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Micro-tensile tests based on small-scale specimens were carried out to investigate the microstructure dependence of strain hardening behavior along a Ni–Cr–Mo–V steel welded joint. Results indicated the weld metal (WM) had higher tensile strength but lower strain hardening exponent than base metal (BM), whereas a gradient distribution of strain hardening exponents was observed within the heat-affected zone (HAZ). Bainitic microstructures showed weaker strain hardening capacity than lathy martensites. A Kocks–Mecking type plot of strain hardening rate versus true stress presented at least two hardening stages (stages III and IV) with varied duration along the whole welds. Larger grain size and more lathy martensites were beneficial to prolong the hardening period. A new strength prediction model was developed by considering the size effect on tensile strength. The predicted strength distributions along the welds were in good agreement with experimental data. [ABSTRACT FROM AUTHOR]