Effect of heat treatment on the allowable stress of 15CrMoR materials

I’ll take care of it myself; this issue is somewhat important for designers, and I hope to clarify it better. At the same time, I hope the experts can give some responses!

1. As for the degree of decrease in material strength after heat treatment, I haven’t checked whether there are any statistical data available. 2. For individual cases, a case can be created to examine the sample analysis results. 3. For designers, there are precedents to refer to: 3.1. There are three thermal processes in the manufacturing process, including a maximum of 2 allowable reheat treatments; 3.2. Two more repairs can be carried out by the user during use. 4. After the aforementioned 5 thermal cycles, the strength of the material remains above the allowable stress value

Post-weld heat treatment reduces the strength of the weld and the base material, but it is difficult to determine a precise value for this reduction. This mainly lies in the control of raw material evaluation and welding process assessment in the early stages. This process must be taken into consideration, and requirements for simulated post-weld heat treatment should be established to ensure that both the base material and the weld are of acceptable quality. If it isn’t brought up, significant risks will arise; therefore, it should be addressed first.

For the current heat treatment equipment, determining the appropriate thickness tolerances for various housings without relevant parameters poses a significant challenge for designers; it would be great if experts in the heat treatment industry could provide guidance

This post was last edited by fzujunru on 2019-2-2 at 14:07. The perspective of the original poster’s question is quite innovative. 15CrMoR containers require post-weld heat treatment; according to standard 150.4, welding specimens must be prepared, and these specimens need to undergo heat treatment along with the containers. The acceptance criteria for these specimens stipulate that their tensile strength must not be lower than the specified value for the base material. In fact, no matter how heat treatment affects the tensile strength of a material, the allowable stress remains the same.

The purpose of post-weld heat treatment is to eliminate residual stresses in the welded joint; the temperature used is generally around 600°C. For 15CrMoR, the standard condition for delivery is normalizing followed by tempering. Post-weld heat treatment is equivalent to performing another tempering process on the base material. Theoretically, there should be no change in the tensile strength of the base material.

Regarding LZ’s question, point 3 is very important, but it is merely a specification regarding the number of heat treatment cycles. As for exactly how much each heat treatment affects the material’s properties and what the corresponding values are, I haven’t come across any information on that

There is basically no research in this area domestically, let alone any established standards

I wonder what everyone thinks of simulated post-weld heat treatment? Foreign standards impose relatively strict requirements in this regard; I haven’t found any explicit requirements in domestic standards, but such requirements should exist for critical equipment. As far as I know, large manufacturing plants carry out simulated post-weld heat treatment on thick-walled low-temperature vessels, CrMo steel vessels, and high-strength steel vessels. If you have established the theoretical heat treatment procedures, as well as the number of heat treatments and the total cumulative number of such treatments, then within the range of simulated post-weld heat treatment, there should be no need to consider this factor; if it is exceeded, there may be problems. Both foreign materials and foreign standards need to be specified clearly during the design process. As for domestic options, due to limited familiarity with manufacturing processes, I’m not really sure if there are any relevant standards or guidelines; I hope someone experienced can provide some information on this.