Steel plate assembly welded by laser welding and laser welding method thereof

A laser welding method for steel plates, comprising the following steps of:

• positioning two steel plates with respective edges of the steel plates in proximity to each other and facing each other, wherein a joint face of the steel plates is defined by said respective edges of the steel plates, the joint face extending along a joint line;
• using a laser to weld the joint face, wherein a defocusing distance of the laser is within ±T/2 mm, wherein T is a thickness of the steel plates, wherein the thickness of the steel plates ranges from 20 mm to 50 mm, wherein the laser has a power of between 20,000 and 30,000 watts, wherein a welding angle is defined between the laser and the joint line, and wherein the welding angle is between 0 degrees and 10 degrees;
• and
• forming a molten region on the joint face using a laser beam of the laser, wherein the molten region extends along the joint line, wherein the molten region has a molten depth of between 20 and 50 mm, and wherein the molten region has a molten width of between 4 and 7 mm, after the molten region is cooled and solidified, the steel plates are combined with each other.