Method for forming multilayer coating film

A multilayer coating film-forming method comprising the following steps (1) to (6):

• (1) applying an electrodeposition coating material onto a steel sheet and heat curing it to form a cured electrodeposition coating film,
• (2) applying a first pigmented coating material (P1) onto the cured electrodeposition coating film obtained in step (1) to form a first pigmented coating film, the first pigmented coating material (P1) having a lightness L* value (L*P1) in the range of 80 to 89 if the first pigmented coating film is formed to a thickness of 30 μm,
• (3) applying a second aqueous pigmented coating material (P2) comprising a binder component (AP2) and a titanium dioxide pigment (B) and having a coating material solid content in the range of 21 to 50 mass % onto the first pigmented coating film obtained in step (2), to form a second pigmented coating film having a cured film thickness (TP2) in the range of 5 to 20 μm and a lightness L* value (L*P2) when cured, in the range of 85 to 95,
• (4) applying a third aqueous pigmented coating material (P3) onto the second pigmented coating film obtained in step (3) to form a third pigmented coating film having a cured film thickness (TP3) in the range of 1 to 10 μm, the third aqueous pigmented coating material (P3) comprising a binder component (AP3) and a light interference pigment (C) and having a coating material solid content in the range of 5 to 20 mass %,
• (5) applying a clear coating material (P4) onto the third pigmented coating film obtained in step (4) to form a clear coating film, and
• (6) heating the multilayer coating film including the second pigmented coating film, the third pigmented coating film and the clear coating film formed in steps (3) to (5), to simultaneously cure the multilayer coating film,
• wherein L*P2 is higher than L*P1, the difference between L*P2 and L*P1 is in the range of 1 to 10, and the ratio of TP2 and TP3 is in the range of TP2/TP3=1.1/1 to 20/1.