Dehydrogenation heat treatment of chromium-molybdenum steel

The heat treatment process is as follows: the temperature is raised at a rate of 200°C/h, reaching 715°C where it is held for 1 hour and 15 minutes; then the temperature is lowered at a rate of 100°C/h, and after reaching 300°C, the material is cooled in air.

2# Zhang Jiahong: They are asking about hydrogen-removing heat treatment, not stress relief.

GB150 specifies that post-weld heat treatment should be carried out immediately after welding, which can exempt the need for hydrogen removal treatment.

The temperature for hydrogen elimination heat treatment is 250–300°C, with a holding time of 2 hours.

Welding of chromium-molybdenum steel is not merely a matter of dehydrogenation heat treatment； Chromomolybdenum steel requires preheating before welding ； Hydrogen removal heat treatment is carried out immediately after welding; the temperature for this treatment is 250–300°C, with a holding time of 2 hours.

The temperature is generally between 200 and 350 degrees. The holding time depends on the thickness of the weld; it should be no less than 0.5 hours. For more details, refer to JB/T4709-2000, Welding Procedures for Steel Pressure Vessels, page 53–7: Post-heating

I agree with what was said on floor 7: the insulation time required for hydrogen removal depends on the thickness

9# tazyh: The temperature and time for post-heating are clearly specified in 4709; the people above also mentioned this. I believe that when post-heating is required, there’s no need to consider the rate of temperature increase or decrease. If post-heating is necessary, then preheating must also be done before welding, right? Alternatively, it is possible to maintain a certain interlayer temperature; in this case, the value for the welding interlayer temperature is almost the same as that for the holding temperature during post-heating. There is no need for a specific heating rate. The holding time depends on the thickness, though the exact relationship isn’t specified. I have worked with 30 MM thick 15CRMOR material, using a post-heating temperature of 280–350 degrees, with a holding time of 1.5 hours, and no delayed cracks occurred. With 14 MM thick 15CRMOR material, a post-heating temperature of 250–300 degrees and a holding time of 1 hour also resulted in no delayed cracks. The original poster can use this as a reference!

Immediately after welding, heat the workpiece to 250–350°; maintain this temperature for 2–6 hours depending on the thickness, and then cool it in air.

Both make sense; I now think that if stress-relief heat treatment is carried out immediately after welding, it’s unnecessary to perform hydrogen removal. The heating and cooling rate in this heat treatment is related to the thickness of the workpiece