Numerical and experimental investigations on the temperature field in local post weld heat treatment of 9% Cr heat resistant steel welded pipes

Author(s):  
Lei Hu ◽  
Xue Wang ◽  
Qunshuang Ma ◽  
Wei Meng ◽  
Shuangshuang Chen
2019 ◽  
Vol 953 ◽  
pp. 32-38
Author(s):  
Xi Wang ◽  
Jiao Zhong ◽  
Hao Ke

ANSYS was used to establish the calculation model of the temperature field for 9% Cr heat-resistant steel pipes in local post-weld heat treatment (PWHT). And the computation model has been validated experimentally. Based on the numerical model, the temperature field distribution was simulated for different pipe lengths in local PWHT, and effects of pipe length on the temperature distribution of heat treatment was further studied. Results show that increase of pipe length has little influence on equivalent temperature measurement point, soak band (SB) width of outer wall and axial temperature gradient, while it causes temperature difference between outer and inner wall to increase and soak band width to reduce significantly in inner wall. And when pipe length increases to a certain extent, the temperature field tends to be stable gradually.


Metals ◽  
2020 ◽  
Vol 10 (10) ◽  
pp. 1321
Author(s):  
Jiankun Xiong ◽  
Ting Li ◽  
Xinjian Yuan ◽  
Guijun Mao ◽  
Jianping Yang ◽  
...  

The effect of the post-weld heat treatment on the microstructures and mechanical properties of the dissimilar joint of G115, a novel developed martensite heat resistant steel, and CB2 steel, currently used in an ultra-super-critical power unit, was investigated. The results indicate that the quenched martensite underwent decomposition and transformation, and the amount of dislocations were sharply decreased in the weld metal after post-weld heat treatment (PWHT). Many nano-scale M23C6 precipitates present in the weldment were distributed on the grain and grain boundary in a dispersed manner with PWHT. The average microhardness of the weldment decreased from about 400 HV to 265–290 HV after PWHT and only a slight decrease in the microhardness of CB2 steel was detected after PWHT at 760 °C. In contrast to the case of the as-received joint, the tensile strength of the joint was improved from 630 MPa to 694 MPa and the fracture location moved from the weld metal to the base metal after PWHT. The fracture surface consisted of a cleavage fracture mode without PWHT, whereas many dimples were observed on the fracture surface with PWHT.


2018 ◽  
Vol 941 ◽  
pp. 400-406 ◽  
Author(s):  
Javier Vivas ◽  
Rosalia Rementeria ◽  
Marta Serrano ◽  
Eberhard Altstadt ◽  
David San Martín ◽  
...  

The major challenge in a heat-resistant steel is to generate thermally stable microstructures that allow increasing the operating temperature, which will improve the thermal efficiency of the power plant without diminishing strength or time to rupture. The strengthening mechanism in tempered martensitic 9Cr steels comes mainly from the combination of solid solution effect and of precipitation hardening by fine MX carbo-nitrides, which enhance the sub-boundary hardening. This work is focused on the effect of ausforming processing on MX nanoprecipitation, on both their distribution and number density, during the subsequent tempering heat treatment. The creep strength at 700 oC was evaluated by small punch creep tests. The creep results after ausforming were compared to those obtained after conventional heat treatment concluding, in general, that ausforming boosts the creep strength of the steel at 700 oC. Therefore, conventional ausforming thermomechanical treatment is a promising processing route to raise the operating temperature of 9Cr heat-resistant steels.


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