooling is recommended.
2.3 Analysis of Welding Technology for 4130 and Proposed Welding Procedures After analyzing weldability, the implementation process of the welding procedure should be examined to establish a reasonable welding method.
Firstly, the welding parameters must ensure no cold or hot cracks occur during welding. Secondly, joint performance should be ensured through post-weld heat treatment.
Based on the previous analysis, preheating, controlled cooling after welding, and post-weld heat treatment are necessary. The specific temperatures and times for these measures are as follows:
Ideal Thermal Treatment Curve:
Requirements for Thermal Treatment: Heating Requirements:
- Initial furnace temperature: ≥150°C.
- Heating rate between 150°C and 400°C: Controlled at 150°C/h to 200°C/h.
- Heating rate after reaching 400°C (up to 730°C): Controlled at 200°C/h to 250°C/h.
Soaking Requirements:
- Soaking time at 730°C: 45 minutes to 1 hour.
Cooling Requirements:
- Cooling rate from 730°C to 400°C: Controlled at 200°C/h to 250°C/h.
- After reaching 400°C: Allow furnace cooling or air cooling.
Selection of Welding Materials
The selection of welding materials was based on three principles for dissimilar metals:
3.1 Alloy Composition: Selected based on the poorer weldability of 4130. 3.2 Equal Strength Principle: Tensile strength determined by the lower-strength 16Mn. 3.3 Economy: Preferably common and easily procurable materials. 3.4 Selected Welding Materials: R307.
Welding Technology Performance Test for 4130 (30CrMo) + 16Mn
Based on the analysis and material selection, we formulated a welding procedure instruction and conducted tests.
Welding Procedure Parameters: Through testing, the proposed welding procedure was found to be feasible.
Engineering Application
After the test, the process was applied on-site. Since thermal treatment could not be performed at the construction site, we used short sections (16Mn) and flanges (4130) welded at the mechanical factory, followed by immediate thermal treatment. After passing non-destructive testing, they were assembled on-site and successfully pressure-tested, providing essential welding technology support for Tuha Oilfield Company’s “Oil Production Increase” goal.